Low-mass Galaxies Research Articles

The PSF smoothing effect on concentration-related parameters of high-redshift galaxies in HST and JWST

Aims. We performed a comprehensive investigation of the PSF smoothing effect on the measurement of concentration-related parameters (C, Gini, and M20) of high-redshift galaxies in the HST and JWST surveys. Methods. Our sample contains massive galaxies (109.5 M⊙ ≤ M* ≤ 1011.5 M⊙) from the CANDELS/EGS survey (at redshift 0 < z < 2), and the CEERS survey (at redshift 1 < z < 3). The non-parametric concentration-related parameters (R20, R80, C, Gini, and M20) and the model-dependent parameters (n and Re) of these galaxies were derived from Statmorph and GALFIT, respectively. The best-fit Sérsic index (n) derived from image modelling is generally robust against the PSF smoothing effect and can be used to describe the intrinsic light distribution of galaxies. On the other hand, the concentration-related parameters are significantly affected by the PSF smoothing effect since they are directly calculated from the pixels of galaxy images. We tried to evaluate the PSF smoothing effect by comparing the concentration-related parameters to the Sérsic index in both observations and mock images. Results. We find that the concentration index is generally underestimated, especially for smaller galaxies with a higher Sérsic index (eventually converging to the concentration index of the PSF). However, galaxies with a lower Sérsic index (n ≤ 1) or larger relative size (Re/FWHM > 3) are less affected by the PSF smoothing effect. Tests with idealised mock images reveal that overestimating the measured R20/Re ratio leads to underestimating the concentration index C. Another commonly used concentration index C59, derived from R50 and R90 values, is less affected by the PSF. The Gini coefficient and the absolute M20 statistic also show a similar behaviour as the concentration index. Caution should be taken for the possible correction of the concentration-related parameters, where both the relative size and the Sérsic index of the galaxy are important. We also generated high-redshift artificial images from the low-redshift HST observations and confirm that the traditional correction method that simply adds a single term to the non-parametric indicators of galaxies at higher redshifts is unable to reliably recover the true distribution of the structural parameters. Compared to the HST images, the PSF smoothing is much less severe for images in the CEERS survey (for the short-wavelength filters) due to the much higher spatial resolution. In fact, it is better to use the Sérsic index rather than the non-parametric morphology indicators to trace the light concentration for galaxies at high redshifts. From the single Sérsic modelling of the HST and JWST images, we also confirm that galaxies at higher redshifts are more compact with smaller Re. The low-mass galaxies are more disc-like (n ∼ 1) compared to the high-mass galaxies that are more spheroid dominated (n ∼ 3).

Great Balls of FIRE

Context. Despite the nearly hundred gravitational-wave detections reported by the LIGO-Virgo-KAGRA Collaboration, the question of the cosmological origin of merging binary black holes (BBHs) remains open. The two main formation channels generally considered are from isolated field binaries or via dynamical assembly in dense star clusters. Aims. Here we focus on understanding the dynamical formation of merging BBHs within massive clusters in galaxies of different masses. Methods. To this end, we applied a new framework to consistently model the formation and evolution of massive star clusters in zoom-in cosmological simulations of galaxies. Each simulation, taken from the FIRE project, provides a realistic star formation environment, with a unique star formation history, that hosts realistic giant molecular clouds that constitute the birthplace of star clusters. Combined with the code for star cluster evolution CMC, we are able to produce populations of dynamically formed merging BBHs across cosmic time in different environments. Results. As the most massive star clusters preferentially form in dense massive clouds of gas, we find that, despite their low metallicities favouring the creation of black holes, low-mass galaxies contain few massive clusters and therefore make a limited contribution to the global production of dynamically formed merging BBHs. Furthermore, we find that massive clusters can host hierarchical BBH mergers with clear, identifiable physical properties. Looking at the evolution of the BBH merger rate in different galaxies, we find strong correlations between BBH mergers and the most extreme episodes of star formation. Finally, we discuss the implications for future LIGO-Virgo-KAGRA gravitational wave observations.

