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(circle dot). 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 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(gas) = 0.81 +/- 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(baryon disk) = 0.15 +/- 0.17. We also estimate two different median baryon to halo mass fractions using the results of semi-analytic models (f(baryon,halo) = 0.04 +/- 0.06) and abundance matching (f(baryon,halo) = 0.04 +/- 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.