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Probing quasar lifetimes with proximate 21-centimetre absorption in the diffuse intergalactic medium at redshifts z ≥ 6

Šoltinský, Tomáš; Bolton, James S.; Molaro, Margherita; Hatch, Nina; Haehnelt, Martin G.; Keating, Laura C.; Kulkarni, Girish; Puchwein, Ewald


Tomáš Šoltinský

Margherita Molaro

Associate Professor

Martin G. Haehnelt

Laura C. Keating

Girish Kulkarni

Ewald Puchwein


Enhanced ionizing radiation in close proximity to redshift z ≳ 6 quasars creates short windows of intergalactic Ly α transmission blueward of the quasar Ly α emission lines. The majority of these Ly α near-zones are consistent with quasars that have optically/UV bright lifetimes of $t_{\rm Q}\sim 10^{5}\!-\!10^{7}\rm \, yr$. However, lifetimes as short as $t_{\rm Q}\lesssim 10^{4}\rm \, yr$ appear to be required by the smallest Ly α near-zones. These short lifetimes present an apparent challenge for the growth of $\sim 10^{9}\rm \, M_{\odot }$ black holes at z ≳ 6. Accretion over longer time-scales is only possible if black holes grow primarily in an obscured phase, or if the quasars are variable on time-scales comparable to the equilibriation time for ionized hydrogen. Distinguishing between very young quasars and older quasars that have experienced episodic accretion with Ly α absorption alone is challenging, however. We therefore predict the signature of proximate 21-cm absorption around z ≳ 6 radio-loud quasars. For modest pre-heating of intergalactic hydrogen by the X-ray background, where the spin temperature $T_{\rm S} \lesssim 10^{2}\rm \, K$ prior to any quasar heating, we find proximate 21-cm absorption should be observable in the spectra of radio-loud quasars. The extent of the proximate 21-cm absorption is sensitive to the integrated lifetime of the quasar. Evidence for proximate 21-cm absorption from the diffuse intergalactic medium within $2\!-\!3\rm \, pMpc$ of a (radio-loud) quasar would be consistent with a short quasar lifetime, $t_{\rm Q}\lesssim 10^{5}\rm \, yr$, and would provide a complementary constraint on models for high-redshift black hole growth.


Šoltinský, T., Bolton, J. S., Molaro, M., Hatch, N., Haehnelt, M. G., Keating, L. C., …Puchwein, E. (2023). Probing quasar lifetimes with proximate 21-centimetre absorption in the diffuse intergalactic medium at redshifts z ≥ 6. Monthly Notices of the Royal Astronomical Society, 519(2), 3027-3045.

Journal Article Type Article
Acceptance Date Dec 12, 2022
Online Publication Date Dec 19, 2022
Publication Date 2023-02
Deposit Date Dec 27, 2022
Publicly Available Date Jan 6, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 519
Issue 2
Pages 3027-3045
Keywords Space and Planetary Science, Astronomy and Astrophysics
Public URL
Publisher URL


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