Galaxy Population Research Articles

Discrepancies between JWST Observations and Simulations of Quenched Massive Galaxies at z > 3: A Comparative Study with IllustrisTNG and ASTRID

Abstract Recent JWST observations have uncovered an unexpectedly large population of massive quiescent galaxies at z > 3. Using the cosmological simulations IllustrisTNG and ASTRID, we identify analogous galaxies and investigate their abundance, formation, quenching mechanisms, and post-quenching evolution for stellar masses 9.5 < log 10 ( M ⋆ / M ⊙ ) < 12 . We apply three different quenching definitions and find that both simulations significantly underestimate the comoving number density of quenched massive galaxies at z ≳ 3 compared to JWST observations by up to ∼2 dex. In both simulations, the high-z quenched massive galaxies often host overmassive central black holes above the local M BH–M ⋆ relation, implying that AGN feedback is key in quenching galaxies in the early Universe. The typical quenching timescales for these galaxies are ∼200–600 Myr. IllustrisTNG primarily employs AGN kinetic feedback, while ASTRID relies on AGN thermal feedback at z > 2.3, which is less effective and has a longer quenching timescale. Although these simulations differ in many aspects, making a direct comparison challenging, our findings suggest the need for improved physical models of AGN feedback in galaxy formation simulations. At lower stellar masses, the quenched galaxies have denser local environments than the star-forming galaxies, suggesting that environmental quenching helps quench less-massive galaxies. We also study the post-quenching evolution of the high-z massive quiescent galaxies and find that many experience subsequent reactivation of star formation, evolving into primary progenitors of z = 0 brightest cluster galaxies.

Two Channels of Metal-rich Compact Stellar System Formation: Starbursts under High Ram Pressure versus Tidal Stripping

Abstract Most galaxies follow a well-defined scaling relation between metallicity and stellar mass; however, some outliers at the low-mass end of the observed galaxy population exhibit unusually high metallicity for their mass. Understanding how these objects get to be so metal-rich is vital for understanding the role of feedback in galaxy formation. Using the TNG50 simulation, we explore the origins of this phenomenon. We identify 227 metal-rich, compact stellar systems (CSSs) that deviate significantly from this scaling relation. These CSSs are satellites located in the vicinity of massive host galaxies, with stellar masses ranging from 108 to 1010 M ⊙ (including six systems that are close analogs of the M31–M32 system). Contrary to the previously assumed scenario that such objects are predominantly products of tidal stripping, we find that more often ram pressure plays a major role in their formation. Indeed, 76% (173) of these CSSs are formed through a burst of star formation occurring around the time of the first pericentric passage, typically at redshifts z ≲ 1, aided by strong ram pressure and tidal forces. The high ram pressure, resulting from the CSSs’ rapid motion near the host halo center, facilitates metal enrichment, producing high-metallicity CSSs by confining the metal-rich gas from bursty star formation, which leads to distinct stellar populations characterized by enhanced metallicity and high α-abundance. The other 24% (54) of metal-rich CSSs are generated through the tidal stripping of massive progenitors. Our results further indicate that M32 is more likely to have formed through intense star formation events rather than through gradual tidal stripping.

Extreme Metallicity Dwarf Galaxies in IllustrisTNG

Abstract The use of extremely metal-deficient dwarf galaxies (XMDs) as nearby analogs for high-redshift protogalaxies is generating renewed interest due to recent JWST observations studying these protogalaxies. However, the existence of a population of unenriched galaxies at z ˷ 0 raises fundamental questions about how galaxies with such pristine gas reservoirs could be formed. To address these questions we study XMDs in the IllustrisTNG simulation. We find that XMDs at z = 0 are not relics of the first galaxies, but dwarf galaxies that experience a dramatic ˷0.3 dex drop in their gas-phase metallicity in the past few Gyr. We investigate possible causes of this drop in metallicity including high gas fractions, outflow efficiency or inflow/outflow rates, unique environments, pristine inflow metallicity, and inflow/SFR interactions. Of these, we find that inflow/outflow interactions, parameterized by the cumulative regional SFR experienced by inflows, has the strongest correlation with dwarf galaxy metallicity and XMD formation. In other words, inefficient gas enrichment during the short time between its accretion from the CGM and the initiation of star formation is the most important cause of XMD formation in the simulation. We identify differences in star formation history between XMDs and non-XMDs (with XMDs having significantly decreased star formation rates on 1 − 5 Gyr timescales) and differences in galaxy size (with XMDs having a more extended young stellar population) as the primary observable differences between the two populations. These results highlight the importance of inflow enrichment efficiency as a possible driver of dwarf galaxy metallicities.

