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

Renzhi Su, Elaine M. Sadler, James R. Allison, Elizabeth K. Mahony, Vanessa A. Moss, Matthew T. Whiting, Hyein Yoon, J. N. H. S. Aditya, Sabine Bellstedt, Aaron S. G. Robotham, Lilian Garratt-Smithson, Minfeng Gu, Barbel S. Koribalski, Roberto Soria, Simon Weng

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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.

Original languageEnglish
Pages (from-to)2947-2970
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 1 Oct 2022


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