Burçin Mutlu-Pakdil, Michael G. Jones, David J. Sand+14 more
AstronomerHST imaging resolves seven Local Volume dwarfs into individual stars, yielding TRGB distances of 3.6–6.5 Mpc, structural parameters, and star formation histories. M83-dw14 and the serendipitously discovered Centaurus C (Cen C) are reported for the first time. Complementary new and existing HI observations constrain their gas content. The environments range from the confirmed satellite M83-dw14 to isolated systems including Cen C. At M_V = −7.96, Cen C is among the faintest known isolated dwarfs; it resembles Leo T in size and luminosity but has no detected HI, with log(M_HI/M_sun) < 5.3, and no recent star formation. Ursa Major C has strongly asymmetric, spatially offset HI, suggesting, but not establishing, efficient gas displacement by feedback. The diversity of star formation and quenching histories does not track simply with present-day environment and is interpreted as consistent with contributions from inhomogeneous reionization, stochastic mass assembly, and internal feedback alongside environmental effects.
PublicHubble images have revealed individual stars in seven small nearby galaxies, allowing researchers to measure their distances and reconstruct their star formation histories. The galaxies lie 3.6–6.5 million parsecs away, and two, M83-dw14 and Centaurus C, are newly reported discoveries. Their surroundings differ: M83-dw14 is a confirmed satellite of another galaxy, while several others are isolated. Centaurus C is among the faintest isolated galaxies known. Although similar in size and brightness to the gas-rich dwarf Leo T, it shows no recent star formation and no detected neutral hydrogen gas; the observations place an upper limit on that gas rather than proving it is absent. Another galaxy, Ursa Major C, has an uneven hydrogen distribution displaced from its stars, possibly because stellar activity pushed the gas aside. Across the sample, star formation histories do not follow a simple pattern based on current surroundings, suggesting that both internal processes and earlier cosmic conditions may also matter.
Young explorerScientists used Hubble to see individual stars in seven small galaxies and learn how far away they are. Two of these galaxies are being announced for the first time. Some are near other galaxies, and some are far from neighbors. One very faint galaxy, called Centaurus C, has not made stars recently, and scientists did not detect its hydrogen gas, though some could still be hiding. In another galaxy, gas sits off to one side. The scientists think activity from stars might have pushed it there, but they are not sure. These galaxies have made stars in different ways, and having neighbors does not explain all those differences.
Zephyr Penoyre, Elena Maria Rossi, Nicholas C. Stone
AstronomerThis theoretical study finds that orbits crossing between the nearly spherical region dominated by a massive black hole and the flattened or irregular surrounding stellar potential are commonly chaotic, particularly diving orbits that reach their minimum possible periapse. Across a wide range of potentials, these orbits can undergo large angular-momentum changes between successive passages. The authors characterize the onset of chaos with a notional critical angular momentum, j_d, and model loss-cone transport including both diving orbits and two-body scattering. Rapid advection away from the boundary after entry into the chaotic region produces a substantial net flux. A probability-density formulation permits a true equilibrium solution. The predicted disruption-rate enhancement over classical loss-cone theory is 1 + ln(j_d/j_t), where j_t is the angular momentum corresponding to disruption; this can amount to an order-of-magnitude increase. These are model results, not an observed enhancement.
PublicCalculations suggest that the changing shape of gravity around a massive black hole can help send more stars toward destruction. Close to the black hole, the gravitational environment is nearly spherical, while farther out the surrounding stars create a flatter or more irregular environment. The study finds that orbits passing between these regions are often chaotic, especially those that plunge as close in as their paths allow. Their angular momentum can change greatly from one passage to the next. By including these paths alongside the effects of gravitational encounters between stars, the researchers predict disruption rates that can be about ten times those in the classical model. This is a theoretical prediction, not a measured increase in stellar disruptions.
Young explorerStars can travel around a giant black hole. In this study, scientists used a model to explore how the black hole and the stars around it change those paths. Some paths become hard to predict and can send stars very close to the black hole, where they can be torn apart. The model suggests this could happen much more often than an older model predicts. The scientists did not watch extra stars being torn apart; this is what their calculations suggest.
Kung-Yi Su, Hyerin Cho, Priyamvada Natarajan+6 more
AstronomerThe authors develop a galaxy-scale black hole accretion and feedback prescription informed by multi-zone GRMHD simulations extending from the event horizon to the Bondi radius. It replaces fixed Bondi-rate suppression with an environment-dependent factor set by the local Bondi-to-gravitational-radius ratio and assigns outflow mass and energy using the simulated angular structure. Tests use idealized isolated M87*-like and Milky Way/Sgr A*-like galaxies spanning more than three orders of magnitude in black hole mass, without tuning accretion or feedback efficiencies to observables. In the M87*-like simulation, angle-dependent feedback reduces late-time stellar mass growth more than isotropic feedback despite similar long-term accretion rates. Varying the uncertain polar mass loading has only modest effects on black hole growth and star formation, suggesting that anisotropy is more consequential within these tests. The variable suppression factor produces markedly different growth histories from fixed-suppression models and, for the Sgr A*-like case, an accretion rate more consistent with EHT constraints. These simulation results support including nuclear-environment dependence and feedback angular structure in subgrid prescriptions; they are not direct observations of galaxy evolution.
PublicResearchers have built a computer model of how a galaxy’s central black hole takes in gas and sends mass and energy back into its surroundings. Drawing on detailed simulations near black holes, the model lets gas intake change with the local environment and sends outflows preferentially in certain directions rather than equally in all directions. They tested it in idealized, isolated galaxies resembling the hosts of M87* and Sagittarius A*, without adjusting accretion or feedback efficiencies to match observations. In the M87*-like simulation, directional feedback limited later growth in stellar mass more effectively than evenly distributed feedback, even though the black hole’s long-term gas intake was similar. Uncertainty in how much mass the narrow polar outflow carries had a relatively modest effect in these tests. In the Sagittarius A*-like simulation, the predicted intake rate agreed better with Event Horizon Telescope constraints than a comparison model using a fixed reduction in gas intake. The findings suggest that both the black hole’s surroundings and the directions of its outflows matter, although the tests are simulations rather than observations of evolving galaxies.
Young explorerScientists used computers to pretend they had galaxies with big black holes in the middle. Their new model lets a black hole take in gas differently depending on what is nearby. It also sends gas and energy out more in some directions than others. In one pretend galaxy, sending things out in particular directions slowed the growth of stars’ total mass more than sending them out evenly. In another, the amount of gas going into the black hole fit telescope clues better than an older model did. These are computer experiments, not things the scientists watched happen in real galaxies.
Olga Borodina, Jake S. Bennett, Yueying Ni+4 more
AstronomerMotivated by observations of roughly kiloparsec-scale AGN jets in galaxies of different morphologies, this study uses idealized turbulent-box simulations with accreting black holes to investigate jet–ISM coupling. In the simulations, turbulence regulates both jet launching and propagation. Without turbulence, feedback initially cuts off the cold gas supply, leading to a steady state with jet power at or below 10^39 erg/s for a 10^6-solar-mass black hole. With turbulence, jets fill voids with hot, diffuse material that turbulent motions carry away, allowing the fuel supply to replenish. Above a critical jet efficiency factor, however, feedback substantially depletes the fuel and produces self-limiting accretion. This threshold depends on the ISM Mach number and is lower for weaker turbulence. Jet power depends on the gas density near the black hole, but at fixed turbulent structure, propagation morphology and extent are largely insensitive to mean background density. Denser media nevertheless receive more total energy and undergo stronger heating. These are results of idealized simulations, not direct observational determinations of jet regulation.
PublicObservations have revealed jets extending roughly a kiloparsec from active galactic nuclei in different kinds of galaxies, but how those jets transfer energy to surrounding gas remains uncertain. This study explores the process using idealized computer simulations. In the models, turbulent gas motions help keep a black hole supplied with fuel: the jets fill gaps with hot, thin gas, which turbulence then carries away so the fuel supply can recover. Without turbulence, the jets initially cut off the cold gas supply and settle into a weak state. Even with turbulence, sufficiently efficient jets deplete their own fuel and limit further feeding; weaker turbulence makes this happen at a lower efficiency. For a fixed turbulent structure, changing the average gas density has little effect on the jets’ shape or reach, although denser gas receives more energy and stronger heating. The simulations therefore point to turbulence as a major influence on jet behavior, rather than establishing this directly in real galaxies.
Young explorerScientists used a computer model to explore how a black hole’s jets interact with gas. In the model, swirling gas helps move hot gas out of the way so the black hole can get more fuel. But if the jets become too efficient, they use up too much of their fuel supply and limit themselves. The swirling matters a lot for how far the jets travel. This is what happened in the model, not something scientists watched happen directly.
Preston G. Waldrop, Dimitrios Psaltis, Feryal Özel+1 more
AstronomerThe authors present a neural network trained on spatially resolved spectra to infer galaxy kinematic properties from spatially integrated spectra. The method learns how internal motions are encoded in Doppler-shaped spectral line profiles, rather than requiring a first-principles mapping between spatial structure and line shape. They report that it remains effective when spectral resolution only marginally resolves the lines. The approach could enable kinematic measurements for millions of unresolved galaxies in existing and future surveys; the abstract does not provide quantitative performance metrics or report such a survey-scale application. These measurements are motivated partly by previous work showing that kinematic parameters can help identify galaxies hosting supermassive black hole binaries, not by a reported binary detection here.
PublicA distant galaxy may look like a single dot, yet its spectrum—the light separated into different wavelengths—can still carry clues to how material moves inside it. The researchers present an artificial neural network trained on spectra that preserve information about different parts of galaxies. It learns to infer internal motion from spectra in which the whole galaxy's light is combined. They report that the method works even when the spectral lines are only barely resolved. It could make motion measurements possible for millions of galaxies, although the abstract gives no numerical accuracy estimates or results from an application on that scale. Such measurements may help researchers study galaxy histories and identify galaxies that could contain pairs of supermassive black holes; this work does not report finding such a pair.
Young explorerA faraway galaxy can look like one tiny dot, so we cannot easily see how things move inside it. But its light holds clues. The scientists trained a computer using light from different parts of galaxies, so it could learn to read those clues even when all the light is mixed together. They say it works even when some clues are only just clear enough to see. This could help scientists study how things move inside millions of galaxies, but they have not reported doing that for millions yet.
