J/A+A/693/A99 Abell 655 radio images (Groeneveld+, 2025)
Serendipitous decameter detection of ultra-steep spectrum radio emission in
Abell 655.
Groeneveld C., van Weeren R.J., Botteon A., Cassano R., de Gasperin F.,
Osinga E., Brunetti G., Roettgering H.J.A.
<Astron. Astrophys. 693, A99 (2025)>
=2025A&A...693A..99G 2025A&A...693A..99G (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radio sources
Keywords: techniques: interferometric - galaxies: clusters: general -
radio continuum: general
Abstract:
Some galaxy clusters contain non-thermal synchrotron emitting plasma
permeating the intracluster medium (ICM). The spectral properties of
this radio emission are not well characterized at decameter
wavelengths (ν<30MHz), primarily due to the severe corrupting
effects of the ionosphere. Using a recently developed calibration
strategy, we present LOFAR images below 30MHz of the low mass galaxy
cluster Abell 655, which was serendipitously detected in an
observation of the bright calibrator 3C 196. We combine this
observation with LOFAR data at 144MHz, and new Band 4 Giant Metrewave
Radio Telescope observations centered at 650MHz. In the 15-30MHz LOFAR
image, diffuse emission is seen with a physical extent of about
700kpc. We argue that the diffuse emission detected in this galaxy
cluster likely has multiple origins. At higher frequencies (650MHz),
the diffuse emission resembles a radio halo, while at lower
frequencies the emission seems to consist of several components and
bar-like structures. It suggests that most low-frequency emission in
this cluster comes from re-energized fossil plasma from old AGN
outbursts, coexisting with the radio halo component. By counting the
number of cluster radio detections in the decameter band, we estimate
that around a quarter of the Planck clusters host re-energised fossil
plasma that is detectable in the decameter band with LOFAR.
Description:
A655 was detected by LOFAR with an 8-hour scan of 3C196. The
observation ran on October 28, 2020, with a frequency coverage between
12-60MHz. The flux density scale for the LOFAR maps are pinned to the
Scaife and Heald (2012MNRAS.423L..30S 2012MNRAS.423L..30S) flux density scale. The lowest
3MHz were discarded as the flux density scale was not stable across
the field of view.
The GMRT Band 4 map is obtained from proposal id. 43_023,
PI R. Cassano.
Objects:
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RA (2000) DE Designation(s)
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08 25 16.11 +47 09 34.2 A655 = Abell 655
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 103 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- 59 F8.4 MHz Freq Observation frequency
61- 65 I5 Kibyte size Size of FITS file
67- 78 A12 --- FileName Name of FITS file, in subdirectory fits
80-103 A24 --- Title Title of the FITS file
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Acknowledgements:
Christian Groeneveld, groeneveld(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 06-Dec-2024