Shining in the Dark: the Spectral Evolution of the First Black Holes

الأصل · EN

Massive Black Hole (MBH) seeds at redshift z 10 are now thought to be key ingredients to explain the presence of the super-massive (10⁹⁻¹⁰ M) black holes in place < 1 Gyr after the Big Bang. Once formed, massive seeds grow and emit copious amounts of radiation by accreting the left-over halo gas; their spectrum can then provide crucial information on their evolution. By combining radiation-hydrodynamic and spectral synthesis codes, we simulate the time-evolving spectrum emerging from the host halo of a MBH seed with initial mass 10⁵ M, assuming both standard Eddington-limited accretion, or slim accretion disks, appropriate for super-Eddington flows. The emission occurs predominantly in the observed infrared-submm (1-1000 μm) and X-ray (0.1 - 100 keV) bands. Such signal should be easily detectable by JWST around 1 μm up to z 25, and by ATHENA (between 0.1 and 10 keV, up to z 15). Ultra-deep X-ray surveys like the Chandra Deep Field South could have already detected these systems up to z 15. Based on this, we provide an upper limit for the z 6 MBH mass density of ρ 2.5 × 10² M Mpc⁻³ assuming standard Eddington-limited accretion. If accretion occurs in the slim disk mode the limits are much weaker, ρ 7.6 × 10³ M Mpc⁻³ in the most constraining case.