Integral Field Spectroscopy and the Hubble Constant

Arguably, the most important question in cosmology today is that of the Hubble tension, i.e., the small discrepancy between the expansion rate of the universe measured locally, and that inferred from the basic physics of the early universe and the application of Einstein’s equations. If this tension is confirmed, then the mysterious Dark Energy that dominates the universe is more complex than even Einstein imagined, and new physics is needed to explain the expansion history of the universe. To address this problem, we need to measure precise distances to galaxies using as many independent methods as possible. Scientists at the Pennsylvania State University propose to develop and test two such methods based on special types of stars that are near the end of their lifetimes: post-asymptotic giant branch stars, and planetary nebulae. Both objects have shown tremendous promise as tools for measuring precise distances, but their use has been limited by technology. The availability of new, large-scale instruments combined with 8-meter class telescopes has changed this. The team will analyze both existing and new data from such instruments to determine whether either or both methods can address the current tension in cosmology. Questions of the origin and evolution of the universe are of great interest to people outside the world of astrophysics and are an excellent way to engage students at all levels of education. This project includes a significant program of public outreach targeted at both the K-12 level and the general public through a series of local outreach events. In addition, the project will help train the generation of scientists now in college by involving them directly in this research effort.Based on current measurements, the Hubble Constant determined from the Cepheid calibration of SNIa does not quite match that derived from the combination of the power spectrum of the cosmic microwave background and the assumption of a Cosmological Constant. To test whether this Hubble tension is real or just an artifact driven by systematic errors, there is a need for additional high-precision extragalactic distance indicators. The goal of this proposal is to develop and test two such standard candles: post-asymptotic giant branch stars and the planetary nebula luminosity function. The former has the potential to produce ~2% distance errors to quiescent galaxies within ~10 Mpc and is tied directly to Gaia measurements; the technique must be calibrated outside the Galaxy, but can be applied to all galaxies with absolute V-band magnitudes brighter than -20 within ~40 Mpc, and can increase the number of SNIa with sub-8% distances by an order of magnitude. The development of both methods is made possible by the availability of two large-scale integral-field unit spectrographs: VIRUS on the Hobby-Eberly Telescope and MUSE on the European Very Large Telescope. The data from these instruments will allow the team to determine whether either or both methods can reach the precision needed to test whether the Hubble tension is real and thus requires new physics to explain it.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.