Journal Article

Radio spectra and polarization properties of radio-loud broad absorption-line quasars

F. M. Montenegro-Montes, K.-H. Mack, M. Vigotti, C. R. Benn, R. Carballo, J. I. González-Serrano, J. Holt and F. Jiménez-Luján

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 388, issue 4, pages 1853-1868
Published in print August 2008 | ISSN: 0035-8711
Published online August 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13520.x
Radio spectra and polarization properties of radio-loud broad absorption-line quasars

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We present multifrequency observations of a sample of 15 radio-emitting broad absorption-line quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They mostly display convex radio spectra which typically peak at about 1–5 GHz (in the observer's rest frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e. ν≳ 20 GHz. Very Large Array (VLA) 22-GHz maps (HPBW ∼80 mas) show unresolved or very compact sources, with linear projected sizes of ≤1 kpc. About two-thirds of the sample looks unpolarized or weakly polarized at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarized intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and in the rest frame, finding steeper spectra among non-BAL QSOs. However, constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarization properties shows that radio BAL QSOs share several properties common to young radio sources like compact steep spectrum or gigahertz peaked spectrum sources.

Keywords: polarization; quasars: absorption lines; radio continuum: galaxies

Journal Article.  12537 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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