21-cm H I emission from the Damped Lyman- 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 (DLy) absorption line in the spectrum of the background QSO HS 1543+5921 (ze =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 10 9 M.W e compareM HI with limits obtained towards two other z 0: 1D Ly 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 systems at even modest redshifts without being detectable from their 21-cm emission.