arXiv subjects

Sanjaya Paudel

Publications and source records attributed to Sanjaya Paudel.

At least 19 recordsLinked to original sources

arXiv2026

The Next Generation Virgo Cluster Survey (NGVS). II. A Catalog of Galaxies in the Virgo Cluster

The Next Generation Virgo Cluster Survey (NGVS) is a deep, high resolution imaging campaign that used the 1 deg$^2$ MegaCam instrument on the Canada-France-Hawaii Telescope to carry out a comprehensive optical survey of the Virgo cluster, from its core to its virial radius. The NGVS covers a contiguous area of 104 deg$^2$ (8.63 Mpc$^2$ at the 16.5 Mpc distance of Virgo) in the $u^*$-,$g$-,$i$-, and $z$-band, with additional limited coverage in $r$. In this paper, we present the final catalog of Virgo galaxies across the entire NGVS area. The catalog includes 3680 galaxies considered to be $bona~fide$ members of the cluster, spanning a factor of 2.5 million in luminosity, from $g = 8.42$ mag to $g = 24.41$ mag ($M_g = -22.67$ mag to $M_g = -6.68$ mag). With 2100 previously uncataloged galaxies, the NGVS catalog augments the number of known Virgo members by a factor 2.3. The catalog is complete down to $g = 18.6$ mag ($M_g=-12.5$ mag, corresponding to a stellar mass $M_* \sim 1.6\times10^7~M_{\odot}$ for an old stellar population) and 50% complete at $g = 22.0$ mag ($M_g=-9.1$ mag, $M_* \sim 6.2\times10^5~M_{\odot}$), three magnitudes deeper than the venerable Virgo Cluster Catalog (VCC), which for over 40 years has served as the reference standard for Virgo. Photometric and structural parameters are derived for all NGVS galaxies and presented in a series of tables, alongside nuclear and morphological classification, as well as stellar masses and, when available, radial velocities.

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arXiv2026

Tidal Grinding of Dwarf Galaxies in Cluster Environments

Dwarf elliptical galaxies (dEs) dominate galaxy clusters and provide key constraints on environmentally driven galaxy evolution. Here we examine whether the projected shapes of dEs retain information about their accretion and transformation histories using a homogeneous sample of 1,108 bright (m_g < 19 mag) dEs in the Virgo cluster. Based on the axis-ratio (b/a), we define flat (< 0.70) and round (> 0.74) subsamples and compare their spatial and kinematic properties. We find that flat dEs are distributed more uniformly across the cluster, whereas round dEs preferentially occupy regions of stronger tidal fields around massive (M_* > 10^{10} M_sun) galaxies. Within the central 5^\circ x 5^\circ region around the Virgo central galaxy (M87), 149 dEs have spectroscopic radial velocities compiled from public archives. In this region, the two shape classes also exhibit clear kinematic segregation: flat dEs have systematically larger line-of-sight velocity offsets from the cluster mean (median $Δv = 654 km/s$), whereas round dEs have smaller offsets (median $Δv = 414 km/s$), as expected for a more dynamically relaxed population. Flat dEs are consistent with a population that has experienced weaker tidal processing and consequently retains more flattened morphologies. By contrast, round dEs are consistent with prolonged tidal processing (``tidal grinding'') that may have transformed initially flattened systems into rounder spheroids. However, projection contamination of the round subsample may have introduced some uncertainty in the interpretation of intrinsic galaxy shapes.

