We present, for five spiral galaxies, HI data which, along with the Hα rotation curves, are used to derive the distribution of dark matter within these objects. A new method for extracting rotation curves from HI data cubes is presented, which takes into account the existence of a warp and minimizes projection effects. The rotation curves obtained are tested by taking them as input in the construction of model data cubes that are compared with the observed ones: the agreement is excellent. Model data cubes built using rotation curves obtained with standard methods, such as the first-moment analysis, however, fail the test. The HI rotation curves agree well with the Hα data, where they coexist. Moreover, the combined Hα + HI rotation curves are smooth, symmetric and extend to large radii.The rotation curves are decomposed into stellar, gaseous and dark matter contributions, and the inferred density distribution is compared with various mass distributions: dark haloes with a central density core, Λ cold dark matter (ΛCDM) haloes (NFW and Moore profiles), HI scaling and MOND. The observations point to haloes with constant-density cores of size rcore ~ ropt and central densities scaling approximately as ρ0 ~ r-2/3core. ΛCDM models (which predict a central cusp in the density profile) are in clear conflict with the data. HI scaling and MOND cannot account for the observed kinematics: we find some counter-examples.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2004
- methods: data analysis: galaxies: kinematics and dynamics: galaxies: spiral: dark matter;
- 23 pages, 15 figures, MNRAS accepted. Comments welcome. Version with Figs. 1 and 3 at full resolution available at http://www.astro.uni-bonn.de/~ggentile/paper_highres.ps.gz