arXiv subjects

Stefano Zarattini

Publications and source records attributed to Stefano Zarattini.

11 recordsLinked to original sources

arXiv2026

From relics to stripped systems: the environmental origin of compact galaxies

Compact galaxies represent a key population for understanding galaxy evolution, but the relative role of internal structure and environment in shaping their origin remains unclear. We aim to investigate how the abundance and quenching of compact galaxies depend on environment, and to determine whether their formation is governed by a single evolutionary pathway or multiple channels. We analyse a large sample of galaxies in the nearby Universe ($z<0.05$) with stellar masses in the range $8.2<\log(M_\star/M_\odot)<10.5$, comparing compact and control populations as a function of local overdensity. We find that the environmental dependence of compact galaxies is non-monotonic, with two characteristic overdensities, the transition overdensity ($\delta_t$) and the critical overdensity ($\delta_c$), defining three distinct regimes. Below $\delta_t$, compact galaxies are relatively more abundant than the control population, while between $\delta_t$ and $\delta_c$ their relative abundance decreases significantly. Above $\delta_c$, compact galaxies become increasingly overabundant again. The environmental trends show a strong stellar-mass dependence, with low-mass galaxies exhibiting the strongest deficit at intermediate overdensities and high-mass galaxies dominating the excess population above $\delta_c$. In addition, the red galaxy fraction increases with local overdensity and is systematically higher in compact galaxies. Our results support a unified evolutionary framework in which compact galaxies do not arise from a single evolutionary channel, but instead reflect multiple pathways whose relative importance depends strongly on stellar mass and environment. Low-mass compact galaxies are closely linked to environmentally driven transformation, whereas high-mass compact galaxies occur across all environments and become increasingly overabundant in the densest regions.

astro-ph.GA↗

arXiv2026

Hierarchical assembly in action: a galaxy tail from a disrupting group in the Virgo cluster outskirts

Group environments are thought to play a key role in shaping galaxy evolution prior to cluster accretion. However, direct observational evidence linking group--cluster interactions to the transformation of low-mass galaxies remains scarce. We reexamine the nature and origin of the W cloud, located in the southern outskirts of the Virgo cluster, to better understand the dynamical processes driving group accretion and galaxy transformation during cluster assembly. Using the spatial distribution, kinematics, and stellar population properties of galaxies in the W cloud and its surroundings, we characterize the three-dimensional structure and dynamical state of the system. We show that the W cloud is not a large-scale filament seen in projection, but is instead dominated by a compact galaxy group (the W group) currently interacting with Virgo. We also identify a previously unknown, dynamically coherent tail of galaxies (the W tail) connecting the W group to the cluster. The tail exhibits a continuous sequence in velocity, velocity dispersion, and three-dimensional distance. Its low-velocity component is already gravitationally bound to Virgo, whereas higher-velocity galaxies remain associated with the W group and are still infalling. The W tail forms a planar structure aligned with the orbital geometry of the W group, strongly supporting a tidal origin. The stellar masses and colours of its members indicate that the stripped population is dominated by low-mass, star-forming dwarf galaxies that remain in the blue cloud. The W group--W tail system provides a well-resolved example of an ongoing group--cluster interaction, illustrating how low-density groups can deliver largely unprocessed dwarf galaxies into clusters. This system provides important observational constraints on the hierarchical assembly of galaxy clusters and the buildup of their dwarf galaxy populations.

astro-ph.GA↗

arXiv2026

Bulgeless Evolution And the Rise of Discs (BEARD) II. The role of mergers in shaping the Milky Way analogues in TNG50

