Romain Meyer
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astrorameyer.bsky.social
Romain Meyer
@astrorameyer.bsky.social
Astronomy postdoc UNIGE - Studying the Universe in the 1st Gyr: Galaxies, SMBH, Reionisation - All views are my own. (he/him)
http://rameyer.github.io
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 👇
October 17, 2025 at 2:37 PM
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!
October 17, 2025 at 2:34 PM
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!
April 4, 2025 at 1:32 PM
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!
April 4, 2025 at 1:32 PM
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!
April 4, 2025 at 1:32 PM
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).
April 4, 2025 at 1:32 PM
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).
April 4, 2025 at 1:32 PM
🧵 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
April 4, 2025 at 1:32 PM
Perks of working in Switzerland: nothing can beat the office window view
January 10, 2025 at 3:11 PM
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/
September 6, 2024 at 2:07 PM
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!
May 22, 2024 at 3:29 PM