The dwarf galaxy satellite system of Centaurus A

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 V I 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.

The properties of dwarf spheroidal galaxies in the Cen A group

“…The extended catalog from McConnachie (2012) includes metallicity measurements based on photometric methods such as RGB colors, isochrones fitting, or full CMD fitting, as well as spectroscopic metallicities from low-resolution Ca triplet or from spectral synthesis based on medium to high-resolution spectra. The latter measurements are based on observations of individual stars and it is interesting therefore to compare along-side with the mean metallicity of Cen A dwarfs obtained from resolved stellar population studies (Rejkuba et al 2006;Crnojević et al 2010Crnojević et al , 2012Crnojević et al , 2019Müller et al 2019c), as well as integrated light analysis with MUSE. The dwarf galaxies of the Cen A group follow the same stellar metallicity-luminosity relation as dwarf galaxies in the Local Group (Fig.…”

“…The survey has two main components: (i) deep imaging to resolve individual bright red giant stars and measure distances to dwarf galaxies by means of the tip of the red giant branch (TRGB) method, and (ii) integrated light spectroscopy to measure the dwarfs' radial velocities. In the first part we used FORS2 at VLT to derive accurate distances, thereby also confirming group membership, and measure mean photometric metallicities and structural parameters for nine dwarf satellites of Cen A (Müller et al 2019b). In this article, we present the MUSE spectroscopic data analysis of 14 putative dwarf galaxies in our survey, study their individual properties, and compare them the to Local Group dwarf galaxies.…”

Abundance of dwarf galaxies around low-mass spiral galaxies in the Local Volume

“…The measured photometric parameters are given in Table 1. We measured the surface brightness limit around our dwarf galaxy candidates in randomly distributed 10 × 10 arcsec boxes (Müller et al 2019c) and derived a 3σ limit of 27.4 mag arcsec −2 in the r band. This limit is consistent with the 50% detection limit we derived from our artificial galaxy tests.…”

Dwarfs from the Dark (Energy Survey): a machine learning approach to classify dwarf galaxies from multi-band images

“…This left us with 5567 low-surface brightness objects. Assuming a distance of 50 Mpc, this cut translates into a radius of 200 pc, corresponding to a typical effective radius for a faint dwarf (Müller et al 2019). The distance of 50 Mpc was chosen to mock the selection of galaxies from the MATLAS survey (Duc 2020).…”

“…E-mail: oliver.muller@astro.unistra.fr by confusion with background galaxies, foreground galactic cirrus, or instrumental noise (Chiboucas et al 2013;Merritt et al 2016;Müller et al 2018Müller et al , 2019Bennet et al 2019). A prime example is the galaxy Cen 8/KK 198, which has been regarded as dwarf galaxy associated with the Centaurus group for more than two decades (Cote 1996;Jerjen et al 2000;Karachentsev et al 2013;Müller et al 2017), until VLT observations have uncovered it as a low-surface brightness spiral galaxy (Müller et al 2019(Müller et al , 2021. Once high-resolution imaging was available to study the morphology of the galaxy in detail, the spiral pattern in the older imaging becomes quite apparent, in other words, this spiral galaxy could have been spotted as an interloper in the dwarf galaxy catalogs before the costly follow-up observations.…”