ATCA detections of massive molecular gas reservoirs in dusty, high-z radio galaxies

I. Heywood, Y. Contreras, D. J. B. Smith, A. Cooray, L. Dunne, L. Gomez, E. Ibar, R. J. Ivison, M. J. Jarvis, M. J. Michalowski, D. A. Riechers, P. van der Werf

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Observations using the 7 mm receiver system on the Australia Telescope Compact Array have revealed large reservoirs of molecular gas in two high-redshift radio galaxies: HATLAS J090426.9+015448 (z = 2.37) and HATLAS J140930.4+003803 (z = 2.04). Optically the targets are very faint, and spectroscopy classifies them as narrow-line radio galaxies. In addition to harbouring an active galactic nucleus the targets share many characteristics of sub-mm galaxies. Far-infrared data from Herschel-ATLAS suggest high levels of dust (>10^9 M_solar) and a correspondingly large amount of obscured star formation (~1000 M_solar / yr). The molecular gas is traced via the J = 1-0 transition of 12CO, its luminosity implying total H_2 masses of (1.7 +/- 0.3) x 10^11 and (9.5 +/- 2.4) x 10^10 (alpha_CO/0.8) M_solar in HATLAS J090426.9+015448 and HATLAS J140930.4+003803 respectively. Both galaxies exhibit molecular line emission over a broad (~1000 km/s) velocity range, and feature double-peaked profiles. We interpret this as evidence of either a large rotating disk or an on-going merger. Gas depletion timescales are ~100 Myr. The 1.4 GHz radio luminosities of our targets place them close to the break in the luminosity function. As such they represent `typical' z > 2 radio sources, responsible for the bulk of the energy emitted at radio wavelengths from accretion-powered sources at high redshift, and yet they rank amongst the most massive systems in terms of molecular gas and dust content. We also detect 115 GHz rest-frame continuum emission, indicating a very steep high-radio-frequency spectrum, possibly classifying the targets as compact steep spectrum objects.
Original languageEnglish
Pages (from-to)1297-1307
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 27 Oct 2016


  • astro-ph.GA
  • astro-ph.CO


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