What is it about?
A basic way to characterize the population of galaxies in the Universe is to count them as a function of their apparent brightness. The James Webb Space Telescope can see very faint galaxies and hence make a very accurate census of the number of galaxies. The counts show a clear change in slope at a magnitude that depends on the band used.
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Photo by NASA Hubble Space Telescope on Unsplash
Why is it important?
The number counts of galaxies can tell us about the background cosmology and about galaxy formation models. Here we use a state-of-the-art model called GALFORM, to probe the numbers of very faint galaxies. This required us to run the model in a very different way to the standard way it is used. The model showed the same break feature as the observed number counts.
Perspectives
After years of using N-body simulations with our galaxy formation models, the new data from JWST presented a case beyond the reach of such calculations. We reverted to a "Monte Carlo" way of growing merger histories, which allows all the resources of the computer to be devoted to one merger tree at a time. This way we can probe rare objects at very high mass resolution.
Professor Carlton M. Baugh
Durham University
Read the Original
This page is a summary of: Explaining JWST Counts with Galaxy Formation Models, The Astrophysical Journal, July 2025, American Astronomical Society,
DOI: 10.3847/1538-4357/ade700.
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