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Rotating Halos and Heavy Disks: The Case of NGC 2915

Published online by Cambridge University Press:  26 May 2016

Frédéric S. Masset  and
Martin Bureau
Frédéric S. Masset
Affiliation:
SAp, CE-Saclay, 91191 Gif/Yvette Cedex, France
Martin Bureau
Affiliation:
Columbia Astrophysics Laboratory, 550 West 120th Street, 1027 Pupin Hall, MC 5247, New York, NY 10027, USA

Abstract

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NGC 2915 is a blue compact dwarf galaxy embedded in an extended, low surface brightness HI disk with a bar and two-armed spiral structure. Common mechanisms are unable to explain those patterns and disk dark matter or a rotating triaxial dark halo were proposed as alternatives. Hydrodynamical simulations were run for each case and compared to observations using customized column density and kinematic constraints. the spiral structure can be accounted for by an unseen bar or triaxial halo, but the large bar mass or halo pattern frequency required make it unlikely that the spiral is driven by an external perturber. in particular, the spin parameter lambda is much higher than predicted by current CDM structure formation scenarios. Massive disk models show that when the gas surface density is scaled up by a factor of about 10, the disk develops a spiral structure matching the observed one in perturbed density as well as velocity. This suggests that the disk of NGC 2915 contains much more mass than is visible, tightly linked to the neutral hydrogen. A classic (quasi-)spherical halo is nevertheless still required, as increasing the disk mass further to fit the circular velocity curve would make the disk violently unstable

Type
Part 9: Disks
Information
Symposium - International Astronomical Union , Volume 220: Dark Matter in Galaxies , 2004 , pp. 293 - 298
Copyright
Copyright © Astronomical Society of the Pacific 2004 

References

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