The Status of the Chicago-Carnegie Hubble Program (with JWST data) - Wendy Freedman & Barry Madore

[@talks_curator728]

*Index to Key Parts of the Talk* [0:00:00] Intro comments by Shaun and Wendy [0:01:22] Two takeaways to remember [0:01:47] Not seeing now extraordinary evidence for Hubble tension; unknown systematics [0:03:18] Background on gold standard methods for measuring H0 [0:09:05] 2 methods agree in their zero point, low scatter against each other [0:09:35] 2 new papers on arXiv and recent CCHP group papers; more coming [0:11:58] First target galaxies; TRGB and JAGB advantages; HST cf JWST [0:20:54] 3 distances indicators - TRGB, Cepheids, JAGB [0:29:14] JAGB details [0:31:29] Data Analysis [0:32:31] Comparison of distances (pre a determination of H0) [0:36:09] TRGB vs JAGB comparison [0:38:22] SN Calibrator M_B with Distance Modulus (potential systematic needs understanding) [0:42:02] Carnegie Supernova Project [0:44:12] Summary of H_0 Values and Statistical Uncertainties (Table 4 in paper) [0:51:09] Distribution of H0 Values for 3 JWST Methods( Fig. 11) [0:52:45] Distribution of H0 Values With Total Errors (Fig. 12) [0:53:21] CCHP JWST H0 Values (Fig. 20) [0:58:38] Conclusions (TRGB, JAGB agree at 1% level; results consistent with Planck, LCDM [1:02:27] What might be cause of high H0 with Cepheids? [1:06:28] What about the possibility of new physics? [1:09:06] What current work in cosmology is interesting but underappreciated?

[@astronomy-channel]

Shaun- you’re a brilliant moderator. I sent you an email with a model to explain the tension simply & intuitively, I hope you take a look. Keep up the great work!

[@astronomy-channel]

Combine great moderation, 2 superstars working symbiotically & great slides & you’ve got magic. What a concise, yet detailed, overview of cutting edge astrophysics. 👏

[@CosmologyTalks]

Thanks for the nice words! :-)

[@astronomy-channel]

@ it was amazing how harmoniously they supported, and clarified each other. Top notch both of them, as are your summaries of what they said. You’re lucky to have had them!

[@StefanMochnacki]

Superb presentation for both technical and lay audiences, explaining the important and massive paper Wendy, Barry et al. have just submitted. Their refinement over many years of the Cepheid, TRGB and JAGB methods, using HST and JWST, is finally establishing the extragalactic distance scale at the precision needed to test fundamental physics. And it all began over forty years ago in a modest infrared instrumentation lab at the University of Toronto, with detector systems in backpacks taken as carry-on luggage to and from Chile 🙂

[@CosmologyTalks]

Wow, I bet there are some cool stories from those days. It must be wonderful for Wendy and Barry to look back on those days and think about how far things have come.

[@awuma]

@@CosmologyTalks I think you remove the brackets and question mark 🙂 . Actually, much of Wendy's own thesis work involved photographic plates, but it was Bob McLaren's lab which introduced Wendy and Barry and several other faculty and students to the infrared for observing Cepheids. The development of large low-noise CCDs for the HST came just as Wendy finished her thesis, and "the rest is history"...

[@CosmologyTalks]

Brackets and question mark removed! 😁

[@MishaRash]

I had a tangential question about the "old" Hubble tension (50 vs 100 (km/s)/Mpc). In short, some of the errorbars quoted back in the day were suprisingly low, putting those measurements in tension not only with each other, but with the modern results too. Is there a clear answer what was wrong with the respective methods?

[@MishaRash]

The most striking is 52±2 in 1990ApJ...365....1S An earlier work by the same team gave 50.3±4.3 (1976ApJ...210....7S) Differences between each of these and many current measurements around 70 are of very high significance if we accept both the central value and the uncertainty estimate (from Sandage & Tammann 1990 or even 1976). This should be explained! Perhaps some error source was underestimated, or the central value was biased?

[@MishaRash]

The errorbars on the 100 side seem to have been more modest (10), e.g. 95±10 in 1982Obs...102..178D and 100±10 in 1979ApJ...233..433D This makes them less inconsistent with the current measurements (≈2 sigma is not extraordinary). P.S. I had some troubles posting these details, because KZbin doesn't seem to like ADS links for some reason, and Authors (YYYY) format is ambiguous for the papers in question.

