Speaker
Description
This work analyzes the expected constraint on the sum of neutrino masses from the Legacy Survey of Space and Time (LSST) $3\times2$pt analyses (galaxy clustering, cosmic shear, and their cross-correlations) with 32 systematic parameters, the impact of these systematic models on the neutrino constraint, and how combining with other probes helps break these degeneracies. We present realistic Fisher forecasts from Rubin LSST photometric probes with the precision expected for the first year of the survey. In a $\nu\Lambda$CDM cosmology, we find $\sigma(\sum m_\nu)=426$ meV, a factor of 2 improvement over previous $3\times2$pt neutrino analyses. When fixing the systematic parameters, the constraint significantly tightens to $\sigma(\sum m_\nu)=187$ meV, showing how much the systematic models degrade the neutrino measurement. Combining our baseline result with Planck and DESI yields a measurement of $\sigma(\sum m_\nu)=37$ meV. We also compare the impact of each systematic model on the neutrino mass constraints, finding that galaxy bias has the strongest correlation with the sum of neutrino masses and is primarily responsible for the weaker baseline constraints. Our work shows that Rubin LSST will achieve the first competitive measurement of the sum of neutrino masses from photometric probes and will add a significant contribution to joint neutrino analyses with external probes. Furthermore, the finding that galaxy bias is the main limitation of LSST constraints suggests that cross-correlating the photometric tracers with CMB lensing (or other tracers of the matter density field) can break degeneracies with galaxy bias and help uncover the neutrino information contained in LSST measurements.