PhD Thesis Defense: Taylor Hoyt

1:30–2:30 pm ERC 401

Taylor Hoyt "The Tip of the Red Giant Branch and its Application to Measurements of the Hubble Constant"

In the Carnegie Chicago Hubble Program (CCHP), our collaboration used the Tip of the Red Giant Branch (TRGB) to calibrate the Type Ia supernova (SN Ia) distance scale and determine a new value of the Hubble constant (H0). Our TRGB-derived value is significantly less in tension with LCDM than that derived using Cepheid variable stars, thereby raising concerns of underestimated systematic errors and weakening the evidence for the so-called Hubble Tension and new physics beyond LCDM. Throughout my PhD, I have developed new methodologies for estimating TRGB distances and associated uncertainties. While doing so I have measured TRGB distances to eleven SN Ia Host galaxies that formed the basis of the CCHP’s H0 determination.

In my dissertation paper on calibrating the TRGB luminosity, I introduced a novel procedure for accurately selecting TRGB stars in the Magellanic Clouds and made the most precise TRGB measurement in that system to date, in turn resolving a recent debate over the brightness of the TRGB in the Clouds. I have continued to improve the TRGB calibration using brand new Hubble Space Telescope (HST) imaging (PI: Hoyt) aimed at the stellar halo of the megamaser host galaxy NGC 4258. These new calibration data will reduce uncertainties in the TRGB zero point to the systematic floor of the maser distance, or 1.5%.

Looking ahead to the method’s use with JWST, I demonstrated in a study of the Large Magellanic Cloud (LMC) that, when observed in the infrared (IR), the TRGB is sufficiently precise that it can be used to discern 2% variations in line-of-sight distance across the LMC, despite the IR application of the method requiring an additional correction that is a function of the colors of the TRGB stars. The TRGB is several times brighter in the IR and with JWST the method promises to revolutionize distance ladder measurements of H0.

Event Type

PhD Thesis Defenses

Jul 14