J/A+A/592/A123 M51 total intensity image at 333MHz (Mulcahy+, 2016)
Modelling the cosmic ray electron propagation in M51.
Mulcahy D.D., Fletcher A., Beck R., Mitra D., Scaife A.M.M.
<Astron. Astrophys. 592, A123 (2016)>
=2016A&A...592A.123M 2016A&A...592A.123M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Radio continuum
Keywords: cosmic rays - galaxies: individual: M51 - galaxies: ISM -
galaxies: magnetic fields - radio continuum: galaxies
Abstract:
Cosmic ray electrons (CREs) are a crucial part of the ISM and are
observed via synchrotron emission.
While much modelling has been carried out on the CRE distribution and
propagation of the Milky Way, little has been done on normal external
star-forming galaxies. Recent spectral data from a new generation of
radio telescopes enable us to find more robust estimations of the CRE
propagation
To model the synchrotron spectral index of M51 using the diffusion
energy-loss equation and to compare the model results with the
observed spectral index determined from recent low-frequency
observations with LOFAR.
We solve the time-dependent diffusion energy-loss equation for CREs in
M51. This is the first time that this model for CRE propagation has
been solved for a realistic distribution of CRE sources, which we
derive from the observed star formation rate, in an external galaxy.
The radial variation of the synchrotron spectral index and
scale-length produced by the model are compared to recent LOFAR and
older VLA observational data and also to new observations of M51 at
325MHz obtained with the GMRT.
We find that propagation of CREs by diffusion alone is sufficient to
reproduce the observed spectral index distribution in M51.
An isotropic diffusion coefficient with a value of 6.6±0.2Dunits is
found to fit best and is similar to what is seen in the Milky Way. We
estimate an escape time of 11Myr from the central galaxy to 88Myr in
the extended disk. It is found that an energy dependence of the
diffusion coefficient is not important for CRE energies in the range
0.01GeV-3GeV. We are able to reproduce the dependence of the observed
synchrotron scale-lengths on frequency, with l∝ν-1/4 in
the outer disk and l∝ν-1/8 in the inner disk.
Description:
Total intensity image M51 with the 325MHz receiver of the GMRT at
15-arcsec resolution.
Only the upperband data was used and thus the central frequency is
333MHz. Full details of the observation,calibration and imaging can be
seen in the paper.
Objects:
--------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------
13 29 52.70 +47 11 42.9 M 51 = NGC 5194
--------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 146 1 Information on fits image
m51_333.fits 2880 1497 Fits image
--------------------------------------------------------------------------------
See also:
J/A+A/568/A74 : Low-frequency (115-175MHz) image of M51 (Mulcahy+, 2014)
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "date" Obs.date Observation date
41- 47 F7.3 MHz Freq Observed frequency
49- 52 I4 Kibyte size Size of FITS file
54- 65 A12 --- FileName Name of FITS file
67-146 A80 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
David Mulcahy, david.mulcahy(at)manchester.ac.uk
(End) Patricia Vannier [CDS] 16-Jun-2016