21-cm H I emission from the Damped Lyman-alpha absorber SBS 1543+593

Abstract

We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS 1543+593, which gives rise to a Damped-Lyalpha (DLyalpha ) absorption line in the spectrum of the background QSO HS 1543+5921 (z_e = 0.807). We obtain an accurate measure of the velocity of the H I gas in the LSB galaxy, v = 2868 km s^-1, and derive a mass of M_{H I} = 1.3*E⁹ M_sun. We compare M_{H I} with limits obtained towards two other z ~ 0.1 DLyalpha systems, and show that SBS 1543+593 would not have been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible for DLyalpha systems at even modest redshifts without being detectable from their 21-cm emission.