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Session 48 - Spiral & Field Galaxies.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center

[48.05] The Highly Flattened Dark Halo of NGC 4244

R. P. Olling (U. Southampton)

In a previous paper (Olling 1995, AJ, 110, 591) a method was developed to determine the shapes of dark matter halos of spiral galaxies from an accurate determination of the rotation curve and the flaring of the gas layer. Here this method is applied to the almost edge-on spiral NGC 4244.

I present sensitive high resolution VLA B, C, and D array observations in the 21-cm spectral line of neutral atomic hydrogen of the nearby Scd galaxy NGC 4244.

The observed flaring of the HI beyond the optical disk puts significant constraints on the dark matter halo, which are almost independent of the stellar mass-to-light ratio. I find that NGC 4244's dark matter halo is highly flattened: c/a=0.1 - 0.5. Alternatively, the measured flaring curve is consistent with a round halo if the gaseous velocity dispersion ellipsoid is anisotropic. In that case the vertical dispersion of the gas is 50 - 70dispersion.

A new technique is presented to determine simultaneously the inclination and the thickness of the gas layer from high resolution HI observations. This procedure uses the apparent widths at many azimuths rather than just the edge channels, and can be used at inclinations as low as 60^o .

Program listing for Tuesday