Black hole growth in the early Universe is self-regulated and largely hidden from view

TL;DR

This study uses deep X-ray observations to show that early universe black holes grow rapidly and are heavily obscured, making them difficult to observe directly and indicating they do not significantly contribute to cosmic re-ionization.

Contribution

It provides new measurements of black hole growth at z=6-8, revealing that most are heavily obscured and grow more than previously estimated during early cosmic epochs.

Findings

Black holes grow in tandem with their host galaxies from early times.

Most accreting black holes at z=6-8 are heavily obscured by gas and dust.

Black hole growth during early epochs does not significantly contribute to re-ionization.

Abstract

The formation of the first massive objects in the infant Universe remains impossible to observe directly and yet it sets the stage for the subsequent evolution of galaxies. While some black holes with masses > billion solar masses? have been detected in luminous quasars less than one billion years after the Big Bang, these individual extreme objects have limited utility in constraining the channels of formation of the earliest black holes. The initial conditions of black hole seed properties are quickly erased during the growth process. From deep, optimally stacked, archival X-ray observations, we measure the amount of black hole growth in z=6-8 galaxies (0.7-1 billion years after the Big Bang). Our results imply that black holes grow in tandem with their hosts throughout cosmic history, starting from the earliest times. We find that most copiously accreting black holes at these epochs are buried in significant amounts of gas and dust that absorb most radiation except for the highest energy X-rays. This suggests that black holes grow significantly more than previously thought during these early bursts, and due to obscuration they do not contribute to the re-ionization of the Universe with their ultraviolet emission.