Alessia D'Angelo, Raffaella Schneider, Luca Graziani+9 more
AstronomerThis simulation study investigates interstellar dust at z ~ 5 using dustyGadget, a semi-analytical stellar dust-production model, and SKIRT radiative-transfer post-processing. From five simulated star-forming galaxies, the analysis emphasizes three with similar stellar masses, log(M_star/M_sun) ~ 8.7, but dust masses spanning log(M_dust/M_sun) ~ 5.1–6.2. Stellar production alone reproduces only the low-dust branch of the dust-to-stellar mass relation; grain growth is needed to recover its S-shape and observed scatter. Efficient growth begins at lower metallicity than locally, consistent with a denser high-redshift ISM. The authors interpret assembly stage as the key regulator: longer star formation histories yield greater enrichment and denser gas, promoting grain growth. Mock observations suggest JWST multi-band imaging can reveal structural diversity, although clumpy morphology may be incompletely reconstructed. The modeled dust continuum emission falls below current ALMA continuum-survey sensitivity. These conclusions derive from simulations, not direct observations of these systems.
PublicWhy might early galaxies with similar amounts of stars contain very different amounts of dust? This study explores that question with computer simulations, focusing on three galaxies at an early stage of cosmic history. In the models, dust made by stars explains only the dust-poor galaxies. Growth of dust grains within galaxies is also needed to reproduce the broader pattern and its observed spread. The researchers link these differences to how far each galaxy has progressed in assembling: longer histories of star formation produce more chemical enrichment and denser gas, encouraging dust growth. The models suggest this growth becomes efficient at lower chemical enrichment than in nearby galaxies. Simulated images indicate that JWST could reveal differences in structure, but might miss some clumps. The predicted dust emission is too faint for current ALMA continuum surveys.
Young explorerSome young galaxies can have about the same amount of stars but very different amounts of dust. Scientists used computer-made galaxies to explore why. In their models, stars making dust were not enough: the dust grains also needed to grow. Galaxies that had been making stars longer had better conditions for that growth. These are clues from computer models, not things the scientists directly watched happen in real galaxies.
Hyungjin Joo, Myungkook James Jee
AstronomerDeep VLT/MUSE integral-field spectroscopy separates the overlapping brightest cluster galaxy (BCG) and intracluster light (ICL) in Abell S1063 (z=0.35) and MACS J1206.2−0847 (z=0.44). Iteratively derived central and outskirts spectral templates are fitted jointly in each spatial bin, recovering component light and kinematics without imposing a boundary or light-profile form. BCG and ICL velocity dispersions are 316±5 and 753±25 km/s in AS1063, and 313±5 and 695 (+47/−45) km/s in MACS1206. The ICL is blueshifted relative to the BCG by 75±22 and 148±38 km/s, respectively. It is also inferred to be approximately 0.7 dex more metal-poor, with a combined statistical significance of only about 2σ. A photometric ICL threshold of μ_B=25 mag/arcsec² assigns two-thirds to three-quarters of the kinematically identified ICL to the BCG. Double-Sérsic models fit the total profiles well but poorly constrain the component division at the current data depth and resolution. The decomposition supplies a physically motivated reference for photometric ICL definitions.
PublicThe brightest galaxy in a galaxy cluster blends smoothly into a surrounding diffuse glow, making the two hard to distinguish in images. Using deep observations of two clusters, researchers separated their light by fitting distinct spectral signatures rather than drawing a boundary between them. The diffuse component shows a much wider spread of stellar velocities than the central galaxy and is shifted toward bluer wavelengths relative to it. There is also tentative evidence that its stars contain fewer elements heavier than helium, but that difference has only modest statistical support. A commonly used brightness cutoff would count two-thirds to three-quarters of the spectrally identified diffuse light as part of the central galaxy. Another approach fits the overall brightness well but cannot reliably divide the components with these data. The study offers a reference for checking image-based ways of measuring diffuse cluster light.
Young explorerIn two big groups of galaxies, the brightest galaxy blends into a faint glow around it. It is hard to tell where one ends and the other begins. Scientists studied the light in detail and used clues about how the stars move to tell the two parts apart. The stars making the faint glow had a bigger mix of speeds. Simply sorting the light by how bright it looks would put much of that glow in the wrong part. This new way helps scientists check their sorting, even though ordinary pictures still make the two parts hard to separate.
Claire Bolda, Casey Papovich, Lu Shen+7 more
AstronomerDeep JWST/NIRISS wide-field slitless spectroscopy from NGDEEP provides Hα or Hβ detections above 3σ for 284 galaxies at 0.5 < z < 3.5 in the Hubble Ultra Deep Field. The authors derive dust-corrected Balmer-line star-formation rates and examine the star-forming main sequence in three redshift bins. Its intrinsic scatter using Hα-based rates, which trace approximately 10 Myr timescales, is approximately 0.35–0.5 dex across the redshift range. At z < 2.5, this exceeds the scatter obtained with UV-based rates, tracing approximately 100 Myr, by approximately 0.2–0.4 dex. The authors interpret this difference as likely evidence for bursts lasting no more than approximately 10 Myr. For galaxies with log(M*/M☉) < 9 at 1.5 < z < 2.5, FIRE simulations underpredict the observed Hα-based scatter by up to approximately 0.25 dex, suggesting more variable short-timescale star formation in low-mass galaxies than those simulations predict.
PublicAstronomers used deep James Webb Space Telescope observations to study star formation in 284 galaxies, including low-mass galaxies. They compared estimates based on hydrogen emission lines, which track star formation over roughly 10 million years, with estimates from ultraviolet light, which track roughly 100 million years. At redshifts below 2.5, the hydrogen-based estimates showed greater variation around the usual relationship between a galaxy’s stellar mass and its star-formation rate. The researchers argue that brief bursts of star formation likely explain this difference; the observations do not directly follow individual bursts through time. In a low-mass subset at redshifts between 1.5 and 2.5, the observed variation also exceeded predictions from the FIRE simulations, suggesting that these galaxies form stars in more uneven bursts than the simulations predict.
Young explorerGalaxies are huge groups of stars, and they can make new stars. Scientists used the James Webb Space Telescope to look at light from 284 galaxies. One kind of light tells them about stars made more recently, while another tells them about a longer time. The recent-star clues showed bigger differences between galaxies than the longer-time clues did. The scientists think this may mean that some galaxies make stars in quick bursts rather than at a steady pace. For some smaller galaxies, the differences were bigger than their computer models expected.
Vaidik Prasal, Yogesh Wadadekar, Pralay Biswas
AstronomerDeep JWST NIRCam imaging from PRIMER and MINERVA is used to study 26 massive quiescent galaxies at 2 < z < 3. Sérsic fits yield size–mass slopes of 0.59 ± 0.12 in F200W and 0.56 ± 0.13 in F356W, with effective radii at 5 × 10^10 solar masses of 0.83 (+0.08/−0.07) and 0.70 (+0.07/−0.06) kpc, respectively. Sizes decrease by approximately 22% from F115W to F444W, interpreted as reflecting negative color gradients and centrally concentrated mass. Bulge–disk decompositions classify two-thirds as bulge-dominated and one-third as disk-dominated; bulges have effective radii near 0.49 kpc with negligible mass dependence, while disks extend to 1.4–1.5 kpc. Resolved SED modeling infers positive radial specific star formation rate gradients and central regions that formed at least approximately 0.7 Gyr earlier and quenched faster than the outskirts. These findings support inside-out quenching. Gas compaction, AGN feedback, and dynamical disk stabilization by compact bulges are consistent interpretations, rather than directly established mechanisms.
PublicAstronomers used deep James Webb Space Telescope images to examine 26 massive galaxies seen in the early universe that had largely stopped making stars. Two-thirds are dominated by a dense central bulge, while one-third are dominated by a disk. The galaxies appear smaller at longer wavelengths, which the researchers interpret as evidence that their mass is especially concentrated toward their centers. Modeling the light from different regions suggests that the central regions formed at least about 700 million years earlier and stopped forming stars faster than the outer regions. This supports a picture in which star formation shut down from the inside outward. Gas gathering into a dense core, feedback from an active galactic nucleus, and a central bulge helping keep the remaining disk stable could explain the pattern, but this study does not directly establish those causes.
Young explorerScientists used a space telescope to look at 26 faraway galaxies where very few new stars are being made. Most have a small, tightly packed middle surrounded by a wider disk. By studying their light, the scientists worked out that the middles likely formed earlier and stopped making new stars faster than the outer parts. It is like a star-making workshop closing in the middle before closing around the edges. The scientists have ideas about why this happened, but they have not shown for sure what caused it.
Zhimin Zhou, Jianfei Liu
AstronomerArchival HST/WFC3 F275W imaging of 70 barred galaxies and 95 unbarred controls, matched in stellar mass, optical color, redshift, and F275W background noise, yields 95,486 UV-bright star-forming clumps identified with a uniform dendrogram-based procedure. Barred galaxies exhibit a relative clump deficit at intermediate radii broadly spanning the bar, a local recovery near R/R_bar ~ 1, and preferential alignment along the bar major axis. Spatial differences are stronger at higher galaxy mass. Normalized bar length is more closely associated with radial redistribution and central F275W concentration than bar ellipticity, but its association with azimuthal structure is less uniform. Clump luminosity and size distribution functions remain broadly similar between samples. These observational comparisons suggest that bars primarily reorganize recent star formation spatially rather than substantially changing individual UV-clump luminosities and sizes; they do not establish whether bars change the total amount of recent star formation.
PublicA comparison of ultraviolet images of 70 galaxies with stellar bars and 95 otherwise matched galaxies without bars finds differences mainly in where young star-forming clumps appear. Barred galaxies have fewer clumps across the region occupied by the bar, followed by a local recovery near its ends, and their clumps tend to line up along the bar. These patterns are stronger in more massive galaxies. The bar’s length relative to the galaxy is more closely linked to some of these patterns than how elongated the bar is. Yet the clumps’ brightness and size distributions are broadly similar in the two groups. The findings suggest that bars mainly rearrange the locations of recent star formation, without substantially changing the brightness or sizes of individual clumps. They do not settle whether bars change the total amount of recent star formation.
Young explorerSome galaxies have a long bar of stars across their middle. Scientists looked at pictures showing bright patches where stars have recently formed. In galaxies with bars, they found fewer patches in the bar’s region, with more again near its ends. The patches also tended to line up with the bar. But the patches had much the same mix of sizes and brightnesses as those in galaxies without bars. This suggests that a bar mostly changes where new stars form. It does not tell us whether the galaxy makes more or fewer new stars overall.
