KIPAC Tea Talk: Lifting astrophysical barriers to small scale cosmology

Abstract: Weak lensing cosmology is now limited by our understanding of astrophysical systematics: intrinsic alignments and baryon feedback. To lift these barriers to small scale cosmology and resolve key questions in galaxy evolution, we made direct measurements of intrinsic alignments and baryon feedback. With over 2 million spectroscopic galaxies from DESI Data Release 1 and imaging from four lensing surveys, we developed a tailored IA modeling approach: building a library of IA measurements across color, luminosity, stellar mass, and redshift. To constrain how baryon feedback reshapes the matter distribution, we jointly analyzed the SDSS/DESI+ACT Sunyaev-Zel’dovich effect profiles and eROSITA X-ray gas mass fractions, each characterized with galaxy-galaxy lensing. Across group and cluster masses and at 0<z<1, we find consistent evidence of more efficient gas expulsion beyond the virial radius than predicted by most state-of-the-art simulations, implying significant suppression of the matter power spectrum on small scales. By incorporating our intrinsic alignment and baryon feedback constraints into data-driven priors for cosmic shear, we significantly improve cosmological constraining power on small scales.