Martha Haynes (Cornell University)

The ALFALFA Census of Gas-Bearing Galaxies at z=0 -- Martha Haynes Colloquium

Marsfield Lecture Theare

Abstract

Capitalizing on the huge collecting area of the Arecibo telescope and the survey capability of the 7-beam Arecibo L-band Feed Array (ALFA), the Arecibo Legacy Fast ALFA (ALFALFA) extragalactic HI 21cm line survey aims to produce a census of HI-bearing objects found over 7000 square
degrees of the high galactic latitude sky out to z < 0.06. The survey observations have just now been completed, and a catalog is available for about 54% of the final survey area. With its completion, ALFALFA provides the first robust census of gas-bearing halos over a cosmologically significant volume, paving the way for the upcoming ASKAP surveys. I will review the nature of the ALFALFA population and discuss some of its more enigmatic objects, including "dark galaxy" candidates and possible very low mass
"mini-halos" in the Local Group. Most surprisingly, ALFALFA detects many more high HI mass objects than predicted by previous determinations of the HI mass function, a result of particular importance since it directly impacts, in a positive sense, estimates of the expected HI detection rate
at high z with the SKA and its pathfinders. Our coordinated multiwavelength program will yield important insight into how some massive galaxies
maintain huge gas reservoirs without converting their gas into stars
and how isolated low mass halos are able to retain some HI gas despite
their fragile thermal state and shallow potential wells.