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 AGN from dusty star forming galaxies (SFGs) in the CANDELS and COSMOS surveys. We calculate 24 µm counts of SFGs, AGN/star forming “Composites”, and AGN. AGN and Composites dominate the counts above 0.8 mJy at 24 µm, 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 AGN and Composite galaxies from z ∼ 1 − 2. With the sensitivity and spacing of MIRI filters, we will detect >4 times as many AGN hosts than with Spitzer/IRAC criteria. Any star formation rates based on the 7.7 µm PAH feature (likely to be applied to MIRI photometry) must be corrected for the contribution of the AGN, or the SFR 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 AGN with an Eddington ratio of λEdd ∼ 0.01 and will identify AGN hosts with a higher sSFR than X-ray techniques alone. JWST/MIRI will enable critical steps forward in identifying and understanding dust-obscured AGN and the link to their host galaxies.
|Original language||English (US)|
|State||Published - Jun 27 2017|
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