HI 21 cm imaging of a nearby damped Lyman-α system

National Centre for Radio Astrophysics, Post Bag 3, Ganeshkhind, Pune 411 007, India

Corresponding authors: J. N. Chengalur, chengalu@ncra.tifr.res.in nissim@ncra.tifr.res.in

Received: 6 November 2001
Accepted: 3 April 2002

Abstract

We present Giant Metrewave Radio Telescope (GMRT) HI 21 cm emission images of the damped Lyman-α (DLA) absorber towards the QSO HS 1543+5921. The DLA has been earlier identified as a low surface brightness galaxy SBS 1543+593 ([CITE]; [CITE]) with small (~400 pc) impact parameter to the QSO line of sight. The extremely low redshift of the absorber allows us to make, for the first time, spatially resolved images of the 21 cm emission; besides the HI mass, this also enables us to determine the velocity field of the galaxy and, hence, to estimate its dynamical mass. We obtain a total HI mass of ~ , considerably smaller than the value of  determined from blind 21 cm emission surveys. This continues the trend of low HI mass in all low redshift DLAs for which HI emission observations have been attempted. We also find that the QSO lies behind a region of low local HI column density in the foreground galaxy. This is interesting in view of suggestions that DLA samples are biased against high HI column density systems. Finally, the dynamical mass of the galaxy is found to be  .