Lenses in the forest: cross correlation of the Lyman-alpha flux with cosmic microwave background lensing.
We present a theoretical estimate for a new observable: the cross correlation between the Lyman-alpha flux fluctuations in quasar spectra and the convergence of the cosmic microwave background as measured along the same line of sight. As a first step toward the assessment of its detectability, we estimate the signal-to-noise ratio using linear theory. Although the signal-to-noise is small for a single line of sight and peaks at somewhat smaller redshifts than those probed by the Lyman-alpha forest, we estimate a total signal-to-noise of 9 for cross correlating quasar spectra of SDSS-III with Planck and 20 for cross correlating with a future polarization based cosmic microwave background experiment. The detection of this effect would be a direct measure of the neutral hydrogen-matter cross correlation and could provide important information on the growth of structures at large scales in a redshift range which is still poorly probed.
Institut d'Astrophysique de Paris, CNRS-UMR 7095, Université Paris VI Pierre et Marie Curie, 98 bis boulevard Arago, 75014 Paris, France. avalli@fnal.gov
Alberto
A
Vallinotto
Sudeep
S
Das
David N
DN
Spergel
Matteo
M
Viel