Physics
Scientific paper
Mar 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aps..mar.k3912k&link_type=abstract
American Physical Society, Annual March Meeting, March 16-20, 1998 Los Angeles, CA, abstract #K39.12
Physics
Scientific paper
It has been proposed that there may exist a large population of quasars that have been previously overlooked due to circumnuclear dust. The dust obscures light at UV and visible wavelengths, but has no effect in the radio. An effective method to find such objects is to look for radio sources without optical counterparts. We compiled a complete sample of about 350 flat-spectrum radio sources, with α > -0.5 (where F_ν ~ ν^α) quasars tend to have flatter radio spectra than radio galaxies. Using the digitized version of the Second Palomar Sky Survey (DPOSS) and subsequent CCD imaging at Palomar, these radio sources were correlated with optically detected objects. We expected a priori some contamination of the sample by radio galaxies, which would be too faint for DPOSS to detect. About 85% of the entire sample of sources were detected by DPOSS, but about 95% of the sources with α > -0.3 were identified. The majority of the remaining DPOSS non-detections have relatively steep spectra (α ≈ -0.5), which is consistent with the expected radio galaxy contamination. Follow up CCD imaging seems to confirm this. We conclude that a significant population of dust-obscured radio-loud quasars does not exist, and that at most only a few percent of radio-loud quasars are obscured by dust.
Banas Ken
Djorgovski Stanislav G.
Gal Roy R.
Kollmeier Juna
Odewahn Steve
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