In this work, we explore the application of intensity mapping to detect extended Lyα emission from the IGM via cross-correlation of PAUS images with Lyα forest data from eBOSS and DESI. Seven narrow-band (FWHM=13nm) PAUS filters have been considered, ranging from 455 to 515 nm in steps of 10 nm, which allows the observation of Lyα emission in a range 2.7<z<3.3. The cross-correlation is simulated first in an area of 100 deg2 (PAUS projected coverage), and second in two hypothetical scenarios: a deeper PAUS (complete up to iAB<24 instead of iAB<23, observation time x6), and an extended PAUS coverage of 225 deg2 (observation time x2.25). A hydrodynamic simulation of size 400 Mpc/h is used to simulate both extended Lyα emission and absorption, while the foregrounds in PAUS images have been simulated using a lightcone mock catalogue. Using an optimistic estimation of uncorrelated PAUS noise, the total probability of a non-spurious detection is estimated to be 1.8\% and 4.5\% for PAUS-eBOSS and PAUS-DESI , from a run of 1000 simulated cross-correlations with different realisations of instrumental noise and quasar positions. The hypothetical PAUS scenarios increase this probability to 15.3\% (deeper PAUS) and 9.0\% (extended PAUS). With realistic correlated noise directly measured from PAUS images, these probabilities become negligible. Despite these negative results, some evidences suggest that this methodology may be more suitable to broad-band surveys.
@article{arxiv.2006.07177,
title = {The PAU survey: Ly$\alpha$ intensity mapping forecast},
author = {Pablo Renard and Enrique Gaztanaga and Rupert Croft and Laura Cabayol and Jorge Carretero and Martin Eriksen and Enrique Fernandez and Juan García-Bellido and Ramon Miquel and Cristobal Padilla and Eusebio Sanchez and Pau Tallada-Crespí},
journal= {arXiv preprint arXiv:2006.07177},
year = {2021}
}