Tracing Matter and Gas using CMB as a Backlight

par Frank Qu (Stanford University)

jeudi 21 mai 2026, 11:00 → 12:00 Europe/Paris

Auditorium Vivargent (LAPTh)

The cosmic microwave background serves as a unique backlight for mapping both the matter distribution and the ionized gas across cosmic time. CMB lensing traces the integrated matter field out to high redshift, while the kinematic Sunyaev-Zel'dovich (kSZ) effect isolates the free electron distribution in and around galaxy halos. Together these probes address questions at the intersection of precision cosmology and galaxy formation: the S₈ tension and the puzzlingly tight upper limits on the neutrino mass sum from recent data combinations, and the poorly constrained baryon distribution within halos that increasingly limits upcoming surveys. In the first part of the talk, I will discuss how CMB lensing has become one of our most robust probes of cosmology, focusing on the joint ACT, SPT, and Planck analysis that delivered one of the most precise measurements of structure growth to date. I will preview preliminary results from an updated analysis of ACT's final data release (DR6+) and outline the decisive role Simons Observatory will play in probing new physics. In the second part, I will present the highest signal-to-noise kSZ measurements to date, obtained by cross-correlating DESI DR2 luminous red galaxies, bright galaxies (BGS), and emission line galaxies (ELGs) with ACT DR6 temperature maps, together the most significant kSZ detections from any spectroscopic survey. Alongside configuration-space analyses based on compensated aperture photometry, I will describe one of the first comprehensive harmonic-space measurements, constructed from kSZ momentum templates cross-correlated with the CMB, and discuss the implications for the gas distribution in halos and for baryonic feedback.