Zhenhao Wang, Shude Mao, Hongjing Yang+3 more
AstronomerMulti-epoch HST/WFC3 UVIS imaging of 27 southern bulge fields, spanning 3–13 years and tied to the Gaia DR3 absolute reference frame, yields absolute proper motions for approximately 400,000 stars. Colour–magnitude diagrams support bulge–disc separation, red clump identification, and extinction and reddening corrections. The mean latitudinal proper motion is consistent with Sgr A*; the longitudinal mean is affected by disc contamination but agrees with Sgr A* after extrapolation to the Galactic plane. Proper motion dispersions rise towards the Galactic centre, with a steeper longitudinal gradient at negative longitude, interpreted as revealing the bulge’s non-axisymmetric bar. The measured anisotropy is σ_l/σ_b = 1.131 ± 0.005, while the normalised covariance is approximately −0.085 at positive longitude and near zero at negative longitude. Both proper motion components have non-Gaussian distributions, attributed mainly to foreground disc contamination.
PublicAstronomers combined Hubble images taken 3–13 years apart with Gaia’s reference frame to measure the apparent motions of about 400,000 stars in 27 fields towards the Milky Way’s central bulge. The spread of stellar motions grows towards the Galactic centre and changes differently on opposite sides, providing evidence of the bulge’s bar-shaped structure. Motions also have a larger spread along the Galactic plane than perpendicular to it. The average perpendicular motion agrees with that of the central black hole, Sgr A*. The average motion along the plane agrees only after extrapolating the measurements to the plane, and is affected by foreground disc stars. Those foreground stars also account for much of the departure of the motion distributions from a bell-shaped curve.
Young explorerAstronomers compared pictures taken years apart to see how about 400,000 stars appear to move near the middle of our galaxy. The stars do not all move alike: their movements are more spread out closer to the middle, and the pattern is different on the two sides. These clues point to a long, bar-shaped group of stars there. Some nearer stars get mixed into the pictures, so the astronomers have to be careful when working out what the faraway stars are doing.
Chen Chen, Wei-Jian Lu, Ying-Ru Lin+1 more
AstronomerMedium-resolution VLT/X-shooter spectroscopy of SDSS J004613.54+010425.7 (z_em = 2.150), obtained for TOLL, resolves twelve narrow absorption components spanning approximately 2700 km/s in C IV, N V, Si IV, and Lyα, approximately 2.4 times the number identified in lower-resolution SDSS spectra. The authors detect fourteen line-locking pairs: three in Si IV, six in N V, and five in C IV, forming one of the largest known line-locking webs. Monte Carlo simulations place the probability of a chance twelve-component web below 10^-5. Cloudy photoionization modeling yields log U approximately -2.4 to -0.6 and log N(H) approximately 18.4 to 20.6. Ion column densities and ionization parameters of shadowing and shadowed clouds typically agree within a factor of approximately three, broadly supporting radiative acceleration. Several outliers suggest that multi-ion locking and cloud-cloud interactions may also influence stability. The study highlights the importance of medium- and high-resolution spectroscopy for resolving line-locked outflows.
PublicA more detailed spectrum of the quasar SDSS J004613.54+010425.7 reveals a complex pattern in gas flowing away from it. Researchers resolved twelve narrow absorption components, about 2.4 times as many as earlier, lower-resolution observations had identified. They found fourteen pairs linked by characteristic velocity patterns called line-locking, providing evidence that radiation drives the outflow. Computer simulations put the probability of this twelve-component pattern arising by chance below one in 100,000. Separate modeling estimated the gas properties. Clouds that shadow others generally have similar ionization conditions and ion column densities to the clouds they shadow, broadly supporting the radiation-driven interpretation. Some exceptions suggest that interactions between clouds and locking involving multiple ions may also help maintain the pattern. The findings show how finer spectral detail can uncover complexity missed in lower-resolution observations.
Young explorerScientists studied light from a very bright object called a quasar. They found twelve parts of gas moving away from it, with patterns that show light is pushing the gas. Their computer tests said the patterns were very unlikely to happen just by chance. Some gas did not fit the usual picture, so the clouds may also affect one another.
Tobias J. Looser, Francesco D'Eugenio, William M. Baker+19 more
AstronomerJWST Cycle 3 OASIS used deep, 28-hour NIRSpec/PRISM spectroscopy to deliberately sample suppressed star formation at z>4. The study identifies three mini-quenched galaxies with log(M*/Msun)=8.3–8.9, undetectable Balmer emission, and star-formation rates at least 1.2–1.7 dex below the star-forming main sequence (SFMS); five lulling galaxies with weak Balmer emission above the quenching threshold; and 17 nearly-main-sequence galaxies just below the SFMS. Spectroscopy was essential: seven of ten photometric suppression candidates proved to lie near or above the SFMS, while photometric fits overestimate current star-formation rates and fail to distinguish lulling from mini-quenching. In tiers not selected by star-formation state, five suppressed systems constitute 29% of galaxies at z=4–5.5 and log(M*/Msun)=8–9.5, implying a number density of approximately 1.6×10^-3 Mpc^-3 dex^-1. Simulations predict roughly tenfold lower abundances at these masses and favor suppression at lower masses. Balmer-break strength and stellar age increase below the SFMS: light-weighted ages rise from 5 Myr above it to approximately 30 Myr for lulling systems and over 100 Myr for mini-quenched systems. Low stellar reddening, E(B−V)<0.2, is consistent with, but does not establish, depleted gas reservoirs. The authors interpret these findings as evidence that suppressed phases are common and lasting components of early galaxy growth.
PublicSome early galaxies slow their star formation dramatically rather than making stars steadily. Using deep JWST spectroscopy, the OASIS team deliberately searched for these quieter galaxies and identified three with no detectable Balmer emission, a sign of strongly suppressed star formation, plus five with weaker suppression. In the part of the sample selected without regard to star-forming activity, suppressed galaxies accounted for 29% within the studied distance and mass range. Simulations predict about ten times fewer at these masses. The quieter galaxies also have older light-weighted stellar populations, supporting the authors’ interpretation that these quiet phases are not merely brief interruptions. Their low dust reddening is consistent with depleted gas supplies, although it does not prove that explanation. Spectroscopy was crucial: estimates based on photometric measurements often misidentified quiet galaxies or overstated their current star formation.
Young explorerGalaxies are huge groups of stars, and some made new stars much more slowly for a while when the universe was young. Astronomers used the JWST telescope to find these quiet galaxies. They found more than computer models expected, and the quieter galaxies had older stars. The team thinks these quiet times are an important part of how early galaxies grew.
Tobias J. Looser, Francesco D'Eugenio, William M. Baker+19 more
AstronomerUsing NIRSpec/PRISM spectra of 54 OASIS galaxies at z>4 with masses of 10^8–10^9.5 solar masses, the authors compare Balmer-line SFRs with 100-Myr stellar-continuum averages. The sample includes three mini-quenched galaxies and five still-star-forming lulling galaxies at least 0.6 dex below the star-forming main sequence (SFMS). Above the SFMS, rising and fading systems occur equally often; below it, fading systems dominate. The lulling galaxies formed little more than a tenth of their stellar mass in the past 100 Myr, with declines beginning tens to roughly 100 Myr before observation. The authors infer suppressed episodes lasting about 100 Myr, comparable to or longer than in most simulations, and much faster recovery, based on the scarcity of rising systems below the SFMS. [OIII]/[OII] decreases toward the lulling population even at fixed mass and after dust correction, tracking SFR_10/SFR_100 more closely than SFMS offset. Two rising galaxies below the SFMS remain highly ionized. The authors interpret these trends as consistent with fewer, softer ionizing photons encountering gas depleted by earlier star formation. Declines faster than passive gas exhaustion favor feedback that expels gas or inhibits star formation, rather than establishing a unique suppression mechanism.
PublicA study of 54 low-mass galaxies in the early universe examines how their star formation slows down and how their gas responds. Comparing estimates of recent star formation with averages over 100 million years, the researchers find that galaxies below the usual star-forming level are mostly fading rather than recovering. They infer that quiet episodes last roughly 100 million years, as long as or longer than in most simulations, while recovery appears much quicker. The gas also changes: a ratio of oxygen emission lines tracks recent changes in star formation more closely than whether a galaxy lies above or below the usual level. Two galaxies below that level but increasing their star formation still have highly ionized gas. The declines appear too fast to explain simply by gradual use of the gas supply. The authors therefore favor feedback that removes gas or prevents it from making stars, although the observations do not establish exactly how this happens.
Young explorerGalaxies make stars from gas, but sometimes they slow down. Scientists studied light from 54 small galaxies in the early universe. They found clues that some stayed quiet for about 100 million years, while starting up again may happen much faster. Light from their gas also changes as star-making changes. The scientists think something pushes gas away or stops it from making stars, rather than the galaxies simply using it all up. They do not yet know exactly how.
William M. Baker, Tobias J. Looser, Francesco D'Eugenio+17 more
AstronomerThe OASIS study combines JWST/NIRSpec MSA PRISM spectroscopy and NIRCam imaging for 51 galaxies at z ≥ 4, sampling main-sequence, starburst, lulling, and mini-quenched systems. Its sensitivity reaches log10(M_star/M_sun) = 8.3 and log10(SFR/[M_sun yr^-1]) < -1.6, extending more than an order of magnitude below the star-forming main sequence. ForcePho UV/optical half-light radii show a clear anti-correlation with burstiness, traced by the ratio of Hα-derived SFR to the non-parametric spectral-fitting SFR averaged over 100 Myr. Partial correlations indicate that this association cannot simply be explained by secondary stellar-mass or redshift dependencies. The authors interpret the trend as centrally concentrated starbursts reducing measured half-light radii in systems with rising SFRs, rather than demonstrating physical contraction. If the same mechanism operates at z > 10, they suggest it could explain the reported size bimodality of UV-luminous galaxies; this extension remains conditional.
PublicUsing James Webb Space Telescope spectra and images, researchers studied 51 galaxies in the early universe, including galaxies forming stars rapidly and others undergoing quieter periods. They found that galaxies with stronger recent bursts of star formation tend to have smaller measured sizes, defined by the radius enclosing half their light. The relationship cannot simply be explained by differences in stellar mass or redshift. The researchers suggest that intense star formation near galaxy centers concentrates the light, making galaxies appear more compact without necessarily making their stars physically move closer together. This is an interpretation of the observed relationship. If the same process operates in even earlier galaxies, it could help explain why ultraviolet-bright galaxies there show two size groupings, but the study does not establish that extension.
Young explorerScientists used the James Webb Space Telescope to study 51 faraway galaxies. Galaxies having bigger bursts of new stars tended to have their light packed into a smaller space. The scientists think bright new stars near the middle could make a galaxy look smaller, even if the whole galaxy has not squeezed together. That is their explanation for what they saw, not something they have proved.
