EMERALD+DIVER | GO-7935 + GO-8018

Science Goals

Primary Objectives

EMERALD (GO-7935)

Measure how frequently accreting black holes appear in normal star-forming galaxies during the first ~1.5 billion years of cosmic history (z~4-9), and build a robust, homogeneous census of AGN incidence in a statistically meaningful galaxy sample.

DIVER (GO-8018)

DIVER adds deep rest-frame UV spectroscopy at z~5-9 to directly address two core goals: (1) clock the star-formation history by determining the distribution and redshift evolution of carbon abundance, and (2) probe the prevalence of extremely high electron density and its connection to bursty star formation and chemical peculiarity. In parallel, DIVER strengthens high-impact science on UV AGN demographics, massive stellar populations, and reionization constraints from LyA, complementing EMERALD rest-optical diagnostics.

Key Science Questions

EMERALD

  • How does AGN incidence vary with galaxy properties, star-formation intensity, and evolutionary stage?
  • How does the AGN population evolve across redshift within the reionization-era and post-reionization universe?
  • What fraction of AGN activity is identifiable through broad-line versus narrow-line and high-ionization signatures?
  • How do selection effects and host-galaxy demographics influence inferred AGN fractions in high-redshift samples?

DIVER

  • How do carbon abundance and electron-density distributions evolve with redshift, and what do they imply for bursty star formation and early chemical enrichment?
  • How do UV diagnostics (for example CIV, HeII, CIII], OIII], LyA) constrain ionization conditions, massive stellar populations, and AGN signatures at z~5-9?
  • How do DIVER UV constraints connect to EMERALD rest-optical diagnostics in the same systems?

Key Measurements and Diagnostics

EMERALD

  • Rest-optical emission-line diagnostics to separate AGN-driven and star-formation-driven ionization.
  • Broad-line AGN identification from deep spectroscopy in wavelength regions where previous wide-field slitless data are less complete.
  • Joint interpretation with ancillary imaging and SED information to connect nuclear activity with host-galaxy context.

DIVER

  • Deep UV line measurements (including CIV, HeII, CIII], OIII]) for ionization, abundance, and density constraints.
  • LyA constraints on reionization-era gas conditions and IGM transmission.
  • Targeted UV spectroscopy of known AGNs, UV emitters from literature or the JADES NIRSpec database, bright high-z sources, and high-EW OIII/Halpha emitters from grism surveys.

Legacy Value

Beyond AGN demographics, EMERALD+DIVER delivers a large, uniform GOODS-N spectroscopic legacy set that supports galaxy assembly studies, ionized-gas physics, stellar-population constraints, and calibration of early-universe diagnostics across UV and rest-optical regimes.

Program references: GO-7935 STScI Program Page | Public PDF ; GO-8018 STScI Program Page | Public PDF