Constraints on the gas masses of low-z damped Lyman α systems

Abstract

We report a deep search for redshifted H I 21 cm emission from three damped and sub-damped Lyman α absorbers (DLAs) at z ≈ 0.1 with the Green Bank Telescope (GBT). No evidence for a redshifted H I 21 cm emission signal was obtained in the GBT spectra of two absorbers, with the data on the third rendered unusable by terrestrial interference. The non-detections of H I 21 cm emission yield strong constraints on the H I masses of the associated galaxies, MH I < 2.3 × 109 × (Δ V/100)^1/2 M_⊙ for the sub-DLA at z = 0.0830 towards J1553+3548 and MH I < 2.7 × 109 × (Δ V/100)1/2 M_⊙ for the DLA at z = 0.0963 towards J1619+3342, where ΔV is the H I 21 cm line width, in km s^-1 . This continues the trend of low H I masses found in all low-z DLAs and sub-DLAs that have been searched for redshifted H I 21 cm emission. Low-redshift absorbers with relatively low H I column densities, ≲ few × 1020 cm^-2 , thus do not typically arise in massive gas-rich galaxies.