The first measurement of the quasar lifetime distribution

Abstract

Understanding the growth of the supermassive black holes (SMBH) powering luminous quasars, their co-evolution with host galaxies, and impact on the surrounding intergalactic medium (IGM) depends sensitively on the duration of quasar accretion episodes. Unfortunately, this time-scale, known as the quasar lifetime, tQ, is still uncertain by orders of magnitude (tQ ≃ 0.01 Myr − 1 Gyr). However, the extent of the He ii Lyα proximity zones in the absorption spectra of zqso ∼ 3 − 4 quasars constitutes a unique probe, providing sensitivity to lifetimes up to ∼30 Myr. Our recent analysis of 22 archival Hubble Space Telescope He ii proximity zone spectra reveals a surprisingly broad range of emission timescales, indicating that some quasars turned on ≲ 1 Myr ago, whereas others have been shining for ≳ 30 Myr. Determining the underlying quasar lifetime distribution (QLD) from proximity zone measurements is a challenging task owing to: 1) the limited sensitivity of individual measurements; 2) random sampling of the quasar light curves; 3) density fluctuations in the quasar environment; and 4) the inhomogeneous ionization state of He ii in a reionizing IGM. We combine a semi-numerical He ii reionization model, hydrodynamical simulations post-processed with ionizing radiative transfer, and a novel statistical framework to infer the QLD from an ensemble of proximity zone measurements. Assuming a lognormal QLD, we infer a mean $\langle {\rm log}_{10}\left( t_{\rm Q} / {\rm Myr} \right)\rangle = 0.22^{+0.22}_{-0.25}$ and standard deviation $\sigma _{{\rm log}_{10}t_{\rm Q}} = 0.80^{+0.37}_{-0.27}$. Our results allow us to estimate the probability of detecting very young quasars with tQ ≤ 0.1 Myr from their proximity zone sizes yielding $p \left( \le 0.1\, {\rm Myr}\right) = 0.19^{+0.11}_{-0.09}$, which is broadly consistent with recent determination at z ∼ 6.

AGN-driven outflows and the formation of Ly$α$ nebulae around high-z quasars

“…We adopt two types of light-curve: (i) the AGN radiates constantly at a fixed bolometric luminosity 𝐿 bol , (ii) the AGN switches on and off, following a square-wave lightcurve with a specific period 𝜏 cycle and quasar lifetime 𝜏 QSO . We assume a duty cycle ≈ 90% (consistent with the cosmological simulations Costa et al 2014) and a quasar lifetime of 1 Myr (consistent with the observational constraints of high-𝑧 quasar lifetimes of Khrykin et al 2021), such that 𝜏 cycle = 1.1 Myr. We sample bolometric luminosities ranging from 𝐿 bol = 10 47 erg s −1 to 𝐿 bol = 5 × 10 47 erg s −1 , encompassing the typical range of observed 𝑧 = 6 quasar luminosities.…”

Infrared Spectral Energy Distribution and Variability of Active Galactic Nuclei: Clues to the Structure of Circumnuclear Material

“…An average extended disk plus torus mass of ∼ 6 × 10 5 M has been determined from ALMA measurements [76]. A typical AGN duty cycle is ∼ 2 × 10 6 years [126]. Therefore, for an average luminosity for local AGNs of ∼ 10 11 L , about 20% of the total disk plus torus mass eventually needs to be accreted by the black hole, a plausible value.…”

Probing the Inner Circumgalactic Medium and Quasar Illumination around the Reddest `Extremely Red Quasar' (ERQ)

“…Their result is consistent with our wide-field data that show no broadening in Ly𝛼 in J0006+1215 down to ∼6 kpc radius. Lifetimes of quasar episodes as measured by their proximity zones are typically (10 5 -10 7 ) yr (e.g., Khrykin et al 2021). Even if an observed episode has been on for 10 7 yr, for a characteristic outflow speed consistent with the kinematics of most Ly𝛼 haloes ∼400 km s −1 , an outflow driven by the episode can only travel out to ∼4 kpc.…”