Gas metallicity of ram-pressure-stripped galaxies at intermediate redshifts with MUSE data

Extraplanar tails of ionized-stripped gas, extending up to several tens of kiloparsecs beyond the stellar disk, are often observed in ram-pressure-stripped (RPS) galaxies in low-redshift clusters. Recent studies have also identified similar tails at high redshifts, and we present here the first analysis of the chemical composition of such tails beyond the local Universe. Specifically, we examined the distribution of the ionized gas metallicity of RPS galaxies in the Abell 2744 (z = 0.308) and Abell 370 (z = 0.375) clusters observed as part of the MUSE-GTO program. We investigated spatially resolved and global metallicities in galactic disks and stripped tails, utilizing both a theoretical calibration from a photoionization model and an empirical calibration. The metallicity gradients and the spatially resolved mass–metallicity relations indicate that the metallicity in the tails reaches values that are up to ∼0.6 dex lower than anywhere in the parent disks, with a few exceptions. Both the disks and tails follow a global mass–metallicity relation, though the tail metallicity is systematically lower than that of the corresponding disk, by up to ∼0.2 dex. These findings demonstrate that additional processes are at play in the tails and are consistent with a scenario of a progressive dilution of the metallicity along the tails due to the mixing of the intracluster medium and interstellar gas, in accordance with previous low-z results. In principle, the same scenario can also explain the flat or positive metallicity gradients observed in low-mass RPS galaxies since in these galaxies the interstellar medium’s metallicity can approach the metallicity levels found in the intracluster medium.

Toward Unveiling Cosmic Reionization: The Ionizing Photon Production Efficiency (ξ ion) of Low-mass Hα Emitters at z ∼ 2.3

We investigate the galaxy properties of ∼400 low-mass (<109 M ⊙) Hα emitters (HAEs) at z ∼ 2.3 in the ZFOURGE survey. The selection of these HAEs is based on the excess in the observed K s broadband flux compared to the stellar continuum estimated from the best-fit spectral energy distribution. These low-mass HAEs have elevated SFR(Hα) above the star formation main sequence, making them potential analogs of the galaxies that reionized the Universe during the Epoch of Reionization. The ionizing photon production efficiencies (ξ ion) of the low-mass HAEs have a median value of log(ξion/erg−1Hz)=25.24−0.13+0.10(25.35−0.15+0.12) , assuming the Calzetti (SMC) curve for the stellar continuum dust correction. This value is higher than that of main-sequence galaxies by ∼0.2 dex at similar redshift, indicating that the low-mass HAEs are more efficient in producing ionizing photons. Our results also consolidate the trend of increasing ξ ion with redshift, but reveal a “downsizing” relationship between ξ ion and stellar mass (M ⊙) with increasing redshift. We further explore the dependence of ξ ion on other galaxy properties, such as the UV spectral slope (β UV), the UV magnitude (M UV), and the equivalent widths of Hα and [O iii] emission lines. Galaxies with bluer UV slopes, fainter UV luminosities, and higher equivalent widths exhibit elevated ξ ion by a factor of ∼2 compared to the median ξ ion of our sample. JWST data will provide an opportunity to extend our method and further investigate the properties of low-mass galaxies at high redshifts.

An Early Dark Matter–dominated Phase in the Assembly History of Milky Way–mass Galaxies Suggested by the TNG50 Simulation and JWST Observations

Whereas well-studied galaxies at cosmic noon are found to be baryon dominated within the effective radius, recent JWST observations of z ∼ 6–7 galaxies with stellar masses of only M * ∼ 108−9 M ⊙ surprisingly indicate that they are dark matter dominated within r e ≈ 1 kpc. Here, we place these high-redshift measurements in the context of the TNG50 galaxy formation simulation by measuring the central (within 1 kpc) stellar, gas, and dark matter masses of galaxies in the simulation. The central baryon fraction varies strongly with galaxy stellar mass in TNG50, and this M * dependence is remarkably constant across 0 < z < 6: galaxies of low stellar mass (M * ∼ 108−9 M ⊙) are dark matter dominated as f baryon(<1 kpc) ∼ 0.25. At z = 6, the baryonic mass in the centers of low-mass galaxies is largely comprised of gas, exceeding the stellar mass component by a factor ∼4. We use the simulation to track the typical evolution of such low-mass, dark matter–dominated galaxies at z = 6 and show that these systems become baryon dominated in their centers at cosmic noon, with high stellar-to-gas mass ratios, and grow to galaxies of M * ∼ 1010.5 M ⊙ at z = 0. Comparing to the dynamical and stellar mass measurements from observations at high redshifts, these findings suggest that the inferred star formation efficiency in the early Universe is broadly in line with the established assumptions for the cosmological simulations. Moreover, our results imply that the JWST observations may indeed have reached the early low-mass regime where the central parts of galaxies transition from being dark matter dominated to being baryon dominated.

