The Infrared Afterglow of Supermassive Black Hole Mergers

TL;DR

This paper models the infrared afterglow signals from supermassive black hole mergers, predicting observable signatures lasting tens of thousands of years and estimating their detectability in current surveys.

Contribution

It introduces a model for the infrared emission following supermassive black hole mergers and estimates the number of observable sources in existing astronomical surveys.

Findings

Infrared afterglow persists for tens of thousands of years.

Approximately 10,000 to 100,000 such IR sources could be observable today.

Predicted IR signals can be identified with multi-wavelength surveys.

Abstract

We model the spectra and light curves of circumbinary accretion disks during the time after the central black holes merge. The most immediate effect of this merger is the dissipation of energy in the outer regions of the disk due to the gravitational wave energy and linear momentum flux released at merger. This has the effect of perturbing the gas in the disk, which then radiates the dissipated energy over a cooling timescale, giving a characteristic infrared signal for tens of thousands of years when the total black hole mass is M~10^8 M_sun. On the basis of a simple cosmological merger model in which a typical supermassive black hole undergoes a few major mergers during its lifetime, we predict that ~10^4-10^5 of these IR sources should be observable today and discuss the possibility of identifying them with multi-wavelength surveys such as SWIRE/XMM-LSS/XBootes and COSMOS.