Abstract
Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep FORS2 VI band images from the ESO Very Large Telescope (VLT) for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of Cen A by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fit theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision, there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, Cen A seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with a root-mean-square (rms) height of 130 kpc and an rms semi-major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.
Highlights
The Markov Chain Monte Carlo (MCMC) scheme comes into play: We propose a new set of parameters by randomizing their values drawn from a normal distribution on top of the current values
For dw1336-44, we find a discrepancy between the center of the galaxy derived by the red giant branch (RGB) stars only and all the stars within the galactic aperture
The ΛCDM small-scale crisis in the Local Group motivates the study of satellite systems in other groups of galaxies
Summary
The hunt for dwarf galaxies in the Local Volume (LV, D < 11 Mpc, Kraan-Korteweg & Tammann 1979; Karachentsev et al 2004, 2013) has become widely popular, with several independent teams searching for nearby dwarf galaxies (Chiboucas et al 2009; Merritt et al 2014; Müller et al 2015, 2017a,b, 2018a; Carlin et al 2016; Crnojevicet al. 2016; Javanmardi et al 2016; Park et al 2017; Blauensteiner et al 2017; Smercina et al 2018). The latter phenomenon is a more fundamental problem mostly unaffected by the baryonic processes within the galaxies (Pawlowski et al 2015) All these studies are mainly based on the dwarf galaxy system in the Local Group. These surveys have more than doubled the currently known dwarf galaxy population around Cen A, assuming that the dwarf galaxy candidates are confirmed with follow-up measurements Their surface brightnesses and estimated absolute magnitudes are in the range of the classical dwarfs, allowing us to perform similar cosmological tests as in the Local Group. For many dwarf galaxies around Cen A, no velocity and distance measurements are available to date Their memberships are mainly based on morphological arguments from integratedlight observations (Müller et al 2015, 2017a; Taylor et al 2018).
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