J/A+A/628/L3 NGC 4565 LOFAR images (Heesen+, 2019)
Warped diffusive radio halo around the quiescent spiral edge-on galaxy NGC 4565.
Heesen V., Whitler L., Schmidt P., Miskolczi A., Sridhar S.S., Horellou C.,
Beck R., Gurkan G., Scannapieco E., Bruggen M., Heald G.H., Krause M.,
Paladino R., Nikiel-Wroczynski B., Wilber A., Dettmar R.-J.
<Astron. Astrophys. 628, L3 (2019)>
=2019A&A...628L...3H 2019A&A...628L...3H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, radio
Keywords: galaxies: halos - galaxies: individual: NGC 4565 -
galaxies: magnetic fields - galaxies: spiral - cosmic rays -
radio continuum: galaxies
Abstract:
Cosmic rays play a pivotal role in launching galactic winds,
particularly in quiescently star-forming galaxies where the hot gas
alone is not sufficient to drive a wind. Except for the Milky Way, not
much is known about the transport of cosmic rays in galaxies. In this
Letter, we present low-frequency observations of the nearby edge-on
spiral galaxy NGC 4565 using the LOw-Frequency ARray (LOFAR). With our
deep 144-MHz observations, we obtain a clean estimate of the emission
originating from old cosmic-ray electrons (CRe), which is almost free
from contamination by thermal emission. We measured vertical profiles
of the non-thermal radio continuum emission that we fitted with
Gaussian and exponential functions. The different profile shapes
correspond to 1D cosmic-ray transport models of pure diffusion and
advection, respectively. We detect a warp in the radio continuum that
is reminiscent of the previously known HI warp. Because the warp is
not seen at GHz-frequencies in the radio continuum, its minimum age
must be about 100Myr. The warp also explains the slight flaring of
the thick radio disc that can otherwise be well described by a
Gaussian profile with an FWHM of 65-arcsec (3.7kpc). The diffusive
radio halo together with the extra-planar X-ray emission may be
remnants of enhanced star-forming activity in the past where the
galaxy had a galactic wind, as GHz-observations indicate only a weak
outflow in the last 40Myr. NGC 4565 could be in transition from an
outflow- to an inflow-dominated phase.
Description:
We present 144-MHz radio continuum maps of NGC 4565 obtained with the
Low-frequency ARray (LOFAR) using the high band antennae (HBA). The
maps were produced with the facet calibration technique, ensuring
direction-dependent calibration, using the FACTOR pipeline. These maps
were imaged and deconvolved with the Common Astronomy Software
Applications using the multi-frequency-multi-scale CLEAN algorithm.
Finally, the maps were convolved in the Astronomical Image Processing
System (AIPS) to a circular synthesised beam. In order to measure flux
densities, we integrated in ellipses encompassing the 3-sigma contour
line.
Low-frequency array (LOFAR), high band antennae (HBA), observed on
August 28th and October 12th 2017.
Objects:
---------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------
12 36 20.80 +25 59 14.6 NGC 4565 = UGC 7772
---------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 220 2 List of fits images
fits/* . 2 Individual fits images
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 deg RAdeg Right Ascension (J2000)
12- 20 F9.6 deg DEdeg Declination (J2000)
22- 28 A7 --- Id Object identifier
30- 33 F4.1 arcsec FWHM Full width at half maximum
35- 39 F5.3 GHz nu1 Observing frequency nu1
41- 44 F4.2 Jy S1 Flux density at nu1
46- 49 F4.2 Jy e_S1 Error of the flux density at nu1
51- 53 F3.1 arcmin maj Major axis
55- 57 F3.1 arcmin min Minor axis
59- 63 F5.1 deg PA Position angle (counter-clockwise)
65- 67 I3 --- Nx Number of pixels along X-axis
69- 71 I3 --- Ny Number of pixels along Y-axis
73- 98 A26 "datime" Obs.date Observation date
100-103 I4 Kibyte size Size of FITS file
105-146 A42 --- FileName Name of FITS file, in subdirectory fits
148-220 A73 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Volker Heesen, volker.heesen(at)hs.uni-hamburg.de
(End) Patricia Vannier [CDS] 24-Jul-2019