The broad H-alpha, [O III] line wings in stellar supercluster A of
  NGC2363 and the turbulent mixing layer hypothesis
  Context. SuperclusterA in the extragalactic HII region NGC2363 is remarkable
for the hypersonic gas seen as faint extended broad emission lines with a full
width zero intensity of 7000km/s. 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 is carried out using the mixing
length approach of Canto & Raga. The code mappings Ic is 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 is carried out analytically. Results. A fast entraining wind of up to
~4300km/s appears to be required to reproduce the faint wings of the broad
H-alpha and [O III] profiles. A slower wind of 3500km/s, however, can still
reproduce the bulk of the broad component and does provide a better fit than an
ad hoc Gaussian profile. Conclusions. Radial acceleration in 3D (away from
supercluster A) 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 4000km/s might have to be considered.
