The internal kinematics of the H II galaxy II Zw 40

Abstract

We present a study of the kinematic properties of the ionized gas in the dominant giant HII region of the well known HII galaxy: II Zw 40. High spatial and spectral resolution spectroscopy has been obtained using the Integral Field Unit mode on the Gemini Multi-Object Spectrograph instrument at the Gemini-North7Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (USA), the Science and Technology Facilities Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina). telescope. The observations allow us to obtain the Hα intensity map, the radial velocity and velocity dispersion maps as well as estimate some physical conditions in the inner region of the starburst, such as oxygen abundance (O/H) and electron density. We have used a set of kinematics diagnostic diagrams, such as the intensity versus velocity dispersion (I-σ), intensity versus radial velocity (I-V), and V-σ, for global and individual analysis in the subregions of the nebula. We aim to separate the main line broadening mechanisms responsible for producing a smooth supersonic integrated line profile for the giant HII region. Bubbles and shells driven by stellar winds and possibly supernovae, covering a large fraction on the face of the nebula, are identified on scales larger than 50 pc. We found that unperturbed or "free from shells" regions showing the lowest σ values (∼20 km s-1) should be good indicators for the σgrav component in II Zw 40. The brightest central region (R ∼50 pc) is responsible for σ derived from a single fit to the integrated line profile. The dominant action of gravity, and possibly unresolved winds of young (<10 Myr) massive stars, in this small region should be responsible for the characteristic Hα velocity profile of the starburst region as a whole (σ = 32-35 km s-1). Our observations show that the complex structure of the interstellar medium of this galactic scale star-forming region is very similar to that of nearby extragalactic giant HII regions in the Local Group galaxies. © 2009. The American Astronomical Society. All rights reserved.