Dwarf Galaxy Discoveries from the KMTNet Supernova Program I. The NGC 2784 Galaxy Group (1708.07326v1)

Abstract: We present $BVI$ surface photometry of 31 dwarf galaxy candidates discovered in a deep image stack from the KMTNet Supernova Program of $\sim$ 30 square degrees centered on the nearby NGC 2784 galaxy group. Our final images have a 3$\sigma$ surface brightness detection limit of $\mu_V\approx 28.5$ mag arcsec$^{-2}$. The faintest central surface brightness that we measure is $\mu_{0,V} = 26.1$ mag arcsec$^{-2}$. If these candidates are at the distance of NGC 2784, then they have absolute magnitudes greater than $M_V = -9.5$ mag and effective radii larger than 170 pc. Their radial number density decreases exponentially with distance from the center of NGC 2784 until it flattens beyond a radius of 0.5 Mpc. We interpret the baseline density level to represent the background contamination and so estimate that 22 of the 31 new candidates are dwarf members of the group. The candidate's average color, $\langle (B-V)_0\rangle\approx 0.7$, and Sersic structural parameters are consistent with those parameters for the dwarf populations of other groups. We find that the central population of dwarfs is redder and brighter than the rest of the population. The measured faint end slope of the luminosity function, $\alpha\approx-1.33$, is steeper than that of the Local Group but consistent with published results for other groups. Such comparisons are complicated by systematic differences among different studies, but will be simpler when the KMTNet survey, which will provide homogenous data for 15 to 20 groups, is completed.