Gauging the Contribution of X-ray Sources to Reionization Through the
  Kinetic Sunyaev-Zel'dovich Effect
  Measurements of the kinetic Sunyaev-Zel'dovich (kSZ) effect from instruments
such as the South Pole Telescope (SPT) and the Atacama Cosmology Telescope
(ACT) will soon put improved constraints on reionization. Popular models assume
that UV photons alone are responsible for reionization of the intergalactic
medium. We explore the effects of a significant contribution of X-rays to
reionization on the kSZ signal. Because X-rays have a large mean free path
through the neutral intergalactic medium, they introduce partial ionization in
between the sharp-edged bubbles created by UV photons. This smooth ionization
component changes the power spectrum of the cosmic microwave background (CMB)
temperature anisotropies. We quantify this effect by running semi-numerical
simulations of reionization. We test a number of different models of
reionization without X-rays that have varying physical parameters, but which
are constrained to have similar total optical depths to electron scattering.
These are then compared to models with varying levels of contribution to
reionization from X-rays. We find that models with more than a 10% contribution
from X-rays produce a significantly lower power spectrum of temperature
anisotropies than all the UV-only models tested. The expected sensitivity of
SPT and ACT may be insufficient to distinguish between our models, however, a
non-detection of the kSZ signal from the epoch of reionization could result
from the contribution of X-rays. It will be important for future missions with
improved sensitivity to consider the impact of X-ray sources on reionization.
