A survey for HI in the distant Universe: the detection of associated 21-cm absorption at z=1.28

作者：Curran S J^*; Whiting M T; Tanna A; Sadler E M; Pracy M B; Athreya R

来源：Monthly Notices of the Royal Astronomical Society, 2013, 429(4): 3402-3410.

DOI：10.1093/mnras/sts604

• galaxies: active
• galaxies: fundamental parameters
• galaxies: high redshift
• quasars: absorption lines
• radio lines: galaxies
• ultraviolet: galaxies

We have undertaken a survey for HI 21-cm absorption within the host galaxies of z similar to 1.2-1.5 radio sources, in the search of the cool neutral gas currently %26apos;missing%26apos; at z greater than or similar to 1. This deficit is believed to be due to the optical selection of high-redshift objects biasing surveys towards sources of sufficient ultraviolet luminosity to ionize all of the gas in the surrounding galaxy. In order to avoid this bias, we have selected objects above blue magnitudes of B similar to 20, indicating ultraviolet luminosities below the critical value of L-UV similar to 10(23) W Hz(-1), above which 21-cm has never been detected. As a secondary requirement to the radio flux and faint optical magnitude, we shortlist targets with radio spectra suggestive of compact sources, in order to maximize the coverage of background emission. From this, we obtain one detection out of 10 sources searched, which at z = 1.278 is the third highest redshift detection of associated 21-cm absorption to date. Accounting for the spectra compromised by radio frequency interference, as well as various other possible pitfalls (reliable optical redshifts and turnover frequencies indicative of compact emission), we estimate a detection rate of approximate to 30 per cent, close to that expected for L-UV less than or similar to 10(23) W Hz(-1) sources.

• 出版日期2013-3