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The radio emission from the ultraluminous far-infrared galaxy NGC 6240We present new radio observations of the 'prototypical' ultraluminous far-infrared galaxy NGC 6240, obtained using the Very Large Array (VLA) at lambda = 20 cm in B-configuration and at lambda = 3.6 cm in A-configuration. These data, along with those from four previous VLA observations, are used to perform a comprehensive study of the radio emission from NGC 6240. Approximately 70% (approximately 3 x 10(exp 23) W/Hz) of the total radio power at 20 cm originates from the nuclear region (approximately less than 1.5 kpc), of which half is emitted by two unresolved (R approximately less than 36 pc) cores and half by a diffuse component. The radio spectrum of the nuclear emission is relatively flat (alpha approximately equals 0.6; S(sub nu) proportional to nu(exp -alpha). The supernova rate required to power the diffuse component is consistent with that predicted by the stellar evolution models of Rieke et al. (1985). If the radio emission from the two compact cores is powered by supernova remnants, then either the remnants overlap and form hot bubbles in the cores, or they are very young (approximately less than 100 yr.) Nearly all of the remaining 30% of the total radio power comes from an 'armlike' region extending westward from the nuclear region. The western arm emission has a steep spectrum (alpha approximately equals 1.0), suggestive of aging effects from synchrotron or inverse-Compton losses, and is not correlated with starlight; we suggest that it is synchrotron emission from a shell of material driven by a galactic superwind. Inverse Compton scattering of far-infrared photons in the radio sources is expected to produce an X-ray flux of approximately 2 - 6 x 10(exp -14) ergs/s/sq cm in the 2 - 10 keV band. No significant radio emission is detected from or near the possible ultramassive 'dark core'.
Document ID
19950037119
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Colbert, Edward J. M.
(Univ. of Maryland, College Park, MD United States)
Wilson, Andrew S.
(Univ. of Maryland, College Park, MD United States)
Bland-Hawthorn, Jonathan
(Anglo-Australian Observatory Epping, Australia)
Date Acquired
August 16, 2013
Publication Date
November 20, 1994
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 436
Issue: 1
ISSN: 0004-367X
Subject Category
Astronomy
Accession Number
95A68718
Funding Number(s)
CONTRACT_GRANT: NAGW-3268
CONTRACT_GRANT: NAGW-2689
Distribution Limits
Public
Copyright
Other

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