The 6-GHz methanol multibeam maser catalogue I: Galactic Centre region,
  longitudes 345 to 6
  We have conducted a Galactic plane survey of methanol masers at 6668 MHz
using a 7-beam receiver on the Parkes telescope. Here we present results from
the first part, which provides sensitive unbiased coverage of a large region
around the Galactic Centre. Details are given for 183 methanol maser sites in
the longitude range 345$^{\circ}$ through the Galactic Centre to 6$^{\circ}$.
Within 6$^{\circ}$ of the Centre, we found 88 maser sites, of which more than
half (48) are new discoveries. The masers are confined to a narrow Galactic
latitude range, indicative of many sources at the Galactic Centre distance and
beyond, and confined to a thin disk population; there is no high latitude
population that might be ascribed to the Galactic Bulge.
  Within 2$^{\circ}$ of the Galactic Centre the maser velocities all lie
between -60 and +77 \kms, a range much smaller than the 540 \kms range observed
in CO. Elsewhere, the maser with highest positive velocity (+107 \kms) occurs,
surprisingly, near longitude 355$^{\circ}$ and is probably attributable to the
Galactic bar. The maser with the most negative velocity (-127 \kms) is near
longitude 346$^{\circ}$, within the longitude-velocity locus of the near side
of the `3-kpc arm'. It has the most extreme velocity of a clear population of
masers associated with the near and far sides of the 3-kpc arm. Closer to the
Galactic Centre the maser space density is generally low, except within 0.25
kpc of the Centre itself, the `Galactic Centre Zone', where it is 50 times
higher, which is hinted at by the longitude distribution, and confirmed by the
unusual velocities.
