The optical polarization properties of quasars

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Abstract

Optical polarimetry is presented for 163 radio-selected quasars, including a complete sample of 90 sources stronger than 2 Jy at 5 GHz. Including new and published data, the polarimetry is over 90% complete. Synchrotron components are detected in over 30% of these flat spectrum quasars, with an optical polarization threshold of p > 3%. The fraction of polarized quasars is a strong function of the compactness of the radio emission, as measured on VLBI scales. Including the duty cycle correction, essentially every quasar with Score > Sext at radio wavelengths has a prominent blazar component at optical wavelengths. Virtually all of the radio sources with weak emission lines (or BL Lac objects) are highly polarized. Optical and radio polarization are not correlated, and there is no difference in the αro distributions of high-and low-polarization quasars, or sources with strong and weak emission lines. Redshift information is incomplete, but BL Lac objects appear to have lower redshifts than strong-lined quasars. The distribution of V/Vmax for radio BL Lac objects indicates much stronger evolution than is found for X-ray-selected BL Lac objects. Overall, there is a strong statistical link between compact radio structure, apparent superluminal motion, strong optical polarization, and weak emission lines. This can be understood if both the optical and the compact radio emission are relativistically beamed. However, the Lorentz factors of the material emitting the optical and radio radiation must be different.

Original languageEnglish (US)
Pages (from-to)124-139
Number of pages16
JournalAstrophysical Journal
Volume354
Issue number1
StatePublished - May 1 1990

Fingerprint

optical polarization
quasars
polarization
radio
polarimetry
radio emission
very long base interferometry
void ratio
wavelengths
wavelength
synchrotrons
very long baseline interferometry
strong motion
cycles
thresholds
radiation
x rays

Keywords

  • BL Lacertae objects
  • Polarization
  • Quasars
  • Radio sources: general radio sources: variability

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

The optical polarization properties of quasars. / Impey, Christopher D; Tapia, S.

In: Astrophysical Journal, Vol. 354, No. 1, 01.05.1990, p. 124-139.

Research output: Contribution to journalArticle

Impey, CD & Tapia, S 1990, 'The optical polarization properties of quasars', Astrophysical Journal, vol. 354, no. 1, pp. 124-139.
Impey, Christopher D ; Tapia, S. / The optical polarization properties of quasars. In: Astrophysical Journal. 1990 ; Vol. 354, No. 1. pp. 124-139.
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AB - Optical polarimetry is presented for 163 radio-selected quasars, including a complete sample of 90 sources stronger than 2 Jy at 5 GHz. Including new and published data, the polarimetry is over 90% complete. Synchrotron components are detected in over 30% of these flat spectrum quasars, with an optical polarization threshold of p > 3%. The fraction of polarized quasars is a strong function of the compactness of the radio emission, as measured on VLBI scales. Including the duty cycle correction, essentially every quasar with Score > Sext at radio wavelengths has a prominent blazar component at optical wavelengths. Virtually all of the radio sources with weak emission lines (or BL Lac objects) are highly polarized. Optical and radio polarization are not correlated, and there is no difference in the αro distributions of high-and low-polarization quasars, or sources with strong and weak emission lines. Redshift information is incomplete, but BL Lac objects appear to have lower redshifts than strong-lined quasars. The distribution of V/Vmax for radio BL Lac objects indicates much stronger evolution than is found for X-ray-selected BL Lac objects. Overall, there is a strong statistical link between compact radio structure, apparent superluminal motion, strong optical polarization, and weak emission lines. This can be understood if both the optical and the compact radio emission are relativistically beamed. However, the Lorentz factors of the material emitting the optical and radio radiation must be different.

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