Red Sequence Galaxies Research Articles

Deciphering the properties of UV upturn galaxies in the Virgo cluster

Abstract The UV upturn refers to the increase in UV flux at wavelengths shorter than 3000 Å observed in quiescent early-type galaxies (ETGs), which still remains a puzzle. In this study, we aim to identify ETGs showing the UV upturn phenomenon within the Virgo galaxy cluster. We utilized a color-color diagram to identify all potential possible UV upturn galaxies. The Spectral Energy Distributions (SED) of these galaxies were then analyzed using the CIGALE software; we confirmed the presence of UV upturn in galaxies within the Virgo cluster. We found that the SED fitting method is the best tool to visualize and confirm the UV upturn phenomenon in ETGs. Our findings reveal that the population distributions regarding stellar mass and star formation rate properties are similar between UV upturn and red sequence galaxies. We suggest that the UV contribution originates from old stellar populations and can be modeled effectively without a burst model. Moreover, by estimating the temperature of the stellar population responsible for the UV emission, we determined it to be 13,000 K to 18,000 K. These temperature estimates support the notion that the UV upturn likely arises from the contribution of low mass evolved stellar populations (extreme horizontal branch stars). Furthermore, the Mg2 index, a metallicity indicator, in the confirmed upturn galaxies shows higher strength and follows a similar trend to previous studies. This study sheds light on the nature of UV upturn galaxies within the Virgo cluster and provides evidence that low-mass evolved stellar populations are the possible mechanisms driving the UV upturn phenomenon.

LoVoCCS. II. Weak Lensing Mass Distributions, Red-sequence Galaxy Distributions, and Their Alignment with the Brightest Cluster Galaxy in 58 Nearby X-Ray-luminous Galaxy Clusters

The Local Volume Complete Cluster Survey is an ongoing program to observe nearly a hundred low-redshift X-ray-luminous galaxy clusters (redshifts 0.03 < z < 0.12 and X-ray luminosities in the 0.1–2.4 keV band L X500c > 1044 erg s−1) with the Dark Energy Camera, capturing data in the u, g, r, i, z bands with a 5σ point source depth of approximately 25th–26th AB magnitudes. Here, we map the aperture masses in 58 galaxy cluster fields using weak gravitational lensing. These clusters span a variety of dynamical states, from nearly relaxed to merging systems, and approximately half of them have not been subject to detailed weak lensing analysis before. In each cluster field, we analyze the alignment between the 2D mass distribution described by the aperture mass map, the 2D red-sequence (RS) galaxy distribution, and the brightest cluster galaxy (BCG). We find that the orientations of the BCG and the RS distribution are strongly aligned throughout the interiors of the clusters: the median misalignment angle is 19° within 2 Mpc. We also observe the alignment between the orientations of the RS distribution and the overall cluster mass distribution (by a median difference of 32° within 1 Mpc), although this is constrained by galaxy shape noise and the limitations of our cluster sample size. These types of alignment suggest long-term dynamical evolution within the clusters over cosmic timescales.

Massive Quiescent Disk Galaxies at 0.5 ≤ z ≤ 1 in CANDELS: Color Gradients and Likely Origin

A rare population of massive disk-dominated quiescent galaxies has recently drawn much attention, which intrudes the red sequence (RS) population without destroying the underlying stellar disks. In this study, we have carefully identified 48 RS, disk-dominated galaxies with M * > 1010 M ⊙ between redshift 0.5 and 1.0 in all five CANDELS fields. These galaxies are well fitted by a two-component bulge plus disk model, and have the bulge-to-total ratio B/T < 0.4 in the both F814W and F160W bands. The fitting results indicate that these galaxies generally have extended stellar disks (∼3 kpc on average) and tiny bulge components (∼0.5 kpc on average). To understand their possible origins, we have also selected two control samples of 156 green valley (GV) and 309 blue cloud (BC) disk-dominated galaxies according to the same selection criteria. We study the UVI(U − V versus V − I) color gradients of these galaxies to infer their specific star formation rate (sSFR) gradients out to the maximum acceptable radii. We show that on average the disks in disk-dominated RS galaxies are fully quenched at all radii, whereas both the BC and GV disks are not fully quenched at any radii. We find that all the BC, GV, and RS disk galaxies generally have nearly flat sSFR profiles. We propose a potential formation mechanism, acknowledging that various other mechanisms (e.g., central compaction and active galactic nucleus feedback) might contribute, where massive quiescent disk-dominated galaxies are predominantly formed via a process of secular disk fading.

