A 3.5 mm POLARIMETRIC SURVEY OF RADIO-LOUD ACTIVE GALACTIC NUCLEI
- Instituto de Astrofisica de AndalucIa (CSIC), Apartado 3004, E-18080 Granada (Spain)
- Institut de Radio Astronomie Millimetrique, 300 Rue de la Piscine, 38406 St. Martin d'Heres (France)
- Instituto de Radio Astronomia Milimetrica, Avenida Divina Pastora, 7, Local 20, E-18012 Granada (Spain)
We present the results from the first large (>100 sources) 3.5 mm polarimetric survey of radio-loud active galactic nuclei (AGNs). This wavelength is favorable within the radio-millimeter range for measuring the intrinsic linearly polarized emission from AGNs, since in general it is only marginally affected by Faraday rotation of the electric vector position angle and depolarization. The I, Q, U, and V Stokes parameter observations were performed with the XPOL polarimeter at the IRAM 30 m Telescope on different observing epochs from 2005 July (when most of the measurements were made) to 2009 October. Our sample consists of 145 flat-radio-spectrum AGNs with declination >-30{sup 0} (J2000.0) and flux density {approx}>1 Jy at {approx}86 GHz, as measured at the IRAM 30 m Telescope from 1978 to 1994. This constraint on the radio spectrum causes our sample to be dominated by blazars, which allows us to conduct new statistical studies on this class of high-luminosity, relativistically beamed emitters. We detect linear and circular polarization (above minimum 3{sigma} levels of {approx}1.5% and {approx}0.3%) for 76% and 6% of the sample, respectively. We find a clear excess in degree of linear polarization detected at 86 GHz with regard to that at 15 GHz by a factor of {approx}2. Over our entire source sample, the luminosity of the jets is anticorrelated with the degree of linear polarization. Consistent with previous findings claiming larger Doppler factors for brighter {gamma}-ray blazars, quasars listed in our sample, and in the Fermi Large Area Telescope Bright Source Catalog (LBAS), show larger luminosities than non-LBAS ones, but our data do not allow us to confirm the same for BL Lac objects. We do not find a clear relation between the linear polarization angle and the jet structural position angle for any source class in our sample. We interpret this as the consequence of a markedly non-axisymmetric character of the 3 mm emitting region in the jets. We find that intrinsic circular polarization is the most likely mechanism for generation of the circular polarization detected in our observations. Our new data can be used to estimate the 3.5 mm AGN contribution to measurements of the linear polarization of the cosmic microwave background, such as those performed by the Planck satellite.
- OSTI ID:
- 21455237
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 189, Issue 1; Other Information: DOI: 10.1088/0067-0049/189/1/1; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
AXIAL SYMMETRY
BL LACERTAE OBJECTS
CATALOGS
DEPOLARIZATION
FARADAY EFFECT
FLUX DENSITY
GALAXIES
GALAXY NUCLEI
GAMMA RADIATION
LUMINOSITY
POLARIMETERS
POLARIZATION
QUASARS
RELICT RADIATION
SATELLITES
STOKES PARAMETERS
TELESCOPES
WAVELENGTHS
COSMIC RADIO SOURCES
DOCUMENT TYPES
ELECTROMAGNETIC RADIATION
IONIZING RADIATIONS
MICROWAVE RADIATION
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
SYMMETRY