We study the formation and evolution of bulgeless galaxies within the Milky Way-Andromeda analogue sample of the TNG50 simulation. Through kinematic decomposition with Mordor, we identified bulgeless galaxies with a bulge-to-disc mass ratio of B/D<0.08, in line with the Bulgeless Evolution And the Rise of Discs (BEARD) survey and Milky Way constraints. We compared them to bulge-dominated galaxies (B/D>1). We find that 74% of bulgeless galaxies experience at least one major merger (stellar mass ratio 1:4) over their lifetime. Bulgeless galaxies form later ($z_{50}\sim 0.7$) than bulge-dominated counterparts ($z_{50}\sim1.2$). Bulgeless galaxies have lower-mass haloes and higher specific stellar angular momentum, compatible with Milky Way observations. However, specific star formation rates and hydrogen gas fractions are slightly higher than Milky Way observations. Our analysis of the redshift evolution of stellar components reveals that bulgeless galaxies have gradual disc growth with high thin disc-to-total mass ratios (D/T>0.5) since $z\sim 1$ and minimal bulge growth (B/T<0.1) since $z\sim1.5$. In contrast, bulge-dominated galaxies have earlier disc formation, which is disrupted, resulting in higher morphology evolution. Bulgeless galaxies are more likely to undergo gas-rich, coplanar, and corotating mergers, promoting disc survival, compared to bulge-dominated galaxies that encounter a broader spectrum of mergers. We also observed differences in galaxy structure between bulgeless and bulge-dominated galaxies without major mergers, suggesting the relevance of early gas accretion and alignment. Bulgeless galaxies have younger stellar populations and more extended star formation histories than bulge-dominated galaxies, which rapidly quench and have older stellar populations. These findings elucidate the distinct merger-driven and secular pathways that give rise to Milky Way galaxies.

astro-ph.GA↗

arXiv2026

Bulgeless Evolution And the Rise of Discs (BEARD) III. A numerical simulation view of satellites around Milky-Way analogues

$Aims$. The existence of massive disc galaxies with little or no bulge challenges conventional $\Lambda$ cold dark matter model, which typically favours dynamically hot central structures due to early collapse and mergers. The study of these bulgeless disc galaxies is the aim of the Bulgeless Evolution And the Rise of Discs (BEARD) survey, as they offer a unique opportunity to investigate the link between galaxy morphology and the properties of their satellite systems. $Methods$. Using the high-resolution cosmological hydrodynamical simulation TNG50-1, we studied the satellite populations of 135 bulgeless galaxies. We compared their satellite properties to those of a bulge-dominated control sample with matched stellar masses. Our analysis focuses on satellite abundance, luminosity functions, spatial distribution, orbital alignment, and infall histories. $Results$. We find that satellite abundance is largely independent of host galaxy morphology. However, satellites around bulgeless galaxies exhibit luminosity functions with a steeper faint-end slope, are more centrally concentrated, and show stronger orbital alignment with the host disc plane. The orbital alignment originates from coherent post-infall dynamical evolution that depends on host galaxy morphology. The infall of more massive satellites can additionally perturb this process, contributing to a weakening or temporary stalling of the secular alignment. $Conclusions$. Due to the co-evolution of the host galaxy and the satellite system, the morphology of the central galaxy leaves a clear imprint on its satellite system. Bulgeless galaxies tend to have dynamically colder, more aligned, and more centrally concentrated satellite populations. These trends reflect a more quiet merger history and support the use of satellite properties as tracers of host galaxy formation pathways.

astro-ph.GA↗

arXiv2025

Why the Northern Hemisphere Needs a 30-40m Telescope and the Science at Stake: Ultra-Low-Mass Dwarf Galaxies Across the Boreal Cosmic Web

Dwarf galaxies dominate the galaxy population in the nearby Universe and occupy the regime where feedback, reionization, and environment exert their strongest influence on galaxy formation. Despite their importance, detailed spectroscopic constraints on the faintest dwarfs are currently limited to a handful of systems in the Local Volume, leaving the role of large-scale environment essentially unexplored at ultra-low stellar masses. A northern 30-40m class telescope equipped with a multiplexed optical integral-field spectrograph will enable a systematic, spatially resolved spectroscopic census of dwarf galaxies with $M_\star \sim 10^{5}-10^{7} M_\odot$ across a wide range of environments. A deep survey of the Coma Cluster, combined with targeted observations of dwarfs in clusters, groups, filaments, and low-density regions, will map star formation histories, chemical enrichment, and internal kinematics at unprecedented depth. This program will directly test models of dark-matter physics, early-Universe feedback, and environmental quenching in the lowest-mass galaxies, establishing dwarf galaxies as precision probes of both galaxy formation and fundamental physics.