A Pride of Satellites in the Constellation Leo? Discovery of the Leo VI Milky Way Satellite Ultra-faint Dwarf Galaxy with DELVE Early Data Release 3

Abstract We report the discovery and spectroscopic confirmation of an ultra-faint Milky Way satellite in the constellation of Leo. This system was discovered as a spatial overdensity of resolved stars observed with Dark Energy Camera (DECam) data from an early version of the third data release of the DECam Local Volume Exploration (or DELVE) survey. The low luminosity ( M V = − 3.5 6 − 0.37 + 0.47 ; L V = 230 0 − 700 + 1200 L ⊙ ), large size ( R 1 / 2 = 9 0 − 30 + 30 pc), and large heliocentric distance ( D = 11 1 − 6 + 9 kpc) are all consistent with the population of ultra-faint dwarf galaxies (UFDs). Using Keck/DEIMOS observations of the system, we were able to spectroscopically confirm nine member stars, while measuring a tentative mass-to-light ratio of 70 0 − 500 + 1400 M ⊙ / L ⊙ and a nonzero metallicity dispersion of σ [ Fe / H ] = 0.1 9 − 0.11 + 0.14 , further confirming Leo VI’s identity as a UFD. While the system has a highly elliptical shape, ϵ = 0.5 4 − 0.29 + 0.19 , we do not find any conclusive evidence that it is tidally disrupting. Moreover, despite the apparent on-sky proximity of Leo VI to members of the proposed Crater-Leo infall group, its smaller heliocentric distance and inconsistent position in energy–angular momentum space make it unlikely that Leo VI is part of the proposed infall group.

ALMA/SCUBA-2 COSMOS Survey: Properties of X-Ray- and SED-selected Active Galactic Nuclei in Bright Submillimeter Galaxies

Abstract We investigate the properties of active galactic nuclei (AGNs) in the brightest submillimeter galaxies (SMGs) in the COSMOS field. We utilize the bright sample of the ALMA/SCUBA-2 COSMOS Survey (AS2COSMOS), which consists of 260 SMGs with S 870 μm = 0.7–19.2 mJy at z = 0–6. We perform optical to millimeter spectral energy distribution (SED) modeling for the whole sample. We identify 24 AGN-host galaxies from the SEDs. Supplemented by 23 X-ray-detected AGNs (X-ray AGNs), we construct an overall sample of 40 AGN-host galaxies. The X-ray luminosity upper bounds indicate that the X-ray-undetected SED-identified AGNs are likely to be nearly Compton thick or have unusually suppressed X-ray emission. From visual classification, we identify 2 5 − 5 + 6 % of the SMGs without AGNs as major merger candidates. This fraction is almost consistent with the general galaxy population at z ∼ 2, suggesting that major mergers are not necessarily required for the enhanced star formation in SMGs. We also identify 4 7 − 15 + 16 % of the AGN hosts as major merger candidates, which is about twice as high as that in the SMGs without AGNs. This suggests that major mergers play a key role in triggering AGN activity in bright SMGs.

Euclid: Relativistic effects in the dipole of the two-point correlation function

Gravitational redshift and Doppler effects give rise to an antisymmetric component of the galaxy correlation function when cross-correlating two galaxy populations or two different tracers. In this paper, we assess the detectability of these effects in the spectroscopic galaxy survey. We model the impact of gravitational redshift on the observed redshift of galaxies in the Flagship mock catalogue using a Navarro--Frenk--White profile for the host haloes. We isolate these relativistic effects, largely subdominant in the standard analysis, by splitting the galaxy catalogue into two populations of faint and bright objects and estimating the dipole of their cross-correlation in four redshift bins. In the simulated catalogue, we detect the dipole signal on scales below $ Mpc $, with detection significances of $4,σ$ and $3,σ$ in the two lowest redshift bins, respectively. At higher redshifts, the detection significance drops below $2,σ$. Overall, we estimate the total detection significance in the spectroscopic sample to be approximately $6,σ$. We find that on small scales, the major contribution to the signal comes from the nonlinear gravitational potential. Our study on the Flagship mock catalogue shows that this observable can be detected in Euclid Data Release 2 and beyond.

