The Atomic Gas Mass of Green Pea Galaxies

We have used the Arecibo Telescope and the Green Bank Telescope (GBT) to carry out a deep search for Hi 21 cm emission from a large sample of "Green Pea" galaxies, yielding 19 detections, and 21 upper limits on the Hi mass. We obtain Hi masses of MHi ≈ (4–300) × 108 M⊙ for the detections, with a median Hi mass of ≈ 2.6 × 109 M⊙; for the non-detections, the median 3σ upper limit on the Hi mass is ≈ 5.5 × 108 M⊙. These are the first estimates of the atomic gas content of Green Pea galaxies. We find that the Hi-to-stellar mass ratio in Green Peas is consistent with trends identified in star-forming galaxies in the local universe. However, the median Hi depletion timescale in Green Peas is ≈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 ≳0.6 dex (2σ) above the local MHi–MB relation, suggesting recent gas accretion. Further, ≈30% of the Green Peas are more than ±2σ deviant from this relation, suggesting possible bimodality in the Green Pea population. We obtain a low Hi 21 cm detection rate in the Green Peas with the highest O32 ≡ [O iii]λ5007/[O ii]λ3727 luminosity ratios, O32 > 10, consistent with the high expected Lyman-continuum leakage from these galaxies.