Abstract

Studies of z<1.5 galaxy clusters and their progenitor structures, protoclusters, are disparate in their observational selection techniques, making it difficult to compare them apples-to-apples. One constraint we are lacking is when and how protoclusters should undergo virial collapse, and at what epoch the intracluster medium becomes important for galaxy evolution. In this talk I will revisit my 2021 paper on a galaxy protocluster at z=2.5 and contextualize this object from a broader evolutionary standpoint given several recent high-redshift protocluster discoveries in various stages of evolution. I will present some upcoming topics I am thinking about in terms of learning about this critical 2<z<3 period for cluster collapse and the evolution of individual galaxies inside protoclusters.

Abstract

I'll start the talk with a conclusion of my Islands of Reionization project where I used deep Keck/MOSFIRE spectroscopy, alongside a rigorous data reduction process to detect Lyα at z=8.661 in the EGS field (Larson et al. 2021 submitted). This new galaxy lies physically close (3.5 pMpc) to another galaxy with Lyα detected at z=8.684 (Zitrin et al. 2015). These two spectroscopic sources and 3 nearby photometric sources might suggest the presence of the highest-redshift overdensity in the reionization era -- indicating the existence of ≥1Mpc ionized bubbles as early as 500Myr after the Big Bang and shedding light on galaxy growth in the early universe. Planned follow-up photometric and spectroscopic observations with JWST will further expand upon our ability to quantify the impact these galaxies had on the reionization of the IGM around them.

Forthcoming JWST data will be taken over a variety of fields, to different depths and across various areas, building up a new era of deep fields. These will be ideal for the discovery and classification of galaxies out to distances previously uncharted, potentially as far as z ~ 15. As spectroscopic redshift measurements for sources in this epoch will not be readily available to compare with our first photometric measurements of z > 8 galaxies, we need to establish optimal processes now to maximize completeness and minimize contamination rates in our survey data. In preparation for the first wave of observations with JWST, we have produced mock catalogs of photometry based upon the semi-analytic models from Yung et al. (2019), which mimic expected field depths and areas of 4 upcoming JWST deep surveys: NGDEEP (m~30.6, 6 arcmin2), PRIMER DEEP (m~29.5, 33 arcmin2), CEERS (m~28.6, 100 arcmin2), and COSMOS-Web (m~27.7, 0.6deg2). Typically the selection of high redshift galaxies involves spectral energy distribution (SED) fitting to photometric data, an expectation for contamination levels, and measurement on sample completeness - all vetted through comparison to spectroscopic redshift measurements of a sub-sample. We have tested a variety of galaxy SED templates and found an appropriate set that matches the colors (β-slope) of our simulated galaxies and performed SED fitting of our simulated sources using the EAZY code (Brammer et al., 2006). I will show preliminary results highlighting the best practices for selecting galaxies at 6 < z < 15 with JWST, providing an important road map for observers venturing into this new era of astronomy.