The broad H$lpha$, [O?III] line wings in stellar supercluster?A of NGC?2363 and the turbulent mixing layer hypothesis

摘要

Context. SuperclusterA in the extragalactic H II region NGC2363 is remarkable for the hypersonic gas seen as faint extended broad emission lines with a full-width zero intensity of 7000.Aims. We explore the possibility that the observed broad profiles are the result of the interaction of a high-velocity cluster wind with dense photoionized clumps. Methods. The geometry considered is that of near static photoionized condensations at the surface of which turbulent mixing layers arise as a result of the interaction with the hot wind. The approximative treatment of turbulence was carried out using the mixing length approach of Cantó & Raga. The code MAPPINGS Ic was used to derive the mean quantities describing the flow and to compute the line emissivities within the turbulent layers. The velocity projection in three dimensions of the line sources was carried out analytically. Results. A fast entraining wind of up to 4300appears to be required to reproduce the faint wings of the broad Hand [O III]profiles. A slower wind of 3500,however, can still reproduce the bulk of the broad component and does provide a better fit than an adhoc Gaussian profile. Conclusions. Radial acceleration in 3D (away from superclusterA) of the emission gas provides a reasonable first-order fit to the broad line component. No broad component is predicted for the [N II] and [S II] lines, as observed. The wind velocity required is uncomfortably high and alternative processes that would provide comparable constant acceleration of the emission gas up to 4000might have to be considered. Key words: ISM: HII regions - line: profiles - turbulence -stars: winds, outflows - stars: formation - galaxies: clusters: general