Constraining low redshift [CII] Emission by Cross-Correlating FIRAS and
  BOSS Data
  We perform a tomographic cross-correlation analysis of archival FIRAS data
and the BOSS galaxy redshift survey to constrain the amplitude of [CII]
$^2P_{3/2}\rightarrow$ $^2P_{1/2}$ fine structure emission. Our analysis
employs spherical harmonic tomography (SHT), which is based on the angular
cross-power spectrum between FIRAS maps and BOSS galaxy over-densities at each
pair of redshift bins, over a redshift range of $0.24<z<0.69$. We develop the
SHT approach for intensity mapping, where it has several advantages over
existing power spectral estimators. Our analysis constrains the product of the
[CII] bias and [CII] specific intensity, $b_{[CII]}I_{[CII]i}$, to be $<0.31$
MJy/sr at $z {\approx} 0.35$ and $<0.28$ MJy/sr at $z {\approx} 0.57$ at $95\%$
confidence. These limits are consistent with most current models of the [CII]
signal, as well as with higher-redshift [CII] cross-power spectrum measurements
from the Planck satellite and BOSS quasars. We also show that our analysis, if
applied to data from a more sensitive instrument such as the proposed PIXIE
satellite, can detect pessimistic [CII] models at high significance.
