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Active galactic nuclei in dusty starbursts at z = 2: Feedback still to kick in

Rodighiero, G., Enia, A., Delvecchio, I., Lapi, A., Magdis, G. E., Rujopakarn, W., Mancini, C., Rodríguez-Muñoz, L., Carraro, R., Iani, E., Negrello, M., Franceschini, A., Renzini, A., Gruppioni, C., Perna, M., Baronchelli, I., Puglisi, A., Cassata, P., Daddi, E., Morselli, L. and Silverman, J. 2019. Active galactic nuclei in dusty starbursts at z = 2: Feedback still to kick in. Astrophysical Journal Letters 877 (2) , -. 10.3847/2041-8213/ab222e

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Abstract

We investigate a sample of 152 dusty sources at 1.5 < z < 2.5 to understand the connection of enhanced star formation rate (SFR) and black hole accretion rate. The sources are Herschel-selected, having stellar masses M * > 1010 M ⊙ and SFR (~100–1000 M ⊙ yr−1) elevated (>4×) above the star-forming "main sequence," classifying them as starbursts (SBs). Through a multiwavelength fitting approach (including a dusty torus component), we divided the sample into active SBs (dominated by an active galactic nucleus (AGN) emission, SBs-AGN, ~23% of the sample) and purely star-forming SBs (SBs-SFR). We visually inspected their Hubble Space Telescope/ultraviolet (UV) rest frame maps: SBs-SFR are generally irregular and composite systems; ~50% of SBs-AGN are instead dominated by regular compact morphologies. We then found archival Atacama Large Millimeter/submillimeter Array continuum counterparts for 33 galaxies (12 SBs-AGN and 21 SBs-SFR). For these sources we computed dust masses, and, with standard assumptions, we also guessed total molecular gas masses. SBs turn into gas-rich systems (f gas = M gas/(M gas + M *) sime 20%–70%), and the gas fractions of the two SB classes are very similar (f gas = 43% ± 4% and f gas = 42% ± 2%). Our results show that SBs are consistent with a mixture of: (1) highly star-forming merging systems (dominating the SBs-SFR) and (2) primordial galaxies, rapidly growing their M * together with their black hole (mainly the more compact SBs-AGN). Feedback effects have not yet reduced their f gas. Indeed, SBs at z = 2, with relatively low bolometric AGN luminosities in the range 1044 < L bol(AGN) < 1046 erg s−1 (compared to bright optical and X-ray quasars), are still relatively far from the epoch when the AGN feedback will quench the SFR in the host and will substantially depress the gas fractions.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Physics and Astronomy
Publisher: American Astronomical Society
ISSN: 2041-8205
Date of First Compliant Deposit: 12 July 2019
Date of Acceptance: 13 May 2019
Last Modified: 15 Jul 2019 14:45
URI: http://orca.cf.ac.uk/id/eprint/124189

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