J/A+A/677/A4 Radio images of NGC 6086 (Candini+, 2023)
New filamentary remnant radio emission and duty cycle constraints in the
radio galaxy NGC 6086.
Candini S., Brienza M., Bonafede A., Rajpurohit K., Biava N., Murgia M.,
Loi F., van Weeren R.J., Vazza F.
<Astron. Astrophys. 677, A4 (2023)>
=2023A&A...677A...4C 2023A&A...677A...4C (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, radio ; Radio continuum
Keywords: radiation mechanisms: non-thermal - radio continuum: galaxies -
galaxies: active - galaxies: groups: general -
galaxies: individual: NGC 6086
Abstract:
Radio galaxies are a subclass of active galactic nuclei (AGN) in which
accretion onto the supermassive black hole releases energy into the
environment via relativistic jets. The jets are not constantly active
throughout the life of the host galaxy and alternate between active
and quiescent phases. Remnant radio galaxies are detected during a
quiescent phase and define a class of unique sources that can be used
to constrain the AGN duty cycle.
We present, for the first time, a spatially resolved radio analysis of
the radio galaxy associated with the galaxy NGC 6086 down to 144MHz
and constraints on the spectral age of the diffuse emission to
investigate the duty cycle and evolution of the source.
We used three new low-frequency, high-sensitivity observations; the
first was performed with the Low Frequency Array at 144MHz and the
other two with the upgraded Giant Metrewave Radio Telescope at 400MHz
and 675MHz, respectively. To these, we add two Very Large Array
archival observations at higher frequencies (1400 and 4700MHz).
In the new observations in the frequency range 144-675MHz, we detect a
second pair of larger lobes and three regions within the remnant
emission with a filamentary morphology. We analysed the spectral index
trend in the inner remnant lobes and see systematically steeper values
αlow∼1.1-1.3) at the lower frequencies compared to the
gigahertz frequencies (αhigh∼0.8-0.9). Steeper spectral
indices are found in the newly detected outer lobes (up to
αouter∼2.1), as expected if they trace a previous phase of
activity of the AGN. However, the differences between the spectra of
the two outer lobes suggest different dynamical evolutions within the
intra-group medium during their expansion and/or different magnetic
field values.
Using a single-injection radiative model and assuming equipartition
conditions, we place constraints on the age of the inner and outer
lobes and derive the duty cycle of the source. We estimate that the
duration of the two active phases was 45Myr and 18Myr and the
duration of the two inactive phases was 66Myr and 33Myr. This
results in a total active time of ton∼39%.
The filamentary structures have a steep spectral index (∼1)
without any spectral index trend, and only one of them shows a
steepening in the spectrum. Their origin is not yet clear, but they
may have formed due to the compression of the plasma or due to
magnetic field substructures.
Description:
The target has been observed by LOFAR with the High Frequency
Antennas at a central frequency of 144 MHz as part of LoTSS (LOFAR
Two-metre Sky Survey, (Shimwell et al., 2017A&A...598A.104S 2017A&A...598A.104S, Cat.
J/A+A/598/A104)).
We observed the target with the uGMRT in September 2020, in
both band-3 (300-500MHz) and band-4 (550-950MHz).
We selected archival VLA observations to expand the frequency
coverage of the source above 675MHz, as needed for a more detailed
spectral analysis. We selected two datasets where NGC 6086 was
observed at 1.4GHz with B and C array configurations and a second
dataset at 4.7GHz with the D array configuration.
Objects:
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RA (2000) DE Designation(s)
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16 12 35.53 +29 29 05.2 NGC 6086 = UGC 10270
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 177 5 List of fits images
fits/* . 5 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- 55 A26 "datime" Obs.date Observation date
57- 63 F7.3 MHz Freq ? Observed frequency
65- 69 I5 Kibyte size Size of FITS file
71-130 A60 --- FileName Name of FITS file, in subdirectory fits
132-177 A46 --- Title Title of the FITS file
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Acknowledgements:
Simone Candini, simone.candini(at)studio.unibo.it
(End) Patricia Vannier [CDS] 06-Jul-2023