J/A+A/632/A12 NGC 891 and NGC 4565 radio images (Schmidt+, 2019)
CHANG-ES XVI. An in-depth view of the cosmic-ray transport in the edge-on spiral
galaxies NGC 891 and NGC 4565.
Schmidt P., Krause M., Heesen V., Basu A., Beck R., Wiegert T., Irwin J.A.,
Heald G., Rand R.J., Li J.-T., Murphy E.J.
<Astron. Astrophys. 632, A12 (2019)>
=2019A&A...632A..12S 2019A&A...632A..12S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Radio continuum ; Magnetic fields
Keywords: galaxies: spiral - galaxies: halos - galaxies: magnetic fields -
galaxies: individual: NGC 891 - galaxies: individual: NGC 4565 -
radio continuum: galaxies
Abstract:
Cosmic-ray electrons (CREs) originating from the star-forming discs of
spiral galaxies frequently form extended radio haloes that are best
observable in edge-on galaxies, where their properties can be directly
investigated as a function of vertical height above the disc.
For the present study, we selected two nearby edge-on galaxies from
the Continuum Halos in Nearby Galaxies - an EVLA Survey (CHANG-ES),
NGC 891 and 4565, which differ largely in their detectable halo extent
and their star- formation rates (SFRs). Our aim is to figure out how
such differences are related to the (advective and/or diffusive) CRE
transport in the disc and in the halo.
We use wide-band 1.5 and 6GHz Very Large Array (VLA) observations
obtained in the B, C, and D configurations, and combine the 6GHz
images with Effelsberg observations to correct for missing short
spacings. After subtraction of the thermal emission, we investigate
the spatially resolved synchrotron spectral index distribution in
terms of CRE spectral ageing. We further compute total magnetic field
strengths assuming equipartition between the cosmic-ray (CR) energy
density and the magnetic field, and measure synchrotron scale heights
at both frequencies. Based on the fitted vertical profiles of the
synchrotron intensity and on the spectral index profile between 1.5
and 6GHz, we create purely advective and purely diffusive CRE
transport models by numerically solving the 1D diffusion-loss
equation. In particular, we investigate for the first time the radial
dependence of synchrotron and magnetic field scale heights, advection
speeds, and diffusion coefficients, whereas previous studies of these
two galaxies only determined global values of these quantities.
Description:
We present maps of the galaxies NGC 891 and NGC 4565 obtained by
wide-band VLA observations at 1.5 and 6GHz and with the 100-m
Effelsberg telescope at 4.85GHz (NGC 891) and 8.35GHz (NGC 4565).
The VLA total intensity maps are presented at various angular
resolutions and were imaged with the Common Astronomy Software
Applications (CASA) using the multi-scale-multi- frequency-synthesis
CLEAN algorithm. At 6 GHz, the VLA maps were combined with the
(re-scaled) Effelsberg data using NOD3 (cf. Mueller et al.,
2017A&A...606A..41M 2017A&A...606A..41M). Maps of the thermal fraction at 1.5 and 6 GHz
were generated based on a combination of Hα and 24um data. We
computed maps of the total and non- thermal spectral index between 1.5
and 6GHz as well as the in-band total and non-thermal spectral index
at both frequencies. Further, we present a map of the equipartition
total magnetic field strength for each galaxy.
Objects:
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RA (2000) DE Designation(s)
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02 22 32.91 +42 20 53.9 NGC 891 = NGC 891
12 36 20.80 +25 59 14.6 NGC 4565 = NGC 4565
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 169 33 List of FITS files
fits/* . 33 Individual FITS files
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See also:
J/A+A/623/A33 : NGC 4666 polarization maps (Stein+, 2019)
J/A+A/632/A10 : NGC 4631 total intensity images (Mora-Partiarroyo+, 2019)
J/A+A/632/A11 : Radio images of NGC 4631 (Mora-Partiarroyo+, 2019)
J/A+A/632/A13 : NGC 4013 radio and polarization map (Stein+, 2019)
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- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 48 A19 "datime" Obs.date Observation date
50- 56 F7.5 GHz Freq ? Observed frequency
58- 66 A9 --- Units Map units
68- 72 F5.1 arcsec FWHM Angular resolution, referred to as the full
width at half maximum (FWHM) of the circular
synthesized beam
74- 78 I5 Kibyte size Size of FITS file
80-115 A36 --- FileName Name of FITS file, in subdirectory fits
117-169 A53 --- Title Title of the FITS file
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Acknowledgements:
Philip Schmidt, philip-schmidt(at)gmx.de
References:
Irwin et al., Paper I 2012AJ....144...43I 2012AJ....144...43I
Irwin et al., Paper II 2012AJ....144...44I 2012AJ....144...44I
Irwin et al., Paper III 2013AJ....146..164I 2013AJ....146..164I
Wiegert et al., Paper IV 2015AJ....150...81W 2015AJ....150...81W
Irwin et al., Paper V 2015ApJ...809..172I 2015ApJ...809..172I
Li et al., Paper VI 2016MNRAS.456.1723L 2016MNRAS.456.1723L
Damas-Segovia et al., Paper VII 2016ApJ...824...30D 2016ApJ...824...30D
Irwin et al., Paper VIII 2017MNRAS.464.1333I 2017MNRAS.464.1333I
Krause et al., Paper IX 2018A&A...611A..72K 2018A&A...611A..72K
Vargas et al., Paper X 2018ApJ...853..128V 2018ApJ...853..128V
Irwin et al., Paper XI 2018MNRAS.476.5057I 2018MNRAS.476.5057I
Miskolczi et al., Paper XII 2019A&A...622A...9M 2019A&A...622A...9M
Stein et al., Paper XIII 2019A&A...623A..33S 2019A&A...623A..33S, Cat. J/A+A/623/A33
Mora Partiarroyo et al., Paper XIV 2019A&A...632A..10M 2019A&A...632A..10M, Cat. J/A+A/632/A10
Mora Partiarroyo et al., Paper XV 2019A&A...632A..11M 2019A&A...632A..11M, Cat. J/A+A/632/A11
Vargas et al., Paper XVII 2019ApJ...881...26V 2019ApJ...881...26V
Stein et al., Paper XIX 2019A&A...632A..13S 2019A&A...632A..13S, Cat. J/A+A/632/A13
Irwin et al., Paper XX 2019AJ....158...21I 2019AJ....158...21I
(End) Patricia Vannier [CDS] 08-Oct-2019