FLASH pilot survey: detections of associated 21 cm H i absorption in GAMA galaxies at 0.42 < z < 1.00. Issue 2 (18th August 2022)

• Record Type: Journal Article
• Authors: Su, Renzhi; Sadler, Elaine M; Allison, James R; Mahony, Elizabeth K; Moss, Vanessa A; Whiting, Matthew T; Yoon, Hyein; Aditya, J N H S; Bellstedt, Sabine; Robotham, Aaron S G; Garratt-Smithson, Lilian; Gu, Minfeng; Koribalski, Bärbel S; Soria, Roberto; Weng, Simon
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 516:Issue 2(2022)
• Page Start: 2947
• Page End: 2970
• Publication Date: 2022-08-18
• Subjects: methods: observational -- galaxies: active -- galaxies: ISM -- galaxies: nuclei -- radio lines: ISM; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac2257
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present the results of a search for associated 21 cm H i absorption at redshift 0.42 &lt; z &lt; 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 mJy, we detected two associated H i absorption systems, in SDSS J090331+010847 at z = 0.522 and SDSS J113622+004852 at z = 0.563. Both galaxies are massive (stellar mass $\gt 10^{11}\, \mathrm{M}_\odot$ ) and have optical spectra characteristic of luminous red galaxies, though spectral energy distribution fitting implies that SDSS J113622+004852 contains a dust-obscured starburst with star formation rate ∼69 M⊙ yr −1 . The H i absorption lines have a high optical depth, with τpk of 1.77 ± 0.16 for SDSS J090331+010847 (the highest value for any z &gt; 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 i absorption lines (with τpk &gt; 0.1 and at least 3σ 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 H i absorption systems at higher redshift. We also searched for OH absorption lines at 0.67 &lt; z &lt; 1.34, but no detection was made in the 145 radio sources searched.