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JWST MIRI color classification of mid-infrared selected galaxies: MIRI color classification toward cosmic noon

Ece Kilerci, Tomotsugu Goto, Matthew A. Malkan