Recovering cores and cusps in dark matter haloes using mock velocity field observations

We present mock DensePak Integral Field Unit (IFU) velocity fields, rotation curves and halo fits for disc galaxies formed in spherical and triaxial cuspy dark matter haloes and spherical cored dark matter haloes. The simulated galaxies are ‘observed' under a variety of realistic conditions to determine how well the underlying dark matter halo can be recovered and to test the hypothesis that cuspy haloes can be mistaken for cored haloes. We find that the appearance of the velocity field is distinctly different depending on the underlying halo type. We also find that we can successfully recover the parameters of the underlying dark matter halo. Cuspy haloes appear cuspy in the data and cored haloes appear cored. Our results suggest that the cores observed using high-resolution velocity fields in real dark matter dominated galaxies are genuine and cannot be ascribed to systematic errors, halo triaxiality or non-circular motion

High Resolution Optical Velocity Fields of Low Surface Brightness Galaxies and the Density Profiles of Dark Matter Halos

This dissertation investigates the behavior of cold dark matter (CDM) on galaxy scales. We present well-resolved Halpha velocity fields of the central regions of 17 dark matter-dominated low surface brightness (LSB) and dwarf galaxies observed with the DensePak Integrated Field Unit. We derive rotation curves from the two-dimensional data and compare them to published long-slit and HI rotation curves. We find broad consistency between the independent data sets. Under several assumptions about the velocity contribution from the baryons, we fit the dark matter component with cuspy NFW and cored pseudoisothermal halos. We find the data to be better described by cored dark matter halos. For the majority of galaxies, NFW halo fits either cannot be made or the implied concentrations are too low for LCDM. The shapes of the NFW rotation curves are also inconsistent with the galaxy rotation curves. We find that CDM predicts a substantial cusp mass excess near the centers of the galaxies and that the ratio of predicted to observed dark matter increases as baryons become more important. We investigate claims that systematic effects including beam smearing, slit misplacement and noncircular motions are responsible for slowly rising long-slit and HI rotation curves. We find the DensePak rotation curves to also be slowly rising, supporting the idea that this is an intrinsic feature of LSB rotation curves. We also model the two-dimensional NFW halo and test several modifications to the potential in an attempt to simultaneously reconcile both the NFW velocity field and rotation curve with observed galaxy data. We present mock DensePak velocity fields and rotation curves of axisymmetric and non-axisymmetric potentials. We find that a non-axisymmetric NFW potential with a constant axis ratio can reduce the cusp mass excess in the observed galaxy data, but the observer's line-of-sight must be along the minor axis of the potential, and the NFW pinch is not erased from the velocity field. We find that a non-axisymmetric NFW potential with a radially varying axis ratio tends to wash out the NFW pinch but introduces a twist to the velocity field

Two Dimensional Velocity Fields of Low Surface Brightness Galaxies

We present high resolution two dimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for LCDM.Comment: 2 pages, 1 figure, to appear in the XXIst IAP Colloquium "Mass Profiles and Shapes of Cosmological Structures", Paris 4-9 July 2005, (Eds.) G. Mamon, F. Combes, C. Deffayet, B. Fort, (EDP Sciences