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Siyang Li

Siyang Li

The J-region Asymptotic Giant Branch (JAGB) refers to a region in a near-infrared color magnitude diagram that contains thermally pulsating carbon stars. Recent studies have proposed that the mean, median, mode, or modelled parameter of the JAGB luminosity function can be used as a standard candle to construct an extragalactic distance ladder to measure the Hubble constant serving the same role as that of Cepheids, Tip of the Red Giant Branch, and Miras. In this talk, I will describe a recent investigation into the consistency of the JAGB method as well as a JAGB measurement of the Hubble constant using JWST NIRCam observations of the maser host NGC 4258 and four Type Ia supernovae hosts. We find evidence of field-to-field variations, as well as non-uniform asymmetry in the JAGB luminosity function that give rise to methodological variations in the JAGB reference magnitude. While our data is consistent with a broad range of H0=71-78 km/s/Mpc, we caution that due to small host sample statistics, few calibration fields (in NGC 4258) and the non-uniformity issue, further work is needed to standardize and sample JAGB before it is competitive and compared to other more established distance indicators. We discuss such efforts to expand and extend the method including from a new JWST Cycle 2 program.