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arXiv2026

Groups of Dwarf Galaxies in the Local Universe

We present a systematic search for dwarf-galaxy groups in the local Universe ($z<0.02$), identifying 28 systems containing at least four spectroscopically confirmed members selected from the SDSS and DESI surveys. Group membership is assigned based on projected separation -within 300\,kpc from the most massive galaxy (designated the ``central'') -and a relative line-of-sight velocity difference of less than 200\,km/s. The sample has a median redshift of $z=0.0131$ ($\sim55$\,Mpc) and a median central stellar mass of $1.7\times10^{9}\,M_\odot$, firmly placing these systems in the low-mass regime. In total, 28 groups contain 129 dwarf galaxy members, with a median stellar mass of $1.63\times10^{8}\,M_\odot$. The median $r$-band apparent magnitude of the member dwarfs is 17.38\,mag, slightly fainter than the spectroscopic observation limit of the SDSS main spectroscopic survey. Remarkably, several groups are centered on galaxies with stellar masses as low as $\sim10^{8}\,M_\odot$, comparable to the Fornax dwarf spheroidal, demonstrating that even very faint galaxies can host bound satellite systems. Most groups exhibit low velocity dispersions ($σ_{v}<50$\,km/s), consistent with being gravitationally bound. The inferred dynamical masses span $\sim10^{10}-10^{12}\,M_\odot$, while the corresponding three-dimensional velocity dispersions ($σ_{3D}$) fall between 50 and 100\,\kms, characteristic of dynamically cold, low-mass halos. Our results provide empirical constraints on small-scale structure formation and show strong consistency with predictions from cosmological volume simulations, supporting the picture that dwarf galaxies can serve as central hosts for their own satellite systems embedded within extended dark-matter halos.

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arXiv2026

SN Ia Population Machine. I. A Unified Cosmological Simulation-Binary Synthesis Framework Establishing Non-universal Delay-time Distributions and Cosmic Progenitor-channel Dominance Crossover

We present a forward-modeling framework for synthesizing Type Ia supernova (SN Ia) populations by coupling cosmological hydrodynamic simulations to binary population synthesis (BPS). Using IllustrisTNG star particles as simple stellar populations, we generate binaries and evolve them with COMPAS to produce synthetic SNe Ia tagged with explosion times and progenitor channels (single- and double-degenerate; SD and DD). This cosmology-BPS pipeline enables self-consistent, end-to-end tracking of SN Ia populations from individual galaxies to cosmic scales. The model reproduces key SN-related observables, including host-galaxy demographics, delay-time distributions (DTDs), SN-rate trends with host properties and redshift, and a progenitor-age 'step' implicated by the mass step in Hubble residuals. Our main findings are as follows. (1) Contrary to the standard assumption, DTDs appear intrinsically non-universal: their form depends on progenitor channel and metallicity, and thus varies systematically across hosts and with redshift. The commonly adopted DTD is therefore best regarded as a population-averaged approximation rather than a fundamental kernel. (2) We predict that the dominant SN Ia progenitor population shifts from SD to DD with cosmic time, with a demographic crossover near z = 0.5 (~5.2 Gyr ago). This non-monolithic SN Ia population with a redshift-dependent SD/DD mixture weakens the universality implicit in a single globally calibrated standardization. Taken together, evolution in both the DTD and the channel mixture can imprint redshift-dependent systematics on SN Ia luminosities, strengthening the case for jointly inferring progenitor/host-driven effects alongside cosmic acceleration. The full catalogue and analysis scripts are available via Zenodo.

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arXiv2026

AVID: A Near-Major Post-Merger of Late-Type Dwarfs beneath a Regularly Rotating HI Disk (VCC 693)

