High-Redshift SDSS Quasars with Weak Emission Lines

TL;DR

This study identifies and characterizes a sample of high-redshift quasars with weak emission lines, revealing their similarities to normal quasars and differences from BL Lac objects, suggesting unique broad-line region properties.

Contribution

The paper presents a new sample of high-redshift WLQs and analyzes their infrared, optical, and radio properties, highlighting their distinct broad-line region characteristics.

Findings

WLQs have hot thermal dust emission similar to normal quasars.

WLQs differ from BL Lacs in variability, polarization, and radio properties.

Continuum boosting by jets is unlikely to explain WLQ properties.

Abstract

We identify a sample of 74 high-redshift quasars (z>3) with weak emission lines from the Fifth Data Release of the Sloan Digital Sky Survey and present infrared, optical, and radio observations of a subsample of four objects at z>4. These weak emission-line quasars (WLQs) constitute a prominent tail of the Lya+NV equivalent width distribution, and we compare them to quasars with more typical emission-line properties and to low-redshift active galactic nuclei with weak/absent emission lines, namely BL Lac objects. We find that WLQs exhibit hot (T~1000 K) thermal dust emission and have rest-frame 0.1-5 micron spectral energy distributions that are quite similar to those of normal quasars. The variability, polarization, and radio properties of WLQs are also different from those of BL Lacs, making continuum boosting by a relativistic jet an unlikely physical interpretation. The most probable scenario for WLQs involves broad-line region properties that are physically distinct from those of normal quasars.