CO OBSERVATIONS OF THE SPIRAL GALAXY NGC-3627

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 t he two prominent spiral arms and the central disk. The two spiral arms are found to be markedly different in their GO-extent and observed ve locity dispersion which is probably caused by interaction with other g alaxies 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 wel l as an investigation of the CO(2-1)/CO(1-0) ratio hint at a considera bly smaller CO/H-2-conversion factor for the central emission maximum than towards other locations of the disk. Heating of the ISM due to tu rbulent motion in the nuclear disk/bar appears to be responsible for t his 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 velocit y field reveals the presence of streaming motions with deprojected vel ocities of approximate to 30 km s(-1) towards both spiral arms despite the relatively low resolution of approximate to 700 pc x 1400 pc alon g the major and minor axis of the galaxy. A position-velocity cut alon g the minor axis reveals a reversal of the gas streaming of > 50 km s( -1), comparable to those found towards M51. We derive an H-2-mass of 1 .6 . 10(9) M.. By comparing this with dust continuum observations and taking a contribution of 2 . 10(8) M. of HI into account, we derive fo r the ISM in NGC 3627 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 1.2 mm dust continuum observations of two other galaxies. A detailed investigation of the the position-velo city diagrams reveal the presense of a small-sized (less than or simil ar to 200 pc) nuclear bar which rotates rigidly with an angular veloci ty of Ohm approximate to 720 km s(-1) kpc(-1) and which has a dynamica l mass of 4.3 . 10(8) M.. This fast rotating bar is surrounded by a di fferentially rotating disk from which, at a radius of approximate to 2 00 pc, a nuclear spiral structure emerges. Both the presence of a nucl ear bar and the inner spiral structure is in agreement with dynamical models concerning bar evolution in tidally interacting disk galaxies.