Bias-free Extragalactic Analysis for Cosmic Origins with NIRCam

A JWST NIRCam pure-parallel survey with multi-band imaging over ~100 fields

Main Science Goals Team Data Release Survey Paper Program Info

Formation and Evolution of the First Galaxies

When did the first galaxies form? Is star formation different at early times? How did the reionization of intergalactic hydrogen occur? The physical conditions in which the first galaxies formed were different from those of today: gas had nearly primordial chemical composition, the radiative background was lower, and gas cooling was limited by the higher temperature of the cosmic microwave background, affecting the formation mode of stars.

HST provided a first glimpse of early galaxy evolution: finding surprisingly bright 𝑧 ∼< 11 galaxies, often showing old stellar populations – indicating formation at 𝑧>15. JWST is not only confirming these galaxies spectroscopically, but it is also extending our frontier of galaxy detection to 𝑧>10 – the first 500 Myr of cosmic history and the initial stages of reionization. Cycle 1 observations discovered an unprecedented abundance of 𝑧 ∼> 10 candidates. These results were unexpected by theoretical models implying we are missing key physics in understanding the formation of the first galaxies. Furthermore, the sources responsible for reionizing intergalactic hydrogen are still unknown. What are the contributions of luminous galaxies with high ionizing photon production and escape fractions, and do (mini)-quasars play a role?

Solving these fundamental questions requires large samples of 𝑧 > 7 sources over a wide luminosity range and sufficient area to be free from cosmic variance. These are some of the questions BEACON can help answer.

Assembly of Stellar Mass Across Time

Tracing the origin of matter back to the earliest times is critical for understanding how the first galaxies formed and evolved into systems like our Milky Way. Galaxies at 𝑧 ∼ 2 appear significantly different from what we see in the local universe — with clumpy and disturbed features in star-forming galaxies, and compact morphology for post-starburst and passively evolving galaxies. Discovery of already quenched populations at 𝑧 >3, along with a few promising candidates at higher redshifts, suggests very early and rapid build-up of stellar mass. Early emergence of such massive quenched populations and their radical transition in morphologies to the local counterparts challenge our theoretical understanding of quenching mechanisms. Theoretical studies predict considerably different fractions of quenched galaxies from different numerical recipes, e.g., mass-loading factor in feedback and star formation efficiency.

Progress had been hindered because of limitations in stellar mass/redshift ranges probed by HST (due to depth, area, and limited wavelength coverage) and spatial resolution by Spitzer. Early JWST NIRCam studies identified a surprisingly large number of massive galaxy candidates at 𝑧 ∼ 4−7. The prevalence of many massive galaxies at such an early epoch is so difficult to reconcile with basic galaxy formation theory that potential solutions may involve revising the cosmological model.

Further identification of such rare, massive galaxies requires a larger volume to build a complete picture of massive galaxy build-up. From BEACON, we can construct a mass complete catalog of 𝑁 ∼ 10^5 galaxies with log 𝑀∗/𝑀⊙ > 9 at 2 < 𝑧 < 7, which will enable a wide range of studies to characterize the build-up of stellar mass & galaxy structure and the onset of quenching.

Legacy Science in the Modern Universe

BEACON will provide a unique and extensive dataset for legacy science, including enabling follow-up spectroscopy of exciting targets in future JWST cycles. Some legacy science highlights are:

Study of brown dwarfs in the Milky Way, and probing its structure from random sightline observations. Spectral coverage at >1 𝜇m is critical to characterize (sub-)dwarf populations.

Dust properties of galaxies at 𝑧 ∼ 0. Stellar continuum and dust emission coexist at restframe 1 - 5 𝜇m. NIRCam filters will enable starburst/AGN diagnostics with F200W-F444W color and 3.3 𝜇m PAH features measured by F356W flux excess.

Galaxy over-densities at 𝑧 <= 2. Our dataset will provide superb quality photometric redshifts at 𝑧<2 enabling searches for galaxy over-densities.