Title:	High-Density, Compact H II Regions in the Starburst Galaxies NGC 3628 and IC 694: High-Resolution VLA Observations of the H92 alpha Radio Recombination Line
Authors:	Zhao, J.H. Anantharamaiah, K.R. Goss, W.M. Viallefond, F.
Keywords:	GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3628 GALAXIES: INDIVIDUAL ALPHANUMERIC: IC 694 GALAXIES: ISM RADIO LINES: GALAXIES GALAXIES: KINEMATICS AND DYNAMICS, GALAXIES: STARBURST
Issue Date:	10-Jun-1997
Publisher:	The University of Chicago Press for the American Astronomical Society
Citation:	Astrophysical Journal 1997, Vol.482, p.186-202
Abstract:	Using the Very Large Array (VLA), 1 we have observed the H92 alpha line in the nuclear regions of NGC 3628 and Arp 299 (IC 694 + NGC 3690) with an angular resolution of 1". The radio recombination lines could provide quite important constraints to the physical conditions for the ionized gas in the nuclear regions. For the central nuclear components in NGC 3628, IC 694, and NGC 3690, we find that the electron density of the ionized gas is in the range 5 x 102 to 5 x 104 cm-3, with corresponding geometrical sizes ranging from 25 to 0.01 pc. For the regions with a large line-to-continuum ratio, such as the anomalous kinematic components in IC 694 and NGC 3628, the electron density of the H II regions is well constrained. The derived parameters suggest the existence of ~100 high-density, compact H II regions (ne ~ 104 cm-3 and l ~ 1--2 pc) in these two components. The large number of high-density, compact H II regions deduced for these components can be regarded as evidence for enhanced massive star formation in anomalous kinematic structures that are often produced in interacting systems. Our new H92 alpha line observations reveal the presence of rotating circumnuclear ionized gas disks in both NGC 3628 and IC 694. From the analysis of the nuclear kinematics, we find that a total dynamical mass of 3 x 108 M⊙ exists within a radius R = 120 pc in NGC 3628 and 7 x 108 M⊙ within R = 200 pc in IC 694. The kinematics of the ionized gas and the models with a collection of H II regions infer that the ratio of H II to dynamical mass in the starburst nuclei varies from 1 x 10-4 (for the high-density, compact H II region model) to 1 x 10-2 (for the low-density, large H II region model).
URI:	http://hdl.handle.net/2289/1406
ISSN:	0004-637X 1538-4357 (online)
Alternative Location:	http://dx.doi.org/10.1086/304135
Copyright:	(1997) by the American Astronomical Society.
Appears in Collections:	Research Papers (A&A)

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