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Title: Magnetic field disorder and faraday effects on the polarization of extragalactic radio sources

Abstract

We present a polarization catalog of 533 extragalactic radio sources that have a 2.3 GHz total intensity above 420 mJy from the S-band Polarization All Sky Survey, S-PASS, with corresponding 1.4 GHz polarization information from the NRAO VLA Sky Survey, NVSS. We studied the selection effects and found that fractional polarization, π, of radio objects at both wavelengths depends on the spectral index, the source magnetic field disorder, the source size, and depolarization. The relationship between depolarization, spectrum, and size shows that depolarization occurs primarily in the source vicinity. The median π{sub 2.3} of resolved objects in NVSS is approximately two times larger than that of unresolved sources. Sources with little depolarization are ∼2 times more polarized than both highly depolarized and re-polarized sources. This indicates that intrinsic magnetic field disorder is the dominant mechanism responsible for the observed low fractional polarization of radio sources at high frequencies. We predict that number counts from polarization surveys will be similar at 1.4 GHz and at 2.3 GHz, for fixed sensitivity, although ∼10% of all sources may currently be missing because of strong depolarization. Objects with π{sub 1.4}≈π{sub 2.3}⩾4% typically have simple Faraday structures, so they are most useful for background samples.more » Almost half of flat-spectrum (α⩾−0.5) and ∼25% of steep-spectrum objects are re-polarized. Steep-spectrum, depolarized sources show a weak negative correlation of depolarization with redshift in the range 0 < z < 2.3. Previous non-detections of redshift evolution are likely due the inclusion of re-polarized sources as well.« less

Authors:
;  [1]; ;  [2]; ;  [3];  [4]
  1. Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States)
  2. Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)
  3. INAF—Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (Canada) (Italy)
  4. Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, NL-6500 GL Nijmegen (Netherlands)
Publication Date:
OSTI Identifier:
22868695
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 829; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; CATALOGS; CORRELATIONS; COSMIC RADIO SOURCES; DEPOLARIZATION; DETECTION; FARADAY EFFECT; GALACTIC EVOLUTION; GALAXIES; GHZ RANGE; INCLUSIONS; MAGNETIC FIELDS; POLARIZATION; RED SHIFT; SPECTRA

Citation Formats

Lamee, Mehdi, Rudnick, Lawrence, Farnes, Jamie S., Gaensler, B. M., Carretti, Ettore, Poppi, Sergio, and Haverkorn, Marijke. Magnetic field disorder and faraday effects on the polarization of extragalactic radio sources. United States: N. p., 2016. Web. doi:10.3847/0004-637X/829/1/5.
Lamee, Mehdi, Rudnick, Lawrence, Farnes, Jamie S., Gaensler, B. M., Carretti, Ettore, Poppi, Sergio, & Haverkorn, Marijke. Magnetic field disorder and faraday effects on the polarization of extragalactic radio sources. United States. https://doi.org/10.3847/0004-637X/829/1/5
Lamee, Mehdi, Rudnick, Lawrence, Farnes, Jamie S., Gaensler, B. M., Carretti, Ettore, Poppi, Sergio, and Haverkorn, Marijke. 2016. "Magnetic field disorder and faraday effects on the polarization of extragalactic radio sources". United States. https://doi.org/10.3847/0004-637X/829/1/5.
@article{osti_22868695,
title = {Magnetic field disorder and faraday effects on the polarization of extragalactic radio sources},
author = {Lamee, Mehdi and Rudnick, Lawrence and Farnes, Jamie S. and Gaensler, B. M. and Carretti, Ettore and Poppi, Sergio and Haverkorn, Marijke},
abstractNote = {We present a polarization catalog of 533 extragalactic radio sources that have a 2.3 GHz total intensity above 420 mJy from the S-band Polarization All Sky Survey, S-PASS, with corresponding 1.4 GHz polarization information from the NRAO VLA Sky Survey, NVSS. We studied the selection effects and found that fractional polarization, π, of radio objects at both wavelengths depends on the spectral index, the source magnetic field disorder, the source size, and depolarization. The relationship between depolarization, spectrum, and size shows that depolarization occurs primarily in the source vicinity. The median π{sub 2.3} of resolved objects in NVSS is approximately two times larger than that of unresolved sources. Sources with little depolarization are ∼2 times more polarized than both highly depolarized and re-polarized sources. This indicates that intrinsic magnetic field disorder is the dominant mechanism responsible for the observed low fractional polarization of radio sources at high frequencies. We predict that number counts from polarization surveys will be similar at 1.4 GHz and at 2.3 GHz, for fixed sensitivity, although ∼10% of all sources may currently be missing because of strong depolarization. Objects with π{sub 1.4}≈π{sub 2.3}⩾4% typically have simple Faraday structures, so they are most useful for background samples. Almost half of flat-spectrum (α⩾−0.5) and ∼25% of steep-spectrum objects are re-polarized. Steep-spectrum, depolarized sources show a weak negative correlation of depolarization with redshift in the range 0 < z < 2.3. Previous non-detections of redshift evolution are likely due the inclusion of re-polarized sources as well.},
doi = {10.3847/0004-637X/829/1/5},
url = {https://www.osti.gov/biblio/22868695}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 829,
place = {United States},
year = {2016},
month = {9}
}