Polarization Structures in the Thomson-Scattered Emission Lines in Active Galactic Nuclei

Abstract

A line photon incident in an electron-scattering medium is transferred in a diffusive way both in real space and in frequency space, and the mean number of scatterings changes as the wavelength shifts from the line center. This leads to the profile broadening and polarization dependence on the wavelength shift as a function of the Thomson optical depth ${\tau }_T$. We find that the polarization of the Thomson-scattered emission lines has a dip around the line center when ${\tau }_T$ does not exceed a few. Various structures such as the polarization flip are also seen. An application to an ionized halo component surrounding the broad emission line region in active galactic nuclei is considered and it is found that the polarization structures may still persist. Brief discussions on observational implications are given.

14 pages, 3 figures, accepted for publication in ApJ Letters

References in corpus (5)

• Scattered Nuclear Continuum and Broad H-alpha in Cygnus A
• Polarization of the Lyman alpha line from an anisotropically expanding H~I shell in primeval galaxies
• Below the Lyman Edge: UV Polarimetry of Quasars
• On the Polarization of H-alpha Lines Scattered by Neutral Hydrogen in Active Galactic Nuclei
• Measuring the Virial Temperature of Galactic Halos Through Electron Scattering of Quasar Emission Lines

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• Unlocking the Full Potential of Extragalactic Ly$\alpha$ through Its Polarization Properties
• Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots
• Polarisation of the Broad H alpha Wing in Symbiotic Stars
• Revealing the Warm and Hot Halo Baryons via Thomson Scattering of Quasar Light