Ionized gas in quiescent galaxies: Temperature measurement and constraint on the ionization source

In non-star-forming, passively evolving galaxies, regions with emission lines dominated by low-ionization species are classified as low-ionization emission regions (LIERs). The ionization mechanism behind such regions has long been a mystery. Active galactic nuclei (AGNs), which were once believed to be the source, have been found not to be the dominant mechanism, especially in regions distant from the galaxy nuclei. The remaining candidates, photoionization by post-asymptotic giant branch (pAGB) stars and interstellar shocks can only be distinguished with in-depth analysis. As the temperature predictions of these two models differ, temperature measurements can provide strong constraints on this puzzle. We selected a sample of 2795 quiescent red-sequence galaxies from the Sloan Digital Sky Survey IV (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We divided the sample spectra into three groups based on the flux ratio, and utilized stacking techniques to improve the signal-to-noise ratio of the observed spectra. We determined the temperature of and through their temperature-sensitive emission line ratios. Subsequently, we compared the measured temperatures with predictions from different models. The results demonstrate consistency with the interstellar shock model with pre-shock density n = 1 $ and solar metallicity, thus supporting shocks as the dominant ionization source of LIERs. Additionally, we also find that the interstellar dust extinction value measured through the Balmer decrement appears to be larger than that implied by the forbidden line ratios of low-ionization lines.

Systematically Measuring Ultra-diffuse Galaxies (SMUDGes). VI. Nuclear Star Clusters

We present our photometric search for potential nuclear star clusters (NSCs) in ultra-diffuse galaxies (UDGs) as an extension of the SMUDGes catalog. We identify 325 SMUDGes galaxies with NSCs and, from the 144 with existing distance estimates, identify 33 NSC hosts as UDGs (μ 0,g ≥ 24 mag arcsec−2, r e ≥ 1.5 kpc). The SMUDGes with NSCs lie on the galaxy red sequence, satisfy the relationship between NSC and host galaxy stellar masses, have a mean NSC stellar mass fraction of 0.02 but reach as high as 0.1, have NSCs that are displaced from the host center with a standard deviation of 0.10r e , and weakly favor higher-density environments. All of these properties are consistent with previous results from higher surface brightness galaxy samples, allowing for at most a relatively weak dependence of NSC behavior on host galaxy surface brightness.

Improving the descendant relationship of cluster galaxies at z &lt; 1

AbstractIn this work, we study how to improve well‐known techniques for detecting progenitors/descendants of galaxies, such as the NDpredict program, when applied to galaxies in clusters. The improvement of this particular method is based on the use of the red sequence of galaxies in those environments. Objects close to the red sequence in the color and magnitude diagram are more likely to belong to the cluster. This defines a probability scale which is then combined with the one generated by NDpredict. This procedure is optimized for the study of galaxies in clusters over different epochs. Our main result is that, for a sample composed of clusters, with masses greater than , selected from the IllustrisTNG simulations (namely, the TNG100 runs). In of the cases (i.e., systems), we obtain better performance with the red sequence method in comparison to the original NDpredict, and the average gain obtained is in the identification of descendants for this sample of cluster galaxies.

