Accession Number : ADA320127

Title :   The Hydrogen Contribution to the Dark Matter in Draco.

Descriptive Note : Master's thesis,

Corporate Author : AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH

Personal Author(s) : Boyd, Marcus A.

PDF Url : ADA320127

Report Date : JAN 1997

Pagination or Media Count : 63

Abstract : High-precision velocity measurements of faint individual stars in the Galactic dwarf spheroidal galaxy Draco indicate that the mass-to-light ratio in this system may be as high as approximately 100. Various possible forms of dark matter have been proposed for this class of objects, but a more recent analysis based on the Projected Mass Estimator technique seems to suggest that the non-luminous mass is distributed and may trace the stellar population. Here, we examine in detail the possible contribution of H2 to the dark matter content of Draco and conclude that most of its mass may be in the form of approximately 10 to 100 M H2 clouds if the typical dust grain size is at least approximately 90 times larger (i.e., approx. greater than 48 microns) than in our galaxy. This may be consistent with the fact that the dominant dust destroying mechanisms (e.g., supernova shocks) that suppress the average grain size in the galactic plane are absent in typical dwarf spheroidals. Thus the absence of dynamical processes (such as supernova explosions) that would normally induce massive star formation (which is non-existent in Draco) may also account for the large grain size. The lack of any observed extinction in this system would be consistent with the very low areal covering fraction (approx. 0.1 - 1%) of the clouds. We show that the predicted H content in Draco is then below current 21 cm detection limits, and that even NICMOS on HST would be hard pressed to detect the prominent J and K band emission lines of excited H2.

Descriptors :   *DWARF STARS, *INTERSTELLAR MATTER, ULTRAVIOLET RADIATION, MOLECULAR VIBRATION, MASS, THESES, EMISSION SPECTRA, HYDROGEN, ASTROPHYSICS, GALACTIC COSMIC RAYS, STELLAR EVOLUTION, SUPERNOVAE, NEUTRON STARS.

Subject Categories : Astrophysics

Distribution Statement : APPROVED FOR PUBLIC RELEASE