arXiv subjects

Arsen Levitskiy

Publications and source records attributed to Arsen Levitskiy.

8 recordsLinked to original sources

arXiv2026

The Stellar Populations of Two Quiescent Low Surface Brightness Dwarf Galaxies in Low Density Environments

Dwarf galaxies located in low density environments that have quiescent stellar populations are extremely rare and the mechanism for quenching their stars is highly uncertain. Here we present two low surface brightness dwarf galaxies with large (>1.2 kpc) effective radii that were previously identified in the Dragonfly Ultrawide Survey for which we have obtained spectra using the KCWI instrument on the Keck II telescope. We derive their stellar populations and star formation histories in several radial bins out to 1.25 effective radii. Globally both galaxies are old (~9 Gyr) and metal-poor ([M/H] ~ -1) and reveal quenching on a relatively rapid timescale (~1 Gyr). We find flat to rising age and metallicity gradients in both galaxies. This is similar to those seen in ultra diffuse galaxies but is in contrast with typical classical dwarf galaxies and predictions from simulations. One galaxy, DFUWS 68, hosts several globular clusters which we find to share similar ages, metallicities and quenching timescales to that of the host galaxy stars.We briefly discuss possible quenching mechanisms and suggest that neither cosmic web stripping nor internal feedback processes alone can explain our results.

astro-ph.GA↗

arXiv2026

Diffuse Dwarf Galaxies in Galaxy Clusters: I. Stellar Populations and Radial Gradients

We use Keck/KCWI spectroscopy to study one ultra-diffuse galaxy (UDG) and five Nearly-UDGs (NUDGEs) in the Perseus cluster, together with an additional UDG in the Coma cluster. As the first paper in a series, we focus on the global and radial stellar population properties of our sample. We find that these galaxies host intermediate-to old stellar populations, with typical ages of ~7 Gyr, low metallicities ([M/H]$\simeq$ -0.9 dex), and enhanced [Mg/Fe] abundances (~0.3 dex), consistent with previous studies. Six galaxies lie within the scatter of the present-day mass-metallicity relation (MZR), whereas the Coma UDG (DF11) is more consistent with the MZR of high-z galaxies (z ~ 2). We find no strong correlation between global stellar population properties and cluster infall parameters, suggesting that any environmental impact is not easily traceable through integrated stellar populations. We go one step further and measure radial gradients for three galaxies. Two show flat age and mildly negative metallicity gradients, similar to classical dwarfs, while one shows a rising metallicity profile as recently found in other UDGs. Comparing with classical dwarfs, we find a continuous correlation between metallicity gradient and globular cluster (GC) richness, where more GC-rich systems tend to show rising profiles. We propose that preferential tidal disruption of GCs in the inner regions of galaxies naturally produces rising metallicity profiles, unlike GC-poor classical dwarfs. This mechanism, potentially coupled with strong stellar feedback from early concentrated star formation, may explain the unusual rising metallicity profiles observed in GC-rich UDGs/NUDGEs.

astro-ph.GA↗

arXiv2025

Connection Between Dwarf Galaxies and Globular Clusters: Insights from the Perseus Cluster Using Subaru Imaging and Keck Spectroscopy

We present a systematic study of 189 dwarf galaxies and their globular cluster (GC) systems in the Perseus cluster, based on deep Subaru Hyper Suprime-Cam imaging and Keck spectroscopy, supplemented by literature data. This constitutes the largest sample of dwarfs in a single galaxy cluster to date with simultaneous deep imaging, spectroscopic coverage, and GC measurements, while uniquely spanning a broad and continuous range of galaxy properties. We find an anti-correlation between GC specific mass and galaxy stellar mass for dwarfs in Perseus similar to observations in other clusters. At fixed stellar mass, dwarfs with lower surface brightness or larger effective radius tend to be more GC-rich -- suggesting either high GC formation efficiency in an earlier compact-galaxy phase, or less efficient GC disruption. The correlation between GC richness and axis ratio in Perseus is weaker than in other environments. We find some connection between GC richness and infall time, but not with the clear correlations found in Virgo, Coma, and cosmological simulations. More complete observations are needed to test for cluster-to-cluster variations in galaxy and GC evolutionary histories. This work demonstrates the potential of new wide-field imaging and spectroscopy surveys for understanding GCs and dwarf galaxies, and highlights the need for further work in theoretical modeling.

