Formed Too Fast: Massive Galaxies at Cosmic Dawn

The pace of galaxy growth in the early Universe offers one of the strongest and most accessible tests of the Lambda-CDM cosmological fremawork.  A growing number of surprisingly massive galaxies are now being found in the first billion years after the Big Bang that pushed the limits of theoretical predictions.  Unusually bright high-redshift galaxies discoverd by JWST challenge our most fundamental models of how fast stars form.  Massive dusty starbursts found with ALMA are requiring new explanations about early dust production.  The spatial distribution of massive galaxies within large scale structure may be more highly clustered than expected, which would impact the timescale and uniforimity of reionization - the last major phase change of the Universe from a neutral to ionized medium.

I will present an overview of large, multi-wavelength observational campaigns I am leading to place the first comprehensive constraints on the rarest, most massive galaxies to emerge at z > 6 and the impact they in turn have on our interpretations of the early Universe.  These efforts unite the unprecedented sensitivity of JWST together with ALMA and Keck to address fundamental challenges of massive galaxy formation using several independent tests and tracers.  Looking ahead, the next Generation of facilities under development - ngVLA, the TMT, Roman, and future NASA probes - will definitively establish the story of when and how the first galaxies assembled.

Speaker: Caitlin Casey, UC Berkeley