Lyman-α line intensity mapping

Lujan Niemeyer, Maja (2026): Lyman-α line intensity mapping: measurements on galactic to cosmological scales. Dissertation, LMU München: Fakultät für Physik

Abstract

Line intensity mapping (LIM) is a novel tool for studying astrophysics and cosmology in the young Universe. LIM maps the intensity of an atomic or molecular emission line in a three-dimensional volume, including the light from otherwise elusive faint galaxies and gas, and traces the matter distribution. In this thesis, we first conduct a small-scale LIM measurement of the Lyα line by stacking Lyα-faint galaxies in the data of the Hobby-Eberly Telescope Dark Energy Experiment (Hetdex) and study the dominant origin of Lyα photons in the circumgalactic medium (CGM) of star-forming galaxies. We find that the outer parts of the ubiquitous Lyα halos is equally bright for Lyα-bright and Lyα-faint galaxies. This indicates that these photons do not originate from the stacked galaxies, but rather from the galaxies’ CGM or from outside of their dark matter halos. In preparation for the analysis and interpretation of LIM data, we develop a fast simulation code to create mock galaxy catalogs and line intensity maps of any emission line, called SIMPLE, assuming that the underlying mass distribution is lognormal and assuming an input power spectrum and line luminosity function. One can apply survey-specific effects to the intensity maps such as angular and spectral smoothing, a mask, and sky subtraction, to make the mock data more realistic. After validating the output of the code to percent-level precision, we create mock data for Hetdex and examine its ability to measure the cross-power spectrum monopole of detected Lyα-emitting galaxies (LAEs) with the Lyα intensity of undetected sources. Lyα photons scatter many times within the interstellar medium, changing the shape and central wavelength of the Lyα emission line escaping the galaxy. Lyα photons can also scatter in the CGM and intergalactic medium (IGM). The scattering probability depends on the matter and velocity distribution, which can introduce a selection effect of LAEs that changes the anisotropy of the LAE auto-power spectrum. Therefore, we investigate the effect of Lyαscattering on LyαLIM power spectra using a linear analytic model and an implementation in the SIMPLE code. We find that the linear analytic model is inadequate to describe this effect because most of the scattering takes place in highly overdense, nonlinear regions near the LAEs. We show that the LAE auto-power spectrum measured by Hetdex will be sensitive to this effect, while the LAE-Lyα intensity cross-power spectrum is too noisy to be affected. Finally, we measure the cross-power spectrum of detected LAEs and the Lyα intensity of undetected sources in Hetdex. We thoroughly clean the spectra to remove systematic contributions. We forward-model the entire data set and data processing using mock data from the SIMPLE code and calculate the expected signal and covariance matrices. We then infer the mean intensity of Lyαphotons permeating the Universe. Our inferred value is significantly smaller than those inferred from cross-correlations of quasars with the Lyα intensity, but slightly higher than the upper limit inferred from a cross-correlation of the Lyα forest with the Lyα intensity. Our results roughly agree with predictions from a cosmological simulation including Lyα radiative transfer modeling. The mean intensity is also consistent with being entirely sourced by star formation in galaxies. In summary, we create a versatile mock simulation code for LIM, model the effect of Lyα radiative transfer on Lyα LIM measurements, and conduct a precise Lyα LIM measurement in Hetdex data. This research paves the way for constraining galaxy formation and evolution models with upcoming, even more precise LIM measurements.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 13. Februar 2026
• 1. Bericht­erstatter:in: Komatsu, Eiichiro