J/A+A/593/A86 Arp 220 LOFAR radio images at 150MHz (Varenius+, 2016)
Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz:
A kpc-scale star forming disk surrounding nuclei with shocked outflows.
Varenius E., Conway J.E., Marti-Vidal I., Aalto S., Barcos-Munoz L.,
Koenig S., Perez-Torres M.A., Deller A.T., Moldon J., Gallagher J.S.,
Yoast-Hull T.M., Horellou C., Morabito L.K., Alberdi A., Jackson N.,
Beswick R., Carozzi T.D., Wucknitz O., Ramirez-Olivencia N.
<Astron. Astrophys. 593, A86 (2016)>
=2016A&A...593A..86V 2016A&A...593A..86V (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, radio ; Radio lines
Keywords: ISM: structure - techniques: high angular resolution -
galaxies: individual: Arp 220 - galaxies: starburst
Abstract:
We analyse new observations with the International Low Frequency Array
(LOFAR) telescope, and archival data from the Multi-Element Radio
Linked Interferometer Network (MERLIN) and the Karl G. Jansky Very
Large Array (VLA). We model the spatially resolved radio spectrum of
Arp 220 from 150MHz to 33GHz. We present an image of Arp 220 at 150MHz
with resolution 0.65"x0.35", sensitivity 0.15mJy/beam, and integrated
flux density 394±59mJy. More than 80% of the detected flux comes
from extended (6"∼2.2kpc) steep spectrum (alpha=-0.7) emission, likely
from star formation in the molecular disk surrounding the two nuclei.
We find elongated features extending 0.3" (110pc) and 0.9" (330pc)
from the eastern and western nucleus respectively, which we interpret
as evidence for outflows. The extent of radio emission requires
acceleration of cosmic rays far outside the nuclei. We find that a
simple three component model can explain most of the observed radio
spectrum of the galaxy. When accounting for absorption at 1.4GHz, Arp
220 follows the FIR/radio correlation with q=2.36, and we estimate a
star formation rate of 220M☉/yr. We derive thermal fractions at
1GHz of less than 1% for the nuclei, which indicates that a major
part of the UV-photons are absorbed by dust. International LOFAR
observations shows great promise to detect steep spectrum outflows and
probe regions of thermal absorption. However, in LIRGs the emission
detected at 150MHz does not necessarily come from the main regions of
star formation. This implies that high spatial resolution is crucial
for accurate estimates of star formation rates for such galaxies at
150MHz.
Description:
The 1.4GHz FITS image was obtained by combining data from the Very
Large Array (VLA) and the Multi-Element Radio Linked Interferometer
Network (MERLIN) arrays. The 150MHz image was obtained from data taken
by the International LOFAR telescope, and image using the
Multi-Frequency-Synthesis algorithm as implemented in the task CLEAN
in CASA 4.5.2 using 2 Taylor terms, which also produced a spectral
index map and a spectral index error map. These two FITS images are
also included in addition to the continuum image. Using these four
FITS images, as well as the CO(1-0) and CO(2-1) maps in Konig et al.
(2012ApJ...754...58K 2012ApJ...754...58K) and 6GHz and 33GHz images in Barcos-Munoz et
al. (2015. Cat. J/ApJ/799/10), it is possible to reproduce the figures
in the paper.
Objects:
------------------------------------------------
RA (2000) DE Designation(s)
------------------------------------------------
15 34 57.22 +23 30 11.6 Arp 220 = IC 4553
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 214 4 *List of fits images
fits/* . 4 Individual fits images
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Note on list.dat: Using these four FITS images, as well as the CO(1-0) and
CO(2-1) maps in Konig et al. (2012ApJ...754...58K 2012ApJ...754...58K) and 6GHz and 33GHz
images in Barcos-Munoz et al. (2015. Cat. J/ApJ/799/10), it is possible to
reproduce the figures in the paper.
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See also:
J/ApJ/799/10 : Arp 220 6 and 33GHz images (Barcos-Munoz+, 2015)
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- 55 A26 --- Obs.date Observation date (YYYY-MM-DDThh:mm:ss.s)
57- 64 F8.6 GHz Freq Observed frequency
66- 70 I5 Kibyte size Size of FITS file
72-111 A40 --- FileName Name of FITS file, in subdirectory fits
113-214 A102 --- Title Title of the FITS file
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Acknowledgements:
Eskil Varenius, varenius(at)chalmers.se
(End) Patricia Vannier [CDS] 18-Jul-2016