Fully comprehensive diagnostic of galaxy activity using principal components of visible spectra: implementation on nearby S0s

Abstract We introduce a novel galaxy classification methodology based on the visible spectra of a sample of over 68,000 nearby (z ≤ 0.1) Sloan Digital Sky Survey lenticular (S0) galaxies. Unlike traditional diagnostic diagrams, which rely on a limited set of emission lines and class dividers to identify ionizing sources, our approach provides a comprehensive framework for characterizing galaxies regardless of their activity level. By projecting galaxies into the 2D latent space defined by the first three principal components (PCs) of their entire visible spectra, our method remains robust even when data from individual emission lines are missing. We employ Gaussian kernel density estimates of the classical Baldwin-Phillips-Terlevich (BPT) activity classes in the new classification subspace, adjusted according to their relative abundance in our S0 sample, to generate probability maps for star-forming, Seyfert, composite, and LINER galaxies. These maps closely mirror the canonical distribution of BPT classes shown by the entire galaxy population, demonstrating that our PC-based taxonomy effectively predicts the dominant ionizing mechanisms through a probabilistic approach that provides a realistic reflection of galaxy activity and allows for refined class membership. Our analysis further reveals that flux-limited BPT-like diagrams are inherently biased against composite and star-forming galaxies due to their weaker [O iii] emission. Besides, it suggests that although most low-activity galaxies excluded from these diagnostics exhibit visual spectra with LINER-like characteristics, their remaining activity is likely driven by mechanisms unrelated to either star formation or supermassive black hole accretion. A machine-readable catalogue listing BPT-class probabilities for the galaxies analysed is available online at CDS website.

Field-level simulation-based inference with galaxy catalogs: the impact of systematic effects

It has been recently shown that a powerful way to constrain cosmological parameters from galaxy redshift surveys is to train graph neural networks to perform field-level likelihood-free inference without imposing cuts on scale. In particular, de Santi et al. [58] developed models that could accurately infer the value of Ωm from catalogs that only contain the positions and radial velocities of galaxies that are robust to different astrophysics and subgrid models. However, observations are affected by many effects, including (1) masking, (2) uncertainties in peculiar velocities and radial distances, and (3) different galaxy population selections. Moreover, observations only allow us to measure redshift, which entangles the galaxy radial positions and velocities. In this paper we train and test our models on galaxy catalogs, created from thousands of state-of-the-art hydrodynamic simulations run with different codes from the CAMELS project, that incorporate these observational effects. We find that while such effects degrade the precision and accuracy of the models, the fraction of galaxy catalogs for which the models retain high performance and robustness is over 90%, demonstrating the potential for applying them to real data.

Unravelling the orbits of cluster galaxy populations according to their dominant gas ionization source

ABSTRACT We investigate the kinematical and dynamical properties of cluster galaxy populations classified according to their dominant source of gas ionization, namely: star-forming (SF) galaxies, optical active galactic nuclei (AGNs), mixed SF plus AGN ionization (transition objects, T), and quiescent (Q) galaxies. We stack 8892 member galaxies from 336 relaxed galaxy clusters to build an ensemble cluster and estimate the observed projected profiles of numerical density and velocity dispersion, $\sigma _P(R)$, of each galaxy population. The MAMPOSSt code and the Jeans equations inversion technique are used to constrain the velocity anisotropy profiles of the galaxy populations in both parametric and non-parametric ways. We find that Q (SF) galaxies display the lowest (highest) typical cluster-centric distances and velocity dispersion values. Transition galaxies are more concentrated and tend to exhibit lower velocity dispersion values than SF galaxies. Galaxies that host an optical AGN are as concentrated as Q galaxies but display velocity dispersion values similar to those of the SF population. MAMPOSSt is able to find equilibrium solutions that successfully recover the observed $\sigma _P(R)$ profile only for the Q, T, and AGN populations. We find that the orbits of all populations are consistent with isotropy in the inner regions, becoming increasingly radial with the distance from the cluster centre. These results suggest that Q galaxies are in equilibrium within their clusters, while SF galaxies have more recently arrived in the cluster environment. Finally, the T and AGN populations appear to be in an intermediate dynamical state between those of the SF and Q populations.

