Optimized Survey Strategies and Selection Methods for Massive Galaxies at z > 3

Massive (log (M✯/M☉) > 10.5) galaxies at z > 3 formed within the first billion years of cosmic history. Their large stellar masses and redshifts estimated from deep near-infrared spectroscopy suggest that they converted > 80% of their halo baryons into stars, nearly at the maximum rate predicted by ΛCDM. Recent JWST observations have revealed candidates at z = 10 that exceed this limit, with stellar masses requiring unphysical (> 100%) baryon-to-stellar conversion efficiencies.

The existence of these massive galaxies is therefore in tension with galaxy formation theory. This is the "impossibly early galaxy" problem.

This tension implies we either have severely underestimated systematic uncertainties in our observations at early times, or we need to reevaluate our understanding of the physics that shapes massive galaxy formation. Only larger samples (N ≫ 10) of massive galaxies at z > 4 will enable this. In this talk, I will discuss my dissertation work, which addresses this tension using: 1) novel infrared instrumentation optimized for maximum sensitivity to these galaxies. 2) new selection methods which reduce contamination from other galaxy populations at low-z; and 3) updated, self-consistent modeling techniques with flexible star formation histories. I will also present results from a recent Keck/MOSFIRE spectroscopic follow-up of 11 massive galaxies at z > 3 (including spectroscopic confirmations of quiescent candidates at z > 4) and 18 extreme emission line galaxies with indications of high [OIII] equivalent widths (>300 Å in the rest-frame at z=3-3.6).