Clustering of red sequence galaxies in the fourth data release of the Kilo-Degree Survey

We present a sample of luminous red sequence galaxies as the basis for a study of the large-scale structure in the fourth data release of the Kilo-Degree Survey. The selected galaxies are defined by a red sequence template, in the form of a data-driven model of the colour-magnitude relation conditioned on redshift. In this work, the red sequence template was built using the broad-band optical+near infrared photometry of KiDS-VIKING and the overlapping spectroscopic data sets. The selection process involved estimating the red sequence redshifts, assessing the purity of the sample and estimating the underlying redshift distributions of redshift bins. After performing the selection, we mitigated the impact of survey properties on the observed number density of galaxies by assigning photometric weights to the galaxies. We measured the angular two-point correlation function of the red galaxies in four redshift bins and constrain the large-scale bias of our red sequence sample assuming a fixed ΛCDM cosmology. We find consistent linear biases for two luminosity-threshold samples (‘dense’ and ‘luminous’). We find that our constraints are well characterised by the passive evolution model.

Early Results from GLASS-JWST. XX. Unveiling a Population of “Red Excess” Galaxies in Abell2744 and in the Coeval Field

We combine JWST/NIRCam imaging and MUSE data to characterize the properties of galaxies in different environmental conditions in the cluster Abell2744 (z = 0.3064) and in its immediate surroundings. We investigate how galaxy colors, morphology, and star-forming fractions depend on wavelength and on different parameterizations of environment. Our most striking result is the discovery of a “red excess” population in F200W−F444W colors in both the cluster regions and the field. These galaxies have normal F115W−F150W colors but are up to 0.8 mag redder than red sequence galaxies in F200W−F444W. They also have rather blue rest-frame B−V colors. Galaxies in the field and at the cluster virial radius are overall characterized by redder colors, but galaxies with the largest color deviations are found in the field and in the cluster core. Several results suggest that mechanisms taking place in these regions might be more effective in producing these colors. Looking at their morphology, many cluster galaxies show signatures consistent with ram pressure stripping, while field galaxies have features resembling interactions and mergers. Our hypothesis is that these galaxies are characterized by dust-enshrouded star formation: a JWST/NIRSpec spectrum for one of the galaxies is dominated by a strong PAH at 3.3 μm, suggestive of dust-obscured star formation. Larger spectroscopic samples are needed to understand whether the color excess is due exclusively to dust-obscured star formation, as well as the role of environment in triggering it.

Observational constraints of an anisotropic boost due to the projection effects using redMaPPer clusters

ABSTRACT Optical clusters identified from red-sequence galaxies suffer from projection effects, where interloper galaxies along the line of sight to a cluster are mistaken as genuine members of the cluster. In the previous study, we found that the projection effects cause the boost on the amplitudes of clustering and lensing on large scale compared to the expected amplitudes in the absence of any projection effects. These boosts are caused by preferential selections of filamentary structure aligned to the line of sight due to distance uncertainties in photometric surveys. We model the projection effects with two simple assumptions and develop a novel method to quantify the size of the boost using cluster-galaxy cross-correlation functions. We validate our method using mock cluster catalogues built from cosmological N-body simulations and find that we can obtain unbiased constraints on the boost parameter with our model. We then apply our analysis on the SDSS redMaPPer clusters and find that the size of the boost is roughly 20 per cent for all the richness bins except the cluster sample with the richness bin λ ∈ [30, 40]. This is the first study to constrain the boost parameter independent from cluster cosmology studies and provides a self-consistency test for the projection effects.

JWST unveils a population of “red-excess” galaxies in Abell2744 and in the coeval field

AbstractWe combine JWST/NIRCam imaging and MUSE data to characterize the properties of galaxies in the cluster Abell2744 (z=0.3064) and in its immediate surroundings. We discover a “red-excess” population in F200W–F444W colors in both the cluster regions and the field. These galaxies have normal F115W-F150W colors and rather blue rest frame B–V colors, but are up to 0.8 mag redder than red sequence galaxies in F200W–F444W. Considering morphology, many cluster galaxies show signatures consistent with ram pressure stripping, while field galaxies have features resembling interactions and mergers. Our hypothesis is that these galaxies are characterized by dust enshrouded star formation: a JWST/NIRSpec spectrum for one of the galaxies is dominated by a strong PAH at 3.3 μm, suggestive of dust obscured star formation.

