1996A&A...306..721R

High resolution CO(1-0) and CO(2-1) observations of the nearby spiral galaxy NGC 3627 are presented. The emission originates mainly from the centre of the galaxy as well as from the transition regions between the two prominent spiral arms and the central disk. The two spiral arms are found to be markedly different in their CO-extent and observed velocity dispersion which is probably caused by interaction with other galaxies in the Leo group. A direct comparison of the CO(1-0) map with a dust continuum map and radio maps at lower angular resolution as well as an investigation of the CO(2-1)/CO(1-0) ratio hint at a considerably smaller CO/H₂-conversion factor for the central emission maximum than towards other locations of the disk. Heating of the ISM due to turbulent motion in the nuclear disk/bar appears to be responsible for this difference. The emission strongly peaks towards the spiral arms as a result of strong density waves being present in the galaxy leading to high arm-interarm contrasts of >4. A detailed study of the velocity field reveals the presence of streaming motions with deprojected velocities of ≃30km/s towards both spiral arms despite the relatively low resolution of ≃700pcx1400pc along the major and minor axis of the galaxy. A position-velocity cut along the minor axis reveals a reversal of the gas streaming of >50km/s, comparable to those found towards M51. We derive an H₂-mass of 1.6x10⁹M_☉. By comparing this with dust continuum observations and taking a contribution of 2x10⁸M_☉ of HI into account, we derive for the ISM in NGC3627 an integrated gas-to-dust ratio of 100 which is identical with the integrated value for the Milky Way. This subject is discussed in the view of recent 1.2mm dust continuum observations of two other galaxies. A detailed investigation of the the position-velocity diagrams reveal the presense of a small-sized (≲200pc) nuclear bar which rotates rigidly with an angular velocity of {OMEGA}≃720km/s/kpc and which has a dynamical mass of 4.3x10⁸M_☉. This fast rotating bar is surrounded by a differentially rotating disk from which, at a radius of ≃200pc, a nuclear spiral structure emerges. Both the presence of a nuclear bar and the inner spiral structure is in agreement with dynamical models concerning bar evolution in tidally interacting disk galaxies.