Lyman-alpha polarization intensity mapping

We present a formalism that incorporates hydrogen Lyman-alpha (Ly$\alpha$) polarization into the intensity mapping approach. Using the halo model, and \lya emission profiles based on galaxy simulations and observations, we derive auto and cross power spectra for the \lya total intensity, $I$, polarized intensity, $\po$, degree of polarization, $\Pi=\po/I$, and two new quantities, the astrophysical $E$ and $B$ modes of \lya polarization. A characteristic turnover is visible for the one-halo terms of the fiducial power spectra of $\Pi$ and $E$. The position of this feature depends on redshift, and it signals the average size of the halos that dominate the polarization signal at a given time. The impact of varying model parameters depends on the considered polarization quantity, as well as on redshift. Therefore, the comparison of various \lya polarization quantities and redshifts can break degeneracies between competing effects, and can reveal the average shape and extent of the emission profiles, which, in turn, are associated to the physical properties of the cool gas in galaxy halos. Furthermore, measurements of \lya $E$ and $B$ modes can be used as probes of the average degree of anisotropy in the emission and in the distribution of neutral gas in halos across redshifts. Our predicted power spectra, in the multipole range $\sim$ a few times $10^2 \lesssim \ell \lesssim 5\times 10^5$, appear detectable with current technology up to the redshifts of early cosmic reionization, $z\sim 11$. The signal-to-noise ratios reach values as high as $S/N\gtrsim100$ at the one-halo peaks, provided that foreground contamination is known. Contamination from interlopers is expected to be small for the case of polarization, because the interlopers need to also be polarized. Overall, \lya polarization appears as a new intensity mapping probe that boosts the amount of physical information on galaxies and their surroundings retrievable from the observations, most of it not achievable with total emission alone.