J/A+A/665/A71 JVLA Observations of Chandra Planck clusters (Osinga+, 2022)
The detection of cluster magnetic fields via radio source depolarisation.
Osinga E., van Weeren R.J., Andrade-Santos F., Rudnick L., Bonafede A.,
Clarke T., Duncan K., Giacintucci S., Mroczkowski T., Roettgering H.J.A.
<Astron. Astrophys. 665, A71 (2022)>
=2022A&A...665A..71O 2022A&A...665A..71O (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Polarization ; Magnetic fields ;
Radio continuum
Keywords: magnetic fields - polarization - galaxies: clusters: general -
galaxies: clusters, intracluster medium -
radiation mechanisms: non-thermal - methods: observational
Abstract:
It has been well established that galaxy clusters have magnetic
fields. The exact properties and origin of these magnetic fields are
still uncertain even though these fields play a key role in many
astrophysical processes. Various attempts have been made to derive the
magnetic field strength and structure of nearby galaxy clusters using
Faraday rotation of extended cluster radio sources. This approach
needs to make various assumptions that could be circumvented when
using background radio sources. However, because the number of
polarised radio sources behind clusters is low, at the moment such a
study can only be done statistically. In this paper, we investigate
the depolarisation of radio sources inside and behind clusters in a
sample of 124 massive clusters at z<0.35 observed with the Karl G.
Jansky Very Large Array. We detect a clear depolarisation trend with
the cluster impact parameter, with sources at smaller projected
distances to the cluster centre showing more depolarisation. By
combining the radio observations with ancillary X-ray data from
Chandra, we compare the observed depolarisation with expectations from
cluster magnetic field models using individual cluster density
profiles. The best-fitting models have a central magnetic field
strength of 5-10uG with power-law indices between n=1 and n=4. We find
no strong difference in the depolarisation trend between sources
embedded in clusters and background sources located at similar
projected radii, although the central region of clusters is still
poorly probed by background sources. We also examine the
depolarisation trend as a function of cluster properties such as the
dynamical state, mass, and redshift. We see a hint that dynamically
disturbed clusters show more depolarisation than relaxed clusters in
the r>0.2R500 region. In the core region, we did not observe enough
sources to detect a significant difference between cool-core and
non-cool-core clusters. Our findings show that the statistical
depolarisation of radio sources is a good probe of cluster magnetic
field parameters. Cluster members can be used for this purpose as well
as background sources because the local interaction between the radio
galaxies and the intracluster medium does not strongly affect the
observed depolarisation trend.
Description:
In this paper, we investigate the depolarisation of radio sources
inside and behind clusters in a sample of 124 massive clusters at
z<0.35 observed with the Karl G. Jansky Very Large Array. We detect a
clear depolarisation trend with the cluster impact parameter, with
sources at smaller projected distances to the cluster centre showing
more depolarisation.
We present VLA L-band (1-2GHz) observations of 124 Planck clusters at
z<0.35 and DEC>-40 deg (VLA project code 15A-270). The observations
were taken in the B(nA) array configuration for about 40 minutes per
target. These catalogues contain the results of the source finding in
both full intensity (Stokes I) and linearly polarised intensity, as
well as the polarisation properties determined from QU-fitting. They
also contain additional information about the location of the optical
host and redshift.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablec1.dat 303 819 Polarised source catalogue
tabled1.dat 388 6807 Full source catalogue (unpolarised)
tablee1.dat 170 124 Cluster catalogue
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Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 deg RAdeg [] Source right ascension (J2000) (RA)
10- 16 F7.3 deg DEdeg Source declination (J2000) (DEC)
18- 23 F6.3 arcsec Maj Source major axis (Maj)
25- 30 F6.3 arcsec Min Source minor axis (Min)
32- 38 F7.3 deg PA [] Source position angle (PA)
40- 44 F5.3 --- PFExtDepol ? Best fit intrinsic polarisation
fraction (PolFrac_ExtDepol)
47- 51 F5.3 --- e_PFExtDepol ? Lower error (PolFracErrNegExtDepol)
53- 57 F5.3 --- E_PFExtDepol ? Upper error (PolFracErrPosExtDepol)