astro-ph.GA↗

arXiv2025

Tidal Disruption of Super Star Clusters as the origin of Bluish Light at the inner region of the Perseus Cluster Central Galaxy

Relatively blue light extends beyond a spiral disk from a radius of ~5 kpc out to ~14 kpc from the center of NGC 1275. Analyses of its spectrum and broadband colors reveal a population of young stars having sub-solar metallicities superposed on a dominant population of old stars having super-solar metallicities. The young stars have a characteristic age of ~160 Myr and may span ages of a few hundred Myr, similar to that of stars comprising the central spiral disk, and a total mass about one-third that of this disk for a combined stellar mass (at birth) of ~4 $\times$ 10$^9$ $\rm M_\odot$. A multitude of arc-like features embedded in the extended blue light have brightnesses comparable to the somewhat older (~500 Myr) super star clusters (SSCs) projected against the central spiral disk. The SSCs have a relatively shallow mass function, suggesting that the tidal disruption of an initially larger population that we estimate could have had an initial total mass (far) exceeding ~1 $\times$ 10$^9$ $\rm M_\odot$ gave rise to the extended blue light -- the arc-like features corresponding to stellar streams tracing disrupted star clusters -- and perhaps also the central spiral disk. We speculate that, beginning about 500 Myr ago, an enhanced episode of AGN activity in NGC 1275, leaving still visible X-ray bubbles, induced vigorous cooling of the intracluster medium to fuel the formation of numerous star clusters: many were tidally disrupted to leave bluish light at the inner region of this galaxy, with the survivors being the SSCs projected against the central spiral disk.

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arXiv2025

A Comprehensive Look at PUDG-R21: Stellar Population and Kinematics of a Globular Cluster-Rich Ultra-Diffuse Galaxy in the Perseus Cluster

We present the analysis of the stellar populations and kinematics of the globular cluster (GC) rich ultra-diffuse galaxy, PUDG-R21, using spectroscopic observations obtained with the Keck Cosmic Web Imager (KCWI). The recessional velocity is measured to be 5536$\pm$10 km s$^{\mathrm{-1}}$, confirming its association with the Perseus cluster. The galaxy exhibits mild rotation of 15.6$\pm$10 km s$^{\mathrm{-1}}$ and a stellar velocity dispersion of 19.4$\pm$3.5 km s$^{\mathrm{-1}}$ within the galaxy effective radius. From this, we infer a dynamical mass of M$_{\mathrm{dyn}}=9.3\pm3.3\times10^{8}$ M$_{\odot}$. Based on a halo mass derived from PUDG-R21 GC counts, we find our dynamical mass is consistent with a cored dark matter profile. The integrated stellar population analysis reveals a predominantly old stellar population of 10.4$\pm$1.2 Gyr, with intermediate-low metallicity ([M/H]=-0.64$\pm$0.12 dex) and elevated alpha abundances ([Mg/Fe]=0.38$\pm$0.25 dex). The inferred star formation history suggests rapid stellar assembly, likely truncating prior to or during the galaxy's infall into the cluster at an early epoch ($\sim$10 Gyr ago). The analysis of stellar population gradients (age and metallicity) indicates a flat profile out to one effective radius. Here, we consider the involvement of two star formation events, initially forming a large population of metal-poor globular clusters, and then the latter contributing to the more metal-enriched diffuse stellar body. The evidence of subsequent star formation suggests this galaxy is more like an extension of the classical dwarf population than the much discussed failed galaxy UDGs.