Vinay Kumar, Philipp Grete
AstronomerThis proof-of-concept simulation study tests whether mixed reconstruction schemes can control the effective magnetic Prandtl number, Pm, in finite-volume implicit large eddy simulations (ILES). The authors simulate driven, subsonic, homogeneous MHD turbulence with five pairs of hydrodynamic and magnetic reconstruction schemes at varying resolutions, inferring effective viscosity and magnetic diffusivity from interscale energy transfer. Higher-order magnetic reconstruction relative to fluid reconstruction raises Pm; reversing the ordering lowers it. Mixing second- and third-order reconstruction produces a change in Pm of at least about a factor of 20. Direct numerical simulations with matched explicit dissipation agree with the ILES. Within the tested setup, mixed reconstruction therefore provides a simple, efficient route to exploring Pm substantially different from unity without adding explicit dissipation.
PublicTurbulence can amplify and reshape magnetic fields in space. Its behavior depends on the magnetic Prandtl number: the ratio of viscosity, which smooths fluid motion, to magnetic diffusivity, which smooths magnetic fields. In some computer simulations, both effects are set by the numerical method rather than chosen directly. This study tests a way to adjust their ratio by using different calculation methods for the fluid and its magnetic field. In simulations of uniformly driven turbulence moving slower than sound, the researchers changed the effective ratio by at least about a factor of 20 using a mix of second- and third-order methods. Simulations with explicitly specified smoothing effects agreed with those results. This is a computational proof of concept, not an astronomical observation, and offers a way to explore a wider range of magnetic turbulence in this type of simulation.
Young explorerScientists use computers to pretend to stir gas that has a magnetic field. The computer's rules can smooth out the gas's swirls and the magnetic field in different ways. The scientists tried different rules for each and found they could change the balance between those two kinds of smoothing a lot. Another kind of computer test agreed. This could help them study magnetic swirls in space, but these results came from computer experiments, not from watching real space gas.
Rojin Bayati, Paolo Salucci
AstronomerAn analysis of recently inferred dark matter halo densities in three dwarf spheroidal galaxies finds strong disagreement with the NFW ΛCDM profile, while a cored Burkert profile reproduces the densities very well. The fitted central densities and core radii are related to each other and to the stellar-component length scale in a manner similar to that found in disk systems. The innermost halo-density properties show no trace of a central intermediate-mass black hole or nuclear stellar cluster; this is a nondetection, not proof of their absence.
PublicResearchers studied estimates of how dark matter is distributed in three small galaxies. A model in which dark matter becomes sharply concentrated toward the center disagrees strongly with those estimates, whereas a model with a flatter central region fits them very well. The central dark matter density, the size of that flatter region, and the scale of the stars’ distribution are linked in ways similar to those seen in disk galaxies. The analysis finds no sign of a central intermediate-mass black hole or a compact central star cluster, though it does not establish that these objects are absent.
Young explorerScientists studied three small galaxies to learn where their invisible dark matter is. Their clues fit a picture where dark matter is spread more evenly near the middle, rather than piling up sharply at the very center. The size of this middle part and how much dark matter it holds seem linked to how the stars are spread out. They found no sign of a black hole or a tight bunch of stars at the center, but that does not prove there is nothing there.
Sijia Li, Xin Wang, Matthew A. Malkan+14 more
AstronomerJWST/NIRISS slitless spectroscopy from PASSAGE provides spatially resolved emission-line maps for 17 spectroscopically confirmed galaxies in candidate interacting systems at z ≈ 1.7–3.2. The sample spans log(M*/M☉) ≈ 7.3–10.4 and global gas-phase oxygen abundances of 12 + log(O/H) ≈ 7.6–8.7. Individually measured radial metallicity gradients range from approximately −0.2 to +0.45 dex kpc⁻¹. Mean gradients in stellar-mass and redshift bins agree with previous measurements, and the scatter is not significantly different from that in a heterogeneous literature compilation. A tentative anti-correlation between gradient and metallicity offset from the mass–metallicity relation has a best-fit slope of −0.30 ± 0.06. Comparable-mass pairs tend toward positive gradients and unequal-mass pairs toward negative gradients, but neither tendency is statistically significant. Interaction-driven changes in star formation, enrichment, and gas redistribution are possible interpretations, not established causes.
PublicAstronomers used the James Webb Space Telescope to map how the abundance of heavy elements changes from the centers to the outskirts of 17 distant galaxies in systems that may be interacting. Some galaxies have more enriched gas toward their centers, while others show the reverse. Their average patterns and the spread of measurements are consistent with earlier studies. The researchers found tentative evidence that galaxies whose overall enrichment is lower than typical for their stellar mass have more outward-increasing enrichment patterns. Galaxies paired with similarly massive companions also tend to differ from those with unequal-mass companions, but those tendencies are not statistically significant. The findings suggest that interactions may help rearrange gas and heavy elements, without establishing that interactions caused the observed patterns.
Young explorerAstronomers used the James Webb Space Telescope to study 17 faraway galaxies that might be interacting with other galaxies. They made maps of heavy elements in the galaxies’ gas. Some galaxies had more of these elements near the middle, and others had more farther out. The scientists found a few clues that galaxies might move gas and elements around when they interact, but they are not sure yet.
Priyanka Jalan, Tomotsugu Goto, Tetsuya Hashimoto+5 more
AstronomerThe study analyzes 2,709 sources in a multiwavelength JWST catalog cross-matched between SMILES and JADES, spanning 0.05 < z < 6 and lookback times of 0.8–12.9 Gyr. Pearson correlations link AGN luminosity strongly to SFR and dust luminosity (approximately 0.8), more weakly to stellar mass (approximately 0.5), and negatively to SFH duration and stellar age (approximately −0.4). The apparent age–AGN luminosity anticorrelation is attributed to cosmic time rather than a direct physical connection. PCA identifies two principal dimensions of diversity: AGN/galaxy activity and stellar age. At higher redshift, AGN accretion, star formation, and dust emission are closely associated; in the present-day Universe, host-dominated systems with f_AGN ≤ 0.2 show distinct quiescent and star-forming populations. The authors interpret these findings as evidence that current cold-gas supply primarily regulates AGN luminosity, with recent star formation tracing that supply and stellar mass setting the overall potential. This physical picture is an interpretation of the observed relationships, not a direct causal measurement.
PublicA study of 2,709 sources observed with the James Webb Space Telescope explores how active galactic centers and their host galaxies change across cosmic history. Brighter active centers are strongly associated with more star formation and brighter dust emission. An apparent connection between brighter centers and younger stars is attributed to when the galaxies are observed in cosmic history, rather than a direct link between stellar age and central activity. In the earlier Universe, central black-hole growth, star formation, and dust emission track one another closely. Near the present day, galaxies whose light is mostly from their hosts fall into two distinct groups: star-forming and quiet. The researchers interpret these patterns as evidence that a shared supply of cold gas links black-hole growth and star formation, especially early in cosmic history; the correlations alone do not establish that explanation as a direct cause.
Young explorerScientists studied lots of galaxies, which are huge groups of stars. They found that galaxies with brighter, busy centers often also make more new stars and have dust that shines more brightly. This link was especially close long ago. They think gas may help both the center and new stars grow, like shared food. But seeing things happen together does not prove why they happen.
Junhee Myong, Jong-Hak Woo, Mohammad-Hassan Naddaf+2 more
AstronomerThe authors investigate the Hβ BLR size–5100 Å luminosity relation with a Bayesian viewing-angle inference framework based on the Failed Radiatively Accelerated Dusty Outflow (FRADO) model. They add a phase factor describing the anisotropic visibility of illuminated cloud surfaces and constrain viewing angles by matching model BLR sizes to measured Hβ lags for 151 AGN. The framework reproduces the observed relation’s slope and intrinsic scatter. Inferred inclinations broadly agree with estimates from dynamical modeling of velocity-resolved reverberation data, but with substantial scatter. Because Hβ lags and line velocities depend on inclination, their calibration typically yields larger black hole masses than reverberation estimates using an average virial factor. These are model-dependent inferences that offer a physical interpretation of the relation and its implications for systematic uncertainties in reverberation and single-epoch mass estimates.
PublicThe researchers examine how the size of a gas region in an active galaxy relates to its brightness, focusing on how the angle from which we see it affects the measurements. They update a model of dusty gas clouds to account for how much of each cloud’s illuminated surface is visible, then compare the model with measured delays in hydrogen emission from 151 active galaxies. Their method reproduces both the trend and the underlying spread in the observed size–brightness relationship. The inferred viewing angles broadly match estimates from another modeling approach, although the differences are substantial. Accounting for viewing angle also typically gives larger central black hole masses than a commonly used reverberation-based calculation. The study offers a model-based explanation for the relationship and highlights uncertainties in black hole mass estimates, rather than providing direct measurements of the viewing angles.
Young explorerGas near a black hole can glow after light reaches it. Scientists measured these light delays in 151 bright galaxy centers. They used a computer model to ask whether looking at the glowing gas from different directions could help explain its apparent size and brightness. The model matched the main pattern and how much the measurements spread out. It also suggested that the black holes are usually heavier than another way of estimating their weight says. But these answers depend on the model, and the viewing directions are still uncertain.
Zoe Harvey, Sahyadri Krishna, Rita Tojeiro+45 more
AstronomerUsing DESI DR2 background-quasar spectra, this statistical study stacks Mg II absorption in approximately 143 million galaxy–quasar pairs to probe cool gas around massive galaxies at 0.4 < z < 0.76. Mean equivalent width decreases with projected separation for every spectral class. Within 71 kpc, post-starburst galaxies show stronger absorption (1.58 ± 0.32 Å) than comparable-mass star-forming (0.69 ± 0.15 Å) or quiescent galaxies (0.22 ± 0.05 Å). Among post-starburst subsamples, younger systems have stronger, more centrally concentrated absorption and steeper radial declines; older systems have weaker inner absorption and enhanced absorption at roughly 300–1000 kpc. Independent Bagpipes star-formation-history fits support the age ordering. The authors interpret these statistical trends as outward redistribution of cool gas by feedback-driven winds, consistent with characteristic speeds of a few hundred km/s and a persistent inner reservoir. The absorption measurements do not directly track individual gas clouds moving outward.
PublicAstronomers used light from background quasars to study cool gas around massive galaxies whose bursts of star formation have ended. Combining many spectra, they found that magnesium absorption is strongest around these post-starburst galaxies, compared with similarly massive galaxies that are still forming stars or are quiescent. Galaxies observed sooner after their burst show absorption more concentrated near the galaxy; those further past the burst show weaker absorption nearby and stronger absorption at intermediate distances. Independent estimates of their star-formation histories support this age sequence. The researchers interpret the pattern as cool gas being pushed outward by winds, while some remains near the galaxy. This is an interpretation of statistical comparisons, not direct observation of gas moving over time.
