Strong orientation dependence of surface mass density profiles of dark
  haloes at large scales
  We study the dependence of surface mass density profiles, which can be
directly measured by weak gravitational lensing, on the orientation of haloes
with respect to the line-of-sight direction, using a suite of $N$-body
simulations. We find that, when major axes of haloes are aligned with the
line-of-sight direction, surface mass density profiles have higher amplitudes
than those averaged over all halo orientations, over all scales from $0.1$ to
$100\,\mathrm{Mpc}/h$ we studied. While the orientation dependence at small
scales is ascribed to the halo triaxiality, our results indicate even stronger
orientation dependence in the so-called two-halo regime, up to
$100\,\mathrm{Mpc}/h$. The orientation dependence for the two-halo term is well
approximated by a multiplicative shift of the amplitude and therefore a shift
in the halo bias parameter value. The halo bias from the two-halo term can be
overestimated or underestimated by up to $\sim 30 \%$ depending on the viewing
angle, which translates into the bias in estimated halo masses by up to a
factor of two from halo bias measurements. The orientation dependence at large
scales originates from the anisotropic halo-matter correlation function, which
has an elliptical shape with the axis ratio of $\sim 0.55$ up to $100\,
\mathrm{Mpc}/h$. We discuss potential impacts of halo orientation bias on other
observables such as optically selected cluster samples and a clustering
analysis of large-scale structure tracers such as quasars.
