CO-Dark Star Formation and Black Hole Activity in 3C 368 at z = 1.131: Coeval Growth of Stellar and Supermassive Black Hole Masses

• Published in: The Astrophysical journal 2017-02, Vol.836 (1), p.123
• Main Authors: Lamarche, C., Stacey, G., Brisbin, D., Ferkinhoff, C., Hailey-Dunsheath, S., Nikola, T., Riechers, D., Sharon, C. E., Spoon, H., Vishwas, A.
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Astrophysics; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; CARBON; CARBON MONOXIDE; DETECTION; EMISSION; EVOLUTION; FAR INFRARED RADIATION; FINE STRUCTURE; GALAXIES; GALAXY NUCLEI; H2 REGIONS; MASS; METALLICITY; Molecular gases; Neon; Organic chemistry; OXYGEN; PHOTONS; RED SHIFT; SPECTRA; Star & galaxy formation; Star formation; STARS; Stars & galaxies; Stellar age; Supermassive black holes
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/836/1/123

We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2–1) and [N ii ] 205 μ m lines, in 3C 368, a well-studied radio-loud galaxy at z  = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ∼6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2–1) line, down to a level twelve times lower than the expected value for star-forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated throughout much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, although we argue it is unlikely, that the ensemble of fine-structure lines is emitted from the region heated by the AGN.