The shape of the dark matter halo of NGC 4244

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Session 6 -- Normal Galaxies: Structure and Dynamics
Display presentation, Monday, 9:20-6:30, Pauley Room

[6.18] The shape of the dark matter halo of NGC 4244

Rob Olling, J.H. van Gorkom (Columbia University)

We present VLA HI observations with unprecedented angular and velocity resolution of the edge-on Sc galaxy NGC 4244. The velocity dispersion in the gas is found to be varying from 10 km/s in the inner galaxy, to 5 km/s at the edge of the stellar disk, beyond which it increases to about 8 km/s. Our measurements of the thickness of the Hydrogen layer and the gaseous velocity dispersion directly yield the local total mass density.

The contribution of the dark halo can be found by subtracting the mass densities from the visible matter, stars \& gas. We parameterize the dark halo as a flattened isothermal sphere with core radius $R_c$, central density $\rho_0$ and flattening $q$. The flattening of the dark halo is found by demanding that the total (luminous \& dark) mass distribution, produces the observed rotation curve.

The possible dark halo flattenings range from E0 to E8, with a ``most likely'' value of E6. Uncertainties in the gaseous velocity dispersion are the dominant source of error.

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