Searching for Low-Redshift Hot Dust-Obscured Galaxies

TL;DR

This study searches for low-redshift Hot Dust-Obscured Galaxies using WISE and Herschel data, identifying a few candidates and analyzing their properties to understand their role in galaxy evolution.

Contribution

It is the first to identify and spectroscopically confirm low-redshift Hot DOGs, expanding understanding of their evolution and properties at z<0.5.

Findings

Three low-redshift Hot DOGs confirmed spectroscopically.

Low-z Hot DOGs have black hole accretion near the Eddington limit.

Surface density of low-z Hot DOGs is an order of magnitude lower than high-z counterparts.

Abstract

Hot Dust-Obscured Galaxies (Hot DOGs), discovered by the "W1W2 dropout" selection at high redshifts ($z\sim$ 2-4), are a rare population of hyper-luminous obscured quasars. Their number density is comparable to similarly luminous type 1 quasars in the same redshift range, potentially representing a short, yet critical stage in galaxy evolution. The evolution in their number density towards low redshift, however, remains unclear as their selection function is heavily biased against objects at $z\lesssim2$. We combine data from the WISE and Herschel archives to search for Hot DOGs at $z<0.5$ based on their unique spectral energy distributions. We find 68 candidates, and spectroscopic observations confirm that 3 of them are at $z<0.5$. For those 3 we find their black hole accretion is close to the Eddington limit, with lower bolometric luminosities and black hole masses than those of higher-$z$ Hot DOGs. Compared to high-$z$ systems, these low-$z$ systems are closer to the local relation between host galaxy stellar mass and black hole mass but still lie above it, and we discuss several possible scenarios for it. Finally, we also find the surface number density of $z<$0.5 Hot DOGs is $\rm 2.4 \times 10^{-3}$ deg$^{-2}$, about an order of magnitude lower than high-$z$ Hot DOGs but comparable to hyper-luminous unobscured quasars in the same redshift range. These results further support the idea that Hot DOGs may be a transitional phase of galaxy evolution.