J/A+A/705/A85 Images of 0954+556 at multi-frequency (Zeng+, 2026)
Jet reorientation revealed by intermittent jet activity in a
radio galaxy 0954+556.
Zeng A.-L., Zhao W., Yang J., Hu X.-Z., Deng F., Lei Y., Hong X., Liu X.,
Chen L., Liao M., Yang X., Shang H.-T.
<Astron. Astrophys. 705, A85 (2026)>
=2026A&A...705A..85Z 2026A&A...705A..85Z (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Magnetic fields ; Polarization ;
Radio continuum ; Radio sources ; VLBI
Keywords: instrumentation: high angular resolution -
techniques: interferometric - galaxies: active - galaxies: jets
Abstract:
Intermittent jet activity of Active Galactic Nuclei (AGNs) is a common
phenomenon, whereas significant jet reorientation during episodic jet
activity in relatively young radio galaxies are rarely reported. The
quasar 0954+556 at z=0.903 is an intriguing source exhibiting an
unusual radio jet structure with significantly different jet
directions at kiloparsec (kpc) scales and at parsec (pc) scales. At
kpc scales, images from Very Large Array (VLA) exhibit a bright core,
a linear jet extending ∼24kpc to the northwest, and a discrete jet
component ∼16kpc to the northeast. At pc scales, images from Very
Long Baseline Array (VLBA) show a two-component structure with a
projected separation of ∼360pc in north-south direction.
The peculiar structure of 0954+556 might result from jet
reorientation. Here, we aim to investigate the possible mechanism via
multiscale and multifrequency deep radio images.
We performed VLA and VLBA observations of 0954+556. Together with some
existing data in the NRAO data archive, we made multiple VLA images at
1.4-22 GHz and VLBA images at 1.7-43 GHz for various image analysis of
the jet structure.
We have identified the location of the radio core at pc scales,
detected the faint counter jets at both pc and kpc scales for the
first time, and revealed a diffuse emission region connecting pc and
kpc-scale forward jets. Our spectral index distribution and spectral
aging analysis indicate that 0954+556 might undergo at least two
episodes of jet activity during the current AGN phase. Moreover,
pc-scale polarization maps display a well-resolved spine-sheath
polarization structure.
It seems that the jet direction of 0954+556 changed significantly
during intermittent jet activity. This may imply the different jet
orientations and spectral ages observed from kpc to pc scales. The
research provides a strong case that AGN jet direction might change
rapidly on timescale of million years.
Description:
The datasets presented in this work are from our observations and
archival data from VLA and VLBA. Our observations include: 2 VLA
datasets at 8.4 and 22.5GHz from December 2000 (observation code:
AH0721); 1 VLBA dataset at 1.7GHz from February 2000 (BH065), and 2
VLBA datasets at 5 and 8.4GHz acquired in July 2002 (BH096), all
designed for polarimetry; 3 VLBA datasets at 5, 22, and 43GHz in
mid-2016 (BZ061, BL222). Archival data comprise: 2 additional VLA
datasets at 1.4 and 5GHz in November 2000 (AM0672), 1 VLA dataset at
15 GHz in October 1996 (TESTT), as well as 5 VLBA datasets at 5GHz
between September 2002 and August 2005 (BM170, BM208) from the NRAO
archive.
All reduced data and corresponding images are provided here. File
naming follows these conventions: for the images in Fig 1, Fig 2, and
Fig7 are named as array-frequency.fits (e.g., vla-lband.fits for the
VLA image at L band); for the calibrated data corresponding to Fig 1,
Fig 2, and Fig7 are named as array-frequency.uvf (e.g., vla-lband.uvf
for the VLA calibrated data at L band); notably, the polarization
image and corresponding data at 5GHz in Fig 7 are named as
vlba-cband-pol.fits and vlba-cband-pol.uvf, respectively. For the
images in Fig 3 and the corresponding data are name as
vlba-yearcom.fits and vlba-yearcom.uvf, e.g., vlba-2002com.fits is the
image in 2002. As the images shown in Fig 3 was reconstructed from
concatenated data, we also provided the individual data, which are
named as vlba-yyyy-mm-dd, e.g., the image in 2002 (vlba-2002com.fits)
is reconstructed by the concatenated data (vlba-2002com.uvf) which is
a combination of data on 20 July 2002 (vlba-2002-07-20) and data on 22
September 2002 (vlba-2002-09-22).
Objects:
---------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------
09 57 38.1850 +55 22 57.768 0954+556 = 4C+55.17
---------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 115 34 List of images and calibrated data
fits/* . 34 Individual fits images
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 13 F7.4 s RAs Right ascension (J2000)
15 A1 --- DE- Declination sign (J2000)
16- 17 I2 deg DEd Declination (J2000)
19- 20 I2 arcmin DEm Declination (J2000)
22- 27 F6.3 arcsec DEs Declination (J2000)
29- 38 A10 "date" Obs.date Observation date (YYYY-MM-DD) (1)
40- 43 A4 --- Array Telescope/array (VLA or VLBA)
46- 64 A19 --- FileName File name (image or calibrated visibilities) in
subdirectory fits (2)
66-115 A50 --- Title Short description of the file contents
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Note (1): Some combined entries use YYYY-00-00 to denote year-combined datasets.
Note (2): File types:
*.fits are images
*.uvf are calibrated visibilities (UVFITS)
FileName naming follows conventions, e.g.:
vla-lband.fits : VLA image at L band
vla-lband.uvf : VLA calibrated data at L band
vlba-cband-pol.fits : VLBA polarization image at 5GHz
vlba-yearcom.fits/.uvf : VLBA year-combined image/data (e.g., 2002com)
vlba-YYYY-MM-DD : Individual VLBA dataset used in combinations
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Acknowledgements:
Ai-Ling Zeng, azeng(at)iaa.es
(End) Patricia Vannier [CDS] 25-Nov-2025