Active Galactic Nuclei in Dusty Starbursts at z=2: Feedback Still to Kick in

G. Rodighiero*, A. Enia, I. Delvecchio, A. Lapi, G. E. Magdis, W. Rujopakarn, C. Mancini, L. Rodriguez-Munoz, R. Carraro, E. Iani, M. Negrello, A. Franceschini, A. Renzini, C. Gruppioni, M. Perna, I. Baronchelli, A. Puglisi, P. Cassata, E. Daddi, L. MorselliJ. Silverman

*Corresponding author for this work

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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 *)  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.
Original languageEnglish
Article numberL38
JournalAstrophysical Journal Letters
Issue number2
Number of pages7
Publication statusPublished - 2019


  • Galaxies: active
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Galaxies: starburst
  • Infrared: galaxies

Cite this

Rodighiero, G., Enia, A., Delvecchio, I., Lapi, A., Magdis, G. E., Rujopakarn, W., Mancini, C., Rodriguez-Munoz, L., Carraro, R., Iani, E., Negrello, M., Franceschini, A., Renzini, A., Gruppioni, C., Perna, M., Baronchelli, I., Puglisi, A., Cassata, P., Daddi, E., ... Silverman, J. (2019). Active Galactic Nuclei in Dusty Starbursts at z=2: Feedback Still to Kick in. Astrophysical Journal Letters, 877(2), [L38].