On the periphery of galaxy clusters, moderately high galaxy densities and velocity dispersions favour interactions and mergers that influence galaxy evolution prior to cluster infall. Observational studies of this phase in dwarfs remain rare. We present a high-resolution study of the merger remnant VCC 693 in the outskirts of Virgo cluster, using observations from the Atomic gas in Virgo Interacting Dwarf galaxies (AVID) project. We explore the origin of VCC 693 and the consequences of the merger on its star formation and structure through a joint analysis of VLA and FAST HI emission line observations, together with complementary optical imaging and spectroscopy. We employ hydrodynamical simulations to help interpret the observations. Our analysis favours a near-major merger between two dwarfs with a stellar mass ratio of 3:1-4:1, with one likely gas-poor progenitor (i.e., a damp merger). The optical appearance of VCC 693 is dominated by complex tidal structures throughout the system, whereas the HI gas has settled to a regular rotating disk. Compared with similar-mass dwarfs, the central star formation and gas-phase metallicity are moderately enhanced. The global star formation rate, HI gas content, and HI-to-optical size ratio of VCC 693 are broadly consistent with those of typical dwarfs of similar mass, albeit somewhat lower. Decomposition of the HI rotation curve into baryonic and dark matter indicates a high halo concentration, suggesting post-merger relaxation into a more centrally peaked configuration. Together with two recent studies of AVID post-merger systems, these results support the view that even major dwarf mergers can produce remnants with overall stellar structures indistinguishable from ordinary dwarfs, and that the environmental effects in cluster outskirts can promote damp or mixed mergers, constituting an integral part of galactic pre-processing.

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arXiv2025

Dwarf galaxies in the MATLAS Survey: Hubble Space Telescope observations of nuclear star clusters

In dwarf galaxies, nuclear star clusters (NSCs) are believed to primarily form from the migration and merger of globular clusters (GCs), with a possible contribution from in-situ star-forming activity triggered by gas infall. We present the study of NSCs in 41 MATLAS survey dwarf galaxies including ultra-diffuse galaxies (UDGs), as part of a large follow-up imaging program with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) using the F606W and F814W filters. The sample is biased towards low-surface brightness and large dwarfs, i.e., UDG-like galaxies, and includes two galaxies with a double nucleus, 13 newly identified nucleated dwarfs thanks to HST's high spatial resolution, and five candidate ultra-compact dwarf progenitors. We modeled the NSCs with a Sérsic profile and derived their structural properties and photometry. We find the NSC Sérsic index to increase with the luminosity and stellar mass, while no obvious trend is seen on the effective radius and ellipticity. The faint NSCs tend to have a constant color profile, whereas the bright ones have a bluer center, suggesting that the most massive NSCs in our sample might have experienced a mixed formation scenario, including in-situ star formation. A significant portion of our NSCs tend to be more massive than for other galaxy samples of similar stellar mass, which could be due to some dwarfs ongoing tidal disruption or an initial formation of massive NSCs from multiple GC mergers and in-situ star forming activity. More observations of resolved NSC are needed to be able to infer their formation scenario from the structural properties and photometry in dwarfs.

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arXiv2025

Different Origins of Nucleated and Non-nucleated Dwarf Elliptical Galaxies: Identified by the Deep-learning

Dwarf elliptical galaxies (dEs) are the dominant population in galaxy clusters and serve as ideal probes for studying the environmental impact on galactic evolution. A substantial fraction of dEs are known to harbor central nuclei, which are among the densest stellar systems in the Universe. The large-scale distribution and the underlying origin of nucleated and non-nucleated dEs remain unresolved. Using a state-of-the-art machine learning framework, we systematically scan the Virgo cluster region ($15\arcdeg \times 20\arcdeg$ centered at $R.A. = 187.2\arcdeg$ and $Dec. = 9.6\arcdeg$) and construct the largest homogeneous sample of dEs (of total 2,123) with robust nucleus classifications. We find that nucleated dEs are more spatially clustered and exhibit a stronger association with massive galaxies than their non-nucleated counterparts. This suggests that most nucleated dEs likely formed alongside massive galaxies within the cluster (i.e, the in-situ formation). In contrast, non-nucleated dEs are more widely distributed across the cluster and align more closely with Virgo's global potential well, as traced by the cluster's hot gas. This indicates that most non-nucleated dEs originated outside the cluster (i.e, the ex-situ formation) and were later accreted and redistributed within it. Our findings shed new light on how dEs and their central nuclei form and evolve.