Discovery and Characterization of Two Ultrafaint Dwarfs outside the Halo of the Milky Way: Leo M and Leo K

We report the discovery of two ultrafaint dwarf galaxies, Leo M and Leo K, that lie outside the halo of the Milky Way (MW). Using Hubble Space Telescope imaging of the resolved stars, we create color–magnitude diagrams reaching the oldest main-sequence turnoff of each system and (i) fit for structural parameters of the galaxies; (ii) measure their distances using the luminosity of the horizontal branch stars; (iii) estimate integrated magnitudes and stellar masses; and (iv) reconstruct the star formation histories. Based on their location in the Local Group, neither galaxy is currently within the halo of the MW although Leo K is located ∼26 kpc from the low-mass galaxy Leo T and these two systems may have had a past interaction. Leo M and Leo K have stellar masses of 1.8−0.2+0.3×104 M ⊙ and 1.2 ± 0.2 × 104 M ⊙, and were quenched 10.6−1.1+2.2 Gyr and 12.8−4.2+0.1 Gyr ago, respectively. Given that the galaxies are at farther distances from the MW, it is unlikely that they were quenched by environmental processing. Instead, given their low stellar masses, their early quenching timescales are consistent with the scenario that a combination of reionization and stellar feedback shut down star formation at early cosmic times.

Measuring the gas reservoirs in 108 &lt; M⋆ &lt; 1011 M⊙ galaxies at 1 ≤ z ≤ 3

Context. Understanding the gas content in galaxies, along with its consumption and replenishment, is vital to our grasp of the evolution of the Universe. Numerous studies have addressed this notion, utilizing various observational tools and analytical methods. These include examining low-transition 12CO millimeter rotational lines and exploring the far-infrared and the (sub-)millimeter emission of galaxies. With the capabilities of present-day facilities, much of this research has been centered on relatively bright galaxies. Aims. This study is aimed at exploring the gas reservoirs of a more general type of galaxy population at 1.0 &lt; z &lt; 3.0 that is not restricted to bright (sub-)millimeter objects. We strive to obtain a measurement that will help to constrain our knowledge of the gas content at 1010 − 11 M⊙, with upper limits at ∼108 − 10 M⊙. Methods. We stacked ALMA 1.1 mm data to measure the gas content of a mass-complete sample of galaxies down to ∼108.6 M⊙ at z = 1 (∼109.2 M⊙ at z = 3) extracted from the HST/CANDELS sample in GOODS-S. The selected sample is composed of 5530 predominantly blue (⟨b − i⟩∼0.12 mag, ⟨i − H⟩∼0.81 mag), star-forming main sequence (MS) objects (ΔMS = log SFR−log SFRMS ∼ −0.03 dex). Results. At 1010 − 11 M⊙, our gas fractions (fgas = Mgas/(Mgas + M⋆)), ranging from 0.32 to 0.48 at these redshifts, are in good agreement with other studies based on mass-complete samples down to 1010 M⊙. These values are, however, lower than expected, according to other works more biased to individual detections. At 109 − 10 M⊙, we obtained 3σ upper limits for the fgas values ranging from 0.69 to 0.77. At 108 − 9 M⊙, these upper limits rise to ∼0.97. The upper limits at 109 − 10 M⊙ are on the level of the extrapolations of scaling relations based on mass-complete samples and below those based on individual detections. As such, these results suggest that the gas content of low-mass galaxies is, at most, equivalent to what has been extrapolated from the literature scaling relations based on mass-complete samples down to 1010 M⊙. Overall, the comparison of our results with the literature reflects how the inclusion of bluer, less obscured, and more MS-like objects progressively pushes the gas content down to lower values.

Star-formation activity of low-mass galaxies at the peak epoch of galaxy formation probed by deep narrow-band imaging

Star-formation activity of low-mass galaxies at the peak epoch of galaxy formation probed by deep narrow-band imaging

Two Distinct Classes of Quiescent Galaxies at Cosmic Noon Revealed by JWST PRIMER and UNCOVER

