J/A+A/693/A172 NGC 315 VLBA maps (Ricci+, 2025)
Spectral and magnetic properties of the jet base in NGC 315.
Ricci L., Boccardi B., Roeder J., Perucho M., Mattia G., Kadler M.,
Benke P., Bartolini V., Krichbaum T.P., Madika E.
<Astron. Astrophys. 693, A172 (2025)>
=2025A&A...693A.172R 2025A&A...693A.172R (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Galaxies, radio ; VLBI
Keywords: techniques: high angular resolution - galaxies: active -
galaxies: individual: NGC 315 - galaxies: jets
Abstract:
The dynamic of relativistic jets in the inner parsec regions is deeply
affected by the nature of the magnetic fields. The level of
magnetization of the plasma, as well as the geometry of these fields
on compact scales, have not yet been fully constrained.
In this paper we employ multi-frequency and multi-epoch very long
baseline interferometry observations of the nearby radio galaxy NGC
315. We aim to derive insights into the magnetic field properties on
sub-parsec and parsec scales by examining observational signatures
such as the spectral index, synchrotron turnover frequency, and
brightness temperature profiles.
This analysis is performed by considering the properties of the jet
acceleration and collimation zone, which can be probed thanks to the
source vicinity, as well as the inner part of the jet conical region.
We observe remarkably steep values for the spectral index on
sub-parsec scales (similar to -2) which flatten around -0.8 on parsec
scales.
We suggest that the observed steep values may result from particles
being accelerated via diffusive shock acceleration mechanisms in
magnetized plasma and subsequently experiencing cooling through
synchrotron losses. The brightness temperature of the 43GHz cores
indicates a dominance of the magnetic energy at the jet base, while
the cores at progressively lower frequencies reveal a gradual
transition towards equipartition.
Based on the spectral index and brightness temperature along the
incoming jet, and by employing theoretical models, we derive that the
magnetic field strength has a close-to-linear dependence with distance
going from parsec scales up to the jet apex.
Description:
New observations at 43GHz performed with the VLBA are presented,
alongside a re-analysis of a multi-frequency (1.4, 2.3, 5.0, 8.4,
15.3, 22.2, 43.0GHz) and simultaneous VLBA data set (BP243) originally
published in Park et al., 2021ApJ...909...76P 2021ApJ...909...76P.
Additionally images used are from the MOJAVE team (available on their
website) and from Boccardi et al., 2021A&A...647A..67B 2021A&A...647A..67B, Cat.
J/A+A/647/A67. The fundamental parameters of the reported images, are
summarized in Table 1.
The goal of this project is to infer the behavior of the magnetic
fields on sub-parsec, parsec scales in NGC 315 by exploring the
properties of the spectrum and of the brightness temperature along the
jet.
Objects:
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RA (2000) DE Designation(s)
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00 57 48.88 +30 21 08.8 NGC 315 = MCG+05-03-031
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 149 10 List of fits maps
fits/* . 10 Individual fits map
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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- 4 F4.1 GHz Freq Observing frequency (from table 1)
6- 11 A6 --- PCode Project code (from table 1)
13- 17 F5.3 mas Beam1 Beam size, major axis (from table 1)
19- 23 F5.3 mas Beam2 Beam size, minor axis (from table 1)
25- 29 F5.1 deg PA [] Beam size, position angle (from table 1)
31- 35 F5.3 Jy Ftot Total flux density (from table 1)
37- 41 F5.3 Jy/beam Fpeak Brightness peak value (from table 1)
43- 47 F5.3 Jy/beam rms Thermal noise (from table 1)
49- 57 F9.5 deg RAdeg Right Ascension of center (J2000)
58- 66 F9.5 deg DEdeg Declination of center (J2000)
68- 71 I4 --- Nx Number of pixels along X-axis
73- 76 I4 --- Ny Number of pixels along Y-axis
78- 87 A10 "datime" Obs.date Observation date
89- 92 I4 Kibyte size Size of FITS file
94-116 A23 --- FileName Name of FITS file, in subdirectory fits
118-149 A32 --- Title Title of the FITS file
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Acknowledgements:
Luca Ricci, luca.ricci(at)uni-wuerzburg.de
(End) Luca Ricci [JMU Wurzburg, Germany], Patricia Vannier [CDS] 05-Dec-2024