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.
BIO
Pablo Renard is a Shuimu Fellow at the Department of Astronomy, Tsinghua University. He obtained his PhD in Physics in Universitat Autonoma de Barcelona (UAB), Spain, in 2021, and did his first year of PhD at National Astronomical Observatories, Chinese Academy of Sciences (NAOC), in 2019. His main research interests are observational cosmology and low-surface brightness science. He is involved in several cosmological surveys (PAUS, JPAS, MUST), and has alternated his research with significant technical work for PAUS, where he holds the Data Manager position and has coordinated its final data release.