We present a measurement of the low-mass quiescent size–mass relation at cosmic noon (1 < z < 3) from the JWST PRIMER and UNCOVER treasury surveys, which highlights two distinct classes of quiescent galaxies. While the massive population is well studied at these redshifts, the low-mass end has been previously underexplored due to a lack of observing facilities with sufficient sensitivity and spatial resolution. We select a conservative sample of low-mass quiescent galaxy candidates using rest-frame UVJ colors and specific star formation rate criteria and measure galaxy morphology in both rest-frame UV/optical wavelengths (F150W) and rest-frame near-infrared (F444W). We confirm an unambiguous flattening of the low-mass quiescent size–mass relation, which results from the separation of the quiescent galaxy sample into two distinct populations at log(M⋆/M⊙)∼10.3 : low-mass quiescent galaxies that are notably younger and have disky structures, and massive galaxies consistent with spheroidal morphologies and older median stellar ages. These separate populations imply mass quenching dominates at the massive end while other mechanisms, such as environmental or feedback-driven quenching, form the low-mass end. This stellar mass-dependent slope of the quiescent size–mass relation could also indicate a shift from size growth due to star formation (low masses) to growth via mergers (massive galaxies). The transition mass between these two populations also corresponds with other dramatic changes and characteristic masses in several galaxy evolution scaling relations (e.g., star formation efficiency, dust obscuration, and stellar-to-halo mass ratios), further highlighting the stark dichotomy between low-mass and massive galaxy formation.

Correcting for the overabundance of low-mass quiescent galaxies in semi-analytic models

ABSTRACT We compare the l-galaxies semi-analytic model to deep observational data from the UKIDSS Ultra Deep Survey (UDS) across the redshift range 0.5 &amp;lt; z &amp;lt; 3. We find that the overabundance of low-mass, passive galaxies at high redshifts in the model can be attributed solely to the properties of ‘orphan’ galaxies, i.e. satellite galaxies where the simulation has lost track of the host dark matter sub-halo. We implement a simple model that boosts the star formation rates in orphan galaxies by matching them to non-orphaned satellite galaxies at a similar evolutionary stage. This straightforward change largely addresses the discrepancy in the low-mass passive fraction across all redshifts. We find that the orphan problem is somewhat alleviated by higher resolution simulations, but the preservation of a larger gas reservoir in orphans is still required to produce a better fit to the observed space density of low-mass passive galaxies. Our findings are also robust to the precise definition of the passive galaxy population. In general, considering the vastly different prescriptions used for orphans in semi-analytic models, we recommend that they are analysed separately from the resolved satellite galaxy population, particularly with JWST observations reigniting interest in the low-mass regime in which they dominate.

Are early-type galaxies quenched by present-day environment? A study of dwarfs in the Fornax Cluster.

Galaxies undergo numerous transformative processes throughout their lifetimes that ultimately lead to the expulsion of gas and the cessation of star-forming activity. This phenomenon is commonly known as quenching, and in this study, we delve into the possibility that this process is caused by the environmental processes associated with the surrounding cluster. To this end, we used the results of our previous paper ---where we analyzed dwarf galaxies in the survey together with massive galaxies from the survey--- to compute the quenching time of each galaxy and compare it with the infall time into the cluster. Using as an approximation of the quenching time and deriving the infall time from phase-space models, we determined the probability of the quenching being produced by the local environment of galaxies. Our results reveal a relation between galaxy mass and quenching probability. Massive galaxies, down to exhibit a low, almost zero probability of quenching, suggesting their independence of environmental effects. As we move into the mass regime of dwarf galaxies, the probability increases with decreasing mass, highlighting their sensitivity to environmental quenching. For dwarfs, 36pm 9&lt;!PCT!&gt; of our observational data are consistent with this hypothesis, challenging the idea that the present-day cluster, Fornax, is the primary driver of quenching in the low-mass galaxies of our sample with stellar mass from to To further investigate the importance of environmental processes, we compared these results with cosmological simulations, selecting galaxies under similar conditions to our observational sample. Remarkably, the simulated sample shows lower quenching probabilities as we move down in mass, and barely 5pm 1&lt;!PCT!&gt; of galaxies meet the quenching criteria. This discrepancy between observations and simulations underlines the fact that the modelling of quenching is still in its infancy. In general, the number of observed galaxies quenched by their environment is lower than expected, which suggests that preprocessing plays a larger role in galaxy evolution. Ultimately, our results highlight the need for higher-quality simulations and refinement of galaxy formation and evolution models.

