FLASH pilot survey: detections of associated 21 cm H I absorption in GAMA galaxies at 0.42 < z < 1.00

Wc present the results of a search for associated 21 cm HI absorption at redshift 0.42 < z < 1,00 in radio -loud galaxies from three Galaxy And Mass Assembly (GAMA) survey fields. These observations were carried out as part of a pilot survey for the Australian SKA Pathfinder (ASKAP) First Large Absorption Survey in H I (FLASH). From a sample of 326 radio sources with 855.5 MHz peak flux density above 10 mIy, we detected two associated H 1 absorption systems, in SDSS J090331+010847 at z = 0.522 and SDSS J113622+004852 at z = 0.563. Both galaxies are massive (stellar mass > 10(11) M-circle dot) and have optical spectra characteristic of luminous red galaxies, though spectral energy distribution fitting implies that SDSSJ113622+004852 contains a dust-obscured starburst with star formation rate similar to 69 M-circle dot, yr(-1). The H I absorption lines have a high optical depth, with Tpk of 1.77 0.16 for SDSS J090331+010847 (the highest value for any z > 0.1 associated system found to date) and 0.14 +/- 0.01 for SDSS J113622+004852. In the redshift range probed by our ASKAP observations, the detection rate for associated H absorption lines (with tau(pk) > 0.1 and at least 3 sigma significance) is 2.9(-2.6)(+9.7) per cent. Although the current sample is small, this rate is consistent with a trend seen in other studies for a lower detection rate of associated 21 cm HI absorption systems at higher redshift. We also searched for 011 absorption lines at 0.67 < z < 1.34, hut no detection was made in the 145 radio sources searched.