astro-ph.IM↗

arXiv2025

Properties of Barred Galaxies with the Environment: II. The case of the Cosmic Web around the Virgo cluster

Context. Bars are elongated structures developed by a large fraction of disk galaxies in their central few kiloparsecs. However, the bar formation process is still not fully understood, particularly the role played by the galaxy environment in the formation and evolution of these structures. Aims. The aim of this work is to establish how the galaxy environment affects the evolution of bars by analyzing the bar structural parameters in a sample of galaxies located in three different galaxy environments: in the Virgo cluster, in filaments in the Cosmic Web around it, and in the field. Methods. We performed structural analysis using optical imaging from the DESI Legacy survey, measuring bar radii and disk scale lengths through Fourier analysis and surface brightness fitting techniques. Results. After defining a homogeneous sample of barred galaxies across the three different galaxy environments in terms of color and magnitude, the median bar radii were found to be 2.54 +/- 0.34 kpc, 3.29 +/- 0.38 kpc, and 4.44 +/- 0.81 kpc in the cluster, filaments, and field environments, respectively. In addition, the median bar radii scaled by the disk scale lengths was found to be 1.26 +/- 0.09, 1.72 +/- 0.11, and 2.57 +/- 0.21 in the cluster, filaments, and field environments, respectively. These results indicate that the galaxy environment has a significant influence on the structural parameters of bars, with bars in high-density environments being shorter and less prominent than those in the field. Conclusions. Our findings can be interpreted in terms of a slowing of the secular evolution of bars in dense galaxy environments. Barred galaxies located in clusters could experience a reduced rate of bar secular evolution due to various physical processes that occur in high-density environments, such as gas stripping, strangulation, or tidal interactions.

astro-ph.GA↗

arXiv2025

Galaxy Transformation Across the Cosmic Web: Evolution of Stellar Colours and Star Formation Rates in Filaments

Galaxies form and evolve within the diverse environments of the cosmic web. However, disentangling the effects of internal properties, local environments, and large-scale structures (LSS) on galaxy evolution involvessignificant complexities, since these effects are frequently overlapping. The aim of this work is to provide evidence of the imprints left by LSS on galaxy properties by selecting samples of galaxies from different environments, while matching their intrinsic characteristics. We investigate the effects of the LSS on the g-r colour and star formation rate (SFR) in galaxies with stellar mass M $> 10^{10}$ M$_\odot$, with the redshift $0.05 \le z \le 0.1$, and selected from the SDSS DR16. We use a catalogue of the LSS available in the literature to define samples of galaxies located in field and filament environments. Galaxies located in the field tend to exhibit bluer g-r stellar colours and higher SFR than those in filaments. These differences persist even in samples of galaxies matched by mass and galaxy local overdensity, indicating that they are not produced by internal processes. These differences cannot be attributed to variations in morphology. There is also a variation in stellar colour and SFR with distance to the filaments (Df). The SFR of galaxies becomes statistically smaller than that of field galaxies for objects located at Df<5 Mpc, while changes in stellar colour occur at smaller distances (Df<1 Mpc). This could indicates that the typical filament width is about 2.5-5 Mpc. The variations in colour and SFR between galaxy samples in the field and in filaments, with matched masses and local overdensities, indicate that large-scale environmental factors drive these transformations rather than local or internal galaxy properties. These transformations are not strong enough to produce changes in galaxy morphology. They could be explained by cosmic web starvation.

astro-ph.GA↗

arXiv2024

CHEX-MATE: Dynamical masses for a sample of 101 Planck Sunyaev-Zeldovich-selected galaxy clusters

