The paper focuses on the OIII luminosity function and the fact that with 0.3 degree squares, we can finally beat down cosmic variance (but only to 15% relative uncertainty). You need wide-area surveys to sample all environments - something difficult with JWST. Lot of structure even in COSMOS 👇

You probably missed it because of some deadline but on Tuesday we published the results of an [OIII] emitters search in the COMOS(-3D) field using slitlless spectroscopy. That's *237* 6.7<z<9 uniformly-selected spec-z galaxies over 0.3 degrees square. See the piled 2D plots below, that's a lot!

Furthermore, we find that both environmental (local galaxy overdensity measured from FRESCO/JADES) and intrinsic (high ionising output/escape) effects are needed to explain the low opacity, and, in turn, the large number of LAEs detected by JADES. The local "ionisation budget" checks out!

We illustrate the latter point in GOODS-South at z=5.8-5.9 where @joriswitstok.bsky.social et al. reported a large number of Lyman-alpha emitters, a line normally suppressed by the neutral IGM. We can explain this as the IGM there is in the top 4-7th percentile of most transparent regions at z=5.9!

In principle you could use galaxies to detect the Lyman-alpha forest z~6, but this is extremely challenging with ground-based observatories. Enter #JWST!! By stacking public spectra of z>5 galaxies in the archive, we finally detect the GP trough in high-redshift galaxies. It's beautiful!

Since then the GP trough and more generally the IGM opacity measurements made from z~6 quasar Lyman-alpha forest have set great constraints on the timing and topology of reionisation (e.g. Eilers+18, below). The drawback is that such luminous quasars are extremely rare (~0.5 / deg^2).

The Gunn-Peterson trough is the full absorption of the Lyman-alpha forest when the IGM becomes ever-so-slightly neutral, signalling the end of reionisation. It was predicted in 1965 but took ~35 years to be observed in z~6 quasars discovered with SDSS (e.g. Becker+2001 below).

🧵 Today is paper day for me! Usually I don’t post about papers but I have a special soft spot for this one: the detection of the Gunn-Peterson trough in high-redshift *galaxies* !!

arxiv.org/abs/2504.02683

#astrosci #extragalactic #cosmology

Perks of working in Switzerland: nothing can beat the office window view

Are you an ECR? Do you like #JWST ? High-z galaxies/SMBHs? Skiing/curling/ice-skating/eating fondue in the Swiss Alps? 🔭

Applications are now open for the 54th Saas-Fee Course on "Galaxies and Black Holes in the 1 Gyr as seen with the JWST" - Jan 27-31, 2025 - more info: astro.unige.ch/saasfee2025/

Only 4 years ago I was a PhD student, and finding a single z>7 galaxy after a long night at Keck/VLT was awesome. Here is just 137 6.8<z<9.0 galaxies in only 50h of JWST time. I know it was built for this but still.. Crazy!