Faint Dwarf Galaxies in Hickson Compact Group 90

Abstract

We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with VLT/VIMOS. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range $0.7\lesssim r_{\mathrm{eff}}/\mathrm{kpc}\lesssim 1.5$ with luminosities of $-11.65\lesssim M_U\lesssim -9.42$ and $-12.79\lesssim M_I\lesssim -10.58$ mag, corresponding to a color range of $(U-I{)}_0\simeq 1.1-2.2$ mag and surface brightness levels of $\hat{I}{¼}_U\simeq 28.1mag/arcse{\mathrm{c}}^2$ and $\hat{I}{¼}_I\simeq 27.4mag/arcse{\mathrm{c}}^2$. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z${}_{\odot }$ metallicities we obtain stellar masses in the range $M_{\ast }{|}_{Z_{\odot }}\simeq 10^{5.7-6.3}{M}_{\odot }$ and $M_{\ast }{|}_{0.02Z_{\odot }}\simeq 10^{6.3-8}{M}_{\odot }$. Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than $\sim 2$ Gyr at any mass/metallicity combination. Altogether, the new LSB dwarf galaxy candidates share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. We find a pair of candidates with $\sim 2$ kpc projected separation, which may represent one of the closest dwarf galaxy pairs found. We also find a nucleated dwarf candidate, with a nucleus size of $r_{\mathrm{eff}}\simeq 46-63$ pc and magnitude M${}_{U,0}=-7.42$ mag and $(U-I{)}_0=1.51$ mag, which is consistent with a nuclear stellar disc with a stellar mass in the range $10^{4.9-6.5}{M}_{\odot }$.

Accepted by MNRAS. 7 pages, 5 figures, 2 tables