Fitting functions for a disk-galaxy model with different ACDM-halo profiles (Research Note) (original) (raw)

2010, Astronomy and Astrophysics

Aims. We present an adaptation of the standard scenario of disk-galaxy formation to the concordant ΛCDM cosmology aimed to derive analytical expressions for the scale length and rotation speed of present-day disks that form within four different, cosmologically motivated protogalactic dark matter halo-density profiles. Methods. We invoke a standard galaxy-formation model that includes virial equilibrium of spherical dark halos, specific angular momentum conservation during gas cooling, and adiabatic halo response to the gas inflow. The mean mass-fraction and mass-to-light ratio of the central stellar disk are treated as free parameters whose values are tuned to match the zero points of the observed sizeluminosity and circular speed-luminosity relations of galaxies. Results. We supply analytical formulas for the characteristic size and rotation speed of disks built inside Einasto r 1/6 , Hernquist, Burkert, and Navarro-Frenk-White dark matter halos. These expressions match simultaneo...

The core density of dark matter halos: a critical challenge to the Lambda-CDM paradigm?

1999

We compare the central mass concentration of Cold Dark Matter halos found in cosmological N-body simulations with constraints derived from the Milky Way disk dynamics and from the Tully-Fisher relation. For currently favored values of the cosmological parameters ($\Omega_0 \sim 0.3$; Lambda0=1−Omega0sim0.7\Lambda_0=1-\Omega_0 \sim 0.7Lambda0=1−Omega0sim0.7; hsim0.7h \sim 0.7hsim0.7; COBE- and cluster abundance-normalized sigma8\sigma_8sigma8; Big-Bang nucleosynthesis Omegab\Omega_bOmegab), we find that halos with circular velocities comparable to the rotation speed of the Galaxy have typically {\it three times} more dark matter inside the solar circle than inferred from observations of Galactic dynamics. Such high central concentrations of dark matter on the scale of galaxy disks also imply that stellar mass-to-light ratios much lower than expected from population synthesis models must be assumed in order to reproduce the zero-point of the Tully-Fisher relation. Indeed, even under the extreme assumption that {\it all} baryons in a dark halo are turned into stars, disks with conventional III-band stellar mass-to-light ratios ($M/L_I \sim 2 \pm 1 (M/L_I)_{\odot}$) are about two magnitudes fainter than observed at a given rotation speed. We examine several modifications to the Lambda\LambdaLambdaCDM model that may account for these discrepancies and conclude that agreement can only be accomplished at the expense of renouncing other major successes of the model. Reproducing the observed properties of disk galaxies thus appears to demand substantial revision to the currently most successful model of structure formation.

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