J/A+A/697/A45 HCG 15 radio images (Riseley+, 2025)
Relighting the fire in Hickson Compact Group (HCG) 15.
Magnetised fossil plasma revealed by the SKA Pathfinders and Precursors,
Riseley C.J., Vernstrom T., Lovisari L., O'Sullivan E., Gastaldello F.,
Brienza M., Nayak P.K., Bonafede A., Carretti E., Duchesne S.W.,
Giacintucci S., Hopkins A.M., Koribalski B.S., Loi F., Pfrommer C., Raja W.,
Ross K., Rubinur K., Ruszkowski M., Shimwell T.W., de Villiers M.S.,
West J., Zovaro H.R.M., Akahori T., Anderson C.S., Bomans D.J., Drabent A.,
Rudnick L., Santra R.
<Astron. Astrophys. 697, A45 (2025)>
=2025A&A...697A..45R 2025A&A...697A..45R (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, group ; Radio continuum
Keywords: magnetic fields - galaxies: groups: individual: HCG15 -
radio continuum: general - X-rays: galaxies
Abstract:
In the context of the life cycle and evolution of active galactic
nuclei (AGNs), environment plays a key role. In particular, the
over-dense environments of galaxy groups, where dynamical interactions
and bulk motions have significant impact, offer an excellent but
under-explored window into the life cycles of AGNs and the processes
that shape the evolution of relativistic plasma. Pilot survey
observations with the Australian Square Kilometre Array Pathfinder
(ASKAP) Evolutionary Map of the Universe (EMU) survey have recovered
diffuse emission associated with the nearby (z=0.0228) galaxy group
HCG15, which was revealed to be strongly linearly polarised. We
studied the properties of this emission in unprecedented detail to
settle questions about its nature and its relation to the group-member
galaxies. We performed a multi-frequency spectropolarimetric study of
HCG15, incorporating our ASKAP EMU observations as well as new data
from MeerKAT, the LOw-Frequency ARray (LOFAR), Giant Metrewave Radio
Telescope (GMRT), and Karl G. Jansky Very Large Array (VLA), along
with X-ray data from XMM-Newton and optical spectra from Himalayan
Chandra Telescope (HCT). Our study confirms that the diffuse
structure represents remnant emission from historic AGN activity that
is likely to be associated with HCG15-D, some 80-86Myr ago (based
on an ageing analysis). We detected significant highly
linearly-polarised emission from a diffuse "ridge-like" structure
with a highly ordered magnetic field. Our analysis suggests that this
emission is generated by the draping of magnetic field lines in the
intra-group medium (IGrM). Subsequent investigations with simulations
would further improve our understanding of this phenomenon. We confirm
that HCG15-C is a group-member galaxy. Finally, we report the
detection of thermal emission associated with a background cluster at
a redshift of z ~=0.87 projected onto the IGrM of HCG15, which matches
the position and redshift of the recent Sunyaev-Zel'dovich (SZ)
detection of ACT-CL J0207.8+0209.
Description:
Radio images of HCG15 from LOFAR (145MHz), GMRT (325MHz and 610MHz),
ASKAP EMU (943MHz), MeerKAT S-band (2.4GHz) and VLA (5GHz and 7GHz).
All images are shown at 20 arcsecond resolution.
Objects:
--------------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------------
02 07 39.00 +02 08 17.9 HCG 15 = RASSCALS SRGb131
--------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 194 7 List of fits images
fits/* . 7 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- 50 A21 "datime" Obs.date Observation date
52- 55 I4 MHz Freq Observed frequency
57- 61 I5 Kibyte size Size of FITS file
63-101 A39 --- FileName Name of FITS file, in subdirectory fits
103-194 A92 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Chris Riseley, riseley(at)astro.ruhr-uni-bochum.de
(End) Patricia Vannier [CDS] 17-Apr-2025