ALFALFA: HI Cosmology in the Local Universe

TL;DR

The ALFALFA survey uses the Arecibo telescope to map HI in the local universe, significantly improving sensitivity and resolution over previous surveys, enabling detailed studies of cosmic structures and dark galaxy candidates.

Contribution

This paper introduces the ALFALFA survey, highlighting its enhanced capabilities and initial results in mapping HI and exploring dark galaxy candidates in the local universe.

Findings

ALFALFA improves sensitivity by an order of magnitude over previous surveys.

The survey has detected a significant number of HI-bearing objects.

Preliminary results include insights into the dark galaxy candidate VirgoHI21.

Abstract

For the last 25 years, the 21 cm line has been used productively to investigate the large-scale structure of the Universe, its peculiar velocity field and the measurement of cosmic parameters. In February 2005 a blind HI survey that will cover 7074 square degrees of the high latitude sky was started at Arecibo, using the 7-beam feed L-band feed array (ALFA). Known as the Arecibo Legacy Fast ALFA (ALFALFA) Survey, the program is producing a census of HI-bearing objects over a cosmologically significant volume of the local Universe. With respect to previous blind HI surveys, ALFALFA offers an improvement of about one order of magnitude in sensitivity, 4 times the angular resolution, 3 times the spectral resolution, and 1.6 times the total bandwidth of HIPASS. ALFALFA can detect 7 X 10**4 D**2 solar masses of HI, where D is the source distance in Mpc. As of mid 2007, 44% of the survey observations and 15% of the source extraction are completed. We discuss the status of the survey and present a few preliminary results, in particular with reference to the proposed "dark galaxy" VirgoHI21.