Modeling the JWST MIRI Counts, Insights Into the Source Properties and Role of Dust-Obscured AGN

Abstract

Understanding the co-evolution of galaxies and active galactic nuclei (AGN) requires accurate modeling of dust-obscured systems. Recent surveys using the Mid Infrared Instrument (MIRI) onboard the James Webb Space Telescope (JWST) have uncovered a large population of dust obscured AGN, 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 (SED) 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 AGN dominate at bright flux densities $(S_ν\gtrsim 20\, μ\rm Jy$ while main sequence galaxies dominate at the faint end. We also quantify the effects of cosmic variance, showing that surveys with areas below $25\, \rm arcmin^2$ suffer from $\sim 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.

Figures (20)

• Figure 1: Kernel density estimation (KDE) contours of galaxies from the SC SAM, color by galaxy classification (Main Sequence, Starburst, Quenched) based on their position in the sSFR vs $M_\star$ plane. Marginal histograms of sSFR and $M_\star$ are shown along the top and right axes, respectively. See Section \ref{['subsec:implenting_SC_SAM']} for classification details.
• Figure 2: Mass-to-light ratio at the 1.22 $\mu$m $J_{\rm rest}$ band for Quiescent galaxies as a function of redshift, based on the SC SAM. A polynomial function of degree 6 fit is shown in blue, and the residuals are shown in the lower panel. For a given redshift, each quiescent galaxy is assigned a mass-to-light ratio using this functional form to de-normalize the Ell2 template.
• Figure 3: A sample of the modified Main Sequence and Starburst Galaxy SEDs from Magdis2012 normalized to $L_{\rm IR, tot} = 1\,L_\odot$. The color bar indicates the mean intensity of the radiation field $\langle U \rangle$, and the SEDs are offset for clarity. Stellar contributions for the Main Sequence and Starburst galaxies are modeled by the Sd and M82 templates (grayscale), respectively, while quenched galaxies are represented by the Ell2 template (black-dashed, normalized to $J_{\rm rest}$); all from the SWIRE library Polletta2007. The stellar contributions are stitched for visualization purposes and do not reflect scaling by stellar mass. The JWST MIRI and PRIMA imager coverages are indicated by blue and purple shaded regions, respectively. Details on SED modifications are provided in section \ref{['subsec:sed assignment']}.
• Figure 4: Sample of the modified MID IR SED template catalog from Kirkpatrick2015 normalized to $L_{\rm IR, tot} = 1 \, L_\odot$. The SEDs are offset for easier interpretation. We adapt the definition of star forming galaxies as $f_{\rm AGN, MIR} < 0.2$, composite galaxies $f_{\rm AGN, MIR} \in [0.2-0.8]$, and AGN as $f_{\rm AGN, MIR} > 0.8$. The procedure for adding the stellar contribution to the SED is summarized in Section \ref{['subsec:AGN_SEDs']}. Note that only modeled galaxies with $f_{\rm AGN} > 0.2$ will adopt this template library
• Figure 5: The normalized probability density functions (PDF) of $f_{\rm AGN}$ in bins of redshift and $L_{\rm IR,SF}$ using $\alpha = 1$ (see text for details). The inset plots are the ECDF used for the inverse sampling procedure as described in Section \ref{['subsec:determining_f_agn']}.