Molecular gas content in obscured AGN at z > 1

Abstract

Aims. The standard active galactic nuclei (AGN)-galaxy co-evolutionary scenario predicts a phase of deeply "buried" supermassive black hole growth coexisting with a starburst (SB) before feedback phenomena deplete the cold molecular gas reservoir of the galaxy and an optically luminous quasar (QSO) is revealed ("SB-QSO evolutionary sequence"). The aim of this work is to measure the cold gas reservoir of three highly obscured QSOs to test if their gas fraction is similar to that of submillimeter galaxies (SMGs), as expected by some models, and place these measurements in the context of the SB-QSO framework. Methods. We target CO(1-0) transition in BzK4892, a Compton Thick (CT) QSO at z=2.6, CO(1-0) in BzK8608 and CO(2-1) in CDF153, two highly obscured (N H ≈ 6 × 10 23 cm −2 ) QSOs at z = 2.5 and z = 1.5, respectively. For all these targets, we place 3σ upper limits on the CO lines, with L CO < (1.5 ÷ 2.8) × 10 10 K km/s pc 2 . We also compare the molecular gas conditions of our targets with those of other systems at z > 1, considering normal star forming galaxies and SMGs, unobscured and obscured AGN from the literature. For the AGN samples, we provide an updated and (almost) complete collection of targets with CO follow-up at z > 1. Results. BzK4892 displays a high star formation efficiency (SFE = L IR /L CO > 410 L /(K km s −1 pc 2 )) and a gas fraction f gas = M gas /(M star + M gas ) < 10%. Less stringent constraints are derived for the other two targets ( f gas < 0.5 and SFE > 10 L /(K km s −1 pc 2 )). From the comparison with literature data, we found that, on average, i) obscured AGN at z > 1 are associated with higher SFE and lower f gas with respect to normal star forming galaxies and SMGs; ii) mildly and highly obscured active galaxies have comparable gas fractions; iii) the SFE of CT and obscured AGN are similar to those of unobscured AGN.Conclusions. Within the SB-QSO framework, these findings could be consistent with a scenario where feedback can impact the host galaxy already from the early phases of the SB-QSO evolutionary sequence.

GOODS-ALMA: The slow downfall of star formation in z = 2–3 massive galaxies

“…The presence of an AGN can influence the measurement of the stellar mass of the galaxy and artificially lower the calculated gas fraction of the galaxies. This result is consistent with the findings of Perna et al (2018) who found systematically low gas fractions in obscured AGN at z > 1 and suggests that AGN feedback could lead to the expulsion of gas. One of these galaxies has a low gas fraction (21%) and does not show any sign of an AGN.…”

Multi-wavelength Properties of Radio- and Machine-learning-identified Counterparts to Submillimeter Sources in S2COSMOS

“…Both theoretical simulations and observational studies suggest a link between the growth of galaxies and their supermassive black holes (SMBHs, M BH =10 6 -10 9 M  , e.g., Hopkins et al 2008;Ishibashi & Fabian 2016). Under this paradigm, starburst-dominated galaxies and the active galactic nuclei (AGNs) dominated QSOs are essentially the same systems observed at different evolutionary stages (e.g., Sanders et al 1988;Perna et al 2018). Therefore, surveying the AGN activity in the SMG population provides insights into not only SMBH growth, but also potentially the evolutionary cycle of massive galaxies.…”

Remarkably high mass and velocity dispersion of molecular gas associated with a regular, absorption-selected type I quasar

“…The detection of powerful multi-phase galactic-scale outflows shows that AGNs are capable of removing large amounts of gas from their host galaxies. As recently discussed by Perna et al (2018), neither the evolutionary sequence nor orientation effects with respect to the obscuring medium alone are able to explain the observed SFEs in obscured and unobscured AGNs.…”

“…For example, WISE has played an important role in selecting these hyperluminous objects, in combination with (e.g., Bischetti et al 2017) or without (Fan et al 2018) photometry from the SDSS. Other works focused on possibly less luminous objects that were still preferentially dust obscured (e.g., Polletta et al 2011;Banerji et al 2017;Kakkad et al 2017;Perna et al 2018), radio loud (e.g., Willott et al 2007), or on the highest redshifts detected in [C ii]λ158 µm (e.g., Venemans et al 2017). In turn, J0015+1842 is not particularly bright, with an i-band magnitude in only the second brightest quartile of SDSS quasars at the same redshift, for instance, and it is only moderately reddened (A V ∼ 0.3−0.4).…”

“…The studies have mostly focused on the bright end of the infra-red luminosity distribution and showed that luminous quasars generally have a low ratio of molecular gas masses to star formation rates (SFR) (e.g., Bischetti et al 2021), while starburst galaxies have much higher ratios of molecular masses to SFR, supporting the evolutionary paradigm. Several studies have also searched for CO emission in obscured quasars, that is, possibly at the short-lived intermediate stage between the SB and optically bright quasar phase (e.g., Polletta et al 2011;Brusa et al 2015), but differences with luminous quasars are apparently found only for Compton-thick cases, which are more likely associated with the initial steps of the blow-out phase (Perna et al 2018).…”