  Let f traverse a sequence of classical holomorphic newforms of fixed weight
and increasing squarefree level q tending to infinity. We prove that the
pushforward of the mass of f to the modular curve of level 1 equidistributes
with respect to the Poincar\'{e} measure.
  Our result answers affirmatively the squarefree level case of a conjecture
spelled out by Kowalski, Michel and Vanderkam (2002) in the spirit of a
conjecture of Rudnick and Sarnak (1994).
  Our proof follows the strategy of Holowinsky and Soundararajan (2008) who
show that newforms of level 1 and large weight have equidistributed mass. The
new ingredients required to treat forms of fixed weight and large level are an
adaptation of Holowinsky's reduction of the problem to one of bounding shifted
sums of Fourier coefficients (which on the surface makes sense only in the
large weight limit), an evaluation of the p-adic integral needed to extend
Watson's formula to the case of three newforms where the level of one divides
but need not equal the common squarefree level of the other two, and some
additional technical work in the problematic case that the level has many small
prime factors.
