Elusive evidence of neutral hydrogen in the distant Universe

Continuing their studies of cool neutral hydrogen gas – the fuel for star formation – in the distant Universe, the research team around CAASTRO researcher Stephen Curran has succeeded in detecting the signal of HI absorption at the third highest redshift reported to date, at a look-back time of approximately 9 billion years. Their current survey specifically targeted very faint sources that lie below their previously determined cut-off luminosity above which all hydrogen in a galaxy is ionised.

The team pre-identified ten candidate sources using Parkes radio source catalogues and observed them at 610 MHz with the 30-antenna array Giant Metrewave Radio Telescope in India in January 2012. Of these galaxies, four had to be excluded due to poor data quality. Taking other factors into account that render data unreliable, only three sources were deemed worthy of full analysis.

One of the three sources (J1545+4751) exhibited the flattest spectral energy distribution and yielded a detection of the 21-cm absorption signal. Observations with the Very Long Baseline Array had previously confirmed this radio source as very compact. The radio power for this source was found to be lower than for the other candidates but higher than in observations at higher redshift where HI absorption is yet to be observed.

Publication details:

S. J. Curran, M. T. Whiting, A. Tanna, E. M. Sadler, M. B. Pracy and R. Athreya “A survey for HI in the distant Universe: the detection of associated 21-cm absorption at z = 1.28” in MNRAS 429, 4302-3410 (2013)