Abigail Lee tells us about how she has used the J-region Asymptotic Giant Branch (JAGB) to measure extragalactic distances, ultimately using them as a rung on the distance ladder to measure the expansion rate of the universe.

The JAGB method is new, at least compared to cepheids and “tip of the red giant” (TRGB) methods, but is also very promising. The stars it uses are bright, so they can be seen at large distances, and they’re numerous, which means they can be observed far from the centres of galaxies (minimising “crowding” from other stars in the same pixels). So, even ignoring Hubble tensions, this is a very exciting time to be involved in extragalactic distance measurements.

Abby used data from JWST to detect the JAGB mode brightness, which is then the distance indicator of the method. With more telescope time, and more local calibrators, JAGB will only go from strength to strength.

When the measured distances are compared to JWST measurements of TRGB and cepheids it has very little scatter with TRGB, but a little more from cepheids. The ultimate Hubble parameter is also on the smaller side, consistent with CMB + ΛCDM and on the border of being inconsistent with SH0ES cepheid+HST based measurements.

Abby: abiglee7.github.io

The paper: arXiv: 2408.03474