The radial alignment of dark matter subhaloes: from simulations to observations

We explore the radial alignment of subhaloes in two-dimensional projections of cosmological simulations. While most other recent studies focused on quantifying the signal utilizing the full three-dimensional spatial information any comparison to observational data has to be done in projection along random lines-of-sight. We have a suite of well-resolved host dark matter haloes at our disposal ranging from 6 x 10(14) to 6 x 10(13) h(-1) M(circle dot). For these host systems, we do observe that the major axis of the projected two-dimensional mass distribution of subhaloes aligns with its (projected) distance vector to the host's centre. The signal is actually stronger than the observed alignment. However, when considering only the innermost 10-20 per cent of the subhalo's particles for the two-dimensional shape measurement, we recover the observed correlation. We further acknowledge that this signal is independent of subhalo mass.