Lyman-alpha Intensity Mapping of the High Redshift Intergalactic Medium

• Applicant: Professor Dr. Lutz Wisotzki
• Subject Area: Astrophysics and Astronomy
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446330471

We propose to perform the first measurement of Lyman-alpha (Lya) emission from the average intergalactic medium at redshifts between 3 and 6.5, a crucial experiment in observational cosmology that so far was impossible because of a lack of sensitivity. We will combine two new and unique datasets obtained by us with the integral-field spectrograph MUSE, constructed under our leadership, with the Intensity Mapping (IM) formalism (adapted to our specific needs) to maximise the sensitivity of the measurement. The observational data comprise the revolutionary "MUSE eXtremely Deep Field" (MXDF) with 155 hours of exposure in a single pointing, augmented by several additional MUSE deep fields of 25-30 hours exposure each. Building on our recent successful work with MUSE we expect to reach an unprecedented surface brightness limit (1sigma for a single Lya emission line) of <1 x 10^(-21) erg s^-1 cm^-2 arcsec^-2 in the mean intensity mapping signal, lower by a factor of several compared to previous work. In order to achieve this top-level goal we have to address several related, but to some extent independent problems, which will produce novel and interesting results by themselves: (1) We have to remove the contribution from lower redshift emission lines by cross-correlating with appropriate tracer samples directly constructed from our MUSE data. This will include the application of the IM method to other strong lines such as [OII] or H-beta. (2) We must account for the contribution of individually undetected, extremely faint Lya-emitting galaxies, which requires measuring the redshift evolution of the faint end of the Lya emitter luminosity function. (3) We have to quantify and subtract the Lya contributions of individually detected galaxies, i.e.\ their interstellar and in particular their circumgalactic Lya emission. We will incorporate new dedicated cosmological numerical simulations produced by collaborators into the analysis, to help validating the IM approach, to guide us disentangling the genuine intergalactic component from the total measured signal, and to interpret the results in terms of physical properties of the intergalactic medium.Besides these main goals, the results of our projects will be relevant for several other scientific questions, such as implications for cosmic reionisation from the faint end of the LAE luminosity function, and the properties of Lya haloes around galaxies at z>3. We underline that our project differs conceptually in several points from most other ongoing or planned IM experiments: (i) We operate directly on 3D spectroscopic datacubes with full area coverage. (ii) While the field of view of MUSE is small, the total volume sampled is still substantial by virtue of the large redshift range covered. (iii) Most importantly, we explicitly aim at removing the dominant part of the signal that can be related to individual galaxies, isolating only the weak glow from the extremely tenuous matter far away from galaxies.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partner: Dr. Roland Bacon