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arXiv2025

Living with Neighbors. V. Better-aligned Spiral+Spiral Galaxy Pairs Show Stronger Star Formation

Enhanced star formation (SF) with star-forming neighboring galaxies bolsters hydrodynamical contributions during paired interactions. Although the relative spin orientation between interacting galaxies can influence this effect, it has not been comprehensively explored. In this study, using a curated sample of nearby (0.02 < z < 0.06) spiral-spiral pairs and an isolated control sample from the Sloan Digital Sky Survey Data Release 7, coupled with Galaxy Zoo 2, and a method to estimate spin-spin alignment (SSA), we systematically compare the impact of the relative orientation, $\cosξ$, on interaction-induced SF. We find that SSA is a key factor alongside the conventional parameters of projected separation and the SF of neighboring galaxies. The SF enhancement increases as configurations transition from perpendicular ($\cosξ\sim 0$) to well aligned ($\cosξ> 0.7$). The effect is strongest when neighboring galaxies have higher SF, indicating a hydrodynamical origin. The trend is consistent with increased hydrodynamical friction via stronger ram pressure and a higher likelihood of prograde orbits in well-aligned pairs.

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arXiv2025

Warped Disk Galaxies. II. From the Cosmic Web to the Galactic Warp

Galactic warps are common in disk galaxies. While often attributed to galaxy--galaxy tides, a non-spherical dark matter (DM) halo has also been proposed as a driver of disk warping. We investigate links among warp morphology, satellite distribution, and large-scale structure using the Sloan Digital Sky Survey catalog of warped disks compiled by Zee et al.\ (2022). Warps are classified into 244 S and 127 U types, hosting 1,373 and 740 satellites, respectively, and are compared to an unwarped control matched in stellar mass, redshift, and local density. As an indirect, population-level proxy for the host halo's shape and orientation, we analyze the stacked spatial distribution of satellites. Warped hosts show a significant anisotropy: an excess at $45^{\circ}<ϕ<90^{\circ}$ (measured from the host major axis), peaking at $P(ϕ)\simeq 0.003$, versus nearly isotropic controls. Satellites of S-type warps preferentially align with the nearest cosmic filament, whereas those of U-type warps are more often perpendicular. The incidence of warps increases toward filaments ($r_{\rm fil}<4,{\rm Mpc},h^{-1}$), while the number of satellites around warped hosts remains approximately constant with filament distance, indicating a direct influence of the large-scale environment. We discuss possible links between galactic warps and the cosmic web, including anisotropic tidal fields and differences in evolutionary stage.

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arXiv2025

An isolated early-type dwarf galaxy that ran away from the group environment

Understanding the quenching mechanisms in dwarf galaxies is crucial for constraining models of galaxy formation and evolution. In this vein, isolated dwarf galaxies offer valuable insight by helping disentangle the relative roles of internal and environmental processes in shutting down star formation. Here we report the discovery of a quiescent early-type dwarf galaxy (dE), SDSS J011754.86+095819.0 (hereafter dE01+09), located in a nearly isolated environment at a projected distance of approximately one megaparsec from its most likely host group, the NGC 524 group. dE01+09 has M_r = -15.72 and g-r = 0.67 mag and its light profile is well described by a Sérsic function with an index n = 1.1, consistent with typical dEs. Using optical spectroscopy from the DESI survey, we derive its simple stellar population properties, finding an intermediate luminosity-weighted age of 8.3$\pm$1.4 Gyr and a subsolar metallicity of -1.19$\pm$0.21 dex -- characteristics comparable to those of classical quiescent dEs. We propose that NGC 524 may represent an extreme example of group dynamics, in which a member galaxy, dE01+09, is ejected from its host group and subsequently evolves as an isolated system in the field.

