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 _ { eff } / { 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 \mu _ { U } \simeq 28.1 { mag / arcsec ^ { 2 } } and \mu _ { I } \simeq 27.4 { mag / arcsec ^ { 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 _ { * } | _ { Z _ { \odot } } \simeq 10 ^ { 5.7 - 6.3 } M _ { \odot } and M _ { * } | _ { 0.02 Z _ { \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 _ { 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 } .