Intensity mapping with SDSS/BOSS Lyman-alpha emission, quasars and their
  Lyman-alpha forest
  We investigate the large-scale structure of Lyman-alpha emission intensity in
the Universe at redshifts z=2-3.5 using cross-correlation techniques. Our Lya
emission samples are spectra of BOSS Luminous Red Galaxies from Data Release 12
with the best fit model galaxies subtracted. We cross-correlate the residual
flux in these spectra with BOSS quasars, and detect a positive signal on scales
1-15 Mpc/h. We identify and remove a source of contamination not previously
accounted for, due to the effects of quasar clustering on cross-fibre light.
Corrected, our quasar-Lya emission cross-correlation is 50 % lower than that
seen by Croft et al. for DR10, but still significant. Because only 3% of space
is within 15 Mpc/h of a quasar, the result does not fully explore the global
large-scale structure of Lya emission. To do this, we cross-correlate with the
Lya forest. We find no signal in this case. The 95% upper limit on the global
Lya mean surface brightness from Lya emission-Lya forest cross-correlation is
mu < 1.2x10^-22 erg/s/cm^2/A/arcsec^2 This null result rules out the scenario
where the observed quasar-Lya emission cross-correlation is primarily due to
the large scale structure of star forming galaxies, Taken in combination, our
results suggest that Lya emitting galaxies contribute, but quasars dominate
within 15 Mpc/h. A simple model for Lya emission from quasars based on
hydrodynamic simulations reproduces both the observed forest-Lya emission and
quasar-Lya emission signals. The latter is also consistent with extrapolation
of observations of fluorescent emission from smaller scales r < 1 Mpc.
