J/ApJ/799/10 Arp 220 6 and 33GHz images (Barcos-Munoz+, 2015)
High-resolution radio continuum measurements of the nuclear disks of Arp 220.
Barcos-Munoz L., Leroy A.K., Evans A.S., Privon G.C., Armus L., Condon J.,
Mazzarella J.M., Meier D.S., Momjian E., Murphy E.J., Ott J., Reichardt A.,
Sakamoto K., Sanders D.B., Schinnerer E., Stierwalt S., Surace J.A.,
Thompson T.A., Walter F.
<Astrophys. J., 799, 10 (2015)>
=2015ApJ...799...10B 2015ApJ...799...10B (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, radio ; Radio lines
Keywords: galaxies: active - galaxies: individual: Arp 220 -
galaxies: interactions - galaxies: starburst -
radio continuum: galaxies
Abstract:
We present new Karl G. Jansky Very Large Array radio continuum images
of the nuclei of Arp 220, the nearest ultra-luminous infrared galaxy.
These new images have both the angular resolution to study the
detailed morphologies of the two nuclei that power the galaxy merger
and sensitivity to a wide range of spatial scales. At 33GHz, we
achieve a resolution of 0.081"x0.063" (29.9x23.3pc) and resolve the
radio emission surrounding both nuclei. We conclude from the
decomposition of the radio spectral energy distribution that a
majority of the 33GHz emission is synchrotron radiation. The spatial
distributions of radio emission in both nuclei are well described by
exponential profiles. These have deconvolved half-light radii (R50d)
of 51 and 35pc for the eastern and western nuclei, respectively, and
they match the number density profile of radio supernovae observed
with very long baseline interferometry. This similarity might be due
to the fast cooling of cosmic rays electrons caused by the presence of
a strong (∼mG) magnetic field in this system. We estimate extremely
high molecular gas surface densities of
2.2-1.0+2.1x105M☉/pc2 (east) and
4.5-1.9+4.5x105M☉/pc2 (west), corresponding to total
hydrogen column densities of NH=2.7-1.2+2.7x1025cm-2 (east)
and 5.6-2.4+5.5x1025cm-2 (west). The implied gas volume
densities are similarly high, nH2∼3.8-1.6+3.8x104cm-3 (east)
and ∼11-4.5+12x104cm-3 (west). We also estimate very high
luminosity surface densities of
ΣIR∼4.2-0.7+1.6x1013L☉/kpc2 (east) and
ΣIR ∼ 9.7-2.4+3.7x1013L☉/kpc2 (west), and star
formation rate surface densities of
ΣSFR∼103.7±0.1M☉/yr/kpc2 (east) and
ΣSFR∼104.1±0.1M☉/yr/kpc2 (west). These values,
especially for the western nucleus are, to our knowledge, the highest
luminosity surface densities and star formation rate surface densities
measured for any star-forming system. Despite these high values, the
nuclei appear to lie below the dusty Eddington limit in which
radiation pressure is balanced only by self-gravity. The small
measured sizes also imply that at wavelengths shorter than
λ=1mm, dust absorption effects must play an important role in
the observed light distribution while below 5GHz free-free absorption
contributes substantial opacity. According to these calculations, the
nuclei of Arp 220 are only transparent in the frequency range
∼5-350GHz. Our results offer no clear evidence that an active galactic
nucleus dominates the emission from either nucleus at 33GHz.
Description:
The FITS images show radio continuum emission towards Arp 220 as
observed by the Karl G. Jansky Very Large Array. The two images are
the "combined" ones, as described in Sect. 2 of the paper, where whe
6GHz image is obtained from the combined 4.7GHz and 7.2GHz data, and
the 33GHz image is obtained from the combined 29GHz and 36GHz data.
Objects:
------------------------------------------------
RA (2000) DE Designation(s)
------------------------------------------------
15 34 57.22 +23 30 11.6 Arp 220 = IC 4553
------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 131 2 List of fits images
fits/* . 2 Individual fits images
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See also:
J/A+A/593/A86 : Arp 220 LOFAR radio images at 150MHz (Varenius+, 2016)
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- 50 A21 --- Obs.date Observation date (YYYY-MM-DDThh:mm:ss.s)
52- 59 F8.5 GHz Freq Observed frequency
61- 64 I4 Kibyte size Size of FITS file
66- 91 A26 --- FileName Name of FITS file, in subdirectory fits
93-131 A39 --- Title Title of the FITS file
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Acknowledgements:
Eskil Varenius, varenius(at)chalmers.se
(End) Patricia Vannier [CDS] 18-Jul-2016