J/A+A/600/A6 NGC628 3.1GHz total intensity & polarised images (Mulcahy+, 2017)
Resolved magnetic structures in the disk-halo interface of NGC 628.
Mulcahy D.D., Beck R., Heald G.
<Astron. Astrophys. 600, A6 (2017)>
=2017A&A...600A...6M 2017A&A...600A...6M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, optical ; Radio lines ; Polarization
Keywords: cosmic rays - galaxies: magnetic fields - galaxies: ISM -
radio continuum: galaxies
Abstract:
Magnetic fields are essential to fully understand the interstellar
medium (ISM) and its role in the disk-halo interface of galaxies is
still poorly understood. Star formation is known to expel hot gas
vertically into the halo and these outflows have important
consequences for mean-field dynamo theory in that they can be
efficient in removing magnetic helicity. We perform new observations
of the nearby face-on spiral galaxy NGC 628 with the Karl G. Jansky
Very Large Array (JVLA) at S-band and the Effelsberg 100-m telescope
at frequencies of 2.6GHz and 8.35GHz. We obtain some of the most
sensitive radio continuum images in both total and linearly polarised
intensity of any external galaxy observed so far in addition to
high-quality images of Faraday depth and polarisation angle from which
we obtained evidence for drivers of magnetic turbulence in the
disk-halo connection. Such drivers include a superbubble detected via
a significant Faraday depth gradient coinciding with a HI hole. We
observe an azimuthal periodic pattern in Faraday depth with a pattern
wavelength of 3.7±0.1kpc, indicating Parker instabilities. The lack
of a significant anti-correlation between Faraday depth and magnetic
pitch angle indicates that these loops are vertical in nature with
little helical twisting, unlike in IC 342. We find that the magnetic
pitch angle is systematically larger than the morphological pitch
angle of the polarisation arms which gives evidence for the action of
a large-scale dynamo where the regular magnetic field is not coupled
to the gas flow and obtains a significant radial component. We
additionally discover a lone region of ordered magnetic field to the
north of the galaxy with a high degree of polarisation and a small
pitch angle, a feature that has not been observed in any other galaxy
so far and is possibly caused by an asymmetric HI hole.
Description:
Total Intensity and polarised intensity/angle images of NGC628 with the
S-Band (3-4GHz) receiver of the JVLA at natural (18arcsec) and robust
weighting(7.5-arcsec).
Full details of the observation, calibration and imaging can be seen
in the paper.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
01 36 41.77 +15 47 00.5 NGC628 = M 74
-----------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 170 6 List of fits images
fits/* . 6 Individual fits images
--------------------------------------------------------------------------------
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- 50 A21 --- Obs.Date Observatrion date (YYYY-MM-DDThh:mm:ss.s)
52- 58 F7.5 GHz Freq observed frequency
60- 64 I5 Kibyte size Size of FITS file
66- 87 A22 --- FileName Name of FITS file, in subdirectory fits
89-170 A82 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
David Mulcahy, david.mulcahy(at)manchester.ac.uk
(End) Patricia Vannier [CDS] 23-Feb-2017