Thursday

We present science results from the ASKAP First Large Absorption in HI (FLASH), a 34,000 square degree wide-field survey for HI 21-cm absorption at cosmological distances. HI absorption provides a unique perspective on the neutral gas in individual galaxies at cosmological distances; it is sensitive to the coldest (T~100K) atomic gas, thereby directly tracing the reservoir of fuel available for star formation, and on smaller scales can reveal accretion and jet-cloud interactions in radio-loud active galaxies.

FLASH is now underway and expected to detect more than a thousand intervening and associated 21-cm absorbers at redshifts 0.4 z 1.0, directly measuring the HI content of individual passive and active galaxies after the peak in global star formation known as "cosmic noon". FLASH also provides a mid-tier L-band continuum image of sky at declinations +40 degrees to a depth of 90uJy/beam.

We have recently completed the first 1000 square degrees of the survey, covering well-studied fields in SDSS-BOSS, GAMA, DES and SPT-SZ regions, and new absorber candidates have been confirmed. We are using these early science results to understand the nature of an HI-absorption selected sample of galaxies at cosmological distances. We will discuss this sample, examples of which include the central gas reservoir in a young and luminous radio galaxy at z = 0.44, which is undergoing an interaction with a gas-rich minor companion, and intra-group gas in a large filament-like structure of galaxies at z = 0.45. We will also discuss how statistical analysis of the detection rate enables us to determine how the fraction of cold neutral medium (CNM) in galaxies has evolved during the rapid decline in cosmic star formation rate.