Extragalactic HI 21-cm absorption line observations with the Five-hundred-meter Aperture Spherical radio Telescope

Abstract

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

arXiv comment13 pages, 14 figures. Accepted by Monthly Notices of the Royal Astronomical Society

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• The First Large Absorption Survey in HI (FLASH): I. Science Goals and Survey Design
• Toward a direct measurement of the cosmic acceleration: the first preparation with FAST
• Constraints on dark matter annihilation from the FAST observation of the Coma Berenices dwarf galaxy
• Detections of 21-cm absorption with a blind FAST survey at z $⩽$ 0.09
• Extragalactic HI survey with FAST : First look of the pilot survey results
• Constraining Axion-Like Particles Dark Matter in Coma Berenices with FAST
• Unveiling the Universe with Emerging Cosmological Probes
• Toward a direct measurement of the cosmic acceleration: The pilot observation of H I 21cm absorption line at FAST
• The FAST HI 21-cm absorption blind survey. II. -- Statistic Exploration for Associated and Intervening systems
• HI Absorption in Low-power Radio AGNs Detected by FAST
• FASHI: An untargeted survey of the 21 cm HI absorption galaxies with FAST
• Statistical distribution of HI 21cm intervening absorbers as potential cosmic acceleration probes