Near-infrared spectroscopy of five Blue Compact Dwarf galaxies: II Zw
  40, Mrk 71, Mrk 930, Mrk 996 and SBS 0335-052E
  We present near-infrared (NIR) spectroscopic observations of five blue
compact dwarf (BCD) galaxies, II Zw 40, Mrk 71, Mrk 930, Mrk 996 and SBS
0335-052E. The NIR spectra which cover the 0.90 micron - 2.40 micron wavelength
range, show hydrogen, molecular hydrogen, helium, sulfur and iron emission
lines. The NIR data for all BCDs have been supplemented by optical spectra. We
found the extinction coefficient in all BCDs to be very similar in both the
optical and NIR ranges. The NIR hydrogen emission lines do not reveal more star
formation than seen in the optical. The same conclusion is reached from Spitzer
data concerning the MIR emission lines. This implies that emission-line spectra
of low-metallicity BCDs in the ~ 0.36 - 25 micron wavelength range are emitted
by relatively transparent ionized gas. The large extinction derived from the
MIR continuum emission in some BCDs implies that the latter arises not from the
visible H II regions themselves, but from locations outside these H II regions.
The H2 emission line fluxes can be accounted for by fluorescence. CLOUDY
stellar photoinization models of all BCDs reproduce well the fluxes of most of
the observed optical and NIR emission lines, except in Mrk 930 where shock
ionization is needed to account for the [Fe II] emission lines. However, some
contribution of shock ionization at the level of < 10% that of stellar
ionization is required to reproduce the observed fluxes of high ionization
species, such as He II 0.469 micron in the optical range and [O IV] 25.89
micron in the MIR range.
