Physics
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998stin...9984014s&link_type=abstract
Nobeyama Radio Observatory Report, p. 13
Physics
Imaging Techniques, Ionized Gases, Vertical Motion, Monatomic Gases, Molecular Gases, Stellar Mass, Star Formation, Spectroscopy, Solvents, Slits, Sensitivity, Narrowband, Massive Stars, High Resolution, Gravitational Fields, H Ii Regions
Scientific paper
We carried out a high-resolution C-12O J = 1 - 0 imaging of NGC 628 (i = 6 deg, D = 10 Mpc) to study the vertical motions of the molecular gas, and a high-dispersion scanning-slit spectroscopy of H(alpha) emission in NGC 628 and NGC 3938 (i = 10 deg, D = 10 Mpc) to trace the vertical motions of the ionized gas. Supplementary images in narrow-band H(alpha) and J- and K' bands were also obtained. The vertical velocity dispersion of the molecular gas is 6.4 +/- 1.5 km/ s throughout the inner (0.5-6 kpc) disk without any systematic radial variation. The vertical velocity dispersion of molecular gas at 5 kpc from the center is smaller than that of atomic gas at the same distance by a factor of approx. equal 1.5. This factor approx. equal 1.5 difference naturally explains the fact that molecular disks in spiral galaxies are generally thinner than atomic gas disks by a factor of approx. equal 1.5. Although there is a significant point-by-point variation of the velocity dispersion, no simple correlations with CO brightness (gas surface density), K'-band brightness (stellar gravitational potential), nor H(alpha) brightness (star-formation activity) are observed. There is no high-velocity (absolute value of(delta)upsilon(sub perpendicular to) greater than 30 km/s) molecular gas detected with our 5(sigma) sensitivity of approx. 5 x 105 solar mass per the 680 pc beam. This suggests that the disk-halo connection of the ISM in the form of molecular gas is a rare phenomenon. In contrast, high-dispersion H(alpha) spectroscopy of NGC 628 and NGC 3938 revealed that there are hints of peculiar vertical motions (absolute value of (delta)upsilon(sub perpendicular to) greater than 30 km/ s) of ionized gas probably related with disk-halo connection of the ISM. The regions with the peculiar motions are associated with bright HII regions and may originate from expanding motions associated with massive star formation activities.
Sakamoto Seiichi
Tomita Akihiko
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