J/A+A/649/A37 Abell 1775 radio images (Botteon+, 2021)
Non-thermal phenomena in the center of Abell 1775:
An 800 kpc head-tail, revived fossil plasma, and slingshot radio halo.
Botteon A., Giacintucci S., Gastaldello F., Venturi T., Brunetti G.,
van Weeren R.J., Shimwell T.W., Rossetti M., Akamatsu H., Brueggen M.,
Cassano R., Cuciti V., de Gasperin F., Drabent A., Hoeft M., Mandal S.,
Roettgering H.J.A., Tasse C.
<Astron. Astrophys. 649, A37 (2021)>
=2021A&A...649A..37B 2021A&A...649A..37B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; X-ray sources ; Radio sources
Keywords: radiation mechanisms: non-thermal - radiation mechanisms: thermal -
galaxies: clusters: general -
galaxies: clusters: intracluster medium - X-rays: galaxies: clusters -
radio continuum: galaxies
Abstract:
Thermal gas in the center of galaxy clusters can show substantial
motions that generate surface brightness and temperature
discontinuities known as cold fronts. The motions may be triggered by
minor or o-axis mergers that preserve the cool-core of the system. The
dynamics of the thermal gas can also generate radio emission from the
intra-cluster medium (ICM) and impact the evolution of clusters radio
sources.
We study the central region of Abell 1775, a system in an ambiguous
dynamical state at z=0.072 which is known to host an extended
head-tail radio galaxy, with the aim of investigating the connection
between thermal and non-thermal components in its center.
We made use of a deep (100ks) Chandra observation accompanied by
LOFAR 144MHz, GMRT 235MHz and 610MHz, and VLA 1.4GHz radio data.
We find a spiral-like pattern in the X-ray surface brightness that is
mirrored in the temperature and pseudo-entropy maps. Additionally, we
characterize an arc-shaped cold front in the ICM. We interpret these
features in the context of a slingshot gas tail scenario. The
structure of the head-tail radio galaxy "breaks" at the position
of the cold front, showing an extension that is detected only at low
frequencies, likely due to its steep and curved spectrum. We speculate
that particle re-acceleration is occurring in the outer region of this
tail, that in total covers a projected size of 800kpc. We also report
the discovery of revived fossil plasma with ultra-steep spectrum radio
emission in the cluster core together with a central diffuse radio
source that is bounded by the arc-shaped cold front.
The results reported in this work demonstrate the interplay between
thermal and non-thermal components in the cluster center and the
presence of ongoing particle re-acceleration in the ICM on different
scales.
Description:
A1775 was observed twice (ObsIDs: 12891, 13510) with Chandra ACIS-S in
VFAINT mode for a total exposure time of 100ks.
A1775 falls within 2.5 from the center of four pointings (P207+25,
P204+25, P207+27, P204+27) of the LOFAR Twometer Sky Survey (LoTSS;
Shimwell et al. 2017A&A...598A.104S 2017A&A...598A.104S, 2019A&A...622A...1S 2019A&A...622A...1S ). Each LoTSS
pointing is observed with the LOFAR High Band Antenna (HBA) array
operating at 120-168MHz and has an integration time of 8 hr book-ended
by 10 min flux calibrator scans.
We re-analyzed GMRT observations of A1775 at 235MHz and 610MHz that
were previously published in Giacintucci et al. (2017ApJ...841...71G 2017ApJ...841...71G).
The cluster was observed in 2005 for 100 minutes at 235MHz and in 2003
for 45 minutes at 610MHz, using the old hardware correlator and a
bandwidth of 8MHz and 16MHz, respectively. We refer to Giacintucci et
al. (2017ApJ...841...71G 2017ApJ...841...71G) for further details on these observations.
We obtained observations of A1775 at 1.4GHz from the VLA public
archive. The cluster was observed in 2001 using the D-array
configuration for a total of 1.4 hour (project AL0515) and in 2004 for
2.5 hour in C-configuration (project AV0265).
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
13 41 55.6 +26 21 53 Abell 1775 = ACO 1775
-------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 142 5 List of fits images
fits/* . 5 Individual fits images
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
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- 48 A19 "datime" Obs.date Observation date
50- 57 F8.3 MHz Freq ? Observed frequency
59- 62 I4 Kibyte size Size of FITS file
64- 83 A20 --- FileName Name of FITS file, in subdirectory fits
85-142 A58 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Andrea Botteon, botteon(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 05-Mar-2021