J/MNRAS/476/158 Radio haloes in nearby galaxies (Heesen+, 2018)
Radio haloes in nearby galaxies modelled with 1D cosmic-ray transport
using SPINNAKER.
Heesen V., Krause M., Beck R., Adebahr B., Bomans D.J., Carretti E.,
Dumke M., Heald G., Irwin J., Koribalski B.S., Mulcahy D.D., Westmeier T.,
Dettmar R.-J.
<Mon. Not. R. Astron. Soc. 476, 158-183 (2018)>
=2018MNRAS.476..158H 2018MNRAS.476..158H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Radio continuum
Keywords: radiation mechanisms: non-thermal - methods: numerical - cosmic rays -
galaxies: haloes - galaxies: magnetic fields -
radio continuum: galaxies
Abstract:
We present radio continuum maps of 12 nearby (D≤27Mpc), edge-on
(i≥76°), late-type spiral galaxies mostly at 1.4 and 5GHz,
observed with the Australia Telescope Compact Array, Very Large Array,
Westerbork Synthesis Radio Telescope, Effelsberg 100-m and Parkes 64-m
telescopes. All galaxies show clear evidence of radio haloes,
including the first detection in the Magellanic-type galaxy NGC 55. In
11 galaxies, we find a thin and a thick disc that can be better fitted
by exponential rather than Gaussian functions. We fit our SPINNAKER
(SPectral INdex Numerical Analysis of K(c)osmic-ray Electron
Radio-emission) 1D cosmic-ray transport models to the vertical model
profiles of the non-thermal intensity and to the non-thermal radio
spectral index in the halo. We simultaneously fit for the advection
speed (or diffusion coefficient) and magnetic field scale height. In
the thick disc, the magnetic field scale heights range from 2 to 8kpc
with an average across the sample of 3.0±1.7kpc; they show no
correlation with either star-formation rate (SFR), SFR surface density
(SigmaSFR) or rotation speed (Vrot). The advection speeds range
from 100 to 700km/s and display correlations of
V∝SFR0.36±0.06 and V∝SigmaSFR0.39±0.09; they
agree remarkably well with the escape velocities (0.5≤V/V_esc≤2),
which can be explained by cosmic-ray driven winds. Radio haloes show
the presence of disc winds in galaxies with
SigmaSFR>10-3M☉/yr/kpc2 that extend over several kpc and
are driven by processes related to the distributed star formation in
the disc.
Description:
We present radio continuum observations of 12 nearby (D=2-27Mpc)
edge-on galaxies at two different frequencies, namely at 1.4 and 5GHz
(one galaxy at 8.5GHz instead of 5GHz). Our sample includes 11
late-type spiral (Sb or Sc) galaxies and one Magellanic-type barred
galaxy (SBm), which are all highly inclined (i≥76°).
As part of our study we have obtained several additional radio
continuum maps. We make these maps publicly available (as well as all
the other radio continuum maps in the paper).
For 4 galaxies (NGC 55, 253, 891 and 4631) we have used single-dish
maps, to correct for the missing zero-spacing flux where necessary.
The Effelsberg maps of NGC 253 and 4631 were already presented in
Heesen et al. (2009A&A...494..563H 2009A&A...494..563H) and Mora & Krause
(2013A&A...560A..42M 2013A&A...560A..42M), respectively, and the Effelsberg map of NGC 891
was already presented in Dumke (1997, PhD thesis, University of Bonn).
We present these maps for completeness.
The 4.80-GHz map of NGC 55 obtained with the 64-m Parkes telescope is
so far unpublished. Furthermore, we show two maps of NGC 4631 at 1.35
and 1.65GHz observed with the VLA in D- configuration (R. Beck 2016,
priv. comm.). The data were observed in August 1996, with 12 h
on-source (ID: AG486) and reduced in standard fashion with AIPS. The
maps have an angular resolution of 52 arcsec, so that we did not use
them in the analysis, but they also show the halo of this galaxy very
well. Lastly, we obtained maps of three further edge-on galaxies
observed with the VLA (NGC 4157, 4217 and 4634). We reduced the data
as described in Section 2, but since we had only one frequency
available and no spectral index map, we did not use them in the
analysis. The maps of NGC 4157 and 4217 were created by re-reducing
archive data (IDs AI23, AF85, AH457 and AS392 for NGC 4157 and ID
AM573 for NGC 4217). The map of NGC 4634 was created by using so far
unpublished data from the VLA (ID: AD538).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 123 12 Radio properties of our sample galaxies
list.dat 150 32 List of fits images
fits/* . 32 Individual fits images
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Galaxy name
9- 18 F10.6 deg RAdeg Right Ascension (J2000)
20- 29 F10.6 deg DEdeg Declination (J2000)
31- 35 F5.2 arcsec thetaFWHM Agular resolution, referred to as the full
width at half maximum (FWHM), of the
circular synthesized beam
37- 40 F4.2 GHz nu1 Observing frequency nu1
42- 45 F4.2 GHz nu2 Observing frequency nu2
47- 52 F6.4 Jy S1 Intergrated flux density at nu1
54- 59 F6.4 Jy e_S1 Error of the flux density at nu1
61- 66 F6.4 Jy S1int Non-thermal integrated flux density at nu1
68- 73 F6.4 Jy e_S1int Error of the flux density at nu1int
75- 80 F6.4 Jy S2 Intergrated flux density at nu2
82- 87 F6.4 Jy e_S2 Error of the flux density at nu2
89- 94 F6.4 Jy S2int Non-thermal integrated flux density at nu2
96-101 F6.4 Jy e_S2int Error of the flux density at nu2int
103-107 F5.2 --- alpha Integrated radio spectral index
between nu1 and nu2
109-112 F4.2 --- e_alpha Error on alpha
114-118 F5.2 --- alphaint Integrated non-thermal radio spectral index
between nu1 and nu2
120-123 F4.2 --- e_alphaint Error on alphaint
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Galaxy name
9- 17 F9.5 deg RAdeg Right Ascension of center (J2000)
18- 26 F9.5 deg DEdeg Declination of center (J2000)
28- 31 I4 --- Nx Number of pixels along X-axis
33- 36 I4 --- Ny Number of pixels along Y-axis
38- 63 A26 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss.ssssss)
65- 71 F7.5 GHz Freq Observed frequency
73- 78 I6 Kibyte size Size of FITS file
80-113 A34 --- FileName Name of FITS file, in subdirectory fits
115-150 A36 --- Title Title of the FITS file
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Acknowledgements:
Volker Heesen, volker.heesen(at)hs.uni-hamburg.de
(End) Patricia Vannier [CDS] 23-Feb-2018