59- 63 F5.3 rad IAExtDepol ? Best fit intrinsic polarisation angle
(IntrAngl_ExtDepol)
66- 70 F5.3 rad e_IAExtDepol ? Lower error (IntrAnglErrNegExtDepol)
72- 76 F5.3 rad E_IAExtDepol ? Upper error (IntrAnglErrPosExtDepol)
78- 86 F9.3 rad/m2 RMExtDepol ? Best fit RM (RM_ExtDepol)
89- 96 F8.3 rad/m2 e_RMExtDepol ? Lower error (RMErrNegExtDepol)
98-105 F8.3 rad/m2 E_RMExtDepol ? Upper error (RMErrPosExtDepol)
107-114 F8.3 rad/m2 sigRMExtDepol ? Best fit depol (sigmaRM)
(sigmaRM_ExtDepol)
117-124 F8.3 rad/m2 e_sigRMExtDepol ? Lower error (sigmaRMErrNegExtDepol)
126-136 F11.3 rad/m2 E_sigRMExtDepol ? Upper error (sigmaRMErrPosExtDepol)
138-145 F8.3 mJy I0ExtDepol ? Best fit I0 (I0ExtDepol)
148-153 F6.3 mJy e_I0ExtDepol ? Lower error (I0ErrNeg_ExtDepol)
155-160 F6.3 mJy E_I0ExtDepol ? Upper error (I0ErrPos_ExtDepol)
162-167 F6.3 --- aExtDepol ? Best fit spectral index (a_ExtDepol)
170-174 F5.3 --- e_aExtDepol ? Lower error (aErrNegExtDepol)
176-180 F5.3 --- E_aExtDepol ? Upper error (aErrPosExtDepol)
182-190 F9.3 --- chi2QU ? Chi2 value for QU fit (chi2_QU)
192-196 F5.3 --- bestz ? Best-estimate redshift (z) (bestz)
198-202 F5.3 --- e_bestz ? Error on best-estimate z (bestz_err)
204 I1 --- r_bestz [0/4]? Source of best estimate z
(bestz_source) (1)
206-210 F5.3 --- rnorm ? Radius/R500 to cluster centre (rnorm)
212-217 F6.3 arcmin thetap Radius to pointing centre (theta_p)
219-231 A13 --- Cluster Name of target cluster (Cluster)
233-239 F7.3 deg RAodeg ? Best estimate optical host
right ascension (J2000) (ra_opthost)
241-247 F7.3 deg DEodeg ? Best estimate host declination (J2000)
(dec_opthost)
249 I1 --- MultiFlag [0/1] If Source is multicomponent
(MultiCompFlag)
251 I1 --- Flagged [0/1] If Source was flagged (Flagged)
253-303 A51 --- Note Additional notes (Note)
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Note (1): References as follows:
0 = NED/Literature (spectroscopic)
1 = SDSS (spectroscopic)
2 = Legacy (photometric)
3 = PANSTARRS (photometric)
4 = SDSS (photometric)
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Byte-by-byte Description of file: tabled1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 21 F21.16 deg RAdeg [] Source right ascension (J2000) (RA)
23- 43 F21.17 deg DEdeg Source declination (J2000) (DEC)
45- 63 F19.16 arcsec Maj Source major axis (Maj)
65- 83 F19.16 arcsec Min Source minor axis (Min)
85-107 F23.19 deg PA Source position angle (PA)
109-130 E22.15 mJy Ftot Source total flux from PyBDSF (Total_flux)
132-153 E22.16 mJy e_Ftot Error on total flux (ETotalflux)
155-176 E22.15 mJy/beam Fpeak Source peak flux from PyBDSF (Peak_flux)
178-199 E22.16 mJy/beam e_Fpeak Error on peak flux (EPeakflux)
201-220 F20.18 --- bestz ? Best estimate redshift (bestz)
222-241 E20.6 --- e_bestz ? Error on best estimate redshift
(bestz_err)
243 I1 --- r_bestz [0/4]? Source of best estimate z
(bestz_source)
245-257 A13 --- Cluster Name of target cluster (GLLL.ll+BB.bbb)
(Cluster)
259-279 F21.19 --- PFlim ? Upper limit on polfrac at 1.5 GHz
(polfrac_uplim)
281-300 F20.18 --- rnorm ? Radius/R500 to cluster centre (rnorm)
302-321 F20.17 arcmin thetap Radius to pointing centre (theta_p)
323 I1 --- VisIns [0/1] If Source was visually inspected
(VisuallyInspected)
325-342 F18.14 deg RAodeg ? Optical counterpart right ascension
(J2000) (ra_opthost)
344-362 F19.15 deg DEodeg ? Optical counterpart declination (J2000)
(dec_opthost)
364 I1 --- MultiFlag [0/1] If Source has multiple components
(MultiCompFlag)
366-388 A23 --- Note Addtional notes (Note)
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Byte-by-byte Description of file: tablee1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Cluster Cluster name in paper (GLLL.ll+BB.bbb)
(Cluster)
15- 27 A13 --- PSZ2 Cluster name in PESZ catalogue (PSZ2 Name)
29- 36 A8 --- Abell Cluster name in Abell catalogue (Abell name)
38- 56 F19.15 deg RAdeg Cluster right ascension (J2000) from X ray
(cRA)
58- 77 F20.16 deg DEdeg Cluster declination (J2000) from X ray (cDEC)
79- 98 F20.18 --- cz ? Cluster redshift (cz)
100-116 F17.12 deg RApdeg Pointing right ascension (J2000) used on
target (pRA)
118-134 F17.13 deg DEpdeg Pointing declination (J2000) used on
target (pDEC)
136-144 F9.6 --- M500 ? Cluster M500 (M500)
146-163 F18.16 --- R500 ? Cluster R500 (R500)
165-168 A4 --- DS-CSB Cluster dynamical state according to C_SB
(DS_CSB)
170 I1 --- RadioHalo [0/1] If the cluster has a radio halo
(RadioHalo)
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Acknowledgements:
Erik Osinga, osinga(at)strw.leidenuniv.nl
(End) Erik Osinga [Univ. Leiden], Patricia Vannier [CDS] 20-Jul-2022