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First black holes: observability and growth
3 ottobre 2017 @ 11:45 - 12:45
The first black hole seeds likely formed when the Universe was younger than 500 Myr old.
They play an important role in the growth of early (z=7) supermassive black holes. While much progress has been made in understanding their formation and growth, their observational signatures remain largely unexplored. As a result, we are yet to detect these sources. We present a novel photometric method to identify black hole seed candidates in deep multi-wavelength surveys. The method relies on infrared and X-ray observations and selects the only two objects with a robust X-ray detection found in the CANDELS/GOODS-S survey with a photometric redshift z>6. To date, these selected objects represent the most promising black hole seed candidates, possibly formed via the direct collapse black hole scenario. While this result is based on the best photometric observations of high-z sources available to date, additional gains are expected from deeper spectroscopic and X-ray data. For this reason, we explore the role that JWST will play in the detecton of the first black holes in the Universe.
Moreover, we present a novel probabilistic model for black hole growth: our results have important implications for the conditions that facilitate efficient black hole growth, particularly at early cosmic epochs. By bringing in a precise definition of “growth probability”, our finding clearly demonstrates quantitatively the generally-accepted concept that the super-massive black holes that we observed at z=7 are the “luckiest” members of the ensemble of high-z black holes. Our formalism has significant and broad consequences for upcoming observations of high-redshift quasars.