Polarization in the radio galaxy 3C 109 - an obscured quasar

Abstract

view Abstract Citations (40) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polarization in the Radio Galaxy 3C 109---An Obscured Quasar Goodrich, Robert W. ; Cohen, Marshall H. Abstract The broad-line radio galaxy 3C 109 is one of the most highly polarized active galaxies known, outside of the "blazars." We present data from a newly commissioned spectropolarimeter on the Hale 5 m telescope which convincingly demonstrate that the continuum and broad-line region are polarized by transmission through aligned dust grains within the host galaxy of 3C 109 itself. The wavelength dependence of the polarization is well fitted by a combination of two Serkowski laws, one representing polarization within our own Galaxy and the other representing polarization at the redshift of 3C 109. The large Balmer decrement of the broad lines also indicates the presence of reddening by dust. The narrow emission lines, such as [O III] λλ4959, 5007, are relatively unpolarized; the implications for the location of the dust are discussed. When dereddened by the implied minimum amount of intervening dust, the continuum becomes very blue (α = 1.0 +/- 0.3, where f_v_ is proportional to valpha^. This is comparable to (2 σ higher than) the bluest slopes seen in other quasars, α ~ 0.5. It almost certainly indicates that the dust grains in 3C 109 have a high polarizing ability, at least as great as the highest seen in our own interstellar medium. When extinction by the intervening dust is taken into account, the absolute V-magnitude of 3C 109 becomes -26.6 or brighter, placing it well into the "quasar" luminosity range. Although classified as an N galaxy by several authors, if the nucleus were seen unobscured, the surrounding galaxy would be invisible on ground-based images, and we would classify the object as a quasar. The radio spectrum and morphology suggest that the radio jets are fairly close to the plane of the sky. These results generally support the view that many radio galaxies may be quasars with their jets pointed away from our direct line of sight. Publication: The Astrophysical Journal Pub Date: June 1992 DOI: 10.1086/171376 Bibcode: 1992ApJ...391..623G Keywords: Active Galaxies; Cosmic Dust; Galactic Radio Waves; Interstellar Extinction; Polarization (Waves); Quasars; Radio Galaxies; Astronomical Polarimetry; Emission Spectra; Galactic Nuclei; Luminosity; Red Shift; Astrophysics; GALAXIES: INDIVIDUAL ALPHANUMERIC: 3C 109; GALAXIES: NUCLEI; INSTRUMENTATION: POLARIMETERS; ISM: DUST; EXTINCTION; POLARIZATION; RADIO CONTINUUM: GALAXIES full text sources ADS | data products SIMBAD (3) NED (1)