Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.1111s&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #11.11; Bulletin of the American Astronomical Society, Vol. 24, p.1136
Astronomy and Astrophysics
Astronomy
Scientific paper
Optical spectropolarimetry of several low-redshift low-polarization quasars (LPQs) included in the Palomar-Green QSO sample are presented. These observations dramatically illustrate the fact that a single polarizing mechanism is not able to account for all of the polarization properties exhibited by LPQs. Our observations of 3C 273 reveal a source of polarized flux consistent with a synchrotron emission component similar to the nonthermal components that dominate the optical continua of radio-selected BL Lacs and OVV quasars. The continuum polarized flux has a steep spectral index (alpha ~ -2.7) which must flatten considerably in the near-IR. Low-polarization emission components typical of LPQs (such as the ``big blue bump'') dilute the polarization so that 3C 273 does not present optical properties similar to those shown by OVVs. The variability of the polarization of 3C 273 and the fact that Hα dilutes the continuum polarization rules out the possibility that a significant fraction of the polarized flux arises through scattering by dust or electrons exterior to the broad-line region. In contrast, the radio-quiet quasar PG 1114+445 shows no evidence for a highly variable, polarized nonthermal component. Both the broad and narrow emission lines are polarized to the same degree as the continuum. This implies that scattering by dust external to the narrow-line region is responsible for the polarization of this QSO. Whether the dust grains are associated directly with the quasar or the body of the host galaxy is not yet clear. This research is supported by NSF grant AST 91-14087 and NASA grant NAG 5-1630.
Allen Richard G.
Schmidt Gary D.
Smith Paul S.
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