Abstract
Knowing how the ambient medium in the vicinity of active galactic nuclei (AGNs) is shaped is crucial to understanding generally the evolution of such cosmic giants as well as AGN jet formation and launching. Thanks to the new broadband capability now available at the Jansky Very Large Array (JVLA), we can study changes in polarization properties, fractional polarization, and polarization angles, together with the total intensity spectra of a sample of 14 AGNs, within a frequency range from 1 to 12 GHz. Depolarization modeling has been performed by means of so-called “qu-fitting” to the polarized data, and a synchrotron self absorption model has been used for fitting to the total intensity data. We found complex behavior both in the polarization spectra and in the total intensity spectra, and several Faraday components with a large rotation measure (RM) and several synchrotron components were needed to represent these spectra. Here, results for three targets are shown. This new method of analyzing broadband polarization data through qu-fitting successfully maps the complex surroundings of unresolved objects.
Highlights
Active galactic nuclei (AGNs) are powerful objects that are fed by supermassive black holes (SMBHs) at their centers
The sample and data reduction are briefly described in Section 2; an explanation on how the qu-fitting has been performed appears in Section 3; results and discussion are given in Section 4, and Section 5 concludes
P0j e2i(χ0j + RMj λ ) sinc(∆rotation measure (RM) j λ2 )e j=1,n where j represents the several Faraday components used for the fitting, p0j is the intrinsic fractional polarization, χ0j is the intrinsic polarization angle, and ∆RM j and σRMj describe the variation of the RM in a regular and turbulent magnetic field, respectively
Summary
Active galactic nuclei (AGNs) are powerful objects that are fed by supermassive black holes (SMBHs) at their centers. Understanding how the surroundings of these powerful radio objects are shaped, how the emitted radio components (i.e., jets and lobes) interact with the ambient medium, is important for studying the evolution and feedback of this class of objects and for understanding the formation and launching mechanism of the radio jets This can be done by studying broadband polarization data. As suggested by the authors of [8], in order to extract information about the magneto-ionic medium, it is necessary to study and model the fractional polarization p(λ2 ) and the polarization angle χ(λ2 ) in the lambda-squared domain, the so-called “qu-fitting.” Recently has this new method been successfully performed (e.g., [5]), thanks to the updated radio receivers at some of the radio observatories. The sample and data reduction are briefly described in Section 2; an explanation on how the qu-fitting has been performed appears in Section 3; results and discussion are given in Section 4, and Section 5 concludes
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