JWST MIRI color classification of mid-infrared selected galaxies

MIRI color classification toward cosmic noon

¹ Department of Astronomy and Space Sciences, Science Faculty, İstanbul University, Beyazıt 34119, İstanbul, Türkiye
² Institute of Astronomy, National Tsing Hua University, 101, Section 2. Kuang-Fu Road, Hsinchu 30013, Taiwan (R.O.C.)
³ Department of Physics and Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USA
⁴ Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁶ Department of Physics, National Chung Hsing University, No. 145, Xingda Rd., South Dist., Taichung 40227, Taiwan (R.O.C.)
⁷ Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia
⁸ Sabancı University, Faculty of Engineering and Natural Sciences, 34956 Istanbul, Türkiye

^⋆ Corresponding author: ecekilerci@istanbul.edu.tr

Received: 31 March 2025
Accepted: 23 September 2025

Abstract

Context. We investigated the James Webb Space Telescope photometric color classification of mid-infrared (MIR) selected galaxies at high redshifts, toward cosmic noon.

Aims. The aim of the present work is to obtain a z-dependent mid-infrared (MIR) photometric galaxy classification tool based on broad spectral emission and absorption lines using the JWST Mid-Infrared Instrument (MIRI) and its broadband filters.

Methods. We used the largest Spitzer MIR spectral database to obtain synthetic photometry in the JWST/MIRI filters. We formed MIRI filter combinations to trace the strong polycyclic aromatic hydrocarbon (PAH) emission features and the 9.7 μm silicate feature in seven redshift windows from z = 0.25 − 2.10.

Results. We present z-dependent MIRI color–color plots that separate active galactic nuclei (AGN), star-forming galaxies (SFGs), and silicate absorption-dominated galaxies up to z ∼ 2. We applied the photometric MIR colors to the largest (∼34 arcmin²) MIRI survey called the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES), to identify AGN, SFGs, and Si-absorption dominated galaxies out to substantial redshifts. Our JWST/MIRI SFGs sample includes galaxies with total IR luminosities of 10^9.2 ∼ 10^11.9 L_⊙ at 0.9 ≤ z < 1.57. The majority of them are consistent with the z ∼ 1 main sequence. We also identified the first examples of z ∼ 1 galaxies with deep silicate absorption.