FASHI: An Untargeted Survey of the 21 cm H i Absorption Galaxies with FAST

Abstract

The FAST All Sky H I survey (FASHI) will cover the entire observable sky (∼22,000 square degrees) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). With the currently released data, we perform an untargeted survey of 21 cm H i absorption galaxies at redshift z ≲ 0.09 over an area of about 10,000 square degrees. We have detected 51 H i absorbers, including 21 previously known and 30 new ones. The probability of occurrence for the H i absorbers in all H i galaxies is 1/1078. The radio flux densities of the FASHI absorbers are mainly concentrated in the range of S _1.4GHz = 10 ∼ 100 mJy, but also as low as 2.6 ± 0.4 mJy. We find that the host galaxies of the associated H i absorbers have relatively high star formation rates, and there is a negative correlation between the H i column density and the stellar mass in the host galaxy. Consequently, FAST has significantly improved the capabilities and performance for H i absorption observations and has provided a true untargeted survey of 21 cm H i absorption galaxies for such studies.

Keywords

• Radio telescopes
• Redshift surveys
• Extragalactic radio sources
• H I line emission