Really important H0 development from the quasar strong lensing community at Barcelona cosmo meeting. Recap - they were consistently getting high H0 values from their measurements, ~73+/-1.8, but decided to see how H0 changed if they freed assumptions about how mass is distributed in galaxies, adding velocity dispersions to constrain that. This made their H0 swing to possibly lower value. Now it turns out these velocity dispersions they used had an error–-the size of the Hubble tension! A 🧵 So in the now famous TDCOSMO-IV paper (arxiv.org/abs/2007.02941) , they use measurements from the ‘SLACS’ sample of lenses to constrain the kinematics of the lens. But the SLACS sample was not the same as the sample of lenses they used in TDCOSMO (e.g. very different redshift), so everyone should take with grain of salt (which the community didn’t 😛 ). The key parameter is this lambda-int below, the mass sheet transformation parameter, and lambda=1 is basically the standard model assumption (which gave high H0)

Lately, there have been different reports about the Hubble Tension from JWST, with different teams and methods. It’s been hard to follow. But initial sample sizes were small so in a new paper we combined, for the first time, all measurements to date, includes 5 JWST programs, and it makes a pretty clear picture. 🧵arxiv.org/abs/2408.11770 The first main question is “Do other techniques/instruments/teams JWST galaxy distances agree with past HST measurements?” It’s a resounding yes! 👏 All the offsets are on the 0.03 mag level and 1sigma from HST SH0ES, much smaller than Hubble tension scale of 0.18 mag. Conclusion, Hubble Tension is not a distance measuring problem.

The main premise of the distance ladder is neither physics nor astrophysics change between rungs because galaxies (identically selected) don’t know which rung they are on. Over the last couple of years, some have proposed breaking that premise to resolve H0 tension. A 🧵. Normally we correct SN dust by the amount it reddens colors and by following “dust rules” which minimize Hubble residuals. These include the ratio of reddening-to-dimming and the likelihood of amount of dust, decreasing from peak at ~0. eg Hatano+98.

Arguably one of biggest curiosities about Hubble Tension is why TRGB+Supernova gives values between the two tentpoles of Tension, 67 and 73. We have new paper from CATS team doing 🍜 to 🥜🥜 analysis of TRGB+SN and get H0=73.2+-2.0 km/s/Mpc. How/why? A 🧵arxiv.org/abs/2304.06693 Idea behind TRGB is relatively simple - red giants, no matter size, should reach brightest phase when Helium ignites-that shows up as break in the Color Magnitude Diagram (CMD). CMD can be made by plotting the brightness of stars (here in ~I band) versus the color (like ~V-I).

So last night arxiv.org/abs/2105.11461 claimed could remove H0 tension because of dust. I’m all for us discovering that dust is really weird, but paper changes H0 by changing Black Body physics for Cepheids, not dust. What has been discovered (something/nothing)? A thread. The paper has two approaches: 1. looks at color excess (i.e., just dust) compared to the intrinsic color and measures the reddening ratio for each host. They get H0=71.8+-1.6, a little lower than SH0ES by making dust weird, but still tension .