Towards a comprehensive picture of powerful quasars, their host galaxies and quasar winds at z ~ 0.5

TL;DR

This study uses Hubble Space Telescope observations to analyze luminous obscured quasars at z ~ 0.5, revealing their host galaxy properties, merger signatures, and quasar wind interactions, providing insights into galaxy evolution and quasar unification.

Contribution

It combines host galaxy imaging with quasar wind measurements, offering new insights into the connection between mergers, star formation, and quasar activity at intermediate redshift.

Findings

Bright merger signatures in about half the host galaxies.

Host galaxies are primarily bulge-dominated with high star formation rates.

Ionized gas is aligned with quasar illumination cones, indicating photo-ionization by the quasar.

Abstract

Luminous type-2 quasars in which the glow from the central black hole is obscured by dust are ideal targets for studying their host galaxies and the quasars' effect on galaxy evolution. Such feedback appears ubiquitous in luminous obscured quasars where high velocity ionized nebulae have been found. We present rest-frame yellow-band (~5000 Angstroms) observations using the Hubble Space Telescope for a sample of 20 luminous quasar host galaxies at 0.2 < z < 0.6 selected from the Sloan Digital Sky Survey. For the first time, we combine host galaxy observations with geometric measurements of quasar illumination using blue-band HST observations and [OIII] integral field unit observations probing the quasar winds. The HST images reveal bright merger signatures in about half the galaxies; a significantly higher fraction than in comparison inactive ellipticals. We show that the host galaxies are primarily bulge-dominated, with masses close to M*, but belong to < 30% of elliptical galaxies that are highly star-forming at z ~ 0.5. Ionized gas signatures are uncorrelated with faint stellar disks (if present), confirming that the ionized gas is not concentrated in a disk. Scattering cones and [OIII] ionized gas velocity field are aligned with the forward scattering cones being co-spatial with the blue-shifted side of the velocity field, suggesting the high velocity gas is indeed photo-ionized by the quasar. Based on the host galaxies' high star-formation rates and bright merger signatures, we suggest that this low-redshift outbreak of luminous quasar activity is triggered by recent minor mergers. Combining these novel observations, we present new quasar unification tests, which are in agreement with expectations of the orientation-based unification model for quasars.