The First Direct Measure of BAL Quasar Orientations

Details The First Direct Measure of BAL Quasar Orientations The First Direct Measure of BAL Quasar Orientations

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21943502d&link_type=abstract

American Astronomical Society, AAS Meeting #219, #435.02

Astronomy and Astrophysics

Astronomy

Scientific paper

Broad Absorption Line (BAL) quasars make up a significant fraction of the population of optically selected quasars, yet their nature is still debated. A common explanation for the presence of BALs in only a subset of all quasar spectra is orientation; it is argued that these sources have high velocity outflows in a mostly equatorial wind, and we only observe them when they are viewed more edge-on (farther from the accretion disk symmetry axis) than normal quasars. However, no direct measure of the orientation of these sources has been done, and several of their observational properties are difficult to explain with only geometrical arguments. This has led to a dichotomy in this area of study, where either BAL sources are seen from a particular viewing angle, or they are a particular evolutionary stage in the lifetime of all quasars. We have conducted a survey with the EVLA at two frequencies of BAL sources and a well-matched sample of unabsorbed quasars found in both SDSS and the FIRST survey. The goal was to measure the radio spectral index (α) of a large sample, as α is a statistical indicator of source orientation. We find that BAL quasars do show a significantly different spectral index distribution compared to normal quasars, though both have a large range, indicating that BAL sources cover a range of orientations but more often have higher viewing angles than non-BAL sources. We then performed Monte-Carlo simulations of these distributions to quantify the range of viewing angles to these objects.
I gratefully acknowledge the Wyoming NASA Space Grant Consortium for funding a portion of this work and travel.

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