A Collection of New Dwarf Galaxies in NGC5128's Western Halo

Abstract

We report the photometric properties of 16 dwarf galaxies, 15 of which are newly identified, in the Western halo of the nearby giant elliptical galaxy NGC5128. All candidates are found at projected distances $\sim 100-225$kpc from their giant host, with luminosities $-10.82\le M_V/\mathrm{mag}\le -7.42$ and effective radii $4^{\prime \prime }\le r_{\mathrm{eff}}\le 17^{\prime \prime }$ (or $75\le r_{\mathrm{eff}}/\mathrm{pc}\le 300$ at the distance of NGC5128). We compare to other low-mass dwarf galaxies in the local universe and find them to populate the faint/compact extension of the size-luminosity relation that was previously not well-sampled by dwarf galaxies in the Centaurus A system, with optical colors similar to compact stellar systems like globular clusters and ultra-compact dwarf galaxies despite having much more diffuse morphologies. From optical $u^{\prime }{g}^{\prime }{r}^{\prime }{i}^{\prime }{z}^{\prime }$ photometry, stellar masses are estimated to be $5.17\le \log {\mathcal{M}}_{\star }/M_{\odot }\le 6.48$, with colors that show them to fall redward of the dwarf galaxy mass-metallicity relation. These colors suggest star formation histories that require some mechanism that would give rise to extra metal enrichment such as primordial formation within the halos of their giant galaxy hosts, non-primordial star formation from previously enriched gas, or extended periods of star formation leading to self-enrichment. We also report the existence of at least two sub-groups of dwarf candidates, each subtending $10-20^{\prime }$ on the sky, corresponding to projected physical separations of $10-20$kpc. True physical associations of these groups, combined with their potentially extended star formation histories, would imply that they may represent dwarf galaxy groups in the early stage of interaction upon infall into a giant elliptical galaxy halo in the very nearby universe.

arXiv comment9 pages, 4 figures, 1 table, ApJL accepted

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