The orientation and polarization of broad absorption line quasars

Abstract

We present new spectropolarimetric observations of 8 radio-loud broad absorption line (BAL) quasars, and combine these new data with our previous spectropolarimetric atlases (of both radio-loud and radio-quiet objects) in order to investigate the polarization properties of BAL quasars as a group. The total (radio-selected) sample includes 36 (26) high-ionization and 22 (15) low-ionization BAL quasars. On average, we confirm that broad emission lines are polarized at a level similar to or less than the continuum and broad absorption troughs are more highly polarized, but we note that these properties are not true for all individual objects. Of the whole sample, 18 (31%) have high (>2%) continuum polarization, including 45% of the LoBALs and 22% of HiBALs. We identify a few correlations between polarization and other quasar properties, as well as some interesting non-correlations. In particular, continuum polarization does not correlate with radio spectral index, which suggests that the polarization is not due to a standard geometry and preferred viewing angle to BAL quasars. The polarization also does not correlate with the amount of intrinsic dust reddening, indicating that the polarization is not solely due to direct light attenuation either. Polarization does appear to depend on the minimum BAL outflow velocity, confirming the results of previous studies, and it may correlate with the maximum outflow velocity. We also find that continuum polarization anti-correlates with the polarization in the C IV broad emission and broad absorption. These results suggest that the polarization of BAL quasars cannot be described by one simple model, and that the scatterer location and geometry can vary significantly from object to object.

14 pages, accepted to MNRAS

References in corpus (7)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• The Intrinsic Fraction of Broad Absorption Line Quasars
• On the Fraction of Quasars with Outflows
• The Physical Nature of Polar Broad Absorption Line Quasars
• Radio Through X-ray Spectral Energy Distributions of 38 Broad Absorption Line Quasars
• Radio spectra and polarisation properties of radio-loud Broad Absorption Line Quasars
• Spectropolarimetry of PKS 0040-005 and the Orientation of Broad Absorption Line Quasars

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• The z=0.54 LoBAL Quasar SDSS J085053.12+445122.5: II. The Nature of Partial Covering in the Broad-Absorption-Line Outflow
• Discovery of strong Balmer line absorption in two luminous LoBAL quasars at z~1.5
• Rest-frame optical properties of luminous, radio-selected, broad absorption line quasars
• Polarization microlensing in the quadruply imaged broad absorption line quasar H1413+117
• Radiation-pressure Waves and Multiphase Quasar Outflows