The First Large Absorption Survey in HI (FLASH) is a wide-field ASKAP survey that will provide world-class science through the provision of new measurements of the amount and distribution of HI in distant galaxies, allowing us for the first time to investigate the relationship between HI gas supply and star formation rate in individual galaxies at z>0.5.
ASKAP will be an array of 36 antennas each 12m in diameter, capable of high dynamic range imaging and using wide-field-of-view phased array feeds. ASKAP is intended to be a world-class telescope in its own right as well as a pathfinder instrument for the Square Kilometre Array.
ASKAP's large spectral bandwidth (300 MHz bandwidth over the frequency range 700-1800 MHz) and wide field of view (30 square degrees) will open up a completely new parameter space for large, blind HI absorption-line surveys using background radio continuum sources. Since the detection limit for such surveys is independent of redshift, ASKAP-FLASH will allow us to learn about the neutral gas content of galaxies in the poorly-explored redshift range 0.5 < z < 1.0, where the HI emission line is too weak to be detectable in even the deepest ASKAP surveys. The FLASH survey aims to detect and measure several hundred HI absorption lines (from both intervening and associated absorbers). This will provide a unique dataset for studies of galaxy evolution as well as a new estimate of the HI mass density at intermediate redshifts. The FLASH data will also be used for HI emission-line stacking experiments in combination with large-area optical redshift surveys like WiggleZ and GAMA.
|The first ASKAP 3-antenna detection (black curve) of HI absorption towards the gravitational lens PKS 1830-211 (Credit: CSIRO and J.R. Allison) compared to an earlier detection made by Chengalur et al. (1999).