DAWN JWST Archive and the angular diameter turnaround

[mikehelland]

Similar to the COSMOSWeb where wherever you look, higher redshift galaxies are smaller on the sky, there's also this:

https://arxiv.org/pdf/2505.21622
DAWN JWST Archive: Morphology from profile fitting of over 340,000 galaxies in major JWST fields

In a universe with a big bang, at some point there's an "angular diameter turnaround"*, where, due to space getting smaller and smaller and approaching a singularity, farther things actually appear larger than things closer to it.

In LCDM, that point is z=1.6.

There is no turnaround according to this data. Farther away things always appear smaller.

• Video on the details on the "cosmic turnaround":
  https://www.youtube.com/watch?v=tvRsXYHW2RU

[LifeIsStrange]

Thanks for sharing, the issue with the evolution of the angular distance is that it can be altered via an evolution with Z of dust opacification and or of galaxy intrinsic size

[RedshiftDrift]

@mikehelland These graphs present the radius in kpc, which means they already corrected for the angular diameter turnaround, as they say at the end of section 1:

We adopt a Planck Collaboration et al. (2020) ΛCDM cosmology with H0 = 67.4 km s−1 Mpc−1

By doing that, they feed the wrong parameters in the 'fundamental plane' and dust models, so the galaxies look like they are evolving. This type of data has been used to refine the fundamental plane and dust models, so unless someone does the analysis all over again, it is not possible to disentangle the $\Lambda\mbox{CDM}$ contamination from these analyses.

So the figure you posted above are meaningless as they cannot be easily interpreted in a Bang-less cosmology.

[mikehelland]

The COSMOS-Web fits files seem to have angular diameters in them (they display as green circles around the galaxies) but I haven't figured out what data that is yet.

[mikehelland]

Here's a description of the data:

https://cosmos2025.iap.fr/catalog.html

This shows what can be done with it:

https://cosmos2025.iap.fr/tutorials/catalog_usage_tutorial.html

I just need to figure out where those green circles are coming from. Possibly the Sersic index?

Maybe disk_radius_deg: