The Evolving AGN Duty Cycle in Galaxies Since z ∼ 3 as Encoded in the X-Ray Luminosity Function

Abstract

We present a new modeling of the X-ray luminosity function (XLF) of Active Galactic Nuclei (AGN) out to z∼3, dissecting the contribution of main-sequence (MS) and starburst (SB) galaxies. For each galaxy population, we convolved the observed galaxy stellar mass (M ) function with a grid of Mindependent Eddington ratio (λ EDD ) distributions, normalised via empirical black hole accretion rate (BHAR) to star formation rate (SFR) relations. Our simple approach yields an excellent agreement with the observed XLF since z∼3. We find that the redshift evolution of the observed XLF can only be reproduced through an intrinsic flattening of the λ EDD distribution, and with a positive shift of the break λ * , consistent with an anti-hierarchical behavior. The AGN accretion history is predominantly made by massive (10 10 <M <10 11 M ) MS galaxies, while SB-driven BH accretion, possibly associated with galaxy mergers, becomes dominant only in bright quasars, at log(L X /erg s −1 )>44.36 + 1.28·(1+z). We infer that the probability of finding highly-accreting (λ EDD > 10%) AGN significantly increases with redshift, from 0.4% (3.0%) at z=0.5 to 6.5% (15.3%) at z=3 for MS (SB) galaxies, implying a longer AGN duty cycle in the early Universe. Our results strongly favor a M -dependent ratio between BHAR and SFR, as BHAR/SFR ∝ M 0.73[+0.22,−0.29] , supporting a non-linear BH buildup relative to the host. Finally, this framework opens potential questions on super-Eddington BH accretion and different λ EDD prescriptions for understanding the cosmic BH mass assembly.

The rapid transition from star formation to AGN-dominated rest-frame ultraviolet light at z ≃ 4

“…Furthermore, both models predict a similarly steep faint-end slope consistent with that found by other empirical predictions (e.g. Veale et al 2014;Ren et al 2020;Delvecchio et al 2020). For sources around UV −23, our two models give different predictions for the importance of scatter in the observed galaxies.…”

The effect of active galactic nuclei on the cold interstellar medium in distant star-forming galaxies

“…Past studies particularly focused on the lowest accessible carbon monoxide (CO) transitions and long-wavelength dust emission in order to constrain the total molecular gas mass across different galaxy types. A great effort has been undertaken to characterize the epoch of maximal growth of galaxies via star formation and subsequent quenching at z ∼ 1−3, when the cosmic SMBH accretion rate peaked (Delvecchio et al 2020). This resulted in claims of null effects of AGN on the star formation A&A 654, A165 (2021) rates (SFRs; Stanley et al 2017;Schulze et al 2019) and the ISM properties of the host (Sharon et al 2016;Kirkpatrick et al 2019) or, at the opposite end, decreased gas fractions and shortened depletion timescales in the presence of AGN (Kakkad et al 2017;Perna et al 2018;Brusa et al 2018;Circosta et al 2021;Bischetti et al 2021), disfavoring and supporting the existence of some kind of AGN feedback, respectively.…”

A census of ultraluminous X-ray sources in the local Universe

“…(ii) The IR component of the AGN emission will overestimate the inferred SFR and M of the host galaxy, and it will bias the measured metallicity (e.g., Mullaney et al 2011;Delvecchio et al 2020). While the magnitude of this effect can be small in the case of low-luminosity AGN, we take the conservative measure of excluding any AGN hosts (or galaxies with no nuclear activity information) from our scaling relations.…”