, C. Henkel
,
R. Wielebinski
, T. Wiklind
, H.-P. Reuter
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69,
D-53121 Bonn, Germany
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel
71, D-53121 Bonn, Germany
Steward Observatory, University of Arizona, Tucson, AZ85721, USA
Onsala Space Observatory, S-43992 Onsala, Sweden
IRAM, Av. Divina Pastora 7, E-18012 Granada, Spain 
of the edge-on starburst galaxy NGC253 has
been mapped in the J=2-1 line of 
CO with the IRAM 30m telescope
(beam width: 12
). After a Lucy deconvolution, the resolution is enhanced
to 
. CO emission is strongly concentrated toward a region elongated
along the major axis with a FWHP size of 
(
at D=2.5Mpc). Toward the center of NGC253, the 
CO
line contributes between 20% and 35% to the total measured 1.3mm
``continuum'' in a 50GHz wide bandpass. Position-velocity maps reveal two
condensations symmetrically placed with respect to the nucleus. Distinct
velocity features suggest the presence of a compact molecular spiral, although
a molecular bar or ring cannot be excluded. The dynamical mass in the inner
480pc is 2.610
M
.
Applying a ``standard'' 
conversion factor of
, the molecular gas mass of the central
condensations would be 
. Other tracers of molecular
mass, namely optically thin C
O rotational lines and the mm-wave dust
continuum yield gas masses of 
. The most
plausible explanation of this discrepancy is that the ``standard'' H
mass/CO luminosity ratio, which has been derived for Galactic disk clouds,
cannot be applied to the bulge region of galaxies such as NGC253. Possible
reasons are discussed in terms of excitation conditions and the influence of
the stellar gravitational potential. It is not the gas mass that makes
NGC253 an outstanding galaxy but its infrared luminosity and the ``star
forming efficiency'' 
of 90
.