Modeling ionized gas in low-metallicity environments: the Local Group
  dwarf galaxy IC10
  Our objective is to investigate the physical properties of the ionised gas of
the low-metallicity dwarf galaxy, IC 10, at various spatial scales: from
individual HII regions to the entire galaxy scale and examine whether
diagnostics for integrated measurements introduce bias in the results. We
modeled the ionised gas combining the mid- and far-infrared fine-structure
cooling lines observed with Spitzer/IRS and Herschel/PACS, with the
photoionisation code Cloudy. The free parameters of the models are the age of
the stellar cluster, the density and the ionisation parameter of the ionised
gas as well as the depth of the cloud. The latter is used to investigate the
leakage of the ionising photons from the analysed regions of IC 10. We
investigate HII regions in the main star-forming body, on scales of ~25 pc,
three in the main star-forming region in the center of the galaxy and two on
the first arc. We then consider larger sizes on the scale of ~200 pc. We find
that most clumps have nearly identical properties, density ~10$^{2.} $ -
10$^{2.6}$ cm$^{-3}$, ionisation parameter between 10$^{-2.2}$ and 10$^{-1.6}$
and age of the stellar cluster ~5.5 Myr. All of them are matter-bounded
regions, allowing ionising photons to leak. The relatively uniform physical
properties of the clumps suggest a common origin for their star formation
activity, which could be related to the feedback from stellar winds or
supernovae of a previous generation of stars. The properties derived for ~200
pc size "zones" have similar properties as the HII regions they encompass, but
with the larger regions tending to be more radiation-bounded. Finally, we
investigate the fraction of [CII] 157.7 {\mu}m, [SiII] 34.8 {\mu}m, and [FeII]
25.9 {\mu}m, emission arising from the ionised gas phase and we find that most
of the emission originates from the neutral gas, not from the ionised gas.