The Cluster HEritage project with XMM-Newton - Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a programme to study a minimally biased sample of 118 galaxy clusters detected by Planck through the Sunyaev-Zeldovich effect. Accurate and precise mass measurements are required to exploit CHEX-MATE as an astrophysical laboratory and a calibration sample for cosmological probes in the era of large surveys. We measured masses based on the galaxy dynamics, which are highly complementary to weak-lensing or X-ray estimates. We analysed the sample with a uniform pipeline that is stable both for poorly sampled or rich clusters - using spectroscopic redshifts from public (NED, SDSS, and DESI) or private archives - and dedicated observational programmes. We modelled the halo mass density and the anisotropy profile. Membership is confirmed with a cleaning procedure in phase space. We derived masses from measured velocity dispersions under the assumed model. We measured dynamical masses for 101 CHEX-MATE clusters with at least ten confirmed members within the virial radius r_200c. Estimated redshifts and velocity dispersions agree with literature values when available. Validation with weak-lensing masses shows agreement within 8+-16(stat.)+-5(sys.)%, and confirms dynamical masses as an unbiased proxy. Comparison with {\it Planck} masses shows them to be biased low by 34+-3(stat.)+-5(sys.)%. A follow-up spectroscopic campaign is underway to cover the full CHEX-MATE sample.

astro-ph.CO↗

arXiv2021

Fossil group origins. XI. The dependence of galaxy orbits on the magnitude gap

We aim to study how the orbits of galaxies in clusters depend on the prominence of the corresponding central galaxies. We divided our data set of $\sim$ 100 clusters and groups into four samples based on their magnitude gap between the two brightest members, $Δm_{12}$. We then stacked all the systems in each sample, in order to create four stacked clusters, and derive the mass and velocity anisotropy profiles for the four groups of clusters using the MAMPOSSt procedure. Once the mass profile is known, we also obtain the (non parametric) velocity anisotropy profile via the inversion of the Jeans equation. In systems with the largest $Δm_{12}$, galaxy orbits are prevalently radial, except near the centre, where orbits are isotropic (or tangential when also the central galaxies are considered in the analysis). In the other three samples with smaller $Δm_{12}$, galaxy orbits are isotropic or only mildly radial. Our study supports the results of numerical simulations that identify radial orbits of galaxies as the cause of an increasing $Δm_{12}$ in groups.

astro-ph.GA↗

arXiv2021

Properties of Fossil Groups of Galaxies

We review the formation and evolution of fossil groups and clusters from both the theoretical and the observational points of view. In the optical band, these systems are dominated by the light of the central galaxy. They were interpreted as old systems that had enough time to merge all the M* galaxies within the central one. During the last two decades many observational studies were performed to prove the old and relaxed state of fossil systems. The majority of these studies, that spans a wide range of topics including halos global scaling relations, dynamical substructures, stellar populations, and galaxy luminosity functions, seem to challenge this scenario. The general picture that can be obtained by reviewing all the observational works is that the fossil state could be transitional. Indeed, the formation of the large magnitude gap observed in fossil systems could be related to internal processes rather than an old formation.

astro-ph.CO↗

arXiv2020

Photometric redshifts for the Pan-STARRS1 survey

We present a robust method to estimate the redshift of galaxies using Pan-STARRS1 photometric data. Our method is an adaptation of the one proposed by Beck et al. (2016) for the SDSS Data Release 12. It uses a training set of 2313724 galaxies for which the spectroscopic redshift is obtained from SDSS, and magnitudes and colours are obtained from the Pan-STARRS1 Data Release 2 survey. The photometric redshift of a galaxy is then estimated by means of a local linear regression in a 5-dimensional magnitude and colour space. Our method achieves an average bias of $\overline{Δz_{\rm norm}}=-2.01 \times 10^{-4}$, a standard deviation of $σ(Δz_{\rm norm})=0.0298$, and an outlier rate of $P_o=4.32\%$ when cross-validating on the training set. Even though the relation between each of the Pan-STARRS1 colours and the spectroscopic redshifts is noisier than for SDSS colours, the results obtained by our method are very close to those yielded by SDSS data. The proposed method has the additional advantage of allowing the estimation of photometric redshifts on a larger portion of the sky ($\sim 3/4$ vs $\sim 1/3$). The training set and the code implementing this method are publicly available at www.testaddress.com.

astro-ph.GA↗