On the relation between the radial alignment of dark matter subhaloes and host mass in cosmological simulations

We explore the dependence of the radial alignment of subhaloes on the mass of the host halo they orbit in. As the effect is seen on a broad range of scales including massive clusters as well as galactic systems it only appears natural to explore this phenomenon by means of cosmological simulations covering the same range in masses. We have 25 well resolved host dark matter haloes at our disposal ranging from 10(15) h(-1)M(circle dot) down to 1012 h(-1)M(circle dot) each consisting of order of a couple of million particles within the virial radius. We observe that subhaloes tend to be more spherical than isolated objects. Both the distributions of sphericity and triaxiality of subhaloes are Gaussian-distributed with peak values of < s >approximate to 0.80 and < T > approximate to 0.56, irrespective of host mass. Interestingly, we note that the radial alignment is independent of host halo mass and the distribution of cos. ( i. e. the angle between the major-axis E-a of each subhalo and the radius vector of the subhalo in the reference frame of the host) is well fitted by a simple power law P(cos theta)alpha cos(4)theta with the same fitting parameters for all host haloes.