Hunting Faint Dwarf Galaxies in the Field Using Integrated Light Surveys

We discuss the approach of searching the lowest mass dwarf galaxies, ≲10⁶ M, in the general field, using integrated light surveys. By exploring the limiting surface brightness-spatial resolution (μeff,lim-θ) parameter space, we suggest that faint field dwarfs in the Local Volume, between 3 and 10 Mpc, are expected to be detected very effectively and in large numbers using integrated light photometric surveys, complementary to the classical star counts method. We use a sample of dwarf galaxies in the Local Group to construct relations between their photometric and structural parameters, M∗-μ _eff,V and M∗-R_eff. We use these relations, along with assumed functional forms for the halo mass function and the stellar mass-halo mass (SMHM) relation, to calculate the lowest detectable stellar masses in the Local Volume and the expected number of galaxies as a function of the limiting surface brightness and spatial resolution. The number of detected galaxies depends mostly on the limiting surface brightness for distances >3 Mpc, while spatial resolution starts to play a role for galaxies at distances >8 Mpc. Surveys with μ μeff,lim ∼30 mag arcsec-2 should be able to detect galaxies with stellar masses down to ∼10⁴ M^e in the Local Volume. Depending on the form of the SMHM relation, the expected number of dwarf galaxies with distances between 3 and 10 Mpc is 0.04-0.35 per square degree, assuming a limiting surface brightness of ∼ 29-30 mag arcsec-2 and a spatial resolution <4″. We plan to search for a population of low-mass dwarf galaxies in the field by performing a blank wide field photometric survey with the Dragonfly Telephoto Array, an imaging system optimized for the detection of extended ultra low surface brightness structures.