J/A+A/692/A179 Five years monitoring of M87 (Marin+, 2024)
Forgotten treasures in the HST/FOC UV imaging polarimetric archives of active
galactic nuclei. III. Five years monitoring of M87.
Marin F., Barnouin T., Wu K., Lopez-Rodriguez E.
<Astron. Astrophys. 692, A179 (2024)>
=2024A&A...692A.179M 2024A&A...692A.179M (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Polarization ; Ultraviolet
Keywords: polarization - instrumentation: polarimeters -
methods: observational - astronomical data bases: miscellaneous -
galaxies: active - quasars: individual: M87
Abstract:
The active galactic nucleus within M87, a giant elliptical galaxy, is
responsible for one of the closest kiloparsec-scale relativistic jets
to Earth. It is thus a perfect target for spatially resolved
observations. This one-sided jet has been extensively observed at
almost all wavelengths, with almost all techniques. Among many other
discoveries, it was found that the optical emission is more
concentrated in the knots and along the center line of the jet, in
comparison to, for example, the radio emission. A remaining question
relates to what we can learn from its polarized counterpart. We
unearthed unpublished polarization maps taken with the Faint Object
Camera (FOC) aboard the Hubble Space Telescope (HST), obtained between
1995 and 1999. At a rate of one observation per year, we can follow
the evolution of the polarized flux knots in the jet. We can thus
constrain the timescale of variation in the magnetic field up to a
spatial resolution of one tenth of an arcsecond (∼11.5pc).
After coherently reducing the five observations using the same
methodology presented in the first paper of this series, the analysis
of polarized maps from POS 1 (base of the jet) and POS 3 (end of the
jet) reveals significant temporal and spatial dynamics in the jet's
magnetic field morphology. Despite minimal changes in the overall
intensity structure, notable fluctuations in polarization degrees and
angles are detected across various knots and inter-knot regions. In
addition, the emission and polarization characteristics of M87's jet
differ significantly between POS1 and POS3. POS1 shows a more
collimated jet with strong variability in polarization, while POS3
reveals a thicker structure, a quasi-absence of variability, and
complex magnetic field interactions. This suggests that the jet may
have coaxial structures with distinct kinetic properties. Theoretical
models like the jet-in-jet scenario, featuring double-helical magnetic
flux ropes, help to explain these observations and indicate a strong
density contrast and higher speeds in the inner jet. Our temporal
analysis demonstrates the importance of high-spatial-resolution
polarization mapping in understanding jets' polarization properties
and overall dynamics, especially if such maps are taken at different
wavelengths (ultraviolet and radio).
Description:
Different fits images taken between 1995 and 1999 of the jet in M87
(two different positions of the jet, POS1 and POS3).
Objects:
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RA (2000) DE Designation(s)
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12 30 49.42 +12 23 28.0 M87 = 3C 274.0
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 89 10 List of fits images
fits/* . 10 Individual fits images
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See also:
J/ApJ/703/42 : HST photometry of M87 globular clusters (Peng+, 2009)
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
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- 21 I2 --- Nx Number of pixels along X-axis
23- 24 I2 --- Ny Number of pixels along Y-axis
26- 35 A10 "datime" Obs.date Observation date
37- 38 I2 Kibyte size Size of FITS file
40- 57 A18 --- FileName Name of FITS file, in subdirectory fits
59- 89 A31 --- Title Title of the FITS file
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Acknowledgements:
Frederic Marin, frederic.marin(at)astro.unistra.fr
References:
Barnouin et al., Paper I 2023A&A...678A.143B 2023A&A...678A.143B
(End) Patricia Vannier [CDS] 11-Oct-2024