Stanford KIPAC

Pulsating ancient stars preserve information about distance, chemical composition and age that can constrain the early history of galaxies. Earl Patrick Bellinger describes advances in stellar-evolution and pulsation simulations, together with machine-learning acceleration, that allow these stellar records to test models of galaxy formation. The talk develops two applications. RR Lyrae stars trace the Galactic halo and Milky Way dwarf galaxies; a new physics-informed approach to their observations enables distance precision of about one percent almost to the Milky Way’s virial radius, supporting galactic archaeology and nearby-universe cosmology. For the distant universe, the presentation examines JWST’s Little Red Dots and evidence for an interpretation as pulsating quasi-stars: black holes surrounded by supermassive, Cepheid-like stellar envelopes. If confirmed, this interpretation could explain both the Little Red Dots and the early formation of supermassive black holes.

Baryonic feedback introduces substantial uncertainty into cosmological inference from weak lensing. Henry Liu presents measurements of radial gas fractions around DESI galaxies that avoid assuming parametric gas profiles. The method combines galaxy-galaxy lensing with the kinematic Sunyaev–Zel’dovich effect, using a modified kSZ filter matched to the lensing delta-Sigma observable to estimate gas fractions directly. The analysis joins DESI DR2 Bright Galaxy Survey and luminous-red-galaxy samples with ACT DR6 microwave-background maps and HSC Y3 shear data. Gas fractions are suppressed at small projected separations and approach the cosmic value farther out. A simulation-calibrated compensation for the ACT beam, designed to be independent of feedback, yields baryon-depletion detections with signal-to-noise ratios of 17.1 for BGS and 15.8 for the first LRG bin. Comparisons with Illustris, IllustrisTNG, SIMBA and FLAMINGO explore different feedback prescriptions. The talk concludes with future directions and implications for feedback and matter-power suppression.