A Study in Blue: The Baryon Content of Isolated Low Mass Galaxies
  We study the baryon content of low mass galaxies selected from the Sloan
Digital Sky Survey (SDSS DR8), focusing on galaxies in isolated environments
where the complicating physics of galaxy-galaxy interactions are minimized. We
measure neutral hydrogen (HI) gas masses and line-widths for 148 isolated
galaxies with stellar mass between $10^7$ and $10^{9.5} M_{\odot}$. We compare
isolated low mass galaxies to more massive galaxies and galaxies in denser
environments by remeasuring HI emission lines from the Arecibo Legacy Fast ALFA
(ALFALFA) survey 40% data release. All isolated low mass galaxies either have
large atomic gas fractions or large atomic gas fractions cannot be ruled out
via their upper limits. We measure a median atomic gas fraction of $f_{\rm gas}
= 0.82 \pm 0.13$ for our isolated low mass sample with no systems below 0.30.
At all stellar masses, the correlations between galaxy radius, baryonic mass
and velocity width are not significantly affected by environment. Finally, we
estimate a median baryon to total dynamical mass fraction of $f_{\rm baryon,
disk} = 0.15 \pm 0.18$. We also estimate two different median baryon to halo
mass fractions using the results of semi-analytic models $(f_{\rm baryon, halo}
= 0.04 \pm 0.06)$ and abundance matching $(f_{\rm baryon, halo} = 0.04 \pm
0.02)$. Baryon fractions estimated directly using HI observations appear
independent of environment and maximum circular velocity, while baryon
fractions estimated using abundance matching show a significant depletion of
baryons at low maximum circular velocities.
