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Title: Detection of H92 alpha recombination line from the galaxies NGC 3628, IC 694, and NGC 1365
Authors: Anantharamaiah, K.R.
Zhao, J.H.
Goss, W.M.
Viallefond, F.
Keywords: GALAXIES
NGC 1365
NGC 3628
Issue Date: Dec-1993
Publisher: The University of Chicago Press for the American Astronomical Society
Citation: Astrophysical Journal, 1993, Vol.419, p585-595
Abstract: Using the Very Large Array with an angular resolution of 3", we have detected the hydrogen recombination line H92alpha (Vrest = 8309.38 MHz) from the starburst nuclei in the galaxies NGC 3628 and IC 694 and also from the Seyfert II nucleus in NGC t365. In each case the line-emitting region extends over a few hundred parsecs. The detected lines have peak intensities in the range 0.5-1.5 mJy and widths (FWHM) 200- 400 km s 1 The line was not detected in three other galaxies (NGC 262, NGC 1068, and NGC 3079) that were observed to a similar sensitivity level. We present a model in which a collection of H ii regions in the nuclear region accounts for the observed H92alpha line. The required number of H ii regions, their temperature, electron density, and linear size are constrained by the observed line flux density, line width, continuum spectrum, and size of the line-emitting region. If the temperature of the H ii regions is above 5000 K, then electron densities in the range 5-50 x 103 cm -3 are permitted by the available constraints. Several hundred H ii regions of a few parsecs in size, with a total mass of a few times 10 M_{0}, are required to account for the observed line flux density. The rate of production of Lyman continuum photons required to maintain the ionization is a few times 10 s -1 Much of the line emission comes from internal stimulated emission due to the continuum generated within the H ii regions which account for 5%-30% of the observed total continuum at 5 GHz. Predictions are made for the expected recombination line and continuum flux density as a function of frequency from the nuclear region of the galaxies.
ISSN: 0004-637X
1538-4357 (online)
Alternative Location:
Copyright: (1993) by the American Astronomical Society. Scanned images provided by the NASA ADS Data System.
Appears in Collections:Research Papers (A&A)

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