J/A+A/702/A96 5 orphaned AGNs HST/FOC UV imaging polarimetry (Barnouin+, 2025)
Forgotten treasures in the HST/FOC UV imaging polarimetric archives of active
galactic nuclei. IV. 5 orphaned AGNs.
Barnouin T., Marin F., Lopez-Rodriguez E.
<Astron. Astrophys. 702, A96 (2025)>
=2025A&A...702A..96B 2025A&A...702A..96B (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Galaxies, Seyfert ; Polarization ;
Ultraviolet
Keywords: instrumentation: polarimeters - methods: observational -
polarization - astronomical data bases: miscellaneous -
galaxies: active - galaxies: Seyfert
Abstract:
The Faint Object Camera (FOC) on board the Hubble Space Telescope
(HST) acquired high-resolution spatially resolved polarimetric images
of nearby active galactic nuclei (AGNs) in the near-ultraviolet
(near-UV) band. Eight of the 25 individual targets in the polarized
archives had no published analysis until the beginning of this series
of papers. We describe the last 5 targets here.
In this paper, we finalize the publication of near-UV imaging
polarimetry of AGNs in the HST/FOC archives. We render available
spatially resolved polarization maps of the [OIII] emission lines for
Mrk 3 and Mrk 78, as well as near-UV continuum polarization maps for
Mrk 3, NGC 3862, Cygnus A, and 3C 109.
We used the generalized reduction pipeline presented in the first
paper in this series to homogeneously analyze the five remaining
polarized observations of AGNs in the FOC archives.
The polarization pattern in Mrk 3 and Mrk 78in the narrow-line regions
is consistent with scattering from an obscured nucleus. For NGC 3862,
we confirm marginal UV polarization parallel with the inner radio jet
that is related to synchrotron emission. In Cygnus A, we report
spatially resolved centro-symmetric polarization patterns in the two
opposite outflows, which highlights the scattering origin of the
polarized light. Finally, 3C 109 shows high nuclear polarization that
is consistent with AGN-dominated emission and parallel with the radio
axis, but differs from the polarization from dichroic absorption
invoked by previous authors.
The imaging polarimetry we obtained for the narrow-line region and the
extended scattering medium surrounding the obscured AGNs is aligned
with the predictions of the unified AGN model and demonstrates the
power of spatially resolved polarimetric observation to decipher the
complex morphologies at work in AGNs.
Description:
The Faint Object Camera (FOC) onboard the Hubble Space Telescope (HST)
acquired high-resolution, spatially resolved polarimetric images of
nearby Active Galactic Nuclei (AGNs) in the near ultraviolet (near-UV)
band. Among the 25 individual targets in the polarized archives, 8 had
no published analysis until the beginning of this series of papers. In
this paper, we reduce and analyze archival observations of Mrk 3,
NGC 3862, Mrk 78, Cygnus A and 3C 109.
Each reduced image consist of a collection of Image HDUs described as
follow, with X = NAXIS1, Y = NAXIS2
--------------------------------------------------------------------------------
No. Name Type Cards Dimensions Explanation
--------------------------------------------------------------------------------
0 STOKES PrimaryHDU 56 (X,Y,4) Stokes I, Q, U and V images
1 STOKES_COV ImageHDU 64 (X,Y,4,4) Covariance matrix for the Stokes
I, Q, U and V images
2 STOKESCOVSTAT ImageHDU 64 (X,Y,4,4) Statistical part of the
covariance matrix
3 POL_DEG ImageHDU 50 (X,Y) Polarization degree image
4 POLDEGDEBIASED ImageHDU 50 (X,Y) Debiased polarization degree
image
5 POLDEGERR ImageHDU 50 (X,Y) Error on the polarization degree
image
6 POLDEGSTAT_ERR ImageHDU 50 (X,Y) Statistical error on the
polarization degree image
7 POL_ANG ImageHDU 50 (X,Y) Polarization angle image
8 POLANGERR ImageHDU 50 (X,Y) Error on the polarization angle
image
9 POLANGSTAT_ERR ImageHDU 50 (X,Y) Statistical error on the
polarization angle image
10 DATA_MASK ImageHDU 50 (X,Y) Mask of the observational data
--------------------------------------------------------------------------------
Objects:
---------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------
06 15 36.28 +71 02 14.8 Mrk 3 = UGC 3426
11 45 05.00 +19 36 22.7 NGC 3862 =UGC 6723
07 42 41.70 +65 10 37.4 Mrk 78 = LEDA 21624
19 59 28.35 +40 44 02.0 Cygnus A = LEDA 63932
04 13 40.34 +11 12 14.7 3C 109 = LEDA 2817533
---------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 338 10 List of fits files
fits/* . 10 Individual fits files
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See also:
J/A+A/692/A179 : Five years monitoring of M87 (Marin+, 2024)
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Target name
10- 13 I4 --- ProposalID Observation proposal ID
15- 19 A5 --- Filter Filter used
21- 24 I4 0.1nm lambda Central wavelength of used filter
(in Angstrom)
26- 30 I5 s ExpTime Total exposure time of the observation
32- 35 F4.1 % Pol ?=- Measured polarization degree in FoV
37- 39 F3.1 % e_Pol ? Measured polarization degree in FoV error
41- 45 F5.1 deg PA ?=- Measured polarization angle in FoV
47- 49 F3.1 deg e_PA ? Measured polarization angle in FoV error
51- 59 F9.5 deg RAdeg Right Ascension of center (J2000)
60- 68 F9.5 deg DEdeg Declination of center (J2000)
70- 72 I3 --- Nx Number of pixels along X-axis
74- 76 I3 --- Ny Number of pixels along Y-axis
78 I1 --- Nz ? Number of pixels along Z-axis
80- 89 A10 "datime" Obs.date Observation date
91- 94 I4 Kibyte size Size of FITS file
96-139 A44 --- FileName Name of FITS file, in subdirectory fits
141-338 A198 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Thibault Barnouin, thibault.barnouin(at)astro.unistra.fr
References:
Barnouin et al, Paper I 2023A&A...678A.143B 2023A&A...678A.143B
Barnouin et al, Paper II 2024A&A...692A.178B 2024A&A...692A.178B
Marin et al., Paper III 2024A&A...692A.179M 2024A&A...692A.179M, Cat. J/A+A/692/A179
(End) Patricia Vannier [CDS] 11-Aug-2025