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The Search for the Farthest Quasar: Consequences for Black Hole Growth and Seed Models

Presentation #213.04 in the session AGN and Quasars III.

Published onJun 29, 2022
The Search for the Farthest Quasar: Consequences for Black Hole Growth and Seed Models

The quest for high-redshift quasars has led to a series of record-breaking sources, with the current record holder at z = 7.642. Here, we show how future detections of z > 8 quasars impact the constraints on the parameters for black hole growth and seed models. Using broad flat priors on the growth parameters (Eddington ratio fEdd, duty cycle π’Ÿ, seed mass Mβ€’,seed and radiative efficiency Ξ΅), we show that the large uncertainties in their determination decrease by a factor ~5 when a quasar’s detection redshift goes from z = 9 to z = 12. In this high-redshift regime, Ξ΅ tends to the lowest value allowed, and the distribution for Mβ€’,seed peaks well inside the heavy seed domain. Remarkably, two quasars detected at z > 7 with low accretion rates (J1243+0100 and J0313-1806) already tighten the available parameter space, requiring Mβ€’,seed > 103.5 MβŠ™ and Ξ΅ < 0.1. The radiative efficiency is a crucial unknown, with factor ~2 changes able to modify the predicted mass by ~3 orders of magnitude already at z ~ 9. The competing roles of inefficient accretion (decreasing Ξ΅) and black hole spin-up (increasing Ξ΅) significantly impact growth models. Finally, we suggest that yields currently predicted by upcoming quasar surveys (e.g., Euclid) will be instrumental for determining the most-likely seed mass regime. For example, assuming thin-disk accretion, a detection of a quasar with mass ~1010 MβŠ™ by z ~ 9–10 would exclude the entire parameter space available for light seeds and dramatically reduce the one for heavy seeds.


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