Spectroscopic observations of ices around embedded young stellar objects
  in the Large Magellanic Cloud with AKARI
  The aim of this study is to understand the chemical conditions of ices around
embedded young stellar objects (YSOs) in the metal-poor Large Magellanic Cloud
(LMC). We performed near-infrared (2.5-5 micron) spectroscopic observations
toward 12 massive embedded YSOs and their candidates in the LMC using the
Infrared Camera (IRC) onboard AKARI. We estimated the column densities of the
H2O, CO2, and CO ices based on their 3.05, 4.27, and 4.67 micron absorption
features, and we investigated the correlation between ice abundances and
physical properties of YSOs.The ice absorption features of H2O, CO2, 13CO2, CO,
CH3OH, and possibly XCN are detected in the spectra. In addition, hydrogen
recombination lines and PAH emission bands are detected toward the majority of
the targets. The derived typical CO2/H2O ice ratio of our samples (~0.36 +-
0.09) is greater than that of Galactic massive YSOs (~0.17 +- 0.03), while the
CO/H2O ice ratio is comparable. It is shown that the CO2 ice abundance does not
correlate with the observed characteristics of YSOs; the strength of hydrogen
recombination line and the total luminosity. Likewise, clear no correlation is
seen between the CO ice abundance and YSO characteristics, but it is suggested
that the CO ice abundance of luminous samples is significantly lower than in
other samples.The systematic difference in the CO2 ice abundance around the
LMC's massive YSOs, which was suggested by previous studies, is confirmed with
the new near-infrared data. We suggest that the strong ultraviolet radiation
field and/or the high dust temperature in the LMC are responsible for the
observed high abundance of the CO2 ice. It is suggested that the internal
stellar radiation does not play an important role in the evolution of the CO2
ice around a massive YSO, while more volatile molecules like CO are susceptible
to the effect of the stellar radiation.
