2016MNRAS.463.1284O

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 Very Large Telescope/Visible Multi-Object Spectrograph. 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 ≲ r_eff/kpc ≲ 1.5 with luminosities of -11.65 ≤ M_U ≤ -9.42 and -12.79 ≤ M_I ≤ -10.58 mag, corresponding to a colour range of (U - I)₀ ~= 1.1-2.2 mag and surface brightness levels of µ_U ~= 28.1 mag arc/sec2 and µ_I ~= 27.4 mag/arcsec2. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z_☉ metallicities we obtain stellar masses in the range M_*|_Z☉_ ~= 10^5.7 - 6.3^ M_☉ and M_*|0.02 Z_☉_ ∼ 10^6.3–8M_☉. Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than ∼ 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 ∼ 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_eff ~= 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_☉.