A Population of Dust-Rich Quasars at z ~ 1.5

TL;DR

This study identifies a population of dust-rich quasars at redshift around 1.5, characterized by significant far-infrared emission and diverse dust temperatures, revealing their potential as ultra- or hyper-luminous infrared galaxy hosts.

Contribution

First comprehensive FIR detection and analysis of dust-rich quasars at z ~ 1.5, highlighting their unique properties and challenging previous assumptions based on shorter wavelength data.

Findings

Most FIR-detected quasars have dust temperatures of 25-60K.

FIR luminosities indicate they are ultra- or hyper-luminous infrared galaxies.

FIR properties are not predictable from shorter wavelength data.

Abstract

We report Herschel SPIRE (250, 350, and 500 micron) detections of 32 quasars with redshifts 0.5 < z < 3.6 from the Herschel Multi-tiered Extragalactic Survey. These sources are from a MIPS 24 micron flux-limited sample of 326 quasars in the Lockman Hole Field. The extensive multi-wavelength data available in the field permit construction of the rest-frame Spectral Energy Distributions (SEDs)from ultraviolet to the mid-infrared for all sources, and to the far-infrared (FIR) for the 32 objects. Most quasars with Herschel FIR detections show dust temperatures in the range of 25K to 60K, with a mean of 34K. The FIR luminosities range from 10^{11.3} to 10^{13.5} Lsun, qualifying most of their hosts as ultra- or hyper-luminous infrared galaxies. These FIR-detected quasars may represent a dust-rich population, but with lower redshifts and fainter luminosities than quasars observed at ~ 1 mm. However, their FIR properties cannot be predicted from shorter wavelengths (0.3--20 micron, rest-frame), and the bolometric luminosities derived using the 5100 A index may be underestimated for these FIR-detected quasars. Regardless of redshift, we observed a decline in the relative strength of FIR luminosities for quasars with higher near-infrared luminosities.