NEUTRAL HYDROGEN IN THE EDGE-ON SPIRAL GALAXY NGC-3044 GLOBAL PROPERTIES AND DISCOVERY OF H-I SUPERSHELLS

The first detailed VLA mapping of the neutral hydrogen distribution in the isolated, edge-on spiral galaxy NGC 3044 is presented. Physical p arameters such as M-HI M-T, etc. determined for this galaxy are typica l for galaxies of its morphological class (SBc). We have modeled the H I spectra in order to derive its global density and velocity distribu tions. An H I scale height of 420 h(-1) pc is thus found. This can be compared to the impressive radio continuum halo, previously found to e xtend to 8 kpc above the midplane. The present study reveals an asymme try in the H I distribution as well as numerous high-latitude H I stru ctures at various galactocentric radii. The approaching (northwest) si de of the galaxy is 14% less massive than the receding side and its ro tation curve does not reach terminal velocity. The rotation curve of t he receding (southeast) side, however, resembles that of a normal gala xy. Twelve high-latitude features were cataloged, of which four exhibi t the signature of an expanding shell. There is some correlation of th ese features with features observed in the radio continuum from indepe ndent data. The most massive shell (feature 10) extends out to 6 h(-1) kpc above the galactic disk. The radii and masses of these shells ran ge from 1.2-2.0 h(-1) kpc and 1.6 x 10(7)-5.5 x 10(7) h(-2) M-., respe ctively. We have investigated the possibility that the supershells cou ld have been produced by external impacting clouds, but conclude that this scenario is unattractive, given the age of the shells, the isolat ion of the galaxy, and the lack of any observed features sufficiently massive to form the shells in the vicinity of the galaxy. Therefore, a n internal origin is suggested. Since the implied input energies from supernovae are extremely high (e.g., from 1.4 x 10(53)-7.4 x 10(55) h( -2) ergs, corresponding to 400-74,000 supernovae), we suggest that som e additional energy (e.g., from magnetic fields) may be needed to prod uce the observed supershells.