Role of Intervening Mg ii Absorbers on the Rotation Measure and Fractional Polarization of the Background Quasars

We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening Mg ii absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute devi...

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Bibliographic Details
Published in:The Astrophysical journal 2020-02, Vol.890 (2), p.132
Main Authors: Malik, Sunil, Chand, Hum, Seshadri, T. R.
Format: Article
Language:English
Subjects:
Absorbers
Astrophysics
Correlation
Correlation analysis
Equipartition theorem
Extragalactic astronomy
Galactic rotation
Galaxies
Galaxy
Local group (astronomy)
Magnetic Fields
Mg II Absorber
Polarization
Quasars
Red shift
Rotation Measure
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Summary:We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening Mg ii absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean ( ), and found it to be 17.1 0.7 rad m−2 for 352 sightlines having Mg ii intervening absorbers in comparison to its value of 15.1 0.6 rad m−2 for 780 sightlines without such absorbers, resulting in an excess broadening ( ) of 8.0 1.9 rad m−2 among these two subsamples. This value of , has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg ii absorbers, to be ∼1.3 0.3 G at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, (with F ∝ ), for flat ( ≥ −0.3; 315 sources) and steep ( ≤ −0.7; 476 sources) spectrum sources shows a significant (at 3.5 level) for the former and absent in the latter. An anticorrelation found between the and percentage polarization (p) with a similar Pearson correlation of −0.62 and −0.87 for subsamples with and without Mg ii, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ab6bd5