The dark matter halo shape of edge-on disk galaxies - IV. UGC 7321

摘要

This is the fourth paper in a series in which we attempt to put constraintson the flattening of dark halos in disk galaxies. We observed for this purposethe HI in edge-on galaxies, where it is in principle possible to measure theforce field in the halo vertically and radially from gas layer flaring androtation curve decomposition respectively. We have analysed the HI channel mapsto accurately measure all four functions that describe the HI kinematics and 3Ddistribution: the radial HI surface density, the HI vertical thickness, therotation curve and the HI velocity dispersion. In this paper we analyse thesedata for the edge-on galaxy UGC7321. We measured the stellar mass distribution($M=3\times10^8$ \msun with $M/L_R\lesim0.2$), finding that the vertical forceof the gas disk dominates the stellar disk at all radii. We find that thevertical force puts a much stronger constraint on the stellar mass-to-lightratio than rotation curve decomposition. Fitting of the vertical force fieldderived from the flaring and velocity dispersion of the HI revealed thatUGC7321 has a spherical halo density distribution with a flattening of $q = c/a= 1.0 \pm 0.1$.