The Atomic Gas Mass of Green Pea Galaxies

Abstract

We have used the Arecibo Telescope and the Green Bank Telescope to carry out a deep search for H{\sc i}~21\,cm emission from a large sample of Green Pea galaxies, yielding 19 detections, and 21 upper limits on the H{\sc i} mass. We obtain H{\sc i} masses of ${\mathrm{M}}_{\mathrm{HI}}\approx (4-300)\times 10^8{\mathrm{M}}_{\odot }$ for the detections, with a median H{\sc i} mass of $\approx 2.6\times 10^9{\mathrm{M}}_{\odot }$; for the non-detections, the median $3\ddot{I}ƒ$ upper limit on the H{\sc i} mass is $\approx 5.5\times 10^8{\mathrm{M}}_{\odot }$. These are the first estimates of the atomic gas content of Green Pea galaxies. We find that the H{\sc i}-to-stellar mass ratio in Green Peas is consistent with trends identified in star-forming galaxies in the local Universe. However, the median H{\sc i} depletion timescale in Green Peas is $\approx 0.6$~Gyr, an order of magnitude lower than that obtained in local star-forming galaxies. This implies that Green Peas consume their atomic gas on very short timescales. A significant fraction of the Green Peas of our sample lie $\gtrsim 0.6$~dex ($2\ddot{I}ƒ$) above the local ${\mathrm{M}}_{\mathrm{HI}}-{\mathrm{M}}_{\mathrm{B}}$ relation, suggesting recent gas accretion. Further, $\approx 30$\% of the Green Peas are more than $\pm 2\ddot{I}ƒ$ deviant from this relation, suggesting possible bimodality in the Green Pea population. We obtain a low H{\sc i}~21\,cm detection rate in the Green Peas with the highest O32~$\equiv$~[O{\sc iii}]$\hat{I}»$5007/[O{\sc ii}]$\hat{I}»$3727 luminosity ratios, O32~$>10$, consistent with the high expected Lyman-continuum leakage from these galaxies.

8 pages, 3 pages, Astrophysical Journal Letters, in press