Active Galactic Nuclei Selection and Demographics: A New Age with JWST/MIRI

Abstract

Understanding the coevolution of supermassive black holes and their host systems requires a comprehensive census of active galactic nuclei (AGNs) behavior across a wide range of redshift, luminosity, obscuration level, and galaxy properties. We report significant progress with JWST toward this goal from the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES). Based on comprehensive spectral energy distribution (SED) analysis of 3273 MIRI-detected sources, we identify 217 AGN candidates over a survey area of ∼34 arcmin2, including a primary sample of 111 AGNs in normal massive galaxies (M * > 109.5 M ☉) at z ∼ 0–4, an extended sample of 86 AGN candidates in low-mass galaxies (M * < 109.5 M ☉), and a high-z sample of 20 AGN candidates at z ∼ 4–8.4. Notably, about 80% of our MIRI-selected AGN candidates are new discoveries despite the extensive pre-JWST AGN searches. Even among the massive galaxies where the previous AGN search is believed to be thorough, 34% of the MIRI AGN identifications are new, highlighting the impact of obscuration on previous selections. By combining our results with the efforts at other wavelengths, we build the most complete AGN sample to date and examine the relative performance of different selection techniques. We find the obscured AGN fraction increases from L AGN,bol ∼ 1010 L ⊙ to 1011 L ⊙ and then drops toward higher luminosity. Additionally, the obscured AGN fraction gradually increases from z ∼ 0 to z ∼ 4 with most high-z AGNs obscured. We discuss how AGN obscuration, intrinsic SED variations, galaxy contamination, survey depth, and selection techniques complicate the construction of a complete AGN sample.

What Is the Nature of Little Red Dots and what Is Not, MIRI SMILES Edition

“…Our final sample includes 14 sources studied in Williams et al (2023a), as well as two sources included in the sample of highredshift obscured AGN candidates presented in Lyu et al (2024), one source identified as an AGN in Matthee et al (2024), and five galaxies selected as high-redshift candidates in Hainline et al (2024b). Compared to the galaxies in common with Williams et al (2023a), the sample in this paper is 0.5 mag fainter in F444W (medians and quartiles 26.5 26.0 27.5 mag versus 26.0 25.4 26.9 mag), and bluer in F277W-F444W (+ + + 1.3 1.1 1.7 mag versus + + + 1.6 1.5 2.5 mag) and F150W-F200W (+ -+ 0.0 0.1 0.2 mag versus + + + 0.2 0.0 0.3 mag).…”

“…This code uses a set of semiempirical AGN SED models, which have been optimized for AGN identification and characterization (Lyu et al 2022(Lyu et al , 2024. For this work, we adopted a similar model configuration as in Lyu et al (2024) for the SMILES+JADES AGN identification: the AGN component includes both the AGN-powered continuum from the UV to the far-IR and the narrow and broad emission lines from the UV to the NIR derived based on empirical observations. The continuum shape and line strengths of the AGN SED can be modified by a hybrid extinction configuration featuring the SMC-like curve for the commonly seen UVoptical extinction in Type-1 AGNs and an empirical attenuation law for the IR obscuration.…”

“…In this paper, we investigate the nature of LRDs using the best multiwavelength, large area MIRI data available to date, those coming from the SMILES survey (Lyu et al 2024). MIRI, in fact, is essential to disentangle the nature of LRDs.…”

The Galaxies Missed by Hubble and ALMA: The Contribution of Extremely Red Galaxies to the Cosmic Census at 3 < z < 8

“…With the improved sensitivity and wavelength coverage of JWST data, significant progress has been made to identify AGN. Based on a semiempirical SED analysis of MIRIdetected sources with JADES NIRCam and SMILES MIRI photometry, Lyu et al (2024) have drastically improved the AGN census in the central regions of GOODS-S. For our sample, three new AGN candidates have been revealed from that study: JADES IDs 57356, 106502, and 204851. Notably, ID 204851 has been confirmed to be a broad-line AGN at z = 5.48 in FRESCO data (Matthee et al 2023).…”

“…We find that 13 out of 66 objects in the NIRCam footprint are candidate LRDs by these criteria (nine of which lie in our MIRI coverage, excluding the probable brown dwarf candidate, ID 190413). Two of the 13 include sources with evidence of an AGN, including ID 204851 (Lyu et al 2024;Matthee et al 2023), as well as ID 154428, which show possible evidence of broadened Hα and a weak narrow component in FRESCO data (F. Sun et al 2024, in preparation). While we do not fold in the explicit compactness cut of Greene et al (2023) to identify LRDs, we note that all candidates identified by the LRD colors are visibly unresolved, or consistent with point sources, in F444W (including ID 204851, which in the single-band cutouts of Figure 11 appears blended with two neighbors).…”