@article{10902/27117,
year = {2012},
month = {6},
url = {https://hdl.handle.net/10902/27117},
abstract = {The origin of broad-absorption-line quasi-stellar objects (BAL QSOs) remains unclear. Accounting for ?20% of the QSO population, these objects have broad absorption lines in their optical spectra generated from outflows with velocities of up to 0.2 c. In this work, we present the results of a multi-frequency study of a well-defined radio-loud BAL QSO sample, and a comparison sample of radio-loud non-BAL QSOs, both selected from the Sloan Digital Sky Survey (SDSS).Aims: We aim to test which of the currently popular models of the BAL phenomenon - "orientation" or " evolutionary" - best accounts for the radio properties of BAL quasars. We also consider a third model in which BALs are produced by polar jets driven by radiation pressure. Methods: Observations from 1.4 to 43 GHz have been obtained with the VLA and Effelsberg telescopes, and data from 74 to 408 MHz have been compiled from the literature. The spectral indices give clues about the orientation, while the determination of the peak frequency can constrain the age, and test the evolutionary scenario, in which BAL QSOs are young QSOs. The fractional polarisation and the rotation measure in part reflect the local magnetic field strength and particle density. Results: The fractions of resolved sources in the BAL and non-BAL QSO samples are similar (16% versus (vs.) 12%). The resolved sources in the two samples have similar linear sizes (20 to 400 kpc) and morphologies. There is weak evidence that the fraction of variable sources amongst BAL QSOs is smaller. The fractions of candidate GHz-peaked sources are similar in the two samples (36 ± 12% vs. 23 ± 8%), suggesting that BAL QSOs are not generally younger than non-BAL QSOs. Both BAL and non-BAL QSOs have a wide range of spectral indices, including flat-spectrum and steep-spectrum sources, consistent with a broad range of orientations. There is weak evidence (91% confidence) that the spectral indices of the BAL QSOs are steeper than those of non-BAL QSOs, mildly favouring edge-on orientations. At a higher level of significance (?97%), the spectra of BAL QSOs are no flatter than those of non-BAL QSOs, which suggests that a polar orientation is not preferred. The distributions of fractional polarisation in the two samples have similar median values (1-3%). The distributions of rotation measure are also similar, the only outlier being the BAL QSO 1624+37, which has an extreme rest-frame rotation measure (from the literature) of -18 350 ± 570 rad m-2.},
organization = {Acknowledgements. We are grateful to F. Mantovani for helping us during the observations at the 100-m Effelsberg telescope. We would also like to thank A. Mignano, from the ALMA Regional Centre (Italian node), for helping us in image analysis with the first release of the CASA astronomical software. Part of this work was supported by a grant of the Italian Programme for Research of Relevant National Interest (PRIN No. 18/2007, PI: K.-H. Mack) The authors acknowledge financial support from the Spanish Ministerio de Ciencia e Innovación under project AYA2008-06311-C02-02. This work has benefited from research funding from the European Union’s sixth framework programme under RadioNet grant agreement No. 227290. This work has been partially based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Infrared Science Archive and NASA/IPAC Extragalactic Database (NED) which are both operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Use has been made of the Sloan Digital Sky Survey (SDSS) Archive. The SDSS is managed by the Astrophysical Research Consortium (ARC) for the participating institutions: The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The John Hopkins University, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.},
publisher = {EDP Sciences},
publisher = {Astronomy and Astrophysics, 2012, 542, A13},
title = {Radio spectra and polarisation properties of a bright sample of radio-loud broad absorption line quasars},
author = {Bruni, Gabriele and Mack, K.-H. and Salerno, E. and Montenegro-Montes, F. M. and Carballo Fidalgo, Ruth and Benn, C. R. and González Serrano, José Ignacio and Holt, J. and Jimenez Lujan, Florencia},
}