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

doi:10.1093/mnras/stw2774

arXiv · 1610.07699

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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Abstract

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.

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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. 2016-10-28. ATCA detections of massive molecular gas reservoirs in dusty, high-z radio galaxies. https://doi.org/10.1093/mnras%2Fstw2774

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