The first all-sky survey of star-forming galaxies with eROSITA. Scaling relations and a population of X-ray luminous starbursts

In this work, we present the results from a study of X-ray normal galaxies, that is, galaxies not harbouring active galactic nuclei (AGN), using data from the first complete all-sky scan of the X-ray survey (eRASS1) obtained with eROSITA on board the Spectrum-Roentgen-Gamma observatory. eRASS1 provides the first unbiased X-ray census of local normal galaxies, thus allowing us to study the X-ray emission (0.2-8.0 ) from X-ray binaries (XRBs) and the hot interstellar medium in the full range of stellar population parameters present in the local Universe. By combining the updated version of the Heraklion Extragalactic Catalogue (HECATE v2.0) value-added catalogue of nearby galaxies (Distance ; lesssim \,200$Mpc) with the X-ray data obtained from eRASS1, we studied the integrated X-ray emission from normal galaxies as a function of their star-formation rate ( ), stellar mass ( ), metallicity, and stellar population age. After applying stringent optical and mid-infrared activity classification criteria, we constructed a sample of 18790 bona fide star-forming galaxies (HEC-eR1 galaxy sample) with measurements of their integrated X-ray luminosity (using each galaxy's D$_ $) over the full range of stellar population parameters present in the local Universe. By stacking the X-ray data in bins, we studied the correlation between the average X-ray luminosity and the average stellar population parameters. We also present updated and -metallicity scaling relations based on a completely blind galaxy sample and accounting for the scatter dependence on the The average X-ray spectrum of star-forming galaxies is well described by a power law ($ $) and a thermal plasma component ($kT = 0.70^ $). We find that the integrated X-ray luminosity of the individual HEC-eR1 star-forming galaxies is significantly elevated (reaching $10^ $) with respect to what is expected from the current standard scaling relations. The observed scatter is also significantly larger. This excess persists even when we measured the average luminosity of galaxies in and metallicity bins, and it is stronger (up to $ sim 2$ dex) towards lower s. Our analysis shows that the excess is not the result of the contribution by hot gas, low-mass XRBs, background AGN, low-luminosity AGN (including tidal disruption events), or stochastic sampling of the XRB X-ray luminosity function. We find that while the excess is generally correlated with lower metallicity galaxies, its primary driver is the age of the stellar populations. Our analysis reveals a sub-population of very X-ray luminous starburst galaxies with higher specific SFRs (sSFRs), lower metallicities, and younger stellar populations. This population drives upwards the X-ray scaling relations for star-forming galaxies and has important implications for understanding the population of XRBs contributing in the most X-ray luminous galaxies in the local and high-redshift Universe. These results demonstrate the power of large blind surveys such eRASS1, which can provide a more complete picture of the X-ray emitting galaxy population and their diversity, revealing rare populations of objects and recovering unbiased underlying correlations.

The Small Sizes and High Implied Densities of “Little Red Dots” with Balmer Breaks Could Explain Their Broad Emission Lines without an Active Galactic Nucleus

Abstract Early JWST studies found an apparent population of massive, compact galaxies at redshifts z ≳ 7. Recently three of these galaxies were shown to have prominent Balmer breaks, demonstrating that their light at λ rest ∼ 3500 Å is dominated by a stellar population that is relatively old (∼200 Myr). All three also have broad Hβ emission with σ > 1000 km s−1, a common feature of such “little red dots.” From Sérsic profile fits to the Near Infrared Camera images in F200W we find that the stellar light of galaxies is extremely compact: the galaxies have half-light radii of r e ∼ 100 pc, in the regime of ultracompact dwarfs in the nearby Universe. Their masses are uncertain, as they depend on the contribution of possible light from an active galactic nucleus (AGN) to the flux at λ rest > 5000 Å. If the AGN contribution is low beyond the Balmer break region, the masses are M * ∼ 1010–1011 M ☉, and the central densities are higher than those of any other known galaxy population by 1 order of magnitude. Interestingly, the implied velocity dispersions of ∼1500 km s−1 are in very good agreement with the measured Hβ line widths. We suggest that some of the broad lines in “little red dots” are not due to AGNs, but simply reflect the kinematics of the galaxies, and speculate that the galaxies are observed in a short-lived phase where the central densities are much higher than at later times. We stress, however, that the canonical interpretation of AGNs causing the broad Hβ lines also remains viable.

