The Effect of AGNs on the Global H I Content of Isolated Low-mass Galaxies

We investigate the global neutral hydrogen (H I) content of isolated galaxies selected from the SDSS spectroscopic survey with optical evidence of Active Galactic Nuclei (AGNs). Our sample includes galaxies with unresolved H I observations from the ALFALFA 70% data release combined with deeper H I observations of low-mass galaxies with 7.0< {log} {M}_* /{M}_⊙ < 9.5. We examine the H I masses of this sample using the distance from the star-forming sequence on the [O III]/Hβ and [N II]/Hα Baldwin Phillips Terlevich (BPT) diagram as a measurement of AGN activity. In agreement with previous studies, we find that, for galaxies with {log} {M}_* /{M}_⊙ > 9.5, AGN activity does not correlate with the global H I content. However, for galaxies with 9.2< {log} {M}_* /{M}_⊙ < 9.5, we identify a set of objects at large distances from the BPT star-forming sequence and lower than expected H I masses. This gas-depleted sample is red in both g - r and NUV - r colors and compact without distinguishable signs of star formation. This is surprising because the vast majority of isolated galaxies in this stellar mass regime are both star-forming and gas-rich. These galaxies are greater than 1.5 Mpc from any massive galaxy, ruling out environmental processes as a source of the gas depletion. We suggest that either black hole feedback or shocks from extremely bursty star formation cause the emission lines and have destroyed or otherwise consumed the cold gas.