High-speed outflows driven by the 30 Doradus starburst

Abstract

ABSTRACT Echelle spectroscopy has been carried out towards a sample region of the halo of thegiantHiiregion30Doradusin the LargeMagellanicCloud.This newkinematicaldatais the amongst the most sensitive yet obtained for this nebula and reveals a wealth offaint, complex high speed features. These are interpreted in terms of localised shellsdue to individual stellar winds and supernova explosions, and collections of discreteknots of emission that still retain the velocity pattern of the giant shells from whichthey fragmented. The high speed velocity featuresmay tracethe baseof the superwindthatemanatesfromthe30Doradusstarburst,distributedaroundthesuperstarclusterR136.Key words: galaxies:starburst – galaxies:Magellanic Clouds – H ii regions – ISM:kinematics and dynamics – ISM:supernova remnants – ISM:individual (30 Doradus) 1 INTRODUCTIONThe 30 Doradus nebula in the Large Magellanic Cloud(LMC) is the closest example of a giant extragalactic Hiiregion and the largest in the local group of galaxies. It isregarded as undergoing intense enough star formation to bereferred to as a ‘mini-starburst’ by Leitherer (1998) and assuch is an important nearby laboratory of both massive starformation and starburst phenomena. The highly dynamicnebulosity (e.g. Meaburn 1981; Meaburn 1987) is poweredby a super star cluster of ∼ 100 massive stars. RemarkableHST imagery of the environment of the central cluster ofmassive stars has recently been presented by Walborn et al.(2002). The combined winds, UV radiation and supernovaexplosions from so many massive stars at a similar evolu-tionary epoch enables the generation of the nested giant (20– 300 pc diameter) shells that comprise the giant Hii re-gion (Meaburn 1980; Meaburn 1990; Leitherer 1998). Onthe largest scales, surrounding 30 Dor are supergiant (600 –1400 pc diameter) interstellar shells such as LMC3.The term ’shell’ will be used in this paper rather thanthe commonly used term ‘bubble’ since it is preferable touse a term that is dynamically neutral and constrained tono specific geometry (e.g. spherical). The term ‘bubble’, of-ten erroneously presupposes a roughly spherical, pressure–driven, energy-conserving shell. This is certainly not thecase for the supergiant shells which are unlikely to be eitherspherical or energy-conserving. The division between ’giant’and ’supergiant’ when applied to the LMC shells will be forthe diameter ranges above and recently confirmed by the H iobservations of Kim et al. (1999). Different, though related,mechanisms must be involved in the formation of LMC shellsin these distinctly separate diameter ranges. The most im-portant difference is that supergiant shells have diametersin excess of the neutral gas scale-height of the LMC.The overlapping giant shells comprising the halo of30 Doradus have been shown to be expanding at around50 km s