The most-luminous heavily-obscured quasars have a high merger fraction: morphological study of WISE-selected hot dust-obscured galaxies

TL;DR

This study reveals that Hot DOGs, highly luminous and obscured quasars, exhibit a high merger fraction and transforming morphologies, supporting a merger-driven evolutionary model for massive galaxy development.

Contribution

It provides the first detailed morphological analysis of Hot DOGs at z~3, linking high merger activity to their extreme luminosity and obscuration, and supports a merger-driven galaxy evolution scenario.

Findings

Hot DOGs have a merger fraction of 62%±14%.

Most Hot DOGs display transforming morphologies with Sersic indices peaking around 2.

The relation between merger fraction and bolometric luminosity aligns with theoretical models.

Abstract

Previous studies have shown that WISE-selected hyperluminous, hot dust-obscured galaxies (Hot DOGs) are powered by highly dust-obscured, possibly Compton-thick AGNs. High obscuration provides us a good chance to study the host morphology of the most luminous AGNs directly. We analyze the host morphology of 18 Hot DOGs at $z\sim3$ using Hubble Space Telescope/WFC3 imaging. We find that Hot DOGs have a high merger fraction ($62\pm 14 \%$). By fitting the surface brightness profiles, we find that the distribution of S\'ersic indices in our Hot DOG sample peaks around 2, which suggests that most of Hot DOGs have transforming morphologies. We also derive the AGN bolometric luminosity ($\sim10^{14}L_\odot$) of our Hot DOG sample by using IR SEDs decomposition. The derived merger fraction and AGN bolometric luminosity relation is well consistent with the variability-based model prediction (Hickox et al. 2014). Both the high merger fraction in IR-luminous AGN sample and relatively low merger fraction in UV/optical-selected, unobscured AGN sample can be expected in the merger-driven evolutionary model. Finally, we conclude that Hot DOGs are merger-driven and may represent a transit phase during the evolution of massive galaxies, transforming from the dusty starburst dominated phase to the unobscured QSO phase.