Extragalactic H<scp> i</scp> 21-cm absorption line observations with the Five-hundred-meter Aperture Spherical radio Telescope

We present a pilot study of extragalactic HI 21-cm absorption lines using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). observed 5 continuum sources with features firstly identified in 40% data release Arecibo Legacy Fast L-Band Feed Array (ALFA) Survey (ALFALFA), including two systems later detected by Westerbork Synthesis Radio (WSRT). Most our observations were carried out during FAST commissioning phase, and we have tested different observing modes, as well reduction methods, to produce best spectra. Our successfully confirmed existence all these systems, that marginally ALFALFA. fitted profiles single or double Gaussian functions, calculated column densities each source. The obtained show much higher spectral resolution S/N ratio than existing literature, thus demonstrating power revealing detailed structures lines. tests enabled us develop strategy search for from survey, which is one key projects undertaken at FAST. expect over 1,500 absorbing could be survey data, based on sensitivity level achieved observations.