Deep 21-cm HI Observations at z~0.1: The Precursor to the Arecibo Ultra Deep Survey

TL;DR

This paper presents precursor 21-cm HI observations at redshifts around 0.1, demonstrating the capabilities of the AUDS survey to detect HI emission and measure its evolution, serving as a foundation for future deep HI studies.

Contribution

It reports the first results from the AUDS precursor observations, showcasing the survey's sensitivity and consistency with local HI mass function predictions at intermediate redshifts.

Findings

Detected 18 HI emission lines at z=0.07-0.15

Measured HI density at z=0.125 consistent with local universe

Demonstrated survey's potential for studying HI evolution

Abstract

The "ALFA Ultra Deep Survey" (AUDS) is an ongoing 21-cm spectral survey with the Arecibo 305m telescope. AUDS will be the most sensitive blind survey undertaken with Arecibo's 300 MHz Mock spectrometer. The survey searches for 21-cm HI line emission at redshifts between 0 and 0.16. The main goals of the survey are to investigate the HI content and probe the evolution of HI gas within that redshift region. In this paper, we report on a set of precursor observations with a total integration time of 53 hours. The survey detected a total of eighteen 21-cm emission lines at redshifts between 0.07 and 0.15 in a region centered around ra~0:00h, dec= 15:42deg. The rate of detection is consistent with the one expected from the local HI mass function. The derived relative HI density at the median redshift of the survey is rho_HI[z=0.125]=(1.0+/-0.3)*rho_0, where rho_0 is the HI density at zero redshift.