First CO(17–16) emission line detected in a z > 6 quasar

• Published in: Monthly notices of the Royal Astronomical Society Vol. 445; no. 3; pp. 2848 - 2853
• Main Authors: Gallerani, S., Ferrara, A., Neri, R., Maiolino, R.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 11-12-2014
• Subjects: Carbon monoxide; Emission; Flux; Galaxies; Interferometers; Interferometry; Quasars; Red shift; Space telescopes; Stars & galaxies; X-ray astronomy; X-rays; intergalactic medium; ISM: clouds; quasars: super massive black holes; X-ray: ISM; ISM: molecules; galaxies: high redshift
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stu2031

We report the serendipitous detection of the CO(17–16) emission line towards the quasar sloan digital sky survey J114816.64+525150.3 (J1148) at redshift z ≃ 6.4 obtained with the Plateau de Bure Interferometer. The CO(17–16) line is possibly contaminated by OH+ emission, that may account for ∼35–60 per cent of the total flux observed. Photodissociation and X-ray-dominated regions (PDRs and XDRs) models show that PDRs alone cannot reproduce the high luminosity of the CO(17–16) line relative to low-J CO transitions and that XDRs are required. By adopting a composite PDR+XDR model, we derive molecular cloud and radiation field properties in the nuclear region of J1148. Our results show that highly excited CO lines represent a sensitive and possibly unique tool to infer the presence of X-ray faint or obscured supermassive black hole progenitors in high-z galaxies.