The XXL survey. XLIX. Linking the members star formation histories to the cluster mass assembly in the z = 1.98 galaxy cluster XLSSC 122

ABSTRACT The most massive protoclusters virialize to become clusters at z ∼ 2, which is also a critical epoch for the evolution of their member galaxies. XLSSC 122 is a z = 1.98 galaxy cluster with 37 spectroscopically confirmed members. We aim to characterize their star formation histories in the context of the cluster accretion history. We measure their photometry in 12 bands and create a PSF-matched catalogue of the cluster members. We employ bagpipes to fit star formation histories characterized by exponentially decreasing star-forming rates. Stellar masses, metal, and dust contents are treated as free parameters. The oldest stars in the red-sequence galaxies display a range of ages, from 0.5 Gyr to ∼3 Gyr. Characteristic times are between ∼0.1 and ∼0.3 Gyr, and the oldest members present the longest times. Using MultiDark Planck 2 dark matter simulations, we calculate the assembly of XLSSC 122-like haloes, weighted by the age posteriors of the oldest members. We found that 74 per cent of these haloes were &amp;lt;10 per cent assembled at the onset of star formation, declining to 67 per cent of haloes when such galaxies had formed half of their z = 1.98 stellar masses. When 90 per cent of their stellar masses were formed, 75 per cent of the haloes were &amp;lt;30 per cent assembled. The star formation histories of the red-sequence galaxies seem consistent with episodes of star formation with short characteristic times. Onset and cessation of star formation in the oldest galaxies are likely to precede XLSSC 122 virialization.

The luminosity of cluster galaxies in the Cluster-EAGLE simulations

ABSTRACT We computed the luminosity of simulated galaxies of the c-eagle project, a suite of 30 high-resolution zoom-in simulations of galaxy clusters based on the eagle simulation. The AB magnitudes are derived for different spectral bands, from ultraviolet to infrared, using the simple stellar population modelling based on the E-MILES stellar spectra library. We take into account obscuration due to dust in star forming regions and diffuse interstellar medium. The g − r colour–stellar mass diagram, at z = 0.1, presents a defined red sequence, reaching g − r ≃ 0.8, 0.05 dex redder than eagle at high masses, and a well populated blue cloud, when field galaxies are included. The clusters’ inner regions are dominated by red-sequence galaxies at all masses, although a non-negligible amount of blue galaxies are still present. We adopt Bayesian inference to compute the clusters LFs, testing for statistical significance of both single and double Schechter functions. The multicolour LFs at z = 0 show a knee luminosity that peaks in the infrared and increases with the cluster’s mass. The faint-end is weakly dependent on colour and mass and shows an upturn in the optical, bounded between −1.25 and −1.39, just moderately steeper than the field. The simulations reproduce, within the observational errors, the spectroscopic LFs of the Hercules and Abell 85 clusters, including their faint end upturn. c-eagle LFs are in broad agreement with observed LFs taken from SDSS and XXL surveys, up to z = 0.67, showing a rather flat faint end when the observational constrains are taken into account.

The gMOSS: the galaxy survey and galaxy populations of the large homogeneous field

ABSTRACT We present the gMOSS (Galaxies of Medium-band One-meter Schmidt telescope Survey) catalogue of ∼19 000 galaxies in 20 filters (4 broad-band SDSS and 16 medium-band filters). We observed 2.386 deg2 on the central part of the HS47.5-22 field with the 1-m Schmidt telescope of the Byurakan Astrophysical Observatory. The gMOSS is a complete flux-limited sample of galaxies with a threshold magnitude of r SDSS ≤ 22.5 AB. From photometric measurements with 16 medium-band filters and u SDSS, we get spectral energy distributions for each object in the field, which are used for further analysis. Galaxy classification and photometric redshift estimation based on spectral template matching with zebra software. The obtained redshift accuracy is σNMAD &amp;lt; 0.0043. Using the SED-fitting cigale code, we obtained the main properties of the stellar population of galaxies, such as rest-frame (u − r)res colour, stellar mass, extinction, and mass-weighted age with a precision of 0.16 ± 0.07 mag, 0.14 ± 0.04 dex, 0.27 ± 0.1 mag, and 0.08 ± 0.04 dex, respectively. Using a dust-corrected colour–mass diagram, we divided the full sample into populations of red and blue galaxies and considered the dependencies between stellar mass and age. Throughout cosmic time, red sequence galaxies remain older and more massive than blue cloud galaxies. The star formation history of a complete subsample of galaxies selected in the redshift range 0.05 ≤ z ≤ 0.015 with &amp;lt;$\mathrm{log} M \mathrm{\gt }_\mathrm{[M_\odot ]}$&amp;gt;8.3 shows an increase in the SFRD up to z ∼ 3, under the results obtained in earlier studies.

