Looking at quasars through galaxies

Abstract

Observations of quasars (QSOs) shining through or close to galaxies offer a way to probe the properties of the foreground matter through dust extinction and gravitational lensing. In this paper the feasibility of measuring the dust extinction properties is investigated using the backlitting of QSOs. We test our method to search for QSOs affected by intervening extinction, by matching the coordinates in the SDSS QSO DR3 catalogue with the New York University Value-Added Galaxy Catalog. In total, 164 QSO-galaxy pairs were found with a distance of less than 30 kpc between the galaxy centre and the QSO line-of-sight at the galaxy redshift. Investigating the QSO colours with multiband SDSS photometry, two pairs with galaxy redshifts z < 0.08 were found to be particularly interesting in that the QSOs show evidence of heavy Galactic type extinction with R_v ~ 3.1 at very large optical radii in the foreground spiral galaxies. With the available data, it remains inconclusive whether the two pairs can be explained as statistical colour outliers, by host extinction or if they provide evidence of dust in the outskirts of spiral galaxies. Deeper galaxy catalogues and/or higher resolution follow-up QSO spectra would help in resolving this problem. We also analyse five QSOs reported in the literature with spectroscopic absorption features originating from an intervening system. These systems are at higher redshifts than the other two and we find in most cases significantly lower best fit values of R_v. The wide range of preferred values of R_v found, although affected by substantial uncertainties, already indicates that the dust properties in other galaxies may be different from the Milky Way. Furthermore, the available data suggests a possible evolution in the dust properties with redshift, with lower R_v at high z.

7 pages, 7 figures. Matches version accepted by A&A

References in corpus (5)

• SALT: a Spectral Adaptive Light curve Template for Type Ia Supernovae
• The Sloan Digital Sky Survey Quasar Catalog III. Third Data Release
• Dust Reddening in SDSS Quasars
• Reddening, Absorption, and Decline Rate Corrections for a Complete Sample of Type Ia Supernovae leading to a Fully Corrected Hubble Diagram to v<30,000kms-1
• Measuring Extinction Curves of Lensing Galaxies

Cited by in corpus (12)

• Observational Constraints on the Nature of the Dark Energy: First Cosmological Results from the ESSENCE Supernova Survey
• The Millennium Galaxy Catalogue: the B-band attenuation of bulge and disc light and the implied cosmic dust and stellar mass densities
• Diversity in extinction laws of Type Ia supernovae measured between $0.2$ and $2\mu \mathrm{m}$
• Extinction Curves of Lensing Galaxies out to z=1
• GMRT mini-survey to search for 21-cm absorption in Quasar-Galaxy Pairs at z~0.1
• 21-cm absorption from galaxies at z ~ 0.3
• J004457+4123 (Sharov 21): not a remarkable nova in M31 but a background quasar with a spectacular UV flare
• Extinction properties of lensing galaxies
• Calibrating Milky Way dust extinction using cosmological sources
• Weighing dark matter haloes with gravitationally lensed supernovae
• Combined constraints on intergalactic dust from quasar colours and the soft X-ray background
• Galaxies in front of Quasars: Mrk 1456 and SDSS J114719.90+522923.2