J/A+A/663/A44 Subarcsecond view on GB6 B1508+5714 by the ILT (Kappes+, 2022)
Subarcsecond view on the high-redshift blazar GB 1508+5714 by the
International LOFAR Telescope.
Kappes A., Burd P.R., Kadler M., Ghisellini G., Bonnassieux E., Perucho M.,
Brueggen M., Cheung C.C., Ciardi B., Gallo E., Haardt F., Morabito L.K.,
Sbarrato T., Drabent A., Harwood J., Jackson N., Moldon J.
<Astron. Astrophys. 663, A44 (2022)>
=2022A&A...663A..44K 2022A&A...663A..44K (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Radio sources
Keywords: galaxies: active - galaxies: jets -
galaxies: individual: GB 1508+5714 - radio continuum: galaxies -
techniques: high angular resolution - techniques: interferometric
Abstract:
Studies of the most distant active galactic nuclei (AGNs) allow us to
test our current understanding of the physics present in radio-jetted
AGNs across a range of environments, and probe their interactions with
these environments. The decrease in apparent luminosity with distance
is the primary difficulty to overcome in the study of these distant
AGNs, which requires highly sensitive instruments.
Our goal is to employ new long wavelength radio data to better
parametrise the broad-band spectral energy distribution (SED) of
GB 1508+5714, a high-redshift (z=4.30) AGN. Its high redshift, high
intrinsic luminosity and classification as a blazar allow us to test
emission models that consider the efficient cooling of jet electrons
via inverse Compton losses in interactions with the dense cosmic
microwave background (CMB) photon field at high redshifts. A
significant detection of this effect in GB 1508+5714 may partly
explain the apparent sparsity of high-redshift radio galaxies in
wide-field surveys, detections of this kind are only becoming possible
with the current generation of Square Kilometre Array (SKA)
precursors.
We used the LOw-Frequency ARray (LOFAR) to image the long wavelength
radio emission around the high-redshift blazar GB 1508+5714 on
arcsecond scales at frequencies between 128MHz and 160MHz. This
allowed us to compare the spatially resolved structure with higher
frequency observations, and construct spectral index maps to study the
spectral properties of the different components.
The LOFAR image shows a compact unresolved core and two resolved
emission regions around 2 arcsec to the east and to the west of the
radio core. We find structure consistent with previous Very Large
Array (VLA) observations, as well as a previously unreported emission
region to the east. The region in the west shows a spectral index of
-1.2(+0.4,-0.2) while the region in the east indicates a spectral
index of ≲-1.1. The radio core features a flat spectral index of
0.02±0.01.
We interpret the arcsecond-scale radio structure of GB 1508+5714 as a
FR II-like radio galaxy at a small viewing angle, and the western
component as the region containing the approaching jet's terminal
hot spot while the eastern diffuse component near the core can be
interpreted as the counter-hot spot region. Our SED modelling shows
that a scenario featuring significant quenching effects caused by
interaction with the CMB provides a good description of the data, and
notably explains the suppressed radio emission.
Description:
LOFAR HBA observation of GB 1508+5714 on June 15, 2015 between 128MHZ
and 160MHZ. Flux calibrated with 3C 196. Observation duration: 4
hours.
Objects:
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RA (2000) DE Designation(s)
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15 10 02.92 +57 02 43.4 GB 1508+5714 = GB6 B1508+5714
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 119 1 Information on fits image
fits/* . 1 fits image
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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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 53 A26 "datime" Obs.date Observation date
55- 61 F7.3 MHz Freq Observed frequency
63- 66 I4 Kibyte size Size of FITS file
68- 79 A12 --- FileName Name of FITS file, in subdirectory fits
81-119 A39 --- Title Title of the FITS file
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Acknowledgements:
Alexander Kappes, alexander.kappes(at)uni-wuerzburg.de
(End) Patricia Vannier [CDS] 12-May-2022