ELVES II: Globular Clusters and Nuclear Star Clusters of Dwarf Galaxies: the Importance of Environment

Abstract

We present the properties of the globular clusters (GCs) and nuclear star clusters (NSCs) of low-mass (105.5 < M ⋆ < 108.5 M ⊙) early-type satellites of Milky Way–like and small group hosts in the Local Volume (LV) using deep, ground-based data from the ongoing Exploration of Local VolumE Satellites Survey. This sample of 177 dwarfs significantly increases the statistics for studying the star clusters of dwarfs in low-density environments, offering an important comparison to samples from nearby galaxy clusters. The LV dwarfs exhibit significantly lower nucleation fractions at fixed galaxy mass than dwarfs in nearby clusters. The masses of NSCs of LV dwarfs show a similar scaling of M ⋆ , NSC ∝ M ⋆ , gal 0.4 as that found in clusters but offset to lower NSC masses. To deal with foreground/background contamination in the GC analysis, we employ both a statistical subtraction and Bayesian approach to infer the average GC system properties from all dwarfs simultaneously. We find that the GC occupation fraction and average abundance are both increasing functions of galaxy stellar mass, and the LV dwarfs show significantly lower average GC abundance at fixed galaxy mass than a comparable sample of Virgo dwarfs analyzed in the same way, demonstrating that GC prevalence also shows an important secondary dependence on the dwarf’s environment. This result strengthens the connection between GCs and NSCs in low-mass galaxies. We discuss these observations in the context of modern theories of GC and NSC formation, finding that the environmental dependencies can be well explained by these models.

The Exploration of Local VolumE Satellites (ELVES) Survey: A Nearly Volume-limited Sample of Nearby Dwarf Satellite Systems

“…Note that these lists are slightly different from the dwarf lists in the ELVES paper on dwarf structure (Carlsten et al 2021a) and the ELVES paper on GCs and nuclear star clusters (Carlsten et al 2022). The former was restricted to small survey coverage radii, a subsample of the full ELVES host sample, and only dwarfs in the mass range 10 5.5 M e < M å < 10 8.5 M e .…”

“…Through extensive tests with injected artificial galaxies, we have verified that the ELVES satellite catalogs are complete to M V ∼ − 9 mag and μ 0,V ∼ 26.5 mag arcsec −2 (see Figure 4). ELVES more than quadruples the number of satellite systems that have been surveyed to such low luminosity and surface brightness, opening the door to many different analyses on dwarf satellites (e.g., Carlsten et al 2021aCarlsten et al , 2022. While some hosts are only surveyed out to 150 projected kpc, the majority are surveyed out to 300 kpc.…”

“…4. Carlsten et al (2022) investigated the nuclear star clusters and globular clusters (GCs) of ELVES dwarfs and compared with those of dwarfs in the Virgo Cluster. They found that dwarfs in the less dense LV environments were less likely to be nucleated, had lower-mass nuclei, and had fewer GCs at fixed dwarf mass than dwarfs in Virgo.…”

“…Since those papers, we have been able to nearly triple the number of surveyed satellite systems, essentially completing the full volume-limited sample. These new dwarf findings have been used in Carlsten et al (2021a) and Carlsten et al (2022) to explore different aspects of dwarf galaxy evolution but have not been fully described until the current paper. This paper is structured as follows: in Section 2 we describe the host selection process and final host list; in Section 3 we outline the different sources of data used; in Section 4 we describe the detection of candidate satellites; in Section 5 we detail how we confirm the distance of the satellites; in Section 6 we describe how we characterize the satellites; in Section 7 we give some overview of the properties of the satellite systems, including satellite abundance, spatial distribution, and the fraction of starforming satellites; and, finally, in Section 8 we give an overview of the key results of the ELVES survey to this point.…”

Around the Spindle Galaxy: The Dark Halo Mass of NGC 3115

“…The images size is 2′ × 2′, north is up and east is left. Table 2 contains: equatorial coordinates of the galaxies, their major angular diameter in arcmin, axial ratio, morphological type, and apparent B magnitude estimated by eye from a comparison of the new putative satellites with other dwarfs, whose g-and rmagnitudes were measured by Carlsten et al (2022). According to our estimates, the error in determining the visual Bmagnitudes is about 0.25 mag.…”