Integral field near-infrared spectroscopy of II Zw 40^*

¹ European Southern Observatory, Alonso de Cordoba 3107, Vitacura, Santiago, Chile
² Department of Electrical Engineering, Pontificia Universidad Catolica de Chile, Av. Vicuña Mackenna, 4860 Santiago, Chile e-mail: lvanzi@ing.puc.cl
³ Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
⁴ Observatorio Nacional, Rua José Cristino 77, 20.921-400 Rio de Janeiro RJ, Brazil
⁵ Astronomy Department, University of Virginia, PO Box 400325, Charlottesville, VA 22904-4325, USA

Received: 20 October 2007
Accepted: 22 February 2008

Abstract

We present integral field spectroscopy in the near-infrared of the nearby starburst galaxy II Zw 40. Our new observations provide an unprecedented detailed view of the interstellar medium and star formation of this galaxy. The radiation emitted by the galaxy is dominated by a giant HII region, which extends over an area of more than 400 pc in size. A few clusters are present in this area, however, one, in particular, appears to be the main source of ionizing photons. We derive the properties of this object and compare them with those of the 30 Doradus cluster in the Large magellanic cloud (LMC). We study the spatial distribution and velocity field of different components of the inetrstellar medium (ISM), mostly through the Bracket series lines, the molecular hydrogen spectrum, and [FeII]. We find that [FeII] and H₂ are mostly photon excited, but while the region emitting [FeII] is almost coincident with the giant HII region observed in the lines of atomic H and He, the H₂ has a quite different distribution in space and velocity. The age of the stellar population in the main cluster is such that no supernova (SN) should be present yet so that the gas kinematics must be dominated by the young stars. We do not see, in the starbursting region, any geometrical or dynamical structure that can be related to the large scale morphology of the galaxy.