Abstract:
Being the first spectral line of HI, Lyman-alpha permeates the cosmic web in emission. It has been largely used to study the close environment of galaxies and QSOs (Lyman-alpha blobs/nebulae); but being a resonant line it should scatter through the intergalactic medium. This should make Lyman-alpha an interesting candidate for Intensity Mapping (IM): the study of large-scale by integrating the flux of a given line, without resolving any objects.
In this talk, I will explore the possibility of performing Lyman-alpha IM studies with optical images. At 121.567 nm, Lyman-alpha can be observed from ground telescopes in the redshift range 2<z<6.5. Hence, every image ever taken from a ground telescope contains unresolved Lyman-alpha emission in the background, tracing the cosmic web, although too faint to be observed. Hence, I propose the cross-correlation of optical Lyman-alpha intensity maps with Lyman-alpha forest data, which traces (in absorption) the same cosmic web we are trying to observe in emission.
First, I will briefly go over my previous work with the narrow-band photometric surveys PAUS and JPAS. Second, I will move onto the prospects of performing Lyman-alpha IM with broad-band photometric surveys. Being the cornerstone of optical astronomy, most of the sky has been observed with broad-bands, but they present a significant challenge for Lyman-alpha IM, given their filter width. I will show that with current surveys (DESI Lyman-alpha forest cross-correlated with DECaLS/BASS), we can place competitive upper bounds on average Lyman-alpha emission. Next-generation imaging surveys (LSST, CSST), cross-correlated with upcoming spectroscopic surveys (MUST, MegaMapper) will yield a clear detection of the cosmic web in Lyman-alpha, kickstarting Lyman-alpha IM as a cosmological/astrophysical probe.
