Blending and obscuration in weak lensing magnification
  We test the impact of some systematic errors in weak lensing magnification
measurements with the COSMOS 30-band photo-$z$ Survey flux limited to
$I_{auto}<25.0$ using correlations of both source galaxy counts and magnitudes.
Systematic obscuration effects are measured by comparing counts and
magnification correlations. We use the ACS-HST catalogs to identify potential
blending objects (close pairs) and perform the magnification analyses with and
without blended objects. We find that blending effects start to be important
($\sim$ 0.04~mag obscuration) at angular scales smaller than 0.1 arcmin.
Extinction and other systematic obscuration effects can be as large as 0.10~mag
(U-band) but are typically smaller than 0.02~mag depending on the band. After
applying these corrections, we measure a $3.9\sigma$ magnification signal that
is consistent for both counts and magnitudes. The corresponding projected mass
profiles of galaxies at redshift $z \simeq 0.6$ ($M_I \simeq -21$) is $\Sigma=
25\pm 6 M_{sun}h^3/pc^2$ at 0.1 Mpc/h, consistent with NFW type profile with
$M_{200} \simeq 2 \times 10^{12} M_{sun} h/pc^2$. Tangential shear and
flux-size magnification over the same lenses show similar mass profiles. We
conclude that magnification from counts and fluxes using photometric redshifts
has the potential to provide complementary weak lensing information in future
wide field surveys once we carefully take into account systematic effects, such
as obscuration and blending.