Studying [C ii] emission in low-mass galaxies at z ∼ 7

ABSTRACT We report on a $\rm {[CII]}_{158\mu \rm {m}}$ search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed Ly α emitting galaxies at z ∼ 7. Our targets are ultraviolet (UV) faint systems with stellar masses on the order of M* ∼ 109 M⊙. We detect a single [C ii] line emission (4σ) from the brightest (L ∼ 2.4 × 1010L⊙) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (z[C ii] = 6.3151 ± 0.0005) for MACS0454-1251 and measure a Ly α velocity offset of $\Delta v \approx 300 \pm 70 \rm {km\, s}^{-1}$. The remaining two galaxies we detect no [C ii] but provide 3σ upper limits on their [C ii] line luminosities which we use to investigate the $L_{\textrm {[CII]}} - \rm {SFR}$ relation. Overall our single [C ii] detection shows agreement with the relation for local dwarf galaxies. Our [C ii] deficient galaxies could potentially be exhibiting low metallicities (Z &amp;lt; Z⊙). Another possible explanation for weaker [C ii] emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of $T_{d}=35 \rm {K}$ dust masses (Mdust) range from &amp;lt;4.8 × 107 M⊙ to 2.3 × 108 M⊙. Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing [C ii] emission.

Repainting the colour–mass diagrams by unearthing the green mountain: dust-rich S0 galaxies in the colour–(galaxy stellar mass) diagram, and the colour–(black hole mass) relations for dust-poor versus dust-rich galaxies

ABSTRACT Lenticular galaxies are notoriously misclassified as elliptical galaxies and, as such, a (disc inclination)-dependent correction for dust is often not applied to the magnitudes of dusty lenticular galaxies. This results in overly red galaxy colours, impacting their distribution in the colour–magnitude diagram. It is revealed how this has led to an underpopulation of the ‘green valley’ by hiding a ‘green mountain’ of massive dust-rich lenticular galaxies – known to be built from gas-rich major mergers – within the ‘red sequence’ of colour–(stellar mass) diagrams. Correcting for dust, a ‘green mountain’ appears at M*,gal ∼ 1011 M⊙, along with signs of an extension to lower masses producing a ‘green range’ or ‘green ridge’ on the green side of the ‘red sequence’ and ‘blue cloud.’ The ‘red sequence’ is shown to be comprised of two components: a red plateau defined by elliptical galaxies with a near-constant colour and by lower-mass dust-poor lenticular galaxies, which are mostly a primordial population but may include faded/transformed spiral galaxies. The presence of the quasi-triangular-shaped galaxy evolution sequence, previously called the ‘Triangal’, is revealed in the galaxy colour–(stellar mass) diagram. It tracks the speciation of galaxies and their associated migration through the diagram. The connection of the ‘Triangal’ to previous galaxy morphology sequences (Fork, Trident, and Comb) is also shown herein. Finally, the colour–(black hole mass) diagram is revisited, revealing how the dust correction generates a blue–green sequence for the spiral and dust-rich lenticular galaxies that is offset from a green–red sequence defined by the dust-poor lenticular and elliptical galaxies.

Scalable hierarchical BayeSN inference: investigating dependence of SN Ia host galaxy dust properties on stellar mass and redshift

ABSTRACT We apply the hierarchical probabilistic spectral energy distribution (SED) model bayesn to analyse a sample of 475 type Ia supernovae (0.015 &amp;lt; z &amp;lt; 0.4) from Foundation, DES3YR and PS1MD to investigate the properties of dust in their host galaxies. We jointly infer the dust law RV population distributions at the SED level in high- and low-mass galaxies simultaneously with dust-independent, intrinsic differences. We find an intrinsic mass step of −0.049 ± 0.016 mag, at a significance of 3.1σ, when allowing for a constant intrinsic, achromatic magnitude offset. We additionally apply a model allowing for time- and wavelength-dependent intrinsic differences between SNe Ia in different mass bins, finding ∼2σ differences in magnitude and colour around peak and 4.5σ differences at later times. These intrinsic differences are inferred simultaneously with a difference in population mean RV of ∼2σ significance, demonstrating that both intrinsic and extrinsic differences may play a role in causing the host galaxy mass step. We also consider a model which allows the mean of the RV distribution to linearly evolve with redshift but find no evidence for any evolution – we infer the gradient of this relation ηR = −0.38 ± 0.70. In addition, we discuss in brief a new, GPU-accelerated python implementation of bayesn suitable for application to large surveys which is publicly available and can be used for future cosmological analyses; this code can be found here: https://github.com/bayesn/bayesn.

