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arXiv · 1209.1095

Limits on the high redshift growth of massive black holes

R. Salvaterra·F. Haardt·M. Volonteri·A. Moretti
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Abstract

We place firm upper limits on the global accretion history of massive black holes at z>5 from the recently measured unresolved fraction of the cosmic X-ray background. The maximum allowed unresolved intensity observed at 1.5 keV implies a maximum accreted-mass density onto massive black holes of rho_acc < 1.4E4 M_sun Mpc^{-3} for z>5. Considering the contribution of lower-z AGNs, the value reduces to rho_acc < 0.66E4 M_sun Mpc^{-3}. The tension between the need for the efficient and rapid accretion required by the observation of massive black holes already in place at z>7 and the strict upper limit on the accreted mass derived from the X-ray background may indicate that black holes are rare in high redshift galaxies, or that accretion is efficient only for black holes hosted by rare galaxies.

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R. Salvaterra, F. Haardt, M. Volonteri, A. Moretti. 2012-09-05. Limits on the high redshift growth of massive black holes. https://doi.org/10.1051/0004-6361/201219965

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