The Second Case of a Major Merger Triggering a Starburst in a Green Pea Galaxy

Abstract

We have used the Karl G. Jansky Very Large Array (VLA) to map H i 21 cm emission from the Green Pea galaxy GP J1148+2546 at z ≈ 0.0451, only the second measurement of the H i spatial distribution of a Green Pea. The VLA H i 21 cm image, the DECaLS optical image, and Sloan Digital Sky Survey spectroscopy show that GP J1148+2546 has two neighbors, the nearer of which is only ≈17.5 kpc away, and that the H i 21 cm emission extends in an inverted “C” shape around the Green Pea and its companions, with the highest H i column density between the two neighboring galaxies. The starburst in GP J1148+2546 is likely to have been triggered by the ongoing merger with its neighbors, although the velocity field and velocity dispersion images do not show clear merger signatures at the Green Pea location. The H i mass of the Green Pea and its immediate surroundings is (3.58 ± 0.37) × 10 ^9 M _⊙ , a factor of ≈7.4 lower than the total H i mass of the system of three interacting galaxies, while the H i depletion timescale of GP J1148+2546 is ≈0.69 Gyr, much shorter than that of typical galaxies at z ≈ 0. We detect damped Ly α absorption and Ly α emission from the Green Pea in a Hubble Space Telescope Cosmic Origins Spectrograph spectrum, obtaining a high H i column density, ≈2.0 × 10 ^21 cm ^−2 , and a low Ly α escape fraction, ≈0.8%, consistent with the relatively low value (≈5.4) of the ratio O32 ≡ [O iii ] λ 5007 + λ 4959/[O ii ] λ 3727,3729.

Keywords

• Galaxies
• Starburst galaxies
• Emission line galaxies
• H I line emission