The alignment of SDSS satellites with the VPOS: effects of the survey
  footprint shape
  It is sometimes argued that the uneven sky coverage of the Sloan Digital Sky
Survey (SDSS) biases the distribution of satellite galaxies discovered by it to
align with the polar plane defined by the 11 brighter, classical Milky Way (MW)
satellites. This might prevent the SDSS satellites from adding significance to
the MW's Vast Polar Structure (VPOS). We investigate whether this argument is
valid by comparing the observed situation with model satellite distributions
confined to the exact SDSS footprint area. We find that the SDSS satellites
indeed add to the significance of the VPOS and that the survey footprint rather
biases away from a close alignment between the plane fitted to the SDSS
satellites and the plane fitted to the 11 classical satellites. Finding the
observed satellite phase-space alignments of both the classical and SDSS
satellites is a ~5{\sigma} event with respect to an isotropic distribution.
This constitutes a robust discovery of the VPOS and makes it more significant
than the Great Plane of Andromeda (GPoA). Motivated by the GPoA, which consists
of only about half of M31's satellites, we also estimate which fraction of the
MW satellites is consistent with being part of an isotropic distribution.
Depending on the underlying satellite plane width, only 2 to 6 out of the 27
considered MW satellites are expected to be drawn from isotropy, and an
isotropic component of >50% of the MW satellite population is excluded at 95%
confidence.
