A Corotating Group of Dwarf Galaxies around NGC 2750 as a Centaurus A Analog

We study a low-mass spiral galaxy NGC 2750 (∼5 times less massive than the Milky Way), located ∼40 Mpc away in a sparse region that hosts seven satellite galaxies within a projected distance of 150 Kpc. Among them six are star-forming dwarfs with stellar masses of >≈107 M⊙ and one is an early-type dwarf with a stellar mass of 2.6 × 106 M⊙. The star-forming dwarfs are gas rich, with gas mass fractions as high as Log(MH i/M*) = 1.2 and their star formation rates vary between 0.03 and 0.35 M⊙ yr−1. The projected distances and measured radial velocities of the six star-forming satellites provide a high probability that they are members of the group. The radial velocity distribution of the six satellites exhibits evidence of a systematic corotation. We devise a method to quantify such a corotation signal by calculating the correlation coefficient between satellites' relative line-of-sight velocities (ΔVr) and their sky-projected distances from the host (Rp). For the NGC 2750 system, we show a clear correlation between ΔVr and Rp, with a Pearson's R correlation coefficient c = 0.90 and p-value = 0.005. We compare the NGC 2750 system with the Centaurus A (NGC 5128) system, a previously known corotating group, and conclude that the former could be a small version of the latter but is located in an isolated field, away from the influence of the large-scale structure. The results open up opportunities to explore the galactic anisotropy phenomenon on a low-mass scale and in a rarified environment.