A Possible Cold Imprint of Voids on the Microwave Background Radiation
  We measure the average temperature decrement on the cosmic microwave
background (CMB) produced by voids selected in the SDSS DR7 spectroscopic
redshift galaxy catalog, spanning redshifts $0<z<0.44$. We find an imprint of
amplitude between 2.6 and 2.9$\mu K$ as viewed through a compensated top-hat
filter scaled to the radius of each void; we assess the statistical
significance of the imprint at ~2$\sigma$. We make crucial use of $N$-body
simulations to calibrate our analysis. As expected, we find that large voids
produce cold spots on the CMB through the Integrated Sachs-Wolfe (ISW) effect.
However, we also find that small voids in the halo density field produce hot
spots, because they reside in contracting, larger-scale overdense regions. This
is an important effect to consider when stacking CMB imprints from voids of
different radius. We have found that the same filter radius that gives the
largest ISW signal in simulations also yields close to the largest detected
signal in the observations. However, although it is low in significance, our
measured signal is much higher-amplitude than expected from ISW in the
concordance $\Lambda$CDM universe. The discrepancy is also at the ~2$\sigma$
level. We have demonstrated that our result is robust against the varying of
thresholds over a wide range.