The eROSITA Final Equatorial-Depth Survey (eFEDS)

Context.In 2019, the eROSITA telescope on board the Russian-German satellite Spectrum-Roentgen-Gamma (SRG) began to perform a deep all-sky X-ray survey with the aim of identifying ~100 000 clusters and groups over the course of four years. As part of its performance verification phase, a ~140 deg2survey, called eROSITA Final Equatorial-Depth Survey (eFEDS), was performed. With a depth typical of the all-sky survey after four years, it allows tests of tools and methods as well as improved predictions for the all-sky survey.Aims.As part of this effort, a catalog of 542 X-ray selected galaxy group and cluster candidates was compiled. In this paper we present the optical follow-up, with the aim of providing redshifts and cluster confirmation for the full sample. Furthermore, we aim to provide additional information on the dynamical state, richness, and optical center of the clusters. Finally, we aim to evaluate the impact of optical cluster confirmation on the purity and completeness of the X-ray selected sample.Methods.We used optical imaging data from the Hyper Suprime-Cam Subaru Strategic Program and from the Legacy Survey to identify optical counterparts to the X-ray detected cluster candidates. We make use of the multi-component matched filter cluster confirmation tool (MCMF), as well as of the optical cluster finder CAMIRA to derive cluster redshifts and richnesses. MCMF provided the probabilities with which an optical structure would be a chance superposition with the X-ray candidate. These probabilities were used to identify the best optical counterpart as well as to confirm an X-ray candidate as a cluster. The impact of this confirmation process on catalog purity and completeness was estimated using optical to X-ray scaling relations as well as simulations. The resulting catalog was furthermore matched with public group and cluster catalogs. Optical estimators of the cluster dynamical state were constructed based on density maps of the red-sequence galaxies at the cluster redshift.Results.By providing redshift estimates for all 542 candidates, we construct an optically confirmed sample of 477 clusters and groups with a residual contamination of 6%. Of these, 470 (98.5%) are confirmed using MCMF, and 7 systems are added through cross-matching with spectroscopic group catalogs. Using observable-to-observable scaling and the applied confirmation threshold, we predict that 8 ± 2 real systems have been excluded with the MCMF cut required to build this low-contamination sample. This number agrees well with the 7 systems found through cross-matching that were not confirmed with MCMF. The predicted redshift and mass distribution of this catalog agree well with simulations. Thus, we expect that these 477 systems include &gt;99% of all true clusters in the candidate list. Using an MCMF-independent method, we confirm that the catalog contamination of the confirmed subsample is 6 ± 3%. Application of the same method to the full candidate list yields 17 ± 3%, consistent with estimates coming from the fraction of confirmed systems of ~17% and with expectations from simulations of ~20%. We also present a sample of merging cluster candidates based on the derived estimators of the cluster dynamical state.

Across the green valley withHSTgrisms: colour evolution, crossing time-scales, and the growth of the red sequence atz = 1.0–1.8

