First black holes: observability and growth

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 ha​s​ 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 ​detect​on of ​the first black holes​ in ​the ​U​niverse.
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.