Modelling the Neutral Hydrogen ISM: A Better Kinematic Distance Tool
Abstract
An advanced approach to the kinematic distance method is developed. The method is applicable to second and third quadrant Galactic objects with known velocities. It is based on fitting a model of the density and velocity features in an isothermal neutral hydrogen disk to observed H I data. The velocity field of the gas is modelled with a power-law for basic circular rotation underlying non-circular motions from a two-armed density wave pattern. With a reasonable number of adjustable parameters and constraints the model reproduces observations towards many Galactic objects, and accurate distances are found from the modelled velocity field. High resolution H I spectral line data from the Canadian Galactic Plane Survey (CGPS) are used to discriminate clouds from the intercloud medium (the "stratum") for which the model is intended. The ability of the model to reproduce these data is demonstrated in one- [Tb(v)] and two- [Tb(l,v)] dimensional fits. Distances to 22 H II regions and SNRs calculated by the fitted velocity field compare extremely well with other kinematically-independent distances. A new picture of the spiral distribution of H II regions in the Outer Galaxy emerges when the method is used on 70 such bright nebulae.The Canadian Galactic Plane Survey is a Canadian project with international partners, and is supported by a grant from the Natural Sciences and Engineering Research Council of Canada (NSERC)
- Publication:
-
American Astronomical Society Meeting Abstracts #208
- Pub Date:
- June 2006
- Bibcode:
- 2006AAS...208.2102F