Young explorerScientists used light from faraway bright objects to look for cool gas around galaxies. Galaxies whose big burst of star-making ended more recently had a stronger gas sign close by. Those whose burst ended longer ago had a stronger sign farther out. The scientists think winds may push some gas away while some stays nearby, but they did not watch the gas move.
Manuel Bayer, Else Starkenburg, Annemarijn Zwerver+8 more
AstronomerThe authors use a hierarchical Bayesian mixture model to distinguish candidate blue horizontal branch (BHB) stars from blue stragglers and outliers in a colour-colour diagram. CaHK photometry from Gaia XP spectra and the Pristine survey yields a shallow catalogue of 7,057 stars and a deeper catalogue of 8,824 stars, with the latter restricted to the Pristine footprint. The shallow sample extends the tracing of previously identified 6D halo substructures beyond their initial identification within 2.5 kpc of the Sun, including Gaia-Enceladus, Thamnos, the Helmi streams, Sequoia, ED-3, ED-4, and ED-6. The deep sample supplies reliable distances for more detailed 3D mapping of the Sagittarius stream and Pisces Overdensity. The authors also add candidate BHB stars with line-of-sight velocities to existing catalogues and confirm previously reported north-south Galactic hemisphere differences. Infall of the Large Magellanic Cloud is presented as the likely explanation, not an established cause.
PublicBlue horizontal branch stars can act as distance markers and tracers of motion in the Milky Way’s halo. This study uses measurements from Gaia and the Pristine survey, together with a statistical method that separates likely members from look-alike stars, to build two catalogues containing 7,057 and 8,824 candidate stars. The deeper catalogue covers a more restricted area of sky. These samples help trace previously known halo structures farther from the Sun and map the Sagittarius stream and Pisces Overdensity in greater three-dimensional detail, reaching beyond distances where Gaia parallaxes are useful. The researchers also add candidates with measured speeds toward or away from us to existing catalogues. They confirm previously reported differences between the Galaxy’s northern and southern halves, likely—but not definitively—linked to the infall of the Large Magellanic Cloud.
Young explorerSome stars can help us tell how far away things are in the cloud of stars around our galaxy. Scientists made two lists of stars they think are good distance markers, while trying to leave out look-alikes. They used these stars to make better maps of star trails and crowded patches. They also checked that the galaxy’s two halves move differently. A smaller galaxy falling in may help explain that difference, but they are not sure.
Claire Guillaume, Alicia Rivero, Titouan Le Guillois+3 more
AstronomerThe study compares simulated stellar-stream disruptions caused by dark matter subhalos, a galactic bar, and a galaxy merger. Spurs arise more frequently from the merger in these simulations, but their morphologies are similar across all three mechanisms. This degeneracy cautions against using spur morphology alone to identify the perturbing mechanism or constrain the nature of dark matter; the findings are simulation-based, not an observational identification of spur origins.
PublicSide branches, or spurs, along streams of stars have been proposed as clues to clumps of dark matter. This study uses simulations to compare disturbances caused by dark matter clumps, a galaxy’s central bar, and a merger between galaxies. The merger produces spurs more often in these simulations, but all three causes produce similar-looking features. A spur’s appearance alone therefore cannot reliably reveal what caused it or establish the nature of dark matter.
Young explorerStars can make long trails with little branches sticking out. Scientists used computer models to see how those branches might form. Clumps of invisible dark matter, a bar-shaped part of a galaxy, and galaxies joining together could all make branches that look alike. So just looking at a branch is not enough to tell what made it.
Manuel Alejandro Chacón, Bernardo Cervantes Sodi, Yara Jaffé
AstronomerUsing a volume-limited NASA-Sloan Atlas sample of central and satellite galaxies with probabilistic morphology and bar identification, this observational study examines bar likelihood across galaxy properties and environments. Stellar mass and morphology show the strongest associations: at fixed morphology, bar probability increases with stellar mass, particularly for late-type galaxies, while early-type galaxies have systematically lower probabilities than late types across the stellar mass range. Apparent trends with halo mass and cluster-centric distance largely reflect changes in morphological composition. In particular, the lower bar likelihood near massive-halo centres is interpreted as reflecting the increased early-type fraction rather than direct environmental suppression. After accounting for stellar mass and morphology, residual analysis detects no statistically significant dependence on halo mass or normalized cluster-centric distance within the sample's sensitivity.
PublicA study of galaxies in environments ranging from isolated systems to massive groups finds that a galaxy's stellar mass and shape are most closely associated with its likelihood of having a stellar bar. These bars are elongated arrangements of stars within galaxies. Among galaxies of the same morphological type, those with more mass in stars are more likely to host bars, especially among late-type galaxies. Early-type galaxies have lower bar probabilities than late-type galaxies across the stellar mass range. Bars also appear less likely near the centres of massive galaxy haloes, but the analysis indicates that this mostly reflects the greater proportion of early-type galaxies there, rather than the surroundings directly suppressing bars. Once stellar mass and morphology are accounted for, no statistically significant environmental dependence remains detectable within this sample's sensitivity.
Young explorerSome galaxies have stars arranged in a long shape called a bar. Astronomers looked at many galaxies and found that a galaxy's shape and how much star stuff it has are the biggest clues to whether it has a bar. For galaxies of the same kind, ones with more star stuff are more likely to have bars. Galaxies near the middle of big groups seem less likely to have bars, but mostly because different kinds of galaxies live there. After allowing for galaxy type and star stuff, the astronomers could not clearly detect an extra link to where a galaxy lives. That does not prove there is no link at all.
Liman Tian, Ziyu Xiang, Wenli Zou+1 more
AstronomerThe study calculates HMgC3N–He rotational excitation and de-excitation data for non-LTE modelling of molecular clouds. A two-dimensional potential energy surface computed with CCSD(T)-F12A/aug-cc-pVTZ feeds quantum close-coupling calculations for transitions with Δj = ±1, ±2 and ±3, covering levels through j = 20 and temperatures of 3–50 K. The calculated rate coefficients favour Δj = ±2 transitions. Incorporating these data into radiative transfer modelling of observed line emission, χ² minimization gives a best-fitting H2 volume density of 1.233 × 10^5 cm^-3 and HMgC3N column density of 1.831 × 10^12 cm^-2. These are model-derived quantities; the abstract describes the column density as approximately consistent with an observational estimate of (3.0 ± 0.6) × 10^12 cm^-2. The calculated collision partner is He, whereas the fitted cloud density is reported for H2; the abstract does not specify how that connection is handled.
PublicResearchers calculated how collisions with helium change the rotation of the molecule HMgC3N, helping interpret the light it emits in molecular clouds where its rotational states are not in thermal equilibrium. Their quantum calculations cover temperatures of 3–50 kelvin and indicate that collisions favour changes of two rotational steps over the other changes studied. They then used the calculated collision data in a model of observed spectral lines to estimate the cloud’s hydrogen density and the amount of HMgC3N along the line of sight. The best-fitting amount was 1.831 × 10^12 molecules per square centimetre, which the authors describe as approximately agreeing with an observational estimate of (3.0 ± 0.6) × 10^12. These estimates depend on modelling, rather than being direct counts of molecules.
Young explorerTiny molecules in space can spin and give off light. Scientists used calculations to work out how bumps from helium change the spin of a molecule called HMgC3N. In their calculations, changes of two spin steps were more likely than the other changes they studied. They used these results to help read light seen from a space cloud and estimate how crowded the cloud is and how much of this molecule is there. Those answers are estimates from a model, not exact counts.
Shengtao Wang, Xiaohui Sun, Jiangtao Li+2 more
AstronomerUsing public ASKAP observations, the study examines integrated 943 MHz radio–infrared and radio–SFR relations for 875 galaxies within 50 Mpc. Excluding identified or candidate AGN leaves 594 galaxies. Bayesian errors-in-variables fits account for measurement uncertainties, intrinsic scatter, and correlated distance errors. The AGN-cleaned radio–infrared relation has a slope of 1.09 ± 0.02 and orthogonal intrinsic scatter of 0.21 ± 0.01 dex, tighter than the AGN-host relation. For 592 AGN-cleaned galaxies, the radio–SFR slope is 1.02 ± 0.02, with intrinsic scatter of 0.25 ± 0.01 dex. Semi-calorimetric models yield weak positive secondary dependences on stellar mass, γ = 0.09 ± 0.03, and rotation velocity, δ = 0.24 ± 0.08. Their consistency suggests, but does not establish, that gravitational potential weakly regulates cosmic-ray electron confinement and synchrotron efficiency. The study provides an integrated 943 MHz radio–SFR calibration for nearby galaxies while retaining these secondary dependences.
PublicRadio emission can help estimate how quickly nearby galaxies form stars, but the relationship is not exact. This study used ASKAP radio observations of 875 galaxies within 50 megaparsecs. After removing galaxies with known or suspected active galactic nuclei, the researchers found that radio brightness tracks infrared brightness closely. In 592 galaxies without such identified or suspected activity, radio luminosity increased almost in direct proportion to the star-formation rate, although individual galaxies varied around that average relationship. Models also indicated weak additional links with stellar mass and rotation speed. The authors interpret these trends as possible evidence that a galaxy’s gravity affects how well it traps the energetic electrons responsible for synchrotron radio emission; that explanation is not established. The results provide a calibration for estimating nearby galaxies’ star-formation rates from their total 943 MHz radio emission.
Young explorerGalaxies are huge groups of stars, and some are busy making new stars. Scientists studied radio signals from nearby galaxies and found that galaxies making stars faster usually send out stronger radio signals. They left out galaxies with known or suspected active centers that could add extra signals. The pattern was not perfect: galaxies with the same star-making speed could send out different amounts of radio light. The scientists think a galaxy’s gravity might help keep tiny, fast-moving particles inside it and affect its radio signal, but they have not proved that idea.
