J/A+A/650/A44 ACS J1149.5+2223 LOFAR and VLA images (Bruno+, 2021)
The LOFAR and JVLA view of the distant steep spectrum radio halo in
MACS J1149.5+2223.
Bruno L., Rajpurohit K., Brunetti G., Gastaldello F., Botteon A.,
Ignesti A., Bonafede A., Dallacasa D., Cassano R., van Weeren R.J.,
Cuciti V., Di Gennaro G., Shimwell T., Brueggen M.
<Astron. Astrophys. 650, A44 (2021)>
=2021A&A...650A..44B 2021A&A...650A..44B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radio sources
Keywords: radiation mechanisms: thermal - radiation mechanisms: non-thermal -
acceleration of particles - large-scale structure of Universe -
galaxies: clusters: individual: MACS J1149.5+2223
Abstract:
Radio halos and relics are Mpc-scale diffuse radio sources in galaxy
clusters, which have a steep spectral index α>1 (defined
as S∝ν-α). It has been proposed that halos and
relics arise from particle acceleration induced by turbulence and weak
shocks that are injected into the intracluster medium (ICM) during
mergers.
MACS J1149.5+2223 is a high-redshift (z=0.544) galaxy cluster
possibly hosting a radio halo and a relic. We analysed LOw Frequency
Array (LOFAR), Giant Metrewave Radio Telescope, and Karl G. Jansky
Very Large Array (JVLA) radio data at 144, 323, and 1500MHz,
respectively. In addition, we analysed archival Chandra X-ray data to
characterise the thermal and non-thermal properties of the cluster.
We obtained radio images at different frequencies to investigate the
spectral properties of the radio halo. We used Chandra X-ray images to
constrain the thermal properties of the cluster and to search for
discontinuities (due to cold fronts or shock fronts) in the surface
brightness of the ICM. By combining radio and X-ray images, we carried
out a point-to-point analysis to study the connection between the
thermal and non-thermal emission.
We measured a steep spectrum of the halo, which can be described by a
power-law with α=1.49±0.12 between 144 and 1500MHz. The
radio surface brightness distribution across the halo is found to
correlate with the X-ray brightness of the ICM. The derived
correlation shows a sub-linear slope in the range 0.4-0.6. We also
report two possible cold fronts in north-east and north-west, but
deeper X-ray observations are required to firmly constrain the
properties of the upstream emission.
We show that the combination of high-redshift, steep radio spectrum,
and sub-linear radio-X scaling of the halo rules out hadronic models.
An old (∼1Gyr ago) major merger likely induced the formation of the
halo through stochastic re-acceleration of relativistic electrons. We
suggest that the two possible X-ray discontinuities may be part of the
same cold front. In this case, the coolest gas pushed towards the
north-west might be associated with the cool core of a sub-cluster
involved in the major merger. The peculiar orientation of the
south-east relic might indicate a different nature of this source and
requires further investigation.
Description:
We analysed archival Chandra X-ray data (first presented by Ogrean et
al., 2016ApJ...819..113O 2016ApJ...819..113O) of MACS J1149, observed in VFAINT mode with
ACIS-I.
We retrieved archival GMRT data (first presented by Bonafede
et al., 2012MNRAS.426...40B 2012MNRAS.426...40B) in the 305-340 MHz band, for a total
bandwidth of 32MHz, split into 256 channels.
Observations of the LOFAR Two-meter Sky Survey (LoTSS; Shimwell et al.
2017, Cat. J/A+A/598/A104, 2019, Cat. J/A+A/622/A1 ) are particularly
suitable for the detection of extended and low brightness diuse
emission with steep spectrum, such as radio halos and radio relics.
MACS J1149 was observed with the JVLA at 1-2GHz (L-band) in B, C, and
D configurations, for 5.5, 2.5, and 1.5 hours onsource time,
respectively with 3C286 as flux density calibrator and J1150+2417 as
phase calibrator.
The name of each radio map reports the instrument, the frequency, and
the resolution. The name of the X-ray map reports the instrument and
the band.
Objects:
--------------------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------------------
11 49 35.8 +22 23 55 MACS J1149.5+2223 = MCS J1149.5+2223
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 147 6 List of fits images
fits/* . 6 Individual fits images
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See also:
J/ApJ/817/60 : Multiply imaged supernova Refsdal (Treu+, 2016)
J/A+A/597/A41 : ALMA Frontier Fields Survey. I. (Gonzalez-Lopez+, 2017)
J/ApJ/854/73 : Full-data results of HFF: galaxies z∼6-9 (Ishigaki+, 2018)
J/A+A/633/A160 : ALMA Frontier Fields Survey. V. (Carvajal+, 2020)
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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 48 A21 "datime" Obs.date Observation date
50- 57 F8.3 MHz Freq ? Observed frequency
59- 62 I4 Kibyte size Size of FITS file
64-100 A37 --- FileName Name of FITS file, in subdirectory fits
102-147 A46 --- Title Title of the FITS file
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Acknowledgements:
Luca Bruno, luca.bruno4(at)unibo.it
(End) Patricia Vannier [CDS] 18-Mar-2021