J/A+A/657/A2 MACS J0717.5+3745 polarization int. maps (Rajpurohit+, 2022)
Turbulent magnetic fields in the merging galaxy cluster MACS J0717.5+3745.
Rajpurohit K., Hoeft M., Wittor D., van Weeren R.J., Vazza F., Rudnick L.,
Rajpurohit S., Forman W.R., Riseley C.J., Brienza M., Bonafede A.,
Rajpurohit A.S., Dominguez-Fernandez P., Eilek J., Bonnassieux E.,
Brueggen M., Loi F., Roettgering H.J.A., Drabent A., Locatelli N.,
Botteon A., Brunetti G., Clarke T.E.
<Astron. Astrophys. 657, A2 (2022)>
=2022A&A...657A...2R 2022A&A...657A...2R (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radio sources ; Polarization
Keywords: galaxies: clusters: general - radiation mechanism: non-thermal -
polarization - acceleration of particles - magnetic field -
large-scale structures of Universe
Abstract:
We present wideband (1-6.5 GHz) polarimetric observations, obtained
with the Karl G. Jansky Very Large Array (VLA), of the merging galaxy
cluster MACS J0717.5+3745, which hosts one of the most complex known
radio relic and halo systems. We use both Rotation Measure Synthesis
and QU-fitting, and find a reasonable agreement of the results
obtained with these methods, in particular, when the Faraday
distribution is simple and the depolarization is mild. The relic is
highly polarized over its entire length (850kpc), reaching a
fractional polarization >30% in some regions. We also observe a strong
wavelength-dependent depolarization for some regions of the relic. The
northern part of the relic shows a complex Faraday distribution
suggesting that this region is located in or behind the intracluster
medium (ICM). Conversely, the southern part of the relic shows a
Rotation Measure very close to the Galactic foreground, with a rather
low Faraday dispersion, indicating very little magnetoionic material
intervening the line-of-sight. From spatially resolved polarization
analysis, we find that the scatter of Faraday depths correlates with
the depolarization, indicating that the tangled magnetic field in the
ICM causes the depolarization. We conclude that the ICM magnetic field
could be highly turbulent. At the position of a well known
narrow-angle-tailed galaxy (NAT), we find evidence of two components
clearly separated in Faraday space. The high Faraday dispersion
component seems to be associated with the NAT, suggesting the NAT is
embedded in the ICM while the southern part of the relic lies in front
of it. If true, this implies that the relic and this radio galaxy are
not necessarily physically connected and thus, the relic may be not
powered by the shock re-acceleration of fossil electrons from the NAT.
The magnetic field orientation follows the relic structure indicating
a well-ordered magnetic field. We also detect polarized emission in
the halo region; however the absence of significant Faraday rotation
and a low value of Faraday dispersion suggests the polarized emission,
previously considered as the part of the halo, has a shock(s) origin.
Description:
The radio observations were performed with the Karl G. Jansky Very
Large Array (VLA) in L, C, and S band. The total on-source observation
time was 40h covering a frequency range of 1-6.5 GHz.
Objects:
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RA (2000) DE Designation(s)
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07 17 35.58 +37 45 21.35 MACSJ0717+3745 = MCS J0717.5+3745
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 169 3 List of fits images
fits/* . 3 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 50 A21 "datime" Obs.date Observation date
52- 56 I5 Kibyte size Size of FITS file
58-100 A43 --- FileName Name of FITS file, in subdirectory fits
102-169 A68 --- Title Title of the FITS file
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Acknowledgements:
Kamlesh Rajpurohit, kamlesh.rajpurohit(at)unibo.it
(End) Patricia Vannier [CDS] 03-Dec-2021