Ices in the Galactic Centre : solid ice and gaseous CO in the central
  parsec
  For the past few years, we have observed the central half parsec of our
Galaxy in the mid-infrared from 2.8 to 5.1 micron. Our aim is to improve our
understanding of the direct environment of SgrA*, the supermassive blackhole at
the centre of the Milky Way. This work is described in the present paper and by
Moultaka et al. 2015 (submitted). Here, we focus on the study of the spatial
distribution of the 12CO ice and gas-phase absorptions. We observed the central
half parsec with ISAAC spectrograph located at the UT3/VLT ESO telescope in
Chile. The slit was placed along 22 positions arranged parallel to each other
to map the region. We built the first data cube in this wavelength range
covering the central half parsec. The wavelength interval of the used M-band
filter ranges from 4.6 to 5.1 micron. It hosts the P- and R- branches of the
ro-vibrational transitions of the gaseous 12CO and 13CO, as well as the
absorption band attributed to the 12CO ice at 4.675 micron. Using two
calibrators, we could disentangle the local from the line-of-sight absorptions
and provide a first-order estimate of the foreground extinction. We find
residual ices and gase-phase CO that can be attributed to local absorptions due
to material from the interstellar and/or the circumstellar medium of the
central parsec. Our finding implies temperatures of the order of 10 to 60K
which is in agreement with the presence of water ices in the region highlighted
by Moultaka et al. (2004, 2005).
