Serendipitous discovery of a faint dwarf galaxy near a Local Volume dwarf
Karachentsev, I. D.; Makarova, L. N.; Tully, R. B.; Makarov, D. I.; Antipova, A. V.
Russia, United States
Abstract
A faint dwarf irregular galaxy has been discovered in the HST/ACS field of LV J1157+5638. The galaxy is resolved into individual stars, including the brightest magnitude of the red giant branch. The dwarf is very likely a physical satellite of LV J1157+5638. The distance modulus of LV J1157+5638 using the tip of the red giant branch (TRGB) distance indicator is 29.82 ± 0.09 mag (D = 9.22 ± 0.38 Mpc). The TRGB distance modulus of LV J1157+5638 sat is 29.76 ± 0.11 mag (D = 8.95 ± 0.42 Mpc). The distances to the two galaxies are consistent within the uncertainties. The projected separation between them is only 3.9 kpc. LV J1157+5638 has a total absolute V magnitude of -13.26 ± 0.10 and linear Holmberg diameter of 1.36 kpc, whereas its faint satellite LV J1157+5638 sat has MV = -9.38 ± 0.13 mag and Holmberg diameter of 0.37 kpc. Such a faint dwarf was discovered for the first time beyond the nearest 4 Mpc from us. The presence of main-sequence stars in both galaxies unambiguously indicates the classification of the objects as dwarf irregulars with recent or ongoing star formation events in both galaxies.