The Hubble Tension refers to a >5 σ discrepancy between local and cosmological measurements of the Hubble constant (H0) and suggests the possibility of undiscovered early-universe physics or underestimated systematics. Probing the Hubble Tension necessitates intense scrutiny of the Cepheid-based distance scale, which currently provides the strongest constraints on local measurements of H0. One powerful approach to crosscheck systematics in the Hubble Space Telescope (HST) Cepheid section of the distance ladder is to develop and improve independent routes to measure distances to the same set of galaxies and H0, such as those using the tip of the red giant branch (TRGB) and J-region asymptotic giant branch (JAGB), or by adding an independent anchor. I will present a sub-2% Cepheid distance to M31, which prepares an additional anchor galaxy that can be used to construct the distance ladder once a high-precision geometric detached eclipsing binary observation
is feasible, as well as work improving standardization and calibration of the
TRGB, including a 2D maximum likelihood formalism enabling Milky Way
field star calibrations and contrast ratio standardization in the maser host
NGC 4258. I will also present recent James Webb Space Telescope (JWST) TRGB
distances to 8 hosts of 10 Type Ia supernovae (SNe Ia), later expanded to 25 hosts, which provides no evidence of a HST Cepheid systematic resolving the Hubble Tension, in addition to a H0 measurement using JWST observations of the JAGB with an expansion to 15 galaxies hosting 18 SNe Ia. While the JAGB remains promising as a tool that can crosscheck Cepheid systematics, non-uniform asymmetry in its luminosity function, caused in part by stellar contamination, presently limits the precision of this candle.
14/07/2025
Speaker: Dr. Siyang Li from John Hopkins University
Date: 14th of July, 4pm JST time=9am CET.
Location: NAOJ Headquarter, South Building C, room 313 and
online zoom link:
Join Zoom Meeting
https://us06web.zoom.us/j/87354349631?pwd=HUE5F1cQOWo1chLSYSHnRiAdimXaFF.1
Meeting ID: 873 5434 9631
Passcode: 953545