ABSTRACTWe measure the colour evolution and quenching time-scales of z = 1.0–1.8 galaxies across the green valley. We derive rest-frame NUVrK colours and select blue-cloud, green-valley, and red-sequence galaxies from the spectral energy distribution modelling of CANDELS GOODS-South and UDS multiband photometry. Separately, we constrain the star-formation history (SFH) parameters (ages, τ) of these galaxies by fitting their deep archival HST grism spectroscopy. We derive the galaxy colour–age relation and show that only rapidly evolving galaxies with characteristic delayed-τ SFH time-scales of &amp;lt;0.5 Gyr reach the red sequence at these redshifts, after a period of accelerated colour evolution across the green valley. These results indicate that the stellar mass build-up of these galaxies stays minimal after leaving the blue cloud and entering the green valley (i.e. it may represent $\lesssim 5{{\ \rm per\ cent}}$ of the galaxies’ final, quiescent masses). Visual inspection of age-sensitive features in the stacked spectra also supports the view that these galaxies follow a quenching sequence along the blue-cloud → green-valley → red-sequence track. For this rapidly evolving population, we measure a green-valley crossing time-scale of $0.99^{+0.42}_{-0.25}$ Gyr and a crossing rate at the bottom of the green valley of $0.82^{+0.27}_{-0.25}$ mag Gyr−1. Based on these time-scales, we estimate that the number density of massive (M⋆ &amp;gt; 1010M⊙) red-sequence galaxies doubles every Gyr at these redshifts, in remarkable agreement with the evolution of the quiescent galaxy stellar mass function. These results offer a new approach to measuring galaxy quenching over time and represent a pathfinder study for future JWST, Euclid, and Roman Space Telescope programs.

The edge-on Galaxies in the Pan-STARRS survey (EGIPS)

ABSTRACT We present a catalogue of 16 551 edge-on galaxies created using the public DR2 data of the Pan-STARRS survey. The catalogue covers the three quarters of the sky above Dec. = −30°. The galaxies were selected using a convolutional neural network, trained on a sample of edge-on galaxies identified earlier in the SDSS survey. This approach allows us to dramatically improve the quality of the candidate selection and perform a thorough visual inspection in a reasonable amount of time. The catalogue provides homogeneous information on astrometry, SExtractor photometry, and non-parametric morphological statistics of the galaxies. The photometry is reliably for objects in the 13.8–17.4 r-band magnitude range. According to the HyperLeda data base, redshifts are known for about 63 per cent of the galaxies in the catalogue. Our sample is well separated into the red sequence and blue cloud galaxy populations. The edge-on galaxies of the red sequence are systematically Δ(g − i) ≈ 0.1 mag redder than galaxies oriented at an arbitrary angle to the observer. We found a variation of the galaxy thickness with the galaxy colour. The red sequence galaxies are thicker than the galaxies of the blue cloud. In the blue cloud, on average, thinner galaxies turn out to be bluer. In the future, based on this catalogue it is intended to explore the three-dimensional structure of galaxies of different morphologies, as well as to study the scaling relations for discs and bulges.

AGN Lifetimes in UV-selected Galaxies: A Clue to Supermassive Black Hole-galaxy Coevolution

The coevolution between supermassive black holes (SMBHs) and their host galaxies has been proposed for more than a decade, albeit with little direct evidence about black hole accretion activities regulating galaxy star formation at z > 1. In this paper, we study the lifetimes of X-ray active galactic nuclei (AGNs) in UV-selected red sequence (RS), blue cloud (BC) and green valley (GV) galaxies, finding that AGN accretion activities are most prominent in GV galaxies at z ∼ 1.5–2, compared with RS and BC galaxies. We also compare AGN accretion timescales with typical color transition timescales of UV-selected galaxies. We find that the lifetime of GV galaxies at z ∼ 1.5–2 is very close to the typical timescale when the AGNs residing in them stay in the high-accretion-rate mode at these redshifts; for BC galaxies, the consistency between the color transition timescale and the black hole strong accretion lifetime is more likely to happen at lower redshifts (z < 1). Our results support the scenario where AGN accretion activities govern UV color transitions of host galaxies, making galaxies and their central SMBHs coevolve with each other.

