AR 16126 (Archival Research)

Sun Jul 14 10:28:04 GMT 2024

Principal Investigator: Wendy Freedman
PI Institution: University of Chicago
Investigators (xml)

Title: An Independent Appraisal of the Cepheid Distance Scale
Cycle: 28

Cepheids are at the nexus of a debate about the possibility that the concordance LCDM model of the Universe is deficient and that new physics is needed to resolve an apparent discrepancy between the local value of H_o and the cosmologically-modeled one. We are proposing to undertake a new and independent determination of H_o using archival imaging of 36 galaxies that contain Cepheids and are hosts to Type Ia supernovae. The Cepheid distance scale is just too imprtant for it not be re-reducded, re-analysed and independently assessed. We have already developed a pipeline that undertakes crowded-field photometry using (DAOPHOT), fine-tuned to the ACS using spatially-variable Tiny Tim PSFs; this will be extended to WFC3 data. Extensive artificial star experiments will be run; and half of our team will undertake the analysis completely blinded, while the other half (without any cross-talk) will run open loop. Both results will be published unchanged. We will make all of the data-reduction and analysis sofware publically available on Github. Intermediate data products will be archived at MAST so that users can re-analyze the data from those intermediate points onwards. Enroute to a new and self-consistent value of the Hubble constant, the other Science Products will be Crowded-field VI photometry, cross-matched for all detected point sources in 36 galaxies. Color-Magnitude diagrams for each of the galaxies. Periods, light curves, mean magnitudes and colors for each of the Cepheids. Period-Luminosity relations and reddening-corrected distances for each of the galaxies. Cepheid-calibrated absolute magnitudes for all Type Ia SNe in Cepheid-host galaxies.