Initial Mass Functions of Young Stellar Clusters from the Gemini Spectroscopic Survey of Nearby Galaxies. I. Young Massive Clusters in the Antennae Galaxies

The stellar initial mass function (IMF) is a key parameter to understand the star formation process and the integrated properties of stellar populations in remote galaxies. We present a spectroscopic study of young massive clusters (YMCs) in the starburst galaxies NGC 4038/9. The integrated spectra of seven YMCs obtained with GMOS-S attached to the 8.1 m Gemini South telescope reveal the spectral features associated with stellar ages and the underlying IMFs. We constrain the ages of the YMCs using the absorption lines and strong emission bands from Wolf–Rayet stars. The internal reddening is also estimated from the strength of the Na i D absorption lines. Based on these constraints, the observed spectra are matched with the synthetic spectra generated from a simple stellar population model. Several parameters of the clusters including age, reddening, cluster mass, and the underlying IMF are derived from the spectral matching. The ages of the YMCs range from 2.5 to 6.5 Myr, and these clusters contain stellar masses ranging from 1.6 × 105 M ☉ to 7.9 × 107 M ☉. The underlying IMFs appear to differ from the universal form of the Salpeter/Kroupa IMF. Interestingly, massive clusters tend to have the bottom-heavy IMFs, although the masses of some clusters are overestimated due to the crowding effect. Based on this, our results suggest that the universal form of the IMF is not always valid when analyzing integrated light from unresolved stellar systems. However, further study with a larger sample size is required to reach a definite conclusion.

The dynamical lineage of isolated, HI-rich ultra-diffuse galaxies

Ultra-diffuse galaxies (UDGs) exhibit morphological similarities with other low-luminosity galaxies, indicating a possible evolutionary connection. We investigated for the common dynamical characteristics of isolated, HI-rich UDGs with other low-luminosity field galaxies, namely the low surface brightness galaxies (LSBs) and the dwarf irregulars (dIrrs). We considered samples of each of the UDGs, LSBs, and the dIrrs. We first obtained scaling relations involving mass and structural parameters for the LSB and the dIrr samples and superposed the UDGs on them. We then carried out a two-sample Anderson-Darling test to analyse whether the UDGs belong to the population of the LSBs or the dIrrs. Thereafter, we constructed distribution function-based stellar-dynamical models of these galaxies to determine their kinematical parameters. We followed up with the Mann-Whitney U-test to determine if our UDG, LSB, and dIrr samples belong to different parent populations so far as kinematics is concerned. Finally, we conducted principal component analyses involving both structural and kinematical parameters to identify the key properties accounting for the variance in the data for the respective galaxy populations. From the galaxy scaling relation studies, we note that the UDGs and the LSBs constitute statistically different populations. However, for the UDGs and the dIrrs, the null hypotheses of these statistical tests cannot be rejected for the following scaling relations: (i) stellar mass versus atomic hydrogen mass, (ii) stellar mass versus dynamical mass, and (iii) dark matter core density versus core radius mass scaling. Interestingly, the dynamical models suggest that the UDGs, LSBs, and the dIrrs constitute different galaxy populations, as reflected by their radial-to-vertical velocity dispersion and the rotational velocity-to-total stellar velocity dispersion. Finally, we observe that the total HI and stellar mass mostly regulate the variance in the structural and kinematical data for both the UDGs and the dIrrs, while the ratio of radial-to-vertical velocity dispersion and the total HI mass dominate the variation in the LSBs. The UDGs and the LSBs represent statistically different galaxy populations with respect to their mass and structural properties. However, the statistical studies do not negate the fact that the structural parameters of the UDGs and the dIrrs follow the same normal distributions. However, the UDGs, LSBs, and the dIrrs constitute very different populations as far as their kinematical parameters are concerned. Finally, we note that the variation in the structural and kinematical data of both the UDGs and the dIrrs is mostly accounted for by their stellar mass and HI mass, whereas for the LSBs, the variance is explained by the ratio of the radial-to-vertical stellar dispersion followed by the HI mass. Thus, we may conclude that the UDGs and dIrrs share a common dynamical lineage.