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arXiv2025

Unveiling the nature and fate of the almost-dark cloud AGC 226178 through HI mapping

The origin of extragalactic, almost dark HI clouds with extreme gas-to-stellar mass ratios remains poorly understood. We investigate the nature and fate of the "almost dark" cloud AGC 226178, projected within the Virgo cluster, with an HI-to-stellar mass ratio of ~1000. We present deep single-dish HI mapping from the Five-hundred-meter Aperture Spherical Telescope (FAST), complemented by high-resolution interferometric data from the Very Large Array (VLA), as part of the Atomic gas in Virgo Interacting Dwarf galaxies (AVID) project. These observations provide the highest-quality HI analysis to date of such a cloud, combining resolution and sensitivity. FAST data reveal a short, low-velocity tail toward the dwarf galaxy VCC 2034, previously proposed as a possible origin for AGC 226178. However, VCC 2034 shows a line-of-sight asymmetric HI feature and cometary morphology indicating a stripping event unrelated to AGC 226178. VLA data reveal a velocity gradient across AGC 226178 and a clumpy internal structure. The velocity dispersion exceeds the thermal linewidth, implying turbulence or unresolved motions. The cloud cannot be gravitationally bound by atomic gas alone. The resolved HI clumps follow standard HI mass-star formation rate and mass-size relations, with those forming stars reaching surface densities above the threshold for self-shielding. We conclude that AGC 226178 is a free-floating HI cloud of unknown origin. The system appears to be in the process of disintegration. It is likely located well outside the Virgo cluster, as the preservation of its extended HI morphology within the cluster environment would otherwise require a substantial reservoir of unseen molecular gas with a mass exceeding that of the observed HI content. While confinement pressure from the hot intracluster medium may aid its stability, it is unlikely to be the dominant factor preventing its disruption.

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arXiv2025

AVID: Formation and evolution of a coalesced major merger of late-type dwarf galaxies (VCC 479) on the outskirts of the Virgo cluster

Dwarf-dwarf galaxy mergers are among the least explored aspects of dwarf galaxy pre-processing as they fall into clusters. We present the first case study of a coalesced late-type dwarf major merger (VCC 479; stellar mass $\sim\,8\,\times\,10^7\,\rm M_\odot$) that has undergone significant environmental influence, with the aim of exploring dwarf galaxy evolution under the combined effects of galaxy interactions and environmental processes, and understanding its relevance to the diversity of dwarf galaxies in cluster environments. Our analysis is based on VLA and FAST HI emission line mapping from the Atomic gas in Virgo Interacting Dwarf galaxies (AVID) survey. We also perform idealized hydrodynamical simulations of dwarf-dwarf mergers to help interpret the observations. We identify symmetric stellar shell structures in VCC 479, indicative of a coalesced major merger of dwarf galaxies. The galaxy features a central starburst, initiated $\sim$600 Myr ago, embedded within an exponential disk quenched $\sim$1 Gyr ago. The starburst contributes only 2.9$\pm$0.5\% of the total stellar mass, and VCC 479's global star formation rate is 0.3 dex lower than typical dwarfs of similar mass. The galaxy is highly HI deficient, with most HI gas concentrated within the central 1 kpc and little extended HI envelope. The misalignment of the HI velocity field with the stellar body is best explained by merger-triggered gas inflow, as seen in our simulations. Our analysis is consistent with a scenario that the majority of HI gas of the progenitor galaxies was removed by the cluster environment prior to the final coalescence. The merger concentrates the remaining gas toward the galaxy center, triggering a central starburst. The combined effect of environment stripping and galaxy merger has transformed VCC 479 into a blue-core dwarf undergoing morphological transition from a late-type to an early-type galaxy.

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arXiv2025

SDSS J134313.15+364457.5: Forming Compact Elliptical through the Merger

Scaling relations are fundamental tools for exploring the morphological properties of galaxies and understanding their formation and evolution. Typically, galaxies follow a scaling relation between mass and size, measured by effective radius. However, a compact class of galaxies exists as outliers from this relation, and the origin of these compact galaxies in the local universe remains unclear. In this study, we investigate the compact dwarf galaxy SDSS J134313.15+364457.5 (J1343+3644), which is the result of a merger. Our analysis reveals that J1343+3644 has a half-light radius of 482~pc, significantly smaller than typical galaxies with the same brightness ($M_\text{r} = -19.17$ mag). With a high star-formation rate (SFR) of 0.87~M$_{\sun}$ year$^{-1}$, J1343+3644 is expected to evolve into a compact elliptical galaxy in a few million years. J1343+3644 could, therefore, be a progenitor of a compact elliptical galaxy. The phenomenon happened in early universe, where compact galaxies were common.

