The AGN–Star Formation Connection: Future Prospects with JWST

Abstract

The bulk of the stellar growth over cosmic time is dominated by IR-luminous galaxies at cosmic noon ( z = 1 – 2 ), many of which harbor a hidden active galactic nucleus (AGN). We use state-of-the-art infrared color diagnostics, combining Spitzer and Herschel observations, to separate dust-obscured AGNs from dusty star-forming galaxies (SFGs) in the CANDELS and COSMOS surveys. We calculate 24 μ m counts of SFGs, AGN/star-forming “Composites,” and AGNs. AGNs and Composites dominate the counts above 0.8 mJy at 24 μ m, and Composites form at least 25% of an IR sample even to faint detection limits. We develop methods to use the Mid-Infrared Instrument (MIRI) on JWST to identify dust-obscured AGNs and Composite galaxies from z ∼ 1 – 2 . With the sensitivity and spacing of MIRI filters, we will detect >4 times as many AGN hosts as with Spitzer /IRAC criteria. Any star formation rates based on the 7.7 μ m PAH feature (likely to be applied to MIRI photometry) must be corrected for the contribution of the AGN, or the star formation rate will be overestimated by ∼35% for cases where the AGN provides half the IR luminosity and ∼50% when the AGN accounts for 90% of the luminosity. Finally, we demonstrate that our MIRI color technique can select AGNs with an Eddington ratio of λ Edd ∼ 0.01 and will identify AGN hosts with a higher specific star formation rate than X-ray techniques alone. JWST /MIRI will enable critical steps forward in identifying and understanding dust-obscured AGNs and the link to their host galaxies.