Detection of H I in Emission in the LYα Emitting Galaxy Haro 11

Abstract

We present the first robust detection of H I 21 cm emission in the blue compact galaxy Haro 11 using the 100 m Robert C. Byrd Green Bank Telescope (GBT). Haro 11 is a luminous blue compact galaxy with emission in both Lyα and the Lyman continuum. We detect (5.1 ± 0.7 × 10⁸) M _⊙ of H I gas at an assumed distance of 88 Mpc, making this galaxy H I deficient compared to other local galaxies with similar optical properties. Given this small H I mass, Haro 11 has an elevated M _H2/M _{H I} ratio and a very low gas fraction compared to most local galaxies, and contains twice as much mass in ionized hydrogen as in neutral hydrogen. The H I emission has a linewidth of 71 km s^-1 and is offset 60 km s^-1 redward of the optical line center. It is undergoing a starburst after a recent merger that has elevated the star formation rate, and will deplete the gas supply in <0.2 Gyr. Although this starburst has elevated the star formation rate (SFR) compared to galaxies with similar H I masses and line widths, Haro 11 matches a trend of lower gas fractions toward higher SFRs and is below the general trend of increasing H I mass with increasing luminosity. Taken together, our results paint Haro 11 as a standard low-mass galaxy that is undergoing an unusually efficient star formation episode.