The Most Luminous Galaxies Discovered by WISE

TL;DR

This paper reports the discovery of extremely luminous infrared galaxies (ELIRGs) using WISE data, revealing highly obscured AGNs with supermassive black holes rapidly growing at high redshifts.

Contribution

The study introduces a new selection method for identifying ELIRGs with bolometric luminosities exceeding 10^14 L_sun, expanding understanding of the most luminous, obscured AGNs at high redshift.

Findings

ELIRGs have hot dust T_d ~ 450K dominating their emission.

These galaxies are powered by highly obscured AGNs, not beamed or lensed.

Supermassive black holes in these systems may grow rapidly via super-Eddington accretion or low radiative efficiency.

Abstract

We present 20 WISE-selected galaxies with bolometric luminosities L_bol > 10^14 L_sun, including five with infrared luminosities L_IR = L(rest 8-1000 micron) > 10^14 L_sun. These "extremely luminous infrared galaxies," or ELIRGs, were discovered using the "W1W2-dropout" selection criteria which requires marginal or non-detections at 3.4 and 4.6 micron (W1 and W2, respectively) but strong detections at 12 and 22 micron in the WISE survey. Their spectral energy distributions are dominated by emission at rest-frame 4-10 micron, suggesting that hot dust with T_d ~ 450K is responsible for the high luminosities. These galaxies are likely powered by highly obscured AGNs, and there is no evidence suggesting these systems are beamed or lensed. We compare this WISE-selected sample with 116 optically selected quasars that reach the same L_bol level, corresponding to the most luminous unobscured quasars in the literature. We find that the rest-frame 5.8 and 7.8 micron luminosities of the WISE-selected ELIRGs can be 30-80% higher than that of the unobscured quasars. The existence of AGNs with L_bol > 10^14 L_sun at z > 3 suggests that these supermassive black holes are born with large mass, or have very rapid mass assembly. For black hole seed masses ~ 10^3 M_sun, either sustained super-Eddington accretion is needed, or the radiative efficiency must be <15%, implying a black hole with slow spin, possibly due to chaotic accretion.