arXiv subjects

Richard T. Pomeroy

Publications and source records attributed to Richard T. Pomeroy.

3 recordsLinked to original sources

arXiv2026

Evidence for Environmental Stripping in the Coma Cluster

The stability and longevity of globular clusters (GCs) make them effective tracers of the dynamical histories of galaxies in cluster environments. We construct a catalog of 23,351 GC candidates in the Coma cluster using imaging from the Hubble Space Telescope Advanced Camera for Surveys. We cross-match galaxy data from the SIMBAD, NED, and SDSS archives to construct a galaxy sample and model their GC populations using the GC specific frequency. We find several galaxies with significantly smaller GC populations than expected from their luminosities, consistent with either tidal stripping or intrinsically low formation efficiencies. We analyze annular and Voronoi GC radial profiles of the BCGs (NGC 4874 and NGC 4889) and other Coma galaxies. A 2D Voronoi density mapping reveals GC populations with marked deficits compared to our modeled expectations, including galaxies in proximity to the BCGs (e.g., IC 3998, NGC 4875, NGC 4876) and others distributed across Coma (e.g., NGC~4908, NGC~4883, IC~4042). Azimuthal symmetry testing suggests past dynamical interactions may have truncated GC systems in some galaxies, while intrinsic deficits are probable in others (e.g., IC 3973, IC 3976, IC 4040, IC 4045). Our results show that GC deficits exist in several Coma galaxies and that the 2D density structure reveals environmental signatures, with asymmetry statistics consistent with directional stripping. These findings highlight GC populations as powerful probes of environmental processing and the dynamical histories of galaxies in dense cluster environments.

astro-ph.GA↗

arXiv2025

A Wide Field Map of Ultra-Compact Dwarfs in the Coma Cluster

A dataset of 23,351 globular clusters (GCs) and ultra-compact dwarfs (UCDs) in the Coma cluster of galaxies was built using Hubble Space Telescope Advanced Camera for Surveys data. Based on the standard magnitude cut of $M_V \leq -11$, a total of 523 UCD candidates are found within this dataset of Compact Stellar Systems (CSS). From a color-magnitude diagram (CMD) analysis built using this catalog, we find a clear mass-magnitude relation extending marginally into the UCD parameter space. The luminosity function defined by this dataset, shows an excess of sources at bright magnitudes, suggesting a bimodal formation scenario for UCDs. We estimate the number of UCDs with a different origin than GC to be $N_{UCD} \geq 32 \pm 1$. We derive the total number of CSS within the core (1 Mpc) of Coma to be $N_{CSS} \approx 69,400 \pm 1400$. The radial distribution of UCDs in Coma shows that, like GCs, UCDs agglomerate around three giant ellipticals: NGC 4874, NGC 4889, and IC 4051. We find UCDs are more centrally concentrated around these three ellipticals than GCs. IC 4051 has a satellite population of UCDs similar to NGC 4874 and NGC 4889. We estimate only ~14% of UCDs, inhabit the intracluster space (ICUCD) between galaxies in the region, in comparison to ~24% for GCs (ICGC). We find red (metal-rich) UCDs are more likely located closer to a host galaxy, with blue (metal-poor) UCDs showing a greater dispersion and lower average density in the region.

astro-ph.GA↗

arXiv2024

A search for intermediate-mass black holes in compact stellar systems through optical emissions from tidal disruption events

Intermediate-mass black holes (IMBH) are expected to exist in globular clusters (GCs) and compact stellar systems (CSS) in general, but none have been conclusively detected. Tidal disruption events (TDEs), where a star is tidally disrupted by the gravitational field of a black hole, have been observed to occur around the supermassive black holes (SMBH) found at the centres of galaxies, and should also arise around IMBHs, especially in the dense stellar cores of CSS's. However, to date none have been observed in such environments. Using data from the Zwicky Transient Facility (ZTF) we search for TDEs associated with CSS, but none are found. This non-detection allows us to set an upper limit on the TDE rate in CSS of $n_\text{TDE,Total}\lessapprox10^{-7} CSS^{-1}\text{yr}^{-1}$ which is two dex. below the observed TDE rate involving SMBH interacting with 1\Msun\ main sequence stars in the nuclei of massive galaxies. We also consider ultra compact dwarfs (UCDs) formed through a tidal stripping process in the surveyed volume. On the assumption these CSS contain SMBH and TDE rates are comparable to current observed optical rates in galactic nuclei ($\approx\num{3.2E-5}\text{gal}^{-1}\text{yr}^{-1}$), we determine an upper limit for the number of UCDs formed through a tidal stripping process in the surveyed volume to be $N_\text{GC, Strip}<\num{1.4E4}$, which we estimate represents $< 6\%$ of the population of GCs $>10^6\Msun$.

astro-ph.GA↗