Securing the Foundation of the IR-TRGB Distance Ladder

The expansion rate of the universe, also known at the Hubble constant, is measured both from a distance scale and from the Cosmic Microwave Background. These two methods give different values. It is possible that systematic errors cause these different values, so independent techniques for the measurement of the Hubble constant need to be developed. The infrared tip of the red giant branch method (IR-TRGB) could be a powerful tool to probe large volumes and a wider set of Type Ia supernova galaxy hosts. However, the IR-TRGB method needs proper calibration, which requires new ground-based observations. This project will develop new tools for the IR-TRGP measurement. Ongoing projects, in collaboration with minority serving institutions, that provide research opportunities for undergraduate students will be enhanced with these tools. A sibling robotic optical telescope with time allocated for E/PO efforts will be made accessible to outreach via the creation of supporting materials and a wide range of E/PO education modes for both classrooms and informal settings. This project will provide two anchor points to a distance scale built on the IR-TRGB and seamlessly connect these anchor points to IR-TRGB measurements made with space-based facilities. The IR-TRGB has the intrinsic brightness and efficient application to measure distances for statistical samples of SN Ia hosts. The team will: (1) Complete the implementation a fully-robotic, dual channel optical/infrared facility capable of monitoring bright stars in the infrared and publish design specifications and operational data for the facility. (2) Use this facility to produce photometry of key calibrations for the IR-TRGB in the Milky Way and LMC. (3) With an on-going HST program, derive or predict filter transformations between ground- and space-based filter systems that enable the IR-TRGB. (4) Calibrate the absolute magnitude-color behavior of the IR-TRGB in two anchor objects with high precision geometric distances (Milky Way Field and LMC). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.