astro-ph.GA↗

arXiv2025

Radial velocities and stellar populations for a sample of MATLAS survey dwarfs

Spectroscopic observations are essential for confirming associations, measuring kinematics, and determining stellar populations in dwarf galaxies. Here, we present Keck Cosmic Web Imager (KCWI) spectra for 12 MATLAS survey dwarfs. For 9, we confirm recession velocities consistent with their literature-assumed host galaxies. We propose revisions of the host galaxy associations for MATLAS-631, 1494, and 1938. For MATLAS-1494, our measured redshift reclassifies it from an ultra-diffuse galaxy candidate to a dwarf galaxy that is of smaller physical size and places it in the field. It also appears old and passive, providing a challenge to models that invoke quenching by tidal effects. Additionally, we measure stellar population estimates for 7 of the 12 galaxies, finding a 'mixed bag' of old quenched galaxies and those that are currently forming stars. Compared to the literature we find generally younger ages and higher metallicities. This result may help reconcile the observed offset of MATLAS survey dwarf galaxies from the universal stellar mass-metallicity relationship reported by Heesters et al. (2023).

astro-ph.GA↗

arXiv2025

Constraining the z $\sim$ 1 Initial Mass Function with {\it HST} and {\it JWST} Lensed Stars in MACS J0416.1-2403

Our understanding of galaxy properties and evolution is contingent on knowing the initial mass function (IMF), and yet to date, the IMF is constrained only to local galaxies. Individual stars are now becoming routinely detected at cosmological distances, where luminous stars such as supergiants in background galaxies strongly lensed by galaxy clusters are temporarily further magnified by huge factors (up to $10^{4}$) by intracluster stars, thus being detected as transients. The detection rate of these events depends on the abundance of luminous stars in the background galaxy and is thus sensitive to the IMF and the star-formation history (SFH), especially for the blue supergiants detected as transients in the rest-frame ultraviolet/optical filters. As a proof of concept, we use simple SFH and IMF models constrained by spectral energy distributions (SEDs) to see how well we can predict the {\it HST} and {\it JWST} transient detection rate in a lensed arc dubbed ``Spock'' ($z = 1.0054$). We find that demanding a simultaneous fit of the SED and the transient detection rate places constraints on the IMF, independent of the assumed simple SFH model. We conclude our likelihood analysis indicates that the data definitively prefers the ``Spock'' galaxy to have a Salpeter IMF ($α= 2.35$) rather than a Top-heavy IMF ($α= 1$) -- which is thought to be the case in the early universe -- with no clear excess of supergiants above the standard IMF.

astro-ph.CO↗

arXiv2024

Star Formation, Nebulae, and Active Galactic Nuclei in CLASH Brightest Cluster Galaxies. I. Dependence on Core Entropy of Intracluster Medium

We set the stage for reassessing how star formation, emission-line nebulae, and active galactic nuclei (AGNs) in brightest cluster galaxies (BCGs) depend on the thermodynamics of the intracluster medium (ICM). Our work is based on the 25 clusters observed in the CLASH program for which the aforementioned attributes in their BCGs can be well scrutinized, as has the thermodynamics of their ICM. Nine of these BCGs display complex UV morphologies tracing recent star formation, whereas the remaining 16 are characterized by a relatively compact central UV enhancement. Here, we show definitively that three of the latter BCGs also display star formation, whereas the diffuse UV of the remaining 13 is entirely consistent with old low-mass stars. The overall results support the previously established dependence of star formation and nebulae in BCGs on an "excess core entropy," K$_{0}$, for the ICM: all 11 clusters with K$_{0}$ $\leq$ 24 keV cm$^{2}$ (but only one of 14 clusters with K$_{0}$ $\geq$ 42 keV cm$^{2}$) host star-forming BCGs that almost if not always possess nebulae. Instead of an entropy floor, we show that K$_{0}$ reflects the degree to which the radial entropy profile decreases inward within $\sim$100 kpc rather than (except perhaps at large K$_{0}$) actually flattening: clusters with lower ICM entropies and hence shorter cooling times at their cores preferentially host BCGs displaying star formation, nebulae, and more radio-luminous AGNs. Nearly all BCGs possess detectable AGNs, however, indicating multiple pathways for fuelling their AGNs.

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