Tung Wei Goh, Satoya Nakano, Kengo Tachihara+1 more
AstronomerGaia DR3 astrometry and ThrUMMS 12CO(J=1–0) data are used to investigate the star-formation history of NGC 6357. HDBSCAN independently recovers the previously cataloged G352.8+0.6 alongside Pismis 24, G353.1+0.6, and G353.2+0.6. Isochrone fitting gives G352.8+0.6 an age of 7.9 (+1.5/−1.4) Myr, versus approximately 1–3 Myr for the other three clusters. A linear traceback, assuming constant relative plane-of-sky motion, places G352.8+0.6 closest to the young clusters’ reference center approximately 1.8 Myr ago. The +2 km/s CO component overlaps G352.8+0.6 in projection and has localized integrated-intensity depressions around three spectroscopically identified massive members. The −4 and +2 km/s components exhibit complementary projected distributions and intermediate-velocity emission in position–velocity space. Conditional on the +2 km/s component being physically associated with G352.8+0.6 and sharing its transverse motion, the authors interpret these findings as evidence for an interaction between the molecular structures around 1.8 Myr ago. Compression from that interaction may have contributed to recent clustered and high-mass star formation and the formation of Shell A, with subsequent stellar feedback potentially reshaping the shell.
PublicResearchers studied the motions of stars and the distribution and velocities of molecular gas in the star-forming region NGC 6357. They recovered a known cluster, G352.8+0.6, and estimated its age at about 7.9 million years, with uncertainty of roughly 1.5 million years, making it older than three nearby clusters estimated to be 1–3 million years old. Projecting the stars’ motions backward at constant relative speed across the sky suggests that the older cluster passed closest to the younger clusters’ reference center about 1.8 million years ago. Two gas structures show complementary patterns on the sky and gas emission at velocities between them. The authors suggest that these structures interacted around that time, possibly compressing gas and helping form the younger clusters, massive stars, and a feature called Shell A. This interpretation depends on an unconfirmed assumption: that one gas structure was physically associated with the older cluster and moved with it across the sky. Later effects from stars may have reshaped the shell.
Young explorerAstronomers looked at groups of stars and clouds of gas in a place called NGC 6357. They found that one star group seems much older than three others. By tracing how the stars move, they think the older group was closer to the younger groups about 1.8 million years ago, if the stars kept moving steadily. The gas also shows clues that two clouds may have bumped into each other. That bump might have squeezed gas and helped new stars form. But this is not certain: the idea depends on one cloud having been near the older stars and moving along with them.
Nashiba Parbin
AstronomerThis theoretical study examines weak-field gravitational lensing by a charged black hole in mimetic Euler-Heisenberg theory. For an asymptotically flat spacetime with both source and observer at finite distances, the authors compute the light-deflection angle using the Gauss-Bonnet theorem and analytically derive the Einstein ring radius. They discuss how the Euler-Heisenberg and charge parameters affect that radius, analyze magnification and distortion, and briefly consider lensing time delays. The calculations indicate that the model parameters significantly influence lensing signatures, but the abstract provides neither quantitative effect sizes nor observational measurements.
PublicThis theoretical study explores how a charged black hole would bend light in a particular gravity model called mimetic Euler-Heisenberg theory. The researchers calculate the bending where gravity is relatively weak, allowing both the light source and the observer to be at finite distances from the black hole. They also derive the size of an Einstein ring, a ring-shaped image produced by gravitational lensing, and examine image brightening, distortion, and light-travel delays. Their calculations indicate that the black hole's charge and another parameter of the model affect these light patterns. The abstract reports theoretical predictions, not observations, and does not specify how large the effects would be.
Young explorerA black hole can bend passing light, a bit like a lens. Scientists used math to study how a black hole with electric charge might bend light in one special theory. They worked out how big a ring of light could look and studied how images could become brighter or change shape. Their math says changing parts of the model changes the light patterns. They did not report seeing these patterns in the sky.
Stanislav Boldyrev, Daniel Humphrey, Vadim Roytershteyn
AstronomerSuprathermal ion tails throughout the heliosphere exhibit a common spectrum, f(v) ∝ v⁻⁵. The authors show that scale-by-scale equipartition between strong Alfvénic turbulence and accelerated ions predicts this slope and the absolute amplitude, F(v) = B²/(16π³m_i v⁵), without free parameters. The prediction agrees within a factor of a few with ACE and Voyager 1 spectra spanning three decades in magnetic energy. They interpret this level as saturation reached through local acceleration by strong turbulence; quiet-time tails fall well below it, consistent with, but not establishing, nonlocal acceleration.
PublicFast-moving ions throughout the region influenced by the Sun show a common pattern: their abundance falls steeply with increasing speed. The authors propose that a balance, at each scale, between energy in strong magnetic turbulence and the ions it accelerates explains both this pattern and its overall strength without adjustable parameters. Their prediction matches ACE and Voyager 1 measurements to within a factor of a few across a thousandfold range in magnetic energy. They argue that ions reach the predicted level where strong turbulence accelerates them nearby. Much weaker populations during quiet periods are consistent with acceleration elsewhere, though this interpretation is not proven.
Young explorerTiny particles around the Sun can move very fast. Scientists made a rule for how many fast particles there should be if strong wiggles in the Sun’s magnetic field give them energy nearby. Their rule comes fairly close to spacecraft measurements, but it does not match exactly. When things are quiet, there are far fewer fast particles. The scientists think those particles may have gotten their push somewhere else.
Tiger Yu-Yang Hsiao, Fengwu Sun, Xiaojing Lin+19 more
AstronomerThe SAPPHIRES Early Data Release reports seven extremely metal-poor galaxy candidates at z ≈ 5–7, selected through low R3 = [O III] λ5008/Hβ ratios in deep JWST/NIRCam wide-field slitless spectroscopy from a single pointing. Estimated abundances are 12 + log(O/H) < 7.0, including three sources below 6.7, corresponding to Z < 1% of solar. If confirmed, these candidates would break the roughly 2%-solar metallicity floor seen in most previously identified z > 5 galaxies. They are faint (F200W ≈ 28–30 AB mag), low-mass (log(M*/M☉) ≈ 6.8–7.8), and have blue UV slopes (−2.8 ≲ β ≲ −1.7), interpreted as reflecting little dust or young stellar ages. Their star formation appears exceptionally bursty relative to galaxies at similar redshift. The findings suggest that faint-galaxy searches may probe below the previously observed floor, whose origin could involve bright-source selection biases or rapid enrichment. Deep NIRSpec follow-up is essential to confirm the candidates' nature and establish detailed abundances; this is not a detection of metal-free Population III stars.
PublicAstronomers using JWST have identified seven candidate galaxies in the early universe that may contain exceptionally small amounts of elements heavier than helium, which astronomers call metals. Their estimated metal content falls below a lower limit seen in most previously identified galaxies from this era; three may have less than 1% of the Sun's metal abundance. The candidates are very faint and low-mass, and their light suggests little dust or young stars. They also appear to form stars in unusually strong bursts compared with galaxies at similar distances. The search used oxygen-to-hydrogen emission-line ratios in data from the SAPPHIRES survey. These findings suggest that looking at faint galaxies could help explain why earlier searches rarely found such metal-poor systems. However, deeper observations with JWST's NIRSpec instrument are needed to confirm what these candidates are and measure their chemical makeup in detail. The hypothetical first generation of metal-free stars has not yet been discovered.
Young explorerThe first stars are still hiding from us. Scientists used the JWST space telescope to find seven very faint galaxies that might have very little of the heavier stuff, such as oxygen, that stars help make. That could make them useful places to learn about the early universe. But scientists need a closer look to check what these galaxies are made of. They have not found the very first stars yet.
Ting-Wen Lan, J. Xavier Prochaska, J. Aguilar+39 more
AstronomerUsing approximately 8,000 DESI emission-line-galaxy–quasar pairs at z ~ 1.5, the authors probe the multiphase CGM through MgII and CIV absorption. Mean rest equivalent widths and covering fractions increase with stellar mass at fixed impact parameter, but show similar distributions when distances are normalized by virial radius. Warm CIV-traced gas extends farther than cool MgII-traced gas. Velocity-offset dispersions rise from about 100 km/s within halos to about 200 km/s beyond them. MgII and CIV equivalent widths are only loosely coupled, with several-fold variation in either at fixed strength of the other; the authors interpret this as evidence for distinct phase kinematics. For strong MgII absorbers within 0.2 virial radius, FeII/MgII is enhanced and CIV/MgII suppressed relative to larger scales, each at approximately 4-sigma significance. The authors argue that the observations require gas phases that are not co-spatial. Combining their measurements with literature results, they examine CGM redshift evolution and estimate circumgalactic neutral-hydrogen, metal, and dust masses comparable to those in the ISM.
PublicResearchers used about 8,000 galaxy–quasar pairs observed by the Dark Energy Spectroscopic Instrument to study gas surrounding emission-line galaxies at a redshift of about 1.5. Quasar light passing through this gas carries absorption signatures of magnesium and carbon. At the same physical distance from a galaxy, more massive galaxies show stronger absorption and a higher fraction of sightlines with absorption, but these differences largely disappear when distances are scaled to each galaxy's virial radius. Warmer gas traced by carbon extends farther out than cooler gas traced by magnesium. The two absorption signatures do not closely track one another. Near the galaxies, iron absorption relative to magnesium is enhanced, while carbon absorption relative to magnesium is reduced; both differences have roughly 4-sigma statistical significance. The researchers interpret these findings as requiring different gas phases to occupy different locations. With earlier studies, they also examine how the surrounding gas changes with redshift and estimate that it contains amounts of neutral hydrogen, metals, and dust comparable to those in the galaxies' interstellar gas.
Young explorerGalaxies have gas around them that is hard to see. Scientists studied light from bright objects behind many galaxies to learn about that gas. They found that warmer gas reaches farther out than cooler gas, and the two kinds do not always show up together. The scientists think this means the different kinds of gas are not all in the same places. They also estimate that the gas around these galaxies holds about as much neutral hydrogen, metals, and dust as the gas inside them.
Minju M. Lee, Georgios Magdis, Gabriel Brammer+10 more
AstronomerECOGAL uniformly reprocesses archival ALMA observations within JWST and HST footprints to deliver continuum images and complementary prior-based optical/NIR and blind ALMA source catalogues. Detection thresholds are assessed using peak signal-to-noise statistics and inverted maps. This release targets the ALMA-accessible CANDELS fields COSMOS, GOODS-S, and UDS, encompassing approximately 130,000 optical/NIR-selected galaxies spanning 0<z<15; this range describes the input sample, not the confirmed ALMA detections. The two methods yield 1,288 detections with optical/NIR counterparts, corresponding to 622 unique sources; 832 detections, or 395 unique sources, appear in both catalogues. Of the 622 unique sources, 307 have spectroscopic redshifts spanning 0.12<z<6.85. Relative to A3COSMOS and A3GOODS-S, ECOGAL adds UDS and incorporates public JWST datasets from the DAWN JWST Archive. Proposed applications include dust-continuum-inferred gas fractions across environments, obscured star formation, and optically dark systems; the abstract does not report results for these applications. Science-ready products are publicly available, with a catalogue-usage post on the DJA webpage.
