The Arecibo Ultra-Deep Survey
Hongwei Xi, Lister Staveley-Smith, Bi-Qing For, Wolfram Freudling,, Martin Zwaan, Laura Hoppmann, Fu-Heng Liang, and Bo Peng

TL;DR
The Arecibo Ultra Deep Survey (AUDS) is a highly sensitive HI survey detecting 247 galaxies up to redshift 0.16, providing insights into the HI mass function and cosmic HI density with no significant evolution observed.
Contribution
This paper presents the deepest blind HI survey to date with detailed measurements of the HI mass function and cosmic HI density up to redshift 0.16, using a novel maximum likelihood method.
Findings
Detected 247 galaxies in the survey.
Measured HI mass function parameters: alpha = -1.37, M* = 10^10.15 M_sun.
Found no significant evolution in HI density from redshift 0 to 0.16.
Abstract
The Arecibo Ultra Deep Survey (AUDS) is a blind HI survey aimed at detecting galaxies beyond the local Universe in the 21-cm emission line of neutral hydrogen (HI). The Arecibo -band Feed Array (ALFA) was used to image an area of 1.35~deg to a redshift depth of 0.16, using a total on-source integration time of over 700 hours. The long integration time and small observation area makes it one of the most sensitive HI surveys, with a noise level of ~Jy per 21.4~kHz (equivalent to 4.5~km~s at redshift ). We detect 247 galaxies in the survey, more than doubling the number already detected in AUDS60. The mass range of detected galaxies is . A modified maximum likelihood method is employed to construct an HI mass function (HIMF). The best fitting Schechter parameters are: low-mass slope $\alpha = -1.37…
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