Intensity Mapping across Cosmic Times with the Lyman-Alpha Line

TL;DR

This paper models Lyman-alpha emission across cosmic history to evaluate the potential of intensity mapping for studying reionization, star formation, and large-scale structure, highlighting the dominance of diffuse IGM emission at high redshifts.

Contribution

It provides a comprehensive model of Ly-alpha emission including IGM and halo contributions, and assesses the feasibility of intensity mapping for probing cosmic evolution and foreground contamination.

Findings

Diffuse IGM emission dominates Ly-alpha intensity up to z~10.

Intensity mapping can detect Ly-alpha fluctuations despite foreground challenges.

Reionization Ly-alpha signals are difficult but possible to measure.

Abstract

We present a quantitative model of Lyman-alpha (Ly-alpha) emission throughout cosmic history and determine the prospects for intensity mapping of spatial fluctuations in the Ly-alpha signal. Since i) our model assumes at z>6 the minimum star formation required to sustain reionization and ii) is based at z<6 on a luminosity function extrapolated from the few observed bright Ly-alpha emitters, this should be considered a lower limit. Mapping the line emission allows probes of reionization, star formation, and large-scale structure (LSS) as a function of redshift. While Ly-alpha emission during reionization has been studied, we also predict the post-reionization signal to test predictions of the intensity and motivate future intensity mapping probes of reionization. We include emission from massive dark matter halos and the intergalactic medium (IGM) in our model. We find agreement with current, measured luminosity functions of Ly-alpha emitters at z<8. However, diffuse IGM emission, not associated with Ly-alpha emitters, dominates the intensity up to z~10. While our model is applicable for deep-optical or near-infrared observers like the SuMIre survey or the James Webb Space Telescope, only intensity mapping will detect the diffuse IGM emission. We also construct a 3D power spectrum model of the Ly\alpha emission, and characterize possible foreground contamination. Finally, we study the prospects of an intensity mapper for measuring Ly-alpha fluctuations while identifying interloper contamination for removal. Our results suggest that while the reionization signal is challenging, Ly-alpha fluctuations can be an interesting new probe of LSS at late times when used in conjunction with other lines like, e.g., H-alpha, to monitor low-redshift foreground confusion.