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arXiv2025

Evidence of star cluster migration and merger in dwarf galaxies

Nuclear star clusters (NSCs) are the densest stellar systems in the Universe. They can be found at the center of all galaxy types, but tend to favor galaxies of intermediate stellar mass around 10$^9\,$M$_{\odot}$[1, 2]. Currently, two main processes are under debate to explain their formation: in-situ star-formation from gas infall[3] and migration and merging of globular clusters (GCs) caused by dynamical friction[4]. Studies[5-9] of NSC stellar populations suggest that the former predominates in massive galaxies, the latter prevails in dwarf galaxies, and both contribute equally at intermediate mass. However, up to now, no ongoing merger of GCs has yet been observed to confirm this scenario. Here we report the serendipitous discovery of five dwarf galaxies with complex nuclear regions, characterized by multiple nuclei and tidal tails, using high resolution images from the Hubble Space Telescope. These structures have been reproduced in complementary N-body simulations, supporting the interpretation that they result from migrating and merging of star clusters. The small detection rate and short simulated timescales (below 100 Myr) of this process may explain why this has not been observed previously. This study highlights the need of large surveys with high resolution to fully map the migration scenario steps.

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arXiv2024

Galaxy mass dependence of metal-enrichment of nuclear star clusters

Nuclear Star Clusters (NSCs) are commonly found in galaxy centers, but their dominant formation mechanisms remain elusive. We perform a consistent analysis of stellar populations of 97 nearby NSCs, based on VLT spectroscopic data. The sample covers a galaxy stellar mass range of 10$^{7}$ to 10$^{11}$ M$_{\odot}$ and is more than 3$\times$ larger than any previous studies. We identify three galaxy stellar mass regimes with distinct NSC properties. In the low-mass regime of $\log M_{\rm host}$ $\lesssim$ 8.5, nearly all NSCs have metallicities lower than circum-NSC host but similar to typical red globular clusters (GCs), supporting the GC inspiral-merger scenario of NSC formation. In the high-mass regime of $\log M_{\rm host}$ $\gtrsim$ 9.5, nearly all NSCs have higher metallicities than circum-NSC host and red GCs, suggesting significant contributions from in-situ star formation (SF). In the intermediate-mass regime, a comparable fraction of NSCs have higher or lower metallicities than circum-NSC host and red GCs, with no clear dependence on NSC mass, suggesting intermittent in-situ SF. The majority of NSCs with higher metallicities than their host exhibit a negative age$-$metallicity correlation, providing clear evidence of long-term chemical enrichment. The average NSC$-$host metallicity difference peaks broadly around $\log M_{\rm host} \sim 9.8$ and declines towards both higher and lower galaxy mass. We find that the efficiency of dynamical friction-driven inspiral of GCs observed in present-day galaxies can explain the NSC mass at $\log M_{\rm host} \lesssim 9.5$ but falls short of observed ones at higher galaxy mass, reinforcing our conclusions based on stellar population analysis.

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arXiv2024

A New Rarity Assessment of the `Disk of Satellites': the Milky Way System Is the Exception Rather than the Rule in the $Λ$CDM Cosmology

