First Identification of Direct Collapse Black Hole Candidates in the Early Universe in CANDELS/GOODS-S

TL;DR

This paper introduces a new photometric method to identify potential direct collapse black hole seeds in the early universe, successfully finding two promising candidates in the CANDELS/GOODS-S survey.

Contribution

The study develops a novel infrared spectral analysis technique supported by simulations to detect high-redshift black hole seed candidates in deep surveys.

Findings

Identified two promising black hole seed candidates at z > 6.

Candidates exhibit steep infrared spectra and cannot be explained by star formation alone.

Results support the direct collapse black hole formation scenario.

Abstract

The first black hole seeds, formed when the Universe was younger than 500 Myr, are recognized to play an important role for the growth of early (z ~ 7) super-massive black holes. While progresses have been made in understanding their formation and growth, their observational signatures remain largely unexplored. As a result, no detection of such sources has been confirmed so far. Supported by numerical simulations, we present a novel photometric method to identify black hole seed candidates in deep multi-wavelength surveys. We predict that these highly-obscured sources are characterized by a steep spectrum in the infrared (1.6-4.5 micron), i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection found in the CANDELS/GOODS-S survey with a photometric redshift z > 6. Fitting their infrared spectra only with a stellar component would require unrealistic star formation rates (>2000 solar masses per year). To date, the selected objects represent the most promising black hole seed candidates, possibly formed via the direct collapse black hole scenario, with predicted mass >10^5 solar masses. While this result is based on the best photometric observations of high-z sources available to date, additional progress is expected from spectroscopic and deeper X-ray data. Upcoming observatories, like the JWST, will greatly expand the scope of this work.