A blind HI Mass Function from the Arecibo Ultra-Deep Survey (AUDS)

TL;DR

The AUDS survey provides the first measurement of the HI mass function at higher redshifts, showing little evolution in the cosmic HI density up to z=0.2, using deep 21cm observations with the Arecibo telescope.

Contribution

This work presents the first determination of the HI mass function parameters at z~0.07 from a single, homogeneous survey dataset.

Findings

Detected 102 galaxies in the HI mass range 10^5.6 to 10^10.3 M_sun.

Measured the HI mass function parameters: alpha=-1.37, Phi=7.72e3 h^3/Mpc^3, log M_HI=9.75.

Estimated the cosmic HI density Omega_HI=(2.33+-0.07)e-4/h at z=0.065.

Abstract

The Arecibo Ultra Deep Survey (AUDS) combines the unique sensitivity of the telescope with the wide field of the Arecibo L-band Feed Array (ALFA) to directly detect 21cm HI emission from galaxies at distances beyond the local Universe bounded by the lower frequency limit of ALFA (z=0.16). AUDS has collected 700 hours of integration time in two fields with a combined area of 1.35 square degrees. In this paper we present data from 60% of the total survey, corresponding to a sensitivity level of 80 micro-Jy. We discuss the data reduction, the search for galaxies, parametrisation, optical identification and completeness. We detect 102 galaxies in the mass range of log M_HI/M_sun-2log h=5.6-10.3. We compute the HI mass function (HIMF) at the highest redshifts so far measured. A fit of a Schechter function results in alpha=-1.37+-0.03, Phi=(7.72+-1.4)*10^3 h^3/Mpc^3 and log M_HI/M_sun=9.75+-0.041+2log h. Using the measured HIMF, we find a cosmic HI density of Omega_HI=(2.33+-0.07)*10^-4/h for the sample z=0.065. We discuss further uncertainties arising from cosmic variance. Because of its depth, AUDS is the first survey that can determine parameters for the HI mass function in independent redshift bins from a single homogeneous data set. The results indicate little evolution of the co-moving mass function and Omega_HI within this redshift range. We calculate a weighted average for Omega_HI in the range $0<z<0.2$, combining the results from AUDS as well as results from other 21cm surveys and stacking, finding a best combined estimate of Omega_HI=(2.63+-0.10)*10-4/h.