JADES: The incidence rate and properties of galactic outflows in low-mass galaxies across 3 &lt; z &lt; 9

We investigate the incidence and properties of ionised gas outflows in a sample of 52 galaxies with stellar masses between 107 M⊙ and 109 M⊙ observed with ultra-deep JWST/NIRSpec MSA spectroscopy as part of the JWST Advanced Deep Extragalactic Survey (JADES). The high-spectral resolution (R2700) NIRSpec observations allowed us to identify for the first time the potential signature of outflows in the rest-frame optical nebular lines in low-mass galaxies at z &gt; 4. The incidence fraction of ionised outflows, traced by broad components, is about 25–40%, depending on the intensity of the emission lines. The low incidence fraction might be due to both the sensitivity limit and the fact that outflows are not isotropic, but have a limited opening angle, which only results in detection when this is directed toward our line of sight. Evidence for outflows increases slightly with stellar mass and star formation rate. The median velocity and mass-loading factor (i.e. the ratio of the mass outflow rate and star formation rate) of the outflowing ionised gas are 350 km s−1 and η = 2.0−1.5+1.6, respectively. These are 1.5 and 100 times higher than the typical values observed in local dwarf galaxies. Some of these high-redshift outflows can escape the gravitational potential of the galaxy and dark matter halo and enrich the circumgalactic medium and possibly even the intergalactic medium. Our results indicate that outflows can significantly impact the star formation activity in low-mass galaxies within the first 2 Gyr of the Universe.

SAGAbg. I. A Near-unity Mass-loading Factor in Low-mass Galaxies via Their Low-redshift Evolution in Stellar Mass, Oxygen Abundance, and Star Formation Rate

Measuring the relation between star formation and galactic winds is observationally difficult. In this work we make an indirect measurement of the mass-loading factor (the ratio between the mass outflow rate and star formation rate) in low-mass galaxies using a differential approach to modeling the low-redshift evolution of the star-forming main sequence and mass–metallicity relation. We use Satellites Around Galactic Analogs (SAGA) background galaxies, i.e., spectra observed by the SAGA Survey that are not associated with the main SAGA host galaxies, to construct a sample of 11,925 spectroscopically confirmed low-mass galaxies from 0.01 ≲ z ≤ 0.21 and measure auroral line metallicities for 120 galaxies. The crux of the method is to use the lowest-redshift galaxies as the boundary condition of our model, and to infer a mass-loading factor for the sample by comparing the expected evolution of the low-redshift reference sample in stellar mass, gas-phase metallicity, and star formation rate against the observed properties of the sample at higher redshift. We infer a mass-loading factor of ηm=0.92−0.74+1.76 , which is in line with direct measurements of the mass-loading factor from the literature despite the drastically different sets of assumptions needed for each approach. While our estimate of the mass-loading factor is in good agreement with recent galaxy simulations that focus on resolving the dynamics of the interstellar medium, it is smaller by over an order of magnitude than the mass-loading factor produced by many contemporary cosmological simulations.

Active Galactic Nuclei Selection and Demographics: A New Age with JWST/MIRI

Understanding the coevolution of supermassive black holes and their host systems requires a comprehensive census of active galactic nuclei (AGNs) behavior across a wide range of redshift, luminosity, obscuration level, and galaxy properties. We report significant progress with JWST toward this goal from the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES). Based on comprehensive spectral energy distribution (SED) analysis of 3273 MIRI-detected sources, we identify 217 AGN candidates over a survey area of ∼34 arcmin2, including a primary sample of 111 AGNs in normal massive galaxies (M * > 109.5 M ☉) at z ∼ 0–4, an extended sample of 86 AGN candidates in low-mass galaxies (M * < 109.5 M ☉), and a high-z sample of 20 AGN candidates at z ∼ 4–8.4. Notably, about 80% of our MIRI-selected AGN candidates are new discoveries despite the extensive pre-JWST AGN searches. Even among the massive galaxies where the previous AGN search is believed to be thorough, 34% of the MIRI AGN identifications are new, highlighting the impact of obscuration on previous selections. By combining our results with the efforts at other wavelengths, we build the most complete AGN sample to date and examine the relative performance of different selection techniques. We find the obscured AGN fraction increases from L AGN,bol ∼ 1010 L ⊙ to 1011 L ⊙ and then drops toward higher luminosity. Additionally, the obscured AGN fraction gradually increases from z ∼ 0 to z ∼ 4 with most high-z AGNs obscured. We discuss how AGN obscuration, intrinsic SED variations, galaxy contamination, survey depth, and selection techniques complicate the construction of a complete AGN sample.

