The Reddest DR3 SDSS/XMM Quasars
Monica Young, Martin Elvis, Guido Risaliti

TL;DR
This study cross-matched SDSS DR3 quasars with XMM-Newton data to identify the causes of red colors, revealing a subset of intrinsically red quasars with unique spectral properties and low accretion rates.
Contribution
It is the first to classify red quasars into dust-reddened and intrinsically red categories using combined optical and X-ray data, highlighting low accretion rates as a possible cause.
Findings
7 quasars are likely intrinsically red with broad MgII lines and low accretion rates.
8 quasars are dust-reddened with significant X-ray absorption.
Some quasars show high X-ray absorption, indicating dust and gas obscuration.
Abstract
We have cross-correlated the SDSS DR3 Schneider et al. (2005) quasar catalog with the XMM-Newton archive. Color and redshift selections (g - r > 0.5 and 0.9 z < 2.1) result in a sample of 17 red, moderate redshift quasars. The redshift selection minimizes possible contamination due to host galaxy emission and Lyalpha forest absorption. Both optical and X-ray information are required to distinguish between the two likely remaining causes of the red colors: 1) dust-reddening and 2) an intrinsically red continuum. We find that 7 of 17 quasars can be classified as probable `intrinsically red' objects. These 7 quasars have unusually broad MgII emission lines (<FWHM>=10,500 km s^{-1}), moderately flat, but unabsorbed X-ray spectra <Gamma>=1.66+/-0.08), and low accretion rates (mdot/mdot_{Edd}} ~ 0.01). We suggest low accretion rates as a possible physical explanation for quasars with…
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