The Ultraviolet-to-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars

TL;DR

This study analyzes the spectral energy distributions of weak-lined quasars across ultraviolet to mid-infrared wavelengths, revealing their intrinsic nature and distinguishing them from jet-dominated sources.

Contribution

It provides the first comprehensive SEDs of WLQs from UV to mid-IR, showing they resemble ordinary quasars rather than jet-dominated objects, and clarifies their intrinsic weak emission lines.

Findings

WLQs have SEDs similar to ordinary quasars with hot dust emission.

They are not dominated by jet synchrotron emission like BL Lac objects.

Their weak emission lines are intrinsic, not due to jet continuum dilution.

Abstract

We present Spitzer Space Telescope photometry of 18 Sloan Digital Sky Survey (SDSS) quasars at 2.7 <= z <= 5.9 which have weak or undetectable high-ionization emission lines in their rest-frame ultraviolet (UV) spectra (hereafter weak-lined quasars, or WLQs). The Spitzer data are combined with SDSS spectra and ground-based, near-infrared (IR) photometry of these sources to produce a large inventory of spectral energy distributions (SEDs) of WLQs across the rest-frame ~0.1-5 mum spectral band. The SEDs of our sources are inconsistent with those of BL Lacertae objects which are dominated by synchrotron emission due to a jet aligned close to our line-of-sight, but are consistent with the SED of ordinary quasars with similar luminosities and redshifts that exhibit a near-to-mid-IR 'bump', characteristic of hot dust emission. This indicates that broad emission lines in WLQs are intrinsically weak, rather than suffering continuum dilution from a jet, and that such sources cannot be selected efficiently from traditional photometric surveys.