Hunting Faint Dwarf Galaxies in the Field Using Integrated Light Surveys

Abstract

We discuss the approach of searching low mass dwarf galaxies, $\lesssim10^6\textrm{ M}_{\odot}$, in the general field, using integrated light surveys. By exploring the limiting surface brightness-spatial resolution ($\mu_{\textrm{eff,lim}}-\theta$) parameter space, we suggest that faint field dwarfs in the Local Volume, between $3$ and $10 \textrm{ Mpc}$, are expected to be detected effectively and in large numbers using integrated light photometric surveys, complementary to the classical star counts method. We use a sample of Local Group dwarf galaxies to construct relations between their photometric and structural parameters, $\textrm{M}_{*}$-$\mu_{\textrm{eff,V}}$ and $\textrm{M}_{*}$-$\textrm{R}_{\textrm{eff}}$. We use these relations, along with assumed functional forms for the halo mass function and the stellar mass-halo mass 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 $>3\textrm{ Mpc}$ while spatial resolution starts to play a role at distances $>8\textrm{ Mpc}$. Surveys with $\mu_{\textrm{eff,lim}}\sim30\textrm{ mag arcsec}^{-2}$ should be able to detect galaxies with stellar masses down to $\sim10^4 \textrm{ M}_{\odot}$ in the Local Volume. Depending on the assumed stellar mass-halo mass relation, the expected number of galaxies between $3$ and $10\textrm{ Mpc}$ is $0.04-0.35\textrm{ deg}^{-2}$, assuming a limiting surface brightness of $\sim29-30\textrm{ mag arcsec}^{-2}$ and a spatial resolution $<4''$. We currently look for field dwarf galaxies by performing a blank wide-field survey with the Dragonfly Telephoto Array, optimized for the detection of ultra-low surface brightness structures.