PublicECOGAL brings together existing ALMA observations of sky regions also covered by the James Webb and Hubble space telescopes. The team processes the ALMA data consistently and searches both at the positions of known galaxies and independently for significant signals. In three survey fields, the searches identify 622 distinct ALMA sources with visible-light or near-infrared counterparts. Of these, 307 have spectroscopically measured redshifts. The roughly 130,000 galaxies covered by the project are the starting sample, not the number detected by ALMA. The publicly released images and catalogues are intended to support future studies of galaxy gas supplies, star formation hidden by dust, and systems difficult to see in visible light; those studies are possibilities highlighted here, rather than findings reported in this abstract.
Young explorerScientists sorted old telescope pictures to make a new collection of galaxies, the big groups of stars in space. They found 622 different sources in ALMA pictures that also have matches in other telescope pictures. They shared their collection so other scientists can use it to learn about galaxies, including how dust can hide places where stars form.
Yoshihisa Asada, Seiji Fujimoto, John Chisholm+16 more
AstronomerUsing ultra-deep JWST/NIRCam and NIRSpec observations of the Abell S1063 lensing field from GLIMPSE, the authors characterize metallicity, dust attenuation, and ionizing photon production efficiency in 16 galaxies fainter than M_UV = -17 mag. Emission lines are generally strong; roughly half cannot be reproduced with standard stellar populations and require an extreme ionizing source, whose nature is not specified. Relatively strong [OIII] emission is detected in every galaxy, which the authors interpret as extending the low-mass mass–metallicity relation to M_star approximately 10^6 solar masses at z approximately 6. Strong [OIII] in the lowest-mass object, at approximately 10^5.6 solar masses, contrasts with recent extremely metal-poor candidates at similar mass and redshift. This suggests, but does not establish, two early enrichment pathways, as predicted by simulations. One galaxy at z = 5.5 with M_star = 10^6.6 solar masses shows both dust attenuation and a galactic outflow. Its dust, metal, and outflow contents can be consistently explained by supernovae, supporting their proposed importance in early galaxy assembly without uniquely establishing that explanation.
PublicAstronomers used deep James Webb Space Telescope observations of the gravitational-lensing field Abell S1063 to study 16 exceptionally faint galaxies in the early universe. Their light reveals generally strong emission lines, with roughly half requiring a more extreme source of ionization than standard stellar populations can provide. The study does not identify that source. All 16 galaxies show relatively strong emission from oxygen, extending evidence for a relationship between galaxy mass and chemical enrichment to very low masses. The smallest galaxy differs from recently reported candidates with exceptionally little metal at similar masses and cosmic times. The authors suggest that early galaxies may therefore have followed two different enrichment paths, a possibility predicted by simulations rather than established here. In another galaxy, they detect both dust dimming the light and gas flowing outward. Exploding stars could consistently explain its dust, metals, and outflow, suggesting an important role for supernovae in shaping early galaxies.
Young explorerScientists used a space telescope to study 16 very faint galaxies from long ago. They found signs of oxygen in all of them. Some of the light was harder to explain with ordinary groups of stars. In one galaxy, they also found dust and gas moving outward. Exploding stars could explain those clues, but that is not proven. The galaxies may have become enriched in different ways.
R. Rodríguez-Cardoso, S. Roca-Fàbrega, Oscar Agertz+7 more
AstronomerUsing five high-resolution VINTERGATAN-GM zoom-in realizations of the same Milky Way-mass halo, this study tests whether satellite planes depend on the mass of a GSE-like merger at z ~ 2. Targeted genetic modifications vary the merger mass ratio from 1:10 to 1:2.1 while holding the final dynamical mass and large-scale environment fixed. More massive mergers yield more planar and kinematically coherent satellite populations; ratios larger than 1:6 produce Kinematic Persistent Planes, with at least 40% of satellites co-orbiting about a common axis over extended periods. The simulations attribute this behavior to sufficiently massive mergers arriving along the Lagrangian volume's maximum-compression direction, producing flattened halos with aligned, anisotropic velocity dispersions. Preferential equatorial infall and anisotropic dynamical friction then organize satellite orbits into persistent planes. These controlled simulations offer a mechanism for structures comparable to those observed in the Milky Way, rather than establishing the Milky Way's actual formation history or the prevalence of the mechanism across independent halos.
PublicMany satellite galaxies in the Local Group lie in thin planes, and many move around their host galaxies in a coordinated way—an arrangement that standard galaxy-formation simulations have historically struggled to reproduce. This study uses five computer simulations of the same Milky Way-mass galaxy to test whether an ancient merger could help explain these patterns. The researchers changed the relative mass of the incoming galaxy while keeping the final galaxy mass and large-scale surroundings fixed. Larger mergers produced flatter, more coordinated satellite systems. In simulations with merger mass ratios larger than 1:6, at least 40% of the satellites orbited around a shared axis for extended periods. The proposed explanation is that a sufficiently massive merger arriving from a particular direction flattens the host's surrounding dark-matter halo; satellites then preferentially enter along its broad plane, while gravitational drag gradually redirects their orbits toward it. The results suggest a possible origin for satellite planes like the Milky Way's, but do not demonstrate that this is how its plane actually formed.
Young explorerLittle galaxies can travel around a big galaxy. Some line up in a thin, flat group and move around together. Scientists made five computer versions of a big galaxy to see whether a smaller galaxy joining it long ago could help make that pattern. In their computer galaxies, bigger joining galaxies made the little galaxies line up and move together more strongly. The scientists think the joining galaxy changed the shape of the big galaxy's invisible surroundings, helping guide the little galaxies into a flat group. This is a possible explanation from computer experiments, not proof of what happened to our own galaxy.
Kiyoaki C. Omori, Marcin Sawicki, Rosa M. Mérida+10 more
AstronomerUsing JWST/NIRCam imaging of 48 spectroscopically selected CANUCS galaxies at 5.0 < z_spec < 5.6, the authors visually identify 21 (44%) as candidate closely interacting systems with multiple components separated by roughly 5 kpc or less. Dense Basis spectral energy distribution fitting yields non-parametric component star formation histories with inferred bursts lasting about 0.2 Gyr. These episodes increase stellar mass by a factor of approximately 2.66 ± 0.85, with an estimated excess mass of approximately 1.58 ± 0.25 times the no-burst expectation. Attributing the enhancements to interactions and assuming the components subsequently merge, the authors estimate that mergers account for approximately 38% of total stellar mass growth at z ≈ 5, with uncertainties of +18 and −20 percentage points. In this interpretation, up to half of the merger-associated growth comes from stars newly formed during interactions, rather than from combining pre-existing stellar populations. The merger contribution is conditional on the interaction attribution and eventual-merger assumption.
PublicThe researchers used James Webb Space Telescope images to study how encounters between galaxies may help galaxies build their stellar mass in the early universe. Of 48 galaxies, they identified 21 as possible close interacting systems with two or more components. By modeling the components’ light, they inferred brief episodes of intense star formation lasting about 200 million years, during which stellar mass grew by roughly a factor of 2.7. If the encounters caused these bursts and the components eventually merge, the researchers estimate that mergers account for about 38% of stellar mass growth in galaxies at this epoch, although the uncertainty is substantial. Up to half of that merger-related growth could come from newly formed stars, not simply from adding together stars already present. The images identify interaction candidates; the star formation histories and the overall merger contribution are inferred rather than directly observed.
Young explorerGalaxies are huge groups of stars. Scientists looked at telescope pictures of faraway galaxies and found some that might be having close encounters. By studying their light, the scientists worked out that these galaxies may have made lots of new stars in short bursts. If the encounters caused those bursts and the galaxies later join together, they could grow in two ways: by bringing their old stars together and by making new ones. The scientists still need to be careful, because these galaxies are only possible partners, not confirmed ones.
Shunta Shimizu, Nobunari Kashikawa, Ryo Emori+15 more
AstronomerCombining JWST/NIRCam F470N and Subaru/HSC NB872 imaging in CEERS, the authors directly measure the Lyα escape fraction of Hα emitters at z ≃ 6.2. Of 84 Hα-selected galaxies, 56 have reliable NB872 photometry and 14 are detected in Lyα. A completeness-weighted stack yields a median Lyα escape fraction of 0.106 with uncertainties of +0.066 and −0.044, consistent with recent measurements at similar redshifts. The stacked escape fraction shows no statistically significant change as the Hα luminosity threshold is lowered over the sampled range. Only if Lyα escape traces Lyman-continuum leakage does this suggest that relatively Hα-luminous galaxies, not just the faintest systems, may contribute importantly to reionization. Individual escape fractions correlate positively with Lyα equivalent width and negatively with UV slope β. A trend toward higher escape fractions at smaller UV sizes is tentative; correlations with SED-derived E(B−V) and optical size are not significant. The limited sample suggests, but does not establish, a closer connection to compact, low-attenuation UV-emitting star-forming components than to global dust attenuation or overall stellar structure.
PublicAstronomers measured how much Lyman-alpha light escapes from galaxies during the early universe’s reionization era by pairing two filters on JWST and Subaru to measure two hydrogen emission lines. They selected 84 galaxies at a redshift of about 6.2; 56 had reliable measurements in the Subaru filter, and 14 were detected in Lyman-alpha. Combining the observations gave an estimated median escape fraction of about 11%, with an uncertainty spanning roughly 6% to 17%. Including galaxies fainter in H-alpha did not significantly change the combined escape fraction over the range studied. If Lyman-alpha escape tracks the escape of radiation capable of ionizing hydrogen, this could mean that relatively H-alpha-bright galaxies also helped reionize the universe; the study does not directly establish that connection. The individual-galaxy results suggest that escaping Lyman-alpha light may be more closely associated with compact, less-obscured star-forming regions seen in ultraviolet light than with a galaxy’s overall dust content or stellar structure, but the sample is limited and the size trend remains tentative.
Young explorerScientists studied faraway galaxies from when the universe was very young. They compared two kinds of light made by hydrogen to find out how much of one kind gets out. Putting many galaxies’ measurements together, they found that about one out of every ten bits of that light escapes, though the exact amount is uncertain. There were hints that light gets out more easily from small star-making patches that are less hidden. But the scientists need more evidence to be sure.
