TY  - JOUR
A1  - Worseck, Gábor
A1  - Khrykin, Ilya Sergeevich
A1  - Hennawi, Joseph F.
A1  - Prochaska, J. Xavier
A1  - Farina, Emanuele Paolo
T1  - Dating individual quasars with the He II proximity effect
T2  - Monthly notices of the Royal Astronomical Society
N2  - Constraints on the time-scales of quasar activity are key to understanding the formation and growth of supermassive black holes (SMBHs), quasar triggering mechanisms, and possible feedback effects on their host galaxies. However, observational estimates of this so-called quasar lifetime are highly uncertain (t(Q) similar to 10(4)-10(9) yr), because most methods are indirect and involve many model-dependent assumptions. Direct evidence of earlier activity is gained from the higher ionization state of the intergalactic medium (IGM) in the quasar environs, observable as enhanced Ly alpha transmission in the so-called proximity zone. Due to the similar to 30 Myr equilibration time-scale of He II in the z similar to 3 IGM, the size of the He II proximity zone depends on the time the quasar had been active before our observation t(on) <= t(Q), enabling up to +/- 0.2 dex precise measurements of individual quasar on-times that are comparable to the e-folding time-scale t(S) <= 44 Myr of SMBH growth. Here we present the first statistical sample of 13 quasars whose accurate and precise systemic redshifts allow for measurements of sufficiently precise He II quasar proximity zone sizes between similar or equal to 2 and similar or equal to 15 proper Mpc from science-grade Hubble Space Telescope (HST) spectra. Comparing these sizes to predictions from cosmological hydrodynamical simulations post-processed with 1D radiative transfer, we infer a broad range of quasar on-times from t(on) less than or similar to 1Myr to t(on) > 30 Myr that does not depend on quasar luminosity, black hole mass, or Eddington ratio. These results point to episodic quasar activity over a long duty cycle, but do not rule out substantial SMBH growth during phases of radiative inefficiency or obscuration.
KW  - intergalactic medium
KW  - quasars: absorption lines
KW  - quasars: general
KW  - quasars: supermassive black holes
KW  - dark ages, reionization, first stars
Y1  - 2021
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/62591
SN  - 0035-8711
SN  - 1365-2966
VL  - 505
IS  - 4
SP  - 5084
EP  - 5103
PB  - Oxford Univ. Press
CY  - Oxford
ER  -