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First Results of a Survey of Neutral Hydrogen in 500 Southern Galaxies

Published online by Cambridge University Press:  25 April 2016

Hugo van Woerden ,
W. M. Goss ,
U. Mebold ,
Betty Siegman  and
T. G. Hawarden
Hugo van Woerden
Affiliation:
Division of Radiophysics, CSIRO, Sydney
W. M. Goss
Affiliation:
Division of Radiophysics, CSIRO, Sydney
Betty Siegman
Affiliation:
Division of Radiophysics, CSIRO, Sydney
T. G. Hawarden
Affiliation:
U.K. Schmidt Telescope Unit, Coonabarabran, N.S.W
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Extract

Observations of the 21 cm line of neutral hydrogen can provide several integral properties of galaxies. The systemic velocity Vsvs indicates the distance Δ via the Hubble relation or through group membership. The integral over velocity of the flux density profile, ∫S dV, immediately yields the amount of neutral hydrogen in the galaxy: MH ∝ Δ2∫S dV (neglecting optical-depth effects). The profile width W and the inclination i (derived from the optical axial ratio), together with the (optical) angular diameter a, supply the ‘indicative mass’ Mi ∝ (W/sin i)2 a △ (Bottinelli et al. 1968; Balkowski 1973), which is a fair estimate of the total mass of the system. In addition, as shown by Tully and Fisher (1976), the profile width is a good indicator of luminosity L. The quantities and L, which are (at least roughly) representative of the amounts of matter and of gaseous and luminous material in the system, give an indication of its composition. Together with the linear diameter a△, these quantities contain clues as to galaxy formation and evolution.

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Contributions
Information
Publications of the Astronomical Society of Australia , Volume 3 , Issue 1 , September 1976 , pp. 68 - 70
Copyright
Copyright © Astronomical Society of Australia 1976

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References

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