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Session 24 - Disks, Bars & Halos.
Oral session, Wednesday, January 07
International Ballroom East,

[24.05] Dark Baryons and Rotation Curves

A. Burkert (MPI for Astronomy, Germany), J. Silk (U. California, Berkeley)

The dark matter rotation curve of DDO 154 has been measured out to about 20 disk scale lengths with high accuracy. It provides an ideal laboratory for testing the universal dark matter density profile predictions of cosmological cold dark matter models. We find that DDO's rotation curve cannot be fit by the cosmological predictions either at small radii, as previously noted, or at large radii. We advocate a resolution of this dilemma by postulating the existence of a dark spheroid of baryons amounting to several times the mass of the observed disk component and comparable to that of the cold dark matter component. Such an additional mass component provides an excellent fit to the rotation curve, provided that the outer halo is still cold dark matter-dominated with a density profile and mass-radius scaling relation as predicted by standard CDM-dominated models. The universal existence of such dark baryonic spheroidal components provides a natural explanation of the universal rotation curves observed in spiral galaxies, may have a similar origin and composition to the local counterpart that has been detected as MACHOs in our own galactic halo via gravitational microlensing, and is consistent with, and even motivated by, primordial necleosynthesis estimates of the baryon fraction.

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Program listing for Wednesday