11 November 2026: Rohan Varadaraj

Speaker: Rohan Varadaraj (University of Oxford)

Date: Wednesday 11 November 2026

Time: 14:00

Location: Physics 3.21 (Berry)

Finding and understanding the rarest, brightest galaxies in the early universe

The most luminous galaxies in the early Universe are ideal laboratories for studying the physics of high-redshift galaxies and the processes that regulate their growth. I will present recent work tracing the bright galaxy population across the first two billion years of cosmic history. I will begin with ground-based, wide-area searches for Lyman-break galaxies at z=7, where measurements of the rest-frame UV luminosity function (UV LF) reveal a surprisingly abundant population of bright galaxies, with the observed bright end of the UV LF suggesting relatively little evolution and potentially limited effects from dust obscuration or mass quenching. I will then show how Euclid is transforming these searches, using its wide-field near-infrared imaging to improve the selection of high-redshift galaxies and distinguish them from Galactic ultra-cool dwarfs.  I will next use JWST imaging to resolve the morphologies of luminous galaxies at z=3-5 showing that compact, disc-like systems are already well established at early times, while larger and more complex systems become increasingly common towards lower redshift. Finally, I will move beyond rest-frame UV selection to present a sample of radio-selected galaxies at z=5, where deep MeerKAT observations combined with JWST grism spectroscopy reveal extreme star formation that can be traced independently of dust obscuration.

Together, these results illustrate how the combination of wide-area ground-based surveys, Euclid, JWST, and deep radio observations is allowing us to move beyond simply finding the brightest galaxies towards understanding how they assembled so rapidly in the early Universe.