Devontae C. Baxter, Alison L. Coil, Ethan O Nadler+2 more
AstronomerThe study tests five observational JWST/NIRCam photometric selections against TNG300 galaxies using synthetic dust-attenuated photometry. The Pérez-González et al. selection is the most reliable and inclusive of those tested, but selects only 1 of 18 simulated galaxies at z~5 with stellar masses of at least 10^11 solar masses; the other 17 are, on average, about 0.5 mag bluer than the color cut under the adopted dust model. The authors construct a revised color-magnitude selection that improves completeness for massive z~5 galaxies in TNG300 while excluding dusty, low-mass contaminants selected by literature criteria. Tracking the most massive NIRCam-selected galaxies at z=7, 4, and 2 shows that they rarely become the most massive galaxies at z=0; those that do generally experience substantial merger-driven growth at z≲0.2. These simulation-based results suggest incompleteness in current observational selections and caution against assuming a direct progenitor link to today's most massive galaxies, but their applicability depends in part on the adopted dust model.
PublicEarly JWST surveys found candidates for surprisingly massive galaxies in the distant, early Universe, although follow-up spectroscopy has supported some candidates and challenged others. This study tests how such galaxies are picked out by applying five existing selection methods to simulated galaxies with modeled dust effects. Even the best-performing method finds only one of 18 very massive simulated galaxies at the epoch studied; the others look too blue to pass its color requirement under the assumed dust model. The researchers devise a revised selection that finds more of these massive simulated galaxies while avoiding dusty, lower-mass impostors. They also trace simulated galaxies forward in time and find that the most massive early galaxies selected this way rarely become today's most massive galaxies. Those that do generally gain substantial mass through very late mergers. The findings raise concerns about current selection methods, but are simulation results rather than confirmation that real surveys miss the same galaxies.
Young explorerScientists use the colors of faraway galaxies to help find ones with lots of stars. They tested their color rules on pretend galaxies inside a computer. Even the rule that worked best missed most of the very big pretend galaxies they checked, because their colors did not fit. A new rule found more of them in the computer test. The scientists also watched how the pretend galaxies grew. The biggest ones early on usually did not become the biggest ones later. The ones that did usually grew a lot by joining with other galaxies very late. Real galaxies may behave differently, so these computer clues still need checking.
Avshalom Badash, Doron Kushnir
AstronomerThe paper presents an analytical framework for inferring column densities from absorption-doublet equivalent widths when saturation makes conventional estimates unreliable. The doublet members must be measured separately, but their velocity structure need not be resolved; for Na I D, resolving power ≳1,000 suffices. For a Gaussian curve of growth, the exact inversion becomes a universal saturation correction depending only on R = EW2/EW1, with column density proportional to EW at fixed R. The framework supplies the exact Gaussian inversion and Doppler parameter, a closed-form second-order approximation, and a strict lower bound valid for arbitrary velocity structure. The authors recommend reporting this optimal, assumption-free lower bound: it lies within a few per cent of the Gaussian estimate for R ≳ 1.4 and is at most a factor of 3.5 below it at R = 1.1. The ratio of the exact Gaussian estimate to the second-order approximation diagnoses saturation for individual objects. Validation uses published profile-fitting Na I D column densities toward Type Ia supernovae and only their integrated EWs. A closed-form extinction estimate relies on the observed log N(Na I)–AV relation, and a public implementation propagates uncertainties.
PublicSodium absorption lines are widely used to estimate how much dust dims an astronomical source, but they become difficult to interpret when they saturate: stronger absorption no longer produces a proportionate increase in line strength. This paper develops a mathematical method using the measured strengths of two sodium lines. The lines must be distinguishable from one another, but the instrument need not separate the different motions of the absorbing gas. The method gives a column-density estimate under a Gaussian model and, more generally, a firm minimum amount of sodium along the line of sight without assuming a particular velocity structure. The authors recommend reporting that minimum rather than treating it as the full amount. They checked the framework against published sodium measurements toward Type Ia supernovae. They also provide a formula for estimating dust dimming using an observed sodium–extinction relationship, plus public software that carries measurement uncertainties through the calculation.
Young explorerLight from space can have two little dark marks made by sodium gas. Those marks help astronomers learn about the gas and estimate how much dust is dimming the light. But when the marks get too strong, reading them is tricky. The researchers made a new math recipe that uses both marks to find the smallest amount of sodium that must be there. There could be more. They checked their recipe against earlier measurements of light from exploding stars.
David Attard, Ilian T. Iliev, Martin P. Rey+3 more
AstronomerUsing the MEGATRON high-redshift zoom simulations, the authors compare four star-formation and stellar-feedback prescriptions evolved from identical initial conditions for galaxies with stellar masses of approximately 10^4–10^8 solar masses at z = 8.5. They classify systems as Star-Forming, Mini-Quenched, or Quenched, with the latter two lacking significant star formation over the preceding 10 and 100 Myr, respectively. Stronger or more clustered feedback produces higher quiescent fractions than the fiducial and Varying IMF models, and duty cycles at fixed mass differ by factors of several. Quenched galaxies' cold-gas profiles are consistent with two interpretations: mechanical evacuation yielding compact, cold-gas-poor systems, and thermodynamic suppression leaving cold gas present but inactive in star formation. The simulations predict that quiescent systems at these masses fall below unlensed JWST/NIRCam detection limits while active counterparts do not, biasing flux-limited samples toward active phases. Measuring mass-dependent quiescent fractions in lensing fields is proposed as a test of feedback models, not reported as an observation.
PublicComputer simulations explore why small galaxies in the early universe alternate between making stars and resting. The researchers compared four ways of modelling star formation and the effects of stars on surrounding gas, starting each simulation from the same conditions. Stronger or more concentrated stellar feedback left more galaxies inactive, and the balance of active and quiet periods differed substantially between models. The simulated gas distributions suggest two possible ways to stop star formation: removing gas, or preventing gas that remains cold from forming stars. These are simulation-based interpretations, not observed explanations. The study also predicts that quiet galaxies in this mass range would be too faint for JWST's NIRCam to detect without gravitational magnification, even when actively star-forming galaxies of the same mass are detectable. Surveys limited by brightness would therefore favor active galaxies. The authors propose using gravitationally magnified views to measure the quiet fraction and test the models.
Young explorerThe researchers made computer versions of small galaxies from long ago. They tried four different recipes for how stars form and affect nearby gas. In some recipes, more galaxies took breaks from making stars. The computer galaxies gave clues that a break might happen because gas gets pushed away, or because gas stays but does not make stars. This does not show which idea happens in real galaxies. The quiet galaxies may also be too dim to see unless gravity makes them look brighter. The researchers suggest looking through these natural magnifying glasses to help test their recipes.
Emanuele Contini, J.K. Jang, Jinsu Rhee+2 more
AstronomerUsing the YS200 cosmological simulation as its reference volume, this study examines FEGA25 semianalytic predictions for black hole mass versus total stellar and bulge mass, including dependence on black hole mass selection, morphology, redshift, and black hole occupation fraction. Black hole mass cuts chiefly alter the low-host-mass regime; selected relations approach the intrinsic, uncut relations at higher host masses. More bulge-dominated galaxies preferentially occupy higher stellar masses in the black hole–stellar mass relation. Across z=0–3, FEGA25 shows no clear systematic evolution of either relation. The hydrodynamical zoom-in simulation NewCluster likewise shows no clear monotonic evolution, but has greater scatter, especially at high host masses. Occupation fraction and scaling relations provide complementary constraints: lower occupation generally accompanies larger selection-induced offsets, but different occupation fractions can produce similar median relations, and bias at fixed occupation depends on the host property and black hole mass distribution. At z=0, FEGA25 is consistent with available observational constraints for both relations and predicts increased scatter and bending at lower host masses.
PublicThis modeling study explores how black hole mass relates to the mass of a galaxy’s stars and its central bulge. In the FEGA25 model, excluding black holes below a chosen mass mainly changes the inferred relationships for lower-mass galaxies. The relationships show no clear systematic change across the redshifts studied. A comparison simulation, NewCluster, also shows no clear one-directional change, though its results are more spread out. The study also finds that these mass relationships do not uniquely reveal what fraction of galaxies contain black holes: very different fractions can produce similar typical relationships. FEGA25 agrees with available present-day observational constraints and predicts more scatter and a bend in the relationships for lower-mass galaxies. These are model findings and predictions, not new observational measurements.
Young explorerScientists used computer models to study how black holes and their home galaxies fit together. In the models, leaving out smaller black holes changes the picture most for smaller galaxies. Different numbers of galaxies with black holes can still make similar patterns, so one pattern cannot tell the whole story. The models fit some things astronomers have measured, but their predictions for smaller galaxies still need checking.
Jingshuo Yang, Cheng Li
AstronomerVisual inspection of two machine-learning ring-galaxy catalogues identified 30 galaxies with apparent Hoag-type morphology in DESI imaging. DESI Legacy Surveys g, r, and z photometry, with two-dimensional core models subtracted for ring measurements, shows predominantly red-sequence cores and a broader ring colour distribution extending toward the blue cloud. Relative to mass-matched SDSS early-type controls, the cores broadly follow early-type mass scaling relations but tend to be slightly bluer, smaller, denser in stellar mass, less concentrated, and lower in Sérsic index. Among the 16 systems with SDSS group information, 14 are centrals, versus approximately 64% of the mass-matched controls; matching central–satellite status makes halo-mass and large-scale overdensity distributions much more similar. Ring stellar-mass surface density and normalized width decrease with increasing core-plus-inner-halo to ring mass ratio. In a simplified core-plus-ring model, most core R90 values fall inside the outermost stable circular orbit, while rings frequently cross the unstable interval. These structural trends suggest a possible secular contribution, but the compact, dense cores disfavor a simple diffuse-pseudobulge origin. Reduced satellite-specific environmental processing may aid gas retention and ring survival, while ring diversity leaves multiple formation pathways open.
PublicResearchers identified 30 galaxies in DESI images that appear to have the unusual Hoag-type shape: a smooth central core separated from an outer ring. Their measurements show that the cores are mostly red, while the rings have a wider range of colours, including bluer ones. Compared with ordinary early-type galaxies of similar stellar mass, the cores tend to be smaller, denser and slightly bluer, with less centrally concentrated light profiles. Of the 16 galaxies with available group information, 14 are central galaxies rather than satellites. The authors suggest that this setting might help them retain gas and preserve their rings, but this is an interpretation, not a demonstrated cause. A simplified model also places many rings partly in a region of unstable circular orbits; it does not establish that the observed rings are unstable. The varied ring properties leave open the possibility that these galaxies formed in more than one way.
Young explorerScientists found 30 galaxies in pictures that look like a smooth middle with a separate ring around it. The middles are mostly red, but the rings come in more colours, including blue. Scientists measured their shapes and tried a simple model to help understand them. They still do not know exactly how these unusual galaxies formed, and there may be more than one way to make them.
