J/A+A/708/A212 NGC 1487 MeerKAT image (Taziaux+, 2026)
MEDUSA. I. Tracing magnetic field structures in tidal arms of the dwarf-dwarf
merger NGC 1487.
Taziaux S., Basu A., Das S., Bomans D., Galvin T., Thomson A., Heald G.,
Kamphuis P., Loi F., Stein M., Chyzy K., Riseley C., Dettmar R.-J.,
Becker Tjus J.
<Astron. Astrophys. 708, A212 (2026)>
=2026A&A...708A.212T 2026A&A...708A.212T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, interacting ; Radio sources
Keywords: cosmic rays - ISM: magnetic fields - ISM: structure -
Galaxy: evolution - galaxies: dwarf - galaxies: individual: NGC 1487
Abstract:
Radio continuum observations of dwarf-dwarf galaxy mergers, such as
NGC 1487, provide crucial insights into magnetic field amplification
and cosmic ray (CR) propagation during galactic assembly. Dwarf
galaxies are important laboratories for studying cosmic magnetism
because they can maintain strong magnetic fields via the action of
turbulent dynamo despite their low mass and weak gravitational
potential.
The Magnetic-field Evolution in Dwarf galaxies from Ultra-deep SKA
Analysis (MEDUSA) survey is the first SKA-pathfinder programme
designed to obtain deep continuum, polarisation, and HI data for dwarf
galaxies, enabling a comprehensive study of their radio spectra,
magnetic fields, and gas kinematics across a representative population
By analysing the radio continuum spectra and polarisation of the
dwarf-dwarf galaxy merger NGC 1487 from the MEDUSA sample, our aim
was to determine its magnetic field strength and to characterise the
large-scale and turbulent components of its magnetic field.
We utilised highly sensitive multi-band radio continuum data from
MeerKAT L-band (1.28GHz) and Australia Telescope Compact Array (ATCA)
L/S (2.1GHz), C (5.5GHz), and X-bands (9GHz). We analysed the
magnetic field configuration using polarisation and rotation measure
(RM) synthesis.
The integrated spectral energy distribution has a non-thermal spectral
index of αnth=-0.678±0.085, indicating a significant
synchrotron contribution, consistent with a CR electron injection
index of gamma=2.36 (N(E)∝E-gamma) typical of supernova
remnants. Synchrotron and inverse Compton losses cause a spectral
break at νb=6.2±1.3GHz. In star-forming regions, the magnetic
field exhibits strong small-scale fluctuations in RM, suggesting the
action of a small-scale dynamo. Conversely, the field becomes more
ordered, aligning with the tidal arms towards the galaxy's
outskirts, showing a large-scale magnetic field over ~=3kpc. The CR
cooling timescale of approximately 11Myr at 1.28GHz is similar to
the escape timescale.
Observations of the dwarf-dwarf merger NGC 1487 show that even
low-mass galaxy mergers, likely the building blocks of larger galaxies
in the early Universe, can rapidly amplify and produce coherent
large-scale magnetic field structures, highlighting their contribution
in the early magnetisation of galaxies.
Description:
NGC 1487 has been observed with MeerKAT (project ID:
SCI-20230907-ST-01; PI: S.Taziaux) in L-band (1.28GHz) and ATCA
(project ID: C3531; PI: S.Taziaux) in L/S-band (2.1GHz), C-band
(5.5GHz) and X-band (9 GHz) between 5-May-2023 and 2-February-2025.
The configurations, total observation time, frequency ranges and
calibrators used during the observations are summarised in Table 2.
The listed observing time represents the total duration, including a
25% overhead. For one ATCA observation, we used the secondary flux
calibrator J0823-500 instead of the primary calibrator J1934-638, and
the flux scale was transferred via phase bootstrapping.
Objects:
---------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------
03 55 46.49 -42 22 00.9 NGC 1487 = IRAS F03540-4230
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 102 1 Information of fits image
fits/* . 1 fits image
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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- 48 A21 "datime" Obs.date Observation date
50- 56 F7.5 GHz Freq Observed frequency
58- 60 I3 Kibyte size Size of FITS file
62- 79 A18 --- FileName Name of FITS file, in subdirectory fits
81-102 A22 --- Title Title of the FITS file
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Acknowledgements:
Sam Taziaux, sam.taziaux(at)rub.de
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Patricia Vannier [CDS] 24-Mar-2026