Abstract:
The intergalactic medium (IGM) represents the dominant reservoir of baryons at high red- shift, traces the architecture of the cosmic web dominated by dark matter, and fuels on-going galaxy evolution. The IGM has been studied using Quasi-Stellar Objects (QSO) absorption lines including the Lyman alpha forest (LAF), which are unable to provide the information that emission maps would give. But because of the low surface brightness and extended, diffuse distribution, direct detection of an emission equivalent to the absorption LAF has not been possible with existing instrumentation and observational approaches. Using a purpose- built instrument, with nod-and-shuffle and dual-field subtraction, we have detected, for the first time, an emission Lyman α forest (ELAF). The emission forest is highly extended, shows filamentary morphology with filaments connecting galaxies, exhibits statistics like the ab- sorption Lyman α forest, displays spectra resembling the absorption forest, and is correlated with galaxy-traced overdensities consistent with bias like dark matter. We conclude that the ELAF may provide a new tool for tracing a significant fraction of the cosmic web of baryons and dark matter. Finally, I will present status of the FIREBALL program, a US/French collaborative balloon experiment, focused on emission from the Circum-QSO and Circum-Galactic Medium. FIREBALL is a pathfinder for a new mission, a Super-pressure Cosmic Web Imager (SCWI), that offers the opportunity to image the cosmic web in the local universe for the first time, and compare its properties to those at high redshift.
