21-cm HI emission from the Damped Lyman-α absorber SBS 1543+593

We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS 1543+593, which gives rise to a Damped-Ly alpha (DLy alpha) 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-HI = 1.3 x 10(9) M-circle dot. We compare M-HI with limits obtained towards two other z similar to 0.1 DLy alpha systems, and show that SBS 1543+593 would not have been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible for DLy alpha systems at even modest redshifts without being detectable from their 21-cm emission.