The majority of satellite galaxies around the Milky Way (MW) show disk-like distributions (the disk of satellites; DoS), which is a small-scale problem of the $Λ$CDM cosmology. The conventional definition of the MW-like DoS is a satellite system with a minor-to-major axis ratio ($c$/$a$) lower than the MW's $c$/$a$ value of 0.181. Here we question the validity of the $c$/$a$-based DoS rarity assessment and propose an alternative approach. How satellites are placed around a galaxy is dictated mainly by two factors: the distributions of satellites' orbital poles and distances from the host. Based on this premise, we construct the `satellite distribution generator' code and generate 10$^5$ `spatially and kinematically analogous systems (SKASs)' sharing these two factors. The SKAS can disclose the intrinsic, underlying $c$/$a$ probability distribution function (PDF), from which a present-day $c$/$a$ value is fortuitously determined. We find that the $c$/$a$ PDF of the MW DoS defined by 11 classical satellites is quite broad ($σ_{c/a}$$\sim$0.105), implying that a simple present-day $c$/$a$ value, combined with its highly time-variable nature, cannot fully represent the degree of flatness. Moreover, based on the intrinsic $c$/$a$ PDF, we re-evaluate the rarity of the MW DoS by comparing it with IllustrisTNG50-1 host-satellite systems and find that even with the new measure, the MW DoS remains rare (0.00$\sim$3.40%). We show that the reason behind the rareness is that both orbital poles and distances of the 11 MW satellites are far more plane-friendly than those of simulated host-satellite systems, challenging the current structure and galaxy formation model.

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arXiv2024

Discovery of a Rare Group of Dwarf Galaxies in the Local Universe

We report the discovery of a rare isolated group of five dwarf galaxies located at z = 0.0086 ($D$ = 36 Mpc). All member galaxies are star-forming, blue, and gas-rich with $g-r$ indices ranging from 0.2 to 0.6 mag, and two of them show signs of ongoing mutual interaction. The most massive member of the group has a stellar mass that is half of the Small Magellanic Cloud stellar mass, and the median stellar mass of the group members is 7.87 $\times$ 10$^{7}$ M$_{\odot}$. The derived total dynamical mass of the group is $M_{\rm dyn}$ = 6.02$\times$10$^{10}$ M$_{\odot}$, whereas its total baryonic mass (stellar + HI) is 2.6$\times$10$^{9}$ M$_{\odot}$, which gives us the dynamical to baryonic mass ratio of 23. Interestingly, all galaxies found in the group are aligned along a straight line in the plane of the sky. The observed spatial extent of the member galaxies is 154 kpc, and their relative line-of-sight velocity span is within 75 km s$^{-1}$. Using the spatially resolved optical spectra provided by DESI EDR, we find that three group members share a common rotational direction. With these unique properties of the group and its member galaxies, we discuss the possible importance of such a system in the formation and evolution of dwarf galaxy groups and in testing the theory of large-scale structure formation.

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arXiv2024

Dwarf Galaxies in the MATLAS Survey: The satellite system of NGC474 under scrutiny with MUSE

A recent study of the distribution of dwarf galaxies in the MATLAS sample in galaxy groups revealed an excess of flattened satellite structures, reminiscent of the co-rotating planes of dwarf galaxies discovered in the local Universe. If confirmed, this lends credence to the plane-of-satellite problem and further challenges the standard model of hierarchical structure formation. However, with only photometric data and no confirmation of the satellite membership, the study could not address the plane-of-satellite problem in full detail. Here we present spectroscopic follow-up observations of one of the most promising planes-of-satellites candidates in the MATLAS survey, the satellite system of NGC 474. Employing MUSE at the VLT and full spectrum fitting, we studied 13 dwarf galaxy candidates and confirmed nine to be members of the field around NGC 474. Measuring the stellar populations of all observed galaxies, we find that the MATLAS dwarfs have lower metallicities than the Local Group dwarfs at given luminosity. Two dwarf galaxies may form a pair of satellites based on their close projection and common velocity. Within the virial radius, we do not find a significant plane-of-satellites, however, there is a sub-population of six dwarf galaxies which seem to be anti-correlated in phase-space. Due to the low number of dwarf galaxies, this signal may arise by chance. With over 2000 dwarf galaxy candidates found in the MATLAS survey, this remains an intriguing data set to study the plane-of-satellites problem in a statistical fashion once more follow-up observations have been conducted.

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