Accession Number : AD0740396

Title :   Gross Properties of Five Scd Galaxies as Determined from 21 CM Observations,

Corporate Author : OWENS VALLEY RADIO OBSERVATORY PASADENA CALIF

Personal Author(s) : Rogstad,D. H. ; Shostak,G. S.

Report Date : 1972

Pagination or Media Count : 21

Abstract : Neutral hydrogen studies of the five Scd galaxies M33, NGC 2403, IC342, M101 and NGC6946 have revealed substantial similarities in their hydrogen distributions and rotation curves. It is found that about 80% of the observable HI lies within the boundary defined by the Holmberg diameter for each galaxy. The ratio of the HI mass to the total mass contained within this same boundary has a mean value of about 0.11. The central HI surface density is also nearly a constant within the Scd classification. We find that all the HI global properties and ratios are nearly constant or scale approximately with Holmberg radius or total mass. An observed correlation of maximal rotation velocity with Holmberg radius allows characterization of the total mass with only one parameter. Because of the very flat rotation curves observed for thse Scd galaxies, total masses extrapolated to infinite radius are not known. Surface mass-luminosities ratios must reach values of about 20 at the Holmberg radius. (Author)

Descriptors :   (*GALAXIES, MICROWAVE SPECTROSCOPY), EXTRATERRESTRIAL RADIO WAVES, HYDROGEN, RADIO ASTRONOMY, BRIGHTNESS

Subject Categories : Astrophysics

Distribution Statement : APPROVED FOR PUBLIC RELEASE