The hot circumgalactic medium in the eROSITA All-Sky Survey. III. Star-forming and quiescent galaxies

The galaxy population shows a characteristic bimodal distribution based on the star formation activity and is sorted into star-forming or quiescent. These two subpopulations have a tendency to be located in different mass halos. The circumgalactic medium (CGM), as the gas repository for star formation, might contain the answer to the mystery of the formation of such bimodality. Here we consider the bimodality of the galaxy population and study the difference between the properties of the hot CGM around star-forming and quiescent galaxies. We used the X-ray data from the first four SRG/eROSITA all-sky surveys (eRASS:4). We selected central star-forming and quiescent galaxies from the Sloan Digital Sky Survey DR7 with stellar mass $10.0< or halo mass $11.5< 200m /M_ within spectroscopic redshift spec <0.2$, and we built approximately volume-limited galaxy samples. We stacked the X-ray emission around star-forming and quiescent galaxies, respectively. We masked detected point sources and carefully modeled the X-ray emission from unresolved active galaxy nuclei (AGN) and X-ray binaries (XRB) to detect the X-ray emission from the hot CGM. We measured the X-ray surface brightness ($S_ X, CGM $) profiles and integrated the X-ray emission from hot CGM within $R_ 500c $ ($L_ X, CGM $) to provide the scaling relations between $L_ X, CGM $ and galaxies' stellar or halo mass. We detect extended X-ray emission from the hot CGM around star-forming galaxies with $ and quiescent galaxies with $ extending out to 500c $. The $S_ X, CGM $ profile of quiescent galaxies follows a beta model with $ 0.4$, where beta quantifies the slope of the profile. Star-forming galaxies with median stellar masses $ *,med /M_ = 10.7, 11.1, 11.3$ have X, CGM erg/s$, while for quiescent galaxies with $ *,med /M_ X, CGM erg/s$. Notably, quiescent galaxies with $ *,med /M_ > 11.0$ exhibit brighter hot CGM than their star-forming counterparts. In halo mass bins, we detect similar X-ray emission around star-forming and quiescent galaxies with $ 200m /M_ > 12.5$, suggesting that galaxies in the same mass dark matter halos host equally bright hot CGM. We emphasize that the observed X, CGM - M_ 500c $ relations of star-forming and quiescent galaxies are sensitive to the stellar-to-halo mass relation (SHMR). A comparison with cosmological hydrodynamical simulations (EAGLE, TNG100, and SIMBA) reveals varying degrees of agreement, contingent on the simulation and the specific stellar or halo mass ranges considered. Either selected in stellar mass or halo mass, the star-forming galaxies do not host brighter stacked X-ray emission from the hot CGM than their quiescent counterparts at the same mass range. The result provides useful constraints on the extent of feedback's impacts as a mechanism for quenching star formation as implemented in current cosmological simulations.

A halo model approach to describe clustering and emission of the two main star-forming galaxy populations for cosmic infrared background studies

The cosmic infrared background (CIB), which is traced by the emission from dusty star-forming galaxies, provides a crucial window into the phases of star formation throughout cosmic history. These galaxies, although challenging to detect individually at high redshifts due to their faintness, cumulatively contribute to the CIB, which then becomes a powerful probe of galaxy formation, evolution, and clustering. Here, we introduce a physically motivated model for the CIB emission spanning a wide range of frequency and angular resolution, employing a halo model approach, and distinguishing, within dark matter halos, between two main populations of star-forming galaxies, namely normal late-type spiral and irregular galaxies, and the progenitors of early-type galaxies. The requirement to have two different galaxy populations is motivated by the dichotomy between elliptical and spiral galaxies observed in number counts. The emission from the two galaxy populations maps onto different regimes in frequency and resolution spaces. This allowed us to test an extended two-population CIB model and to constrain its clustering parameters – Mmin, the mass of a halo with 50% probability of having a central galaxy, and α, the power-law index regulating the number of satellite galaxies – through a fit to Planck and Herschel-SPIRE CIB anisotropy measurements. We find that while we were able to place constraints on some of the clustering parameters, the Planck frequency and multipole coverage cannot effectively disentangle the contributions from the two galaxy populations. On the other hand, the Herschel-SPIRE measurements separate out and constrain the clustering of both populations. Nonetheless, our work highlights an inconsistency of the results between the two data sets and therefore we are unable to provide a joint fit. This outcome has already been reported in other literature when fitting a single-population model and is still present in our extended scenario.