Overmassive Black Holes at Cosmic Noon: Linking the Local and the High-redshift Universe

We report for the first time a sample of 12 supermassive black holes (SMBHs) hosted by low-mass galaxies at cosmic noon, i.e., in a redshift range consistent with the peak of star formation history: z ∼ 1–3. These black holes are 2 orders of magnitude too massive for the stellar content of their hosts when compared with the local relation for active galaxies. These overmassive systems at cosmic noon share similar properties with the high-z sources found ubiquitously in recent James Webb Space Telescope (JWST) surveys (same range of black-hole-to-stellar-mass ratio, bolometric luminosity, and Eddington ratio). We argue that black hole feedback processes, for which there is possible evidence in five of the sources, and the differing environments in galactic nuclei at these respective epochs play a key role in these overmassive systems. These findings contribute to our understanding of the growth and coevolution of SMBHs and their host galaxies across cosmic time, offering a link between the early Universe (z > 4) observed by JWST and observations of the present-day Universe (z ≲ 1).

The MUSE Ultra Deep Field (MUDF). V. Characterizing the Mass–Metallicity Relation for Low-mass Galaxies at z ∼ 1–2

Using more than 100 galaxies in the MUSE Ultra Deep Field with spectroscopy from the Hubble Space Telescope’s (HST) Wide Field Camera 3 and the Very Large Telescope’s Multi Unit Spectroscopic Explorer, we extend the gas-phase mass–metallicity relation (MZR) at z ≈ 1–2 down to stellar masses of M ⋆ ≈ 107.5 M ⊙. The sample reaches 6 times lower in stellar mass and star formation rate (SFR) than previous HST studies at these redshifts, and we find that galaxy metallicities decrease to log(O/H) + 12 ≈ 7.8 ± 0.1 (15% solar) at log(M ⋆/M ⊙) ≈ 7.5, without evidence of a turnover in the shape of the MZR at low masses. We validate our strong-line metallicities using the direct method for sources with [O iii] λ4363 and [O iii] λ1666 detections, and find excellent agreement between the techniques. The [O iii] λ1666-based metallicities double existing measurements with a signal-to-noise ratio ≥ 5 for unlensed sources at z > 1, validating the strong-line calibrations up to z ∼ 2.5. We confirm that the MZR resides ∼0.3 dex lower in metallicity than local galaxies and is consistent with the fundamental metallicity relation if the low-mass slope varies with SFR. At lower redshifts (z ∼ 0.5) our sample reaches ∼0.5 dex lower in SFR than current calibrations and we find enhanced metallicities that are consistent with extrapolating the MZR to lower SFRs. Finally, we detect only an ∼0.1 dex difference in the metallicities of galaxies in groups versus isolated environments. These results are based on robust calibrations and reach the lowest masses and SFRs that are accessible with HST, providing a critical foundation for studies with the Webb and Roman Space Telescopes.

New insight on the nature of cosmic reionizers from the CEERS survey

The Epoch of Reionization (EoR) began when galaxies grew in abundance and luminosity, so their escaping Lyman continuum (LyC) radiation started ionizing the surrounding neutral intergalactic medium (IGM). Despite significant recent progress, the nature and role of cosmic reionizers are still unclear: in order to define them, it would be necessary to directly measure their LyC escape fraction (fesc). However, this is impossible during the EoR due to the opacity of the IGM. Consequently, many efforts at low and intermediate redshift have been made to determine measurable indirect indicators in high-redshift galaxies so that their fesc can be predicted. This work presents the analysis of the indirect indicators of 62 spectroscopically confirmed star-forming galaxies at 6 ≤ z ≤ 9 from the Cosmic Evolution Early Release Science (CEERS) survey, combined with 12 sources with public data from other JWST-ERS campaigns. From the NIRCam and NIRSpec observations, we measured their physical and spectroscopic properties. We discovered that on average 6 &lt; z &lt; 9 star-forming galaxies are compact in the rest-frame UV (re ∼ 0.4 kpc), are blue sources (UV-β slope ∼ − 2.17), and have a predicted fesc of about 0.13. A comparison of our results to models and predictions as well as an estimation of the ionizing budget suggests that low-mass galaxies with UV magnitudes fainter than M1500 = −18 that we currently do not characterize with JWST observations probably played a key role in the process of reionization.