J/A+A/698/A157 Low-power compact symmetric objects VLBA images (Orienti+, 2025)
VLBA observations of a sample of low-power compact symmetric objects.
Orienti M., D'Ammando F., Dallacasa D., Migliori G., Rossi P., Bodo G.
<Astron. Astrophys. 698, A157 (2025)>
=2025A&A...698A.157O 2025A&A...698A.157O (SIMBAD/NED BibCode)
ADC_Keywords: Radio continuum ; Active gal. nuclei
Keywords: radiation mechanisms: non-thermal - galaxies: active -
radio continuum: general
Abstract:
Compact symmetric objects (CSOs) are intrinsically compact
extragalactic radio sources that are thought to be the progenitors of
classical radio galaxies. To date, evolutionary models have mainly
focused on the formation and growth of high-power radio sources,
leaving unanswered many questions related to low-power objects, whose
relativistic jets are likely more prone to instabilities. We present a
new sample of candidate low-power CSOs selected from the Faint Images
of the Radio Sky at Twenty-cm (FIRST) survey. The main selection
criteria are (i) a parsec-scale double radio morphology from archival
Very Long Baseline Array (VLBA) images and (ii) a VLBA total flux
density consistent with that from the FIRST survey, which rules out
the presence of significant radio emission extending beyond the parsec
scale. The final sample consists of 60 sources with radio luminosities
between 1024 and 1027W/Hz at 1.4GHz and projected linear sizes
between 45 and 430pc, which fill a region in the radio power-size
plane that is currently underpopulated. We carried out VLBA
observations at 4.98GHz of a sub-sample of 20 sources among the
brightest candidate CSOs with the aim of confirming their
classification. We classify 12 sources as CSOs on the basis of their
radio structure and spectral index distribution. In two out of the
four CSOs with core identification, the asymmetry in the flux density
of the outer components is in agreement with light travel time
effects, and there is no evidence of jet-cloud interaction. If we
assume a simplistic parametric model, most of the sources in the total
sample have a jet power of ∼1044-1045erg/s , making their
evolutionary paths sensitive to the individual conditions of the jet
and its environment.
Description:
VLBA images at 1.38GHz and 4.98GHz of the low-power compact
symmetric objects studied in the paper and presented in Figure A.1.
Source name, observing frequency, peak brightness in mJy/beam, and the
first contour (f.c.) in mJy/beam are reported on each image. The first
contour corresponds to three times the off-source noise level measured
on the image plane. Contours increase by a factor of 2. The restoring
beam is plotted in the bottom left-hand corner of each image.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 103 40 List of fits images
fits/* . 40 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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 37 A10 "date" Obs.date Observation date
39- 45 F7.5 GHz Freq Observed frequency
47- 50 I4 Kibyte size Size of FITS file
52- 66 A15 --- FileName Name of FITS file, in subdirectory fits
68-103 A36 --- Title Title of the FITS file
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Acknowledgements:
Monica Orienti, monica.orienti(at)inaf.it
(End) Monica Orienti [INAF-IRA Bologna], Patricia Vannier [CDS] 13-May-2025