Modeling the JWST MIRI Counts, Insights into the Source Properties and Role of Dust-obscured AGNs

Abstract Understanding the coevolution of galaxies and active galactic nuclei (AGNs) requires accurate modeling of dust-obscured systems. Recent surveys using the Mid Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) have uncovered a large population of dust obscured AGNs, challenging current theoretical frameworks. We present an updated version of the Simulated Infrared Extragalactic Dusty Sky (SIDES) simulation framework. Our updates include modified star-forming and starburst galaxy spectral energy distribution templates as well as quiescent and AGN templates. We also incorporate a probabilistic assignment of the fraction of the IR emission that is due to an AGN. Our simulations successfully reproduce the observed MIRI source number counts, redshift distributions, and AGN population fractions. We find that AGNs dominate at bright flux densities ( S ν ≳ 20 μ Jy) while main-sequence galaxies dominate at the faint end. We also quantify the effects of cosmic variance, showing that surveys with areas below <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>25</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">arcmin</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> suffer from ∼30% uncertainty in bright AGN counts. Finally, we provide diagnostic color–color diagrams and joint Near Infrared Camera (NIRCam) and MIRI flux distributions to aid interpretation of current and upcoming JWST surveys.