Luminous and obscured quasars and their host galaxies

TL;DR

This study investigates luminous, heavily-obscured quasars at redshifts 1-3, revealing their association with merging galaxies and suggesting an evolutionary phase in black hole and galaxy development.

Contribution

It provides new insights into the prevalence of obscured quasars in merging galaxies and their potential role in galaxy evolution, based on mid-infrared selected samples.

Findings

80% of quasars are obscured in X-ray data

30% are so obscured they are undetected in deep X-ray observations

Heavily-obscured quasars are more common in merging/disturbed galaxies

Abstract

The most heavily-obscured, luminous quasars might represent a specific phase of the evolution of actively accreting supermassive black holes and their host galaxies, possibly related to mergers. We investigated a sample of the most luminous quasars at $z\approx 1-3$ in the GOODS fields, selected in the mid-infrared band through detailed spectral energy distribution (SED) decomposition. The vast majority of these quasars (~80%) are obscured in the X-ray band and ~30% of them to such an extent, that they are undetected in some of the deepest (2 and 4 Ms) Chandra X-ray data. Although no clear relation is found between the star-formation rate of the host galaxies and the X-ray obscuration, we find a higher incidence of heavily-obscured quasars in disturbed/merging galaxies compared to the unobscured ones, thus possibly representing an earlier stage of evolution, after which the system is relaxing and becoming unobscured.