# Host galaxies of high-redshift extremely red and obscured quasars

## TL;DR

This study uses Hubble imaging to analyze host galaxies of high-redshift extremely red quasars and type 2 quasar candidates, revealing their luminosities, merger activity, and implications for galaxy evolution models.

## Contribution

It provides detailed observations of host galaxy properties and merger activity of high-redshift ERQs and type 2 quasars, challenging existing galaxy formation theories.

## Key findings

- ERQ hosts are very luminous, with some in ongoing mergers.
- Type 2 quasar hosts are less luminous and show less merger activity.
- Results suggest ERQs may be associated with late-stage mergers, contrasting with some models.

## Abstract

We present Hubble Space Telescope 1.4-1.6 micron images of the hosts of ten extremely red quasars (ERQs) and six type 2 quasar candidates at z=2-3. ERQs, whose bolometric luminosities range between 10^47 and 10^48 erg/sec, show spectroscopic signs of powerful ionized winds, whereas type 2 quasar candidates are less luminous and show only mild outflows. After performing careful subtraction of the quasar light, we clearly detect almost all host galaxies. The median rest-frame B-band luminosity of the ERQ hosts in our sample is 10^11.2 L_Sun, or 4 L* at this redshift. Two of the ten hosts of ERQs are in ongoing mergers. The hosts of the type 2 quasar candidates are 0.6 dex less luminous, with 2/6 in likely ongoing mergers. Intriguingly, despite some signs of interaction and presence of low-mass companions, our objects do not show nearly as much major merger activity as do high-redshift radio-loud galaxies and quasars. In the absence of an overt connection to major ongoing gas-rich merger activity, our observations are consistent with a model in which the near-Eddington accretion and strong feedback of ERQs are associated with relatively late stages of mergers resulting in early-type remnants. These results are in some tension with theoretical expectations of galaxy formation models, in which rapid black hole growth occurs within a short time of a major merger. Type 2 quasar candidates are less luminous, so they may instead be powered by internal galactic processes.