J/A+A/555/A23 M82-A radio continuum and polarisation study I. (Adebahr+, 2013)
M82 - A radio continuum and polarisation study.
I. Data reduction and cosmic ray propagation
Adebahr B., Krause M., Klein U., Wezgowiec M., Domans D. J., Dettmar, R.-J.
<Astron. Astrophys. 555, A23 (2013)>
=2013A&A...555A..23A 2013A&A...555A..23A
ADC_Keywords: Galaxies, radio ; Magnetic fields ; Radio continuum
Keywords: galaxies: individual: M 82 - galaxies: starburst -
galaxies: magnetic fields - galaxies: halos -
techniques: interferometric
Abstract:
In order to study the cosmic ray propagation and determine the
magnetic field strength and dominant loss processes in the nearby
prototypical starbursting galaxy M82, a multi-frequency analysis at
four radio wavelengths is presented.
Archival data from the Westerbork Synthesis Radio Telescope (WSRT) was
reduced and a new calibration technique introduced to reach the high
dynamic ranges needed for the complex source morphology. These data
were combined with archival Very Large Array (VLA) data, yielding
total power maps at λ3cm, λ6cm, λ22cm, and
λ92cm.
The data show a confinement of the emission at wavelengths of
λ3/λ6cm to the core region and a largely extended halo
reaching up to 4kpc away from the galaxy midplane at wavelengths of
λ22/λ92cm up to a sensitivity limit of 90uJy and 1.8mJy
respectively indicating different physical processes in the core and
halo regions. The results are used to calculate the magnetic field
strength to 98uG in the core region and to 24uG in the halo regions.
From the observation of ionisation losses, the filling factor of the
ionised medium could be estimated to 2%. This leads to a revised view
of the magnetic field distribution in the core region and the
propagation processes from the core into the halo regions.
Description:
The 3cm and 6cm data were obtained from the VLA archive (already
published by Seaquist & Odegard (1991ApJ...369..320S 1991ApJ...369..320S) and Reuter et
al. 1992A&A...256...10R 1992A&A...256...10R), combined and calibration improved for our
studies. We chose only the data from the compact D-configuration to
match the resolution to our WSRT data and to restore most of the
diffuse halo structure of M82. All observations used two subbands at
central frequencies of 8.465GHz and 8.415GHz and 4.885GHz and
4.835GHz, respectively.
The WSRT archive was inspected for archival datasets of M82. One
dataset at 18cm, two at 22cm, and one at 92cm were found. From this
data, only a total power image of the 18cm dataset has been published
so far by Braun et al. (2007A&A...461..455B 2007A&A...461..455B).
The FITS files contain the total power images from the VLA at 3cm and
6cm and from the WSRT at 22cm and 92cm that have been created as well
as spectral index maps between the wavelengths. From this a map of
total the magnetic field strength was calculated.
Objects:
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RA (2000) DE Designation(s)
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09 55 52.43 +69 40 46.9 M 82 = NAME CIGAR GALAXY = NGC 3034
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fits.dat 90 8 Summary of FITS maps
fits/* . 8 Individual FITS files
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See also:
VIII/17 : The North 20cm Survey (White+ 1992)
VIII/14 : 87GB Catalog of radio sources (Gregory et al., 1991)
VIII/23 : 6C Survey of radio sources - IV. (Hales+ 1991)
VIII/13 : A new catalog of 53522 4.85GHz sources (Becker+ 1991)
VIII/56 : Compendium of Radio Measurements of Bright Galaxies (Haynes+ 1975)
J/MNRAS/391/1384 : Deep MERLIN 5GHz radio sources in M82 (Fenech+, 2008)
J/ApJ/554/803 : New VLA Sky Survey (NVSS) Cat of IRAS 2 Jy Galaxies (Yun+ 2001)
J/A+AS/114/21 : Shapley-Ames Galaxies at 2.8cm (Niklas+, 1995)
J/A+A/293/703 : Outflow in M82 halo (McKeith+, 1995)
J/ApJ/252/102 : Radio sources in bright spiral galaxies. II. (Condon+, 1982)
Byte-by-byte Description of file: fits.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- 19 F10.5 deg DEdeg Declination of center (J2000)
21- 25 F5.3 arcsec/pix scale [0.396] Scale of the image
27- 30 I4 pix Nx [5456/5458] Number of pixels along X-axis
31 A1 --- --- [x]
32- 35 I4 pix Ny [5456/5458] Number of pixels along Y-axis
37- 49 A13 --- FileName Name of FITS file in subdirectory fits
51- 90 A40 --- Title Title of the FITS file
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History:
* 26-Jul-2013: Original version
* 29-Jul-2013: Changes in the headers of fits/SI_* files:
Replaced header keywords CDELT1 and CDELT2 originally set to 1.0
into CDELT1 = -1.09955001160E-04 and CDELT2 = 1.09955001160E-04
Acknowledgements:
Bjoern Adebahr, <bjoern.adebahr( at )astro.ruhr-uni-bochum.de>,
Astronomisches Institut, Ruhr-Universitat Bochum
(End) Bjoern Adebahr [AIRUB], Emmanuelle Perret [CDS] 26-Jul-2013