[@CosmologyTalks]

KZbin can be weird about external links. It isn't even within my power to approve such comments, YT just hides them and doesn't even put them in the "review" tab. I *think* if someone posts a number of comments on a channel over time without the channel owner marking the comments as spam then eventually external links are allowed, but the process is very vague/unclear. That's a good question. I don't know what was wrong with the Sandage measurements and all review articles of the history just kind of imply that they became obsolete, without explaining why (e.g. this one arxiv.org/abs/2305.11950 is really good, but like most others just accepts that the Key Project won). I had a quick look through the literature, in particular Sandage's own papers to see if he ever explained what *he* thought was going wrong. I didn't find any explanation, but in his later papers (e.g. this one from 2006 ui.adsabs.harvard.edu/abs/2006ApJ...653..843S/abstract) he was claiming 62.3 +-1.3+-5 which would be consistent, within 2 sigma, with SH0ES. And this one from 2010 (ui.adsabs.harvard.edu/abs/2010ASSP...15..289T/abstract) has the following claim in the abstract "The basis of this value has been weakened because the period-luminosity relation of Cepheids is not universal, but depends on their metallicity and possibly other parameters.", which might be part of the reason? It is a bit scary how people could be so confident earlier on though with results that in 2024 appear to have been wrong, and one hopes that the community is not making similar mistakes (and even if astrophysics is the Hubble tension resolution that it is something newly understood not just under-estimations of things we already know of).

[@DrBrianKeating]

🎉

[@thorntontarr2894]

Honestly, aside the very early comment RE: Hubble Tension "not extraordinary evidence for", it took a very long time to get to the 'punch line" @ 44:30 with Table 4. Perhaps, the speakers were trying to avoid the wrath of Adam Riess & Shoes team; I felt that they kept 'skirting' around the issue they have uncovered: Cephids may need much more study. You, Shaun (sp?) did question Barry regarding a 'reason' being 'crowding' by stating that Adam Reiss appeared on a CT a while back and said that crowding was not the systematic causing the tension (or something like that). My point: you were asking the speakers good questions & points. I await the upcoming talk about JAGB for more input. However, I found Table 4 difficult to read; how does Table 4 adhere to best practices of significant figures? For example, Combined Results show Ho as 69.96 +/- 1.05 Stat +/- 1.12 Syst. Would it not be better to show 70 +/- 1 Stat +/- 1 Syst? The graphic @51:10 is much easier to interpret and get an appreciation of the results presented in Table 4. Yes, this is a style point but getting the message out to a wide audience as CT is doing does require aiding the audience as much a possible.

[@CosmologyTalks]

Thanks for both the positive and critical feedback, both are valuable! And yep, that's the correct spelling of my name 🙂. I had similar thoughts while editing. We probably should have had that plot, with the posterior probabilities for H0 from each method, presented within the first few minutes, so viewers know what the details are then building back towards (like we did with the DESI talk). Otherwise all we have is the vague claim of "not seeing extraordinary evidence", without it being clear what that precisely means until much later. Yeah, the table probably isn't something one should show to undergraduate students if encouraging them to quote the "right" number of significant figures 😅 - "you marked me down, but even Freedman et al. did it!" The table being on the screen for long was a bit of an accident, I think. My hunch is that Wendy only intended to show it for 10 seconds or so to briefly comment on, and then to spend most of the time talking about the figures. Unfortunately, I didn't wait with my questions and then we had a long-ish discussion before Wendy had introduced the figure. I couldn't jump ahead with the slides before the figure was introduced because it would be a distraction. Maybe I should have moved to fullscreen speakers though instead?

[@CosmologyTalks]

I gave you a shout out in the JAGB talk when they quoted their H0 values again (i.e. mentioning your observation about the number of significant figures in the reported values 😅).

[@MishaRash]

While watching the talk, I also remembered the more recent claim by the SH0ES team that crowding can not explain the Hubble tension based on JWST data (arXiv:2401.04773). But towards the end (1:03:27) Wendy says that the furthest galaxy they checked was only ~40 Mpc away, and the crowding may still be a significant problem at larger distances. And this counter-argument actually applies to the 2024 paper (I checked the list of target galaxies). That might be a little unclear from the video, because only Adam Riess's talk from 2020 was mentioned specifically by Shaun, and it couldn't have relied on JWST observations.

[@MishaRash]

At school we did indeed have a rule to leave one significant figure in the uncertainty. However, there was an exception: leave two if the first digit is 1 (I guess because rounding is particularly crude then). In scientific materials, two significant figures in the uncertainties seem more common overall. Maybe three significant figures in the table arise from the combination of these two considerations.

[@MishaRash]

Also, I remember some of the SH0ES people arguing that the TRGB detection in a color-magnitude diagram is not so clean and definite as Wendy and Barry claim, there are allegedly arbitrary choices affecting the results. IIRC, the slope of the boundary is not understood too well, and/or it is often blurred so that one can draw a sharp line in different ways. In a few papers (e.g. arXiv:2304.06693 or arXiv:1908.00993) they used TRGB as the middle rung of the distance ladder and get values consistent with Cepheids. On the other hand, even the later work seems pre-JWST. Moreover, I haven't seen/heard such objections regarding JAGB yet.

[@fractalnomics]

2:06 Wow!

[@CosmologyTalks]

Indeed! I expect SH0ES still disagree though and Wendy does also say later in the video that their results are at least consistent with there being a tension. So this is far from a smoking gun that there is no new physics and something is definitely wrong with our understanding of cepheids. We'll all have to wait and see where the *dust* eventually settles.