CLASH-VLT: Galaxy cluster MACS J0329–0211 and its surroundings using galaxies as kinematic tracers

Context. The study of substructure is an important step in determining how galaxy clusters form. Aims. We aim to gain new insights into the controversial dynamical status of MACS J0329–0211 (MACS0329), a massive cluster at z = 0.4503 ± 0.0003, through a new analysis using a large sample of member galaxies as kinematic tracers. Methods. Our analysis is based on extensive spectroscopic data for more than 1700 galaxies obtained with the VIMOS and MUSE spectrographs at the Very Large Telescope (VLT) in combination with B and RC Suprime-Cam photometry from the Subaru archive. According to our member selection procedure, we defined a sample of 430 MACS0329 galaxies within 6 Mpc, corresponding to approximately three times the virial radius. Results. We estimated the global velocity dispersion, σV841-36+26 km s−1, and present the velocity dispersion profile. We estimated a mass of M200 = (9.2 ± 1.5)×1014 M⊙ using 227 galaxies within R200 = (1.71 ± 0.07) Mpc, for which σV,200841-48+40 km s−1. The spatial distribution of the red galaxies traces a SE-NW elongated structure without signs of a velocity gradient. This structure likely originates from the main phase of cluster assembly. The distribution of the blue galaxies is less concentrated and more rounded, and it shows signs of substructure, all characteristics indicating a recent infall of groups from the field. We detected two loose clumps of blue galaxies in the south and southwest at a distance of ∼R200 from the cluster center. The strong spatial segregation among galaxy populations is not accompanied by a kinematical difference. Thanks to our extensive catalog of spectroscopic redshift, we were able to study galaxy systems that are intervening along the line of sight. We identified two foreground galaxy systems, GrG1 at z ∼ 0.31 and GrG2 at z ∼ 0.38, and one background system, GrG3 at z ∼ 0.47. We point out that the second brightest galaxy projected onto the MACS0329 core is in fact the dominant galaxy of the foreground group GrG2. MACS0329, GrG3, and two other systems detected using DESI DR9 photometric redshifts are close to each other, suggesting the presence of a large-scale structure. Conclusions. MACS0329 is close to a state of dynamical equilibrium despite being surrounded by a very rich environment. We emphasize that the use of an extensive spectroscopic redshift survey is essential to avoiding misinterpretation of structures projected along the line of sight.

Using relativistic effects in large-scale structure to constrain astrophysical properties of galaxy populations

Upcoming large-scale structure surveys will be able to measure new features in the galaxy two point correlation function. Relativistic effects appear on large scales as subtle corrections to redshift-space distortions, showing up as a dipole and octupole when cross-correlating two different tracers of dark matter.The dipole and octupole are very sensitive to the evolution and magnification biases of the observed tracers which are hard to model accurately as they depend upon the derivative of the luminosity function at the flux limit of the survey.We show that splitting a galaxy population into bright and faint samples allows us to cross-correlate these and constrain both the evolution bias and magnification bias of the two samples — using the relativistic odd multipoles of the correlation function, together with the even Newtonian multipoles.Although the octupole has much lower signal-to-noise than the dipole, it significantly improves the constraints by breaking parameter degeneracies.We illustrate this in the case of a futuristic survey with the Square Kilometre Array, and demonstrate how splitting the samples in different ways can help improve constraints.This method is quite general and can be used on different types of tracers to improve knowledge of their luminosity functions. Furthermore, the signal-to-noise of the dipole and octupole peaks on intermediate scales, which means that they can deliver a clean measurement of the magnification bias and evolution bias without contamination from local primordial non-Gaussianities or from systematics on very large scales.

