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Molecular distribution and kinematics in nearby galaxies: I. NGC253

R. Mauersberger, 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
Abstract: The central 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 2.610M.

Applying a ``standard'' conversion factor of , the molecular gas mass of the central condensations would be . Other tracers of molecular mass, namely optically thin CO 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.


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Robert Lucas
Fri Jul 7 18:58:08 METDST 1995