The SAMI Galaxy Survey: trends in [α/Fe] as a function of morphology and environment

ABSTRACT We present a new set of index-based measurements of [α/Fe] for a sample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, we fit a global relation between [α/Fe] and the galaxy velocity dispersion σ for red sequence galaxies, $[\alpha /\text{Fe}]=(0.378\pm 0.009)\rm {log}_{10}\left(\sigma /100\right)+(0.155\pm 0.003)$. We observe a correlation between the residuals and the local environmental surface density, whereas no such relation exists for blue cloud galaxies. In the full sample, we find that elliptical galaxies in high-density environments are α-enhanced by up to 0.057 ± 0.014 dex at velocity dispersions σ &amp;lt; 100 km s−1, compared with those in low-density environments. This α-enhancement is morphology-dependent, with the offset decreasing along the Hubble sequence towards spirals, which have an offset of 0.019 ± 0.014 dex. At low velocity dispersion and controlling for morphology, we estimate that star formation in high-density environments is truncated ∼1 Gyr earlier than in low-density environments. For elliptical galaxies only, we find support for a parabolic relationship between [α/Fe] and σ, with an environmental α-enhancement of at least 0.03 dex. This suggests strong contributions from both environment and mass-based quenching mechanisms. However, there is no evidence for this behaviour in later morphological types.

On the Properties of Spectroscopically Confirmed Ultra-diffuse Galaxies across Environments

Abstract We present new redshift measurements for 19 candidate ultra-diffuse galaxies (UDGs) from the Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) survey after conducting a long-slit spectroscopic follow-up campaign on 23 candidates with the Large Binocular Telescope. We combine these results with redshift measurements from other sources for 29 SMUDGes and 20 non-SMUDGes candidate UDGs. Together, this sample yields 44 spectroscopically confirmed UDGs (r e ≥ 1.5 kpc and μ g (0) ≥ 24 mag arcsec−2 within uncertainties) and spans cluster and field environments, with all but one projected on the Coma cluster and environs. We find no statistically significant differences in the structural parameters of cluster and noncluster confirmed UDGs, although there are hints of differences among the axis ratio distributions. Similarly, we find no significant structural differences among those in locally dense or sparse environments. However, we observe a significant difference in color with respect to projected clustercentric radius, confirming trends observed previously in statistical UDG samples. This trend strengthens further when considering whether UDGs reside in either cluster or locally dense environments, suggesting starkly different star formation histories for UDGs residing in high- and low-density environments. Of the 16 large (r e ≥ 3.5 kpc) UDGs in our sample, only one is a field galaxy that falls near the early-type galaxy red sequence. No other field UDGs found in low-density environments fall near the red sequence. This finding, in combination with our detection of Galaxy Evolution Explorer NUV flux in nearly half of the UDGs in sparse environments, suggests that field UDGs are a population of slowly evolving galaxies.

Estimating Lifetimes of UV-selected Massive Galaxies at 0.5 ≤ z ≤ 2.5 in the COSMOS/UltraVISTA Field through Clustering Analyses

Abstract To investigate the lifetimes of red sequence (RS), blue cloud (BC), and green valley (GV) galaxies, we derive their lifetimes using clustering analyses at 0.5 ≤ z ≤ 2.5 in the COSMOS/UltraVISTA field. Several essentials that may influence the lifetime estimation have been explored, including the dark matter (DM) halo mass function (HMF), the width of the redshift bin, the growth of DM halos within each redshift bin, and the stellar mass. We find that the HMF difference results in scatters of ∼0.2 dex on the lifetime estimation, adopting a redshift bin width of Δz = 0.5 is good enough to estimate the lifetime, and no significant effect on lifetime estimation is found due to the growth of DM halos within each redshift bin. The galaxy subsamples with higher stellar masses generally have shorter lifetimes, but the lifetimes in different subsamples at z &gt; 1.5 tend to be independent of stellar mass. Consistently, the clustering-based lifetime for each galaxy subsample agrees well with that inferred using the spectral energy distribution modeling. Moreover, the lifetimes of the RS and BC galaxies also coincide well with their typical gas-depletion timescales attributed to the consumption of star formation. Interestingly, the distinct lifetime behaviors of the GV galaxies at z ≤ 1.5 and z &gt; 1.5 cannot be fully accounted for by their gas-depletion timescales. Instead, this discrepancy between the lifetimes and gas-depletion timescales of the GV galaxies suggests that there are additional physical processes, such as feedback of active galactic nuclei, which accelerates the quenching of GV galaxies at high redshifts.