The Application of Manifold Learning to a Selection of Different Galaxy Populations and Scaling Relation Analysis

The growing volume of data produced by large astronomical surveys necessitates the development of efficient analysis techniques capable of effectively managing high-dimensional data sets. This study addresses this need by demonstrating some applications of manifold learning and dimensionality reduction techniques, specifically the self-organizing map (SOM), on the optical+near-infrared spectral energy distribution (SED) space of galaxies, with a focus on sample comparison, selection biases, and predictive power using a small subset. To this end, we utilize a large photometric sample from the five Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields and a subset with spectroscopic measurements from the KECK MOSDEF survey in two redshift bins at z ∼ 1.5 and z ∼ 2.2. We trained the SOM with the photometric data and mapped the spectroscopic data onto it as our study case. We found that MOSDEF targets do not cover all SED shapes existing in the SOM. Our findings reveal that active galactic nuclei within the MOSDEF sample are mapped onto the more massive regions of the SOM, confirming previous studies and known selection biases toward higher-mass, less dusty galaxies. Furthermore, SOMs were utilized to map measured spectroscopic features, examining the relationship between metallicity variations and galaxy mass. Our analysis confirmed that more massive galaxies exhibit lower [O iii]/Hβ and [O iii]/[O ii] ratios and higher Hα/Hβ ratios, consistent with the known mass–metallicity relation. These findings highlight the effectiveness of SOMs in analyzing and visualizing complex, multidimensional data sets, emphasizing their potential in data-driven astronomical studies.

Dust-obscured Galaxies in the XMM-SERVS Fields: Selection, Multiwavelength Characterization, and Physical Nature

Dust-obscured galaxies (DOGs) are enshrouded by dust and many are believed to host accreting supermassive black holes (SMBHs), which makes them unique objects for probing the coevolution of galaxies and SMBHs. We select and characterize DOGs in the 13 deg2 XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS), leveraging the superb multiwavelength data—from X-rays to radio. We select 3738 DOGs at z ≈ 1.6–2.1 in XMM-SERVS, while maintaining good data quality without introducing significant bias. This represents the largest DOG sample with thorough multiwavelength source characterization. Spectral energy distribution modeling shows DOGs are a heterogeneous population consisting of both normal galaxies and active galactic nuclei (AGNs). Our DOGs are massive ( logM⋆/M☉≈10.7-11.3 ), 174 are detected in X-rays, and they are generally radio-quiet systems. X-ray detected DOGs are luminous and are moderately to heavily obscured in X-rays. Stacking analyses for the X-ray undetected DOGs show highly significant average detections. Critically, we compare DOGs with matched galaxy populations. DOGs have similar AGN fractions compared with typical galaxy populations. X-ray detected DOGs have higher M ⋆ and higher X-ray obscuration, but they are not more star-forming than typical X-ray AGNs. Our results potentially challenge the relevance of the merger-driven galaxy-SMBH coevolution framework for X-ray detected DOGs.

Mergers, Radio Jets, and Quenching Star Formation in Massive Galaxies: Quantifying Their Synchronized Cosmic Evolution and Assessing the Energetics

The existence of a population of massive quiescent galaxies with little to no star formation poses a challenge to our understanding of galaxy evolution. The physical process that quenched the star formation in these galaxies is debated, but the most popular possibility is that feedback from supermassive black holes lifts or heats the gas that would otherwise be used to form stars. In this paper, we evaluate this idea in two ways. First, we compare the cumulative growth in the cosmic inventory of the total stellar mass in quiescent galaxies to the corresponding growth in the amount of kinetic energy carried by radio jets. We find that these two inventories are remarkably well-synchronized, with about 50% of the total amounts being created in the epoch from z ≈ 1 to 2. We also show that these agree extremely well with the corresponding growth in the cumulative number of major mergers that result in massive (>1011 M ʘ) galaxies. We therefore argue that major mergers trigger the radio jets and also transform the galaxies from disks to spheroids. Second, we evaluate the total amount of kinetic energy delivered by jets and compare it to the baryonic binding energy of the galaxies. We find the jet kinetic energy is more than sufficient to quench star formation, and the quenching process should be more effective in more massive galaxies. We show that these results are quantitatively consistent with recent measurements of the Sunyaev–Zel’dovich effect seen in massive galaxies at z ≈ 1.