Spectral imaging of the Central Molecular Zone in multiple 3-mm
  molecular lines
  We have mapped 20 molecular lines in the Central Molecular Zone (CMZ) around
the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m
Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth UNSW-MOPS
digital filter bank, obtaining \sim 2 km/s spectral and \sim 40 arcsec spatial
resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+,
SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+
molecules. The area covered is Galactic longitude -0.7 to 1.8 deg. and latitude
-0.3 to 0.2 deg., including the bright dust cores around Sgr A, Sgr B2, Sgr C
and G1.6-0.025. We present images from this study and conduct a principal
component analysis on the integrated emission from the brightest 8 lines. This
is dominated by the first component, showing that the large-scale distribution
of all molecules are very similar. We examine the line ratios and optical
depths in selected apertures around the bright dust cores, as well as for the
complete mapped region of the CMZ. We highlight the behaviour of the bright
HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues
of these species, and compare the behaviour with that found in extra-galactic
sources where the emission is unresolved spatially. We also find that the
isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing
red-shifted velocity in some locations. Line luminosities are also calculated
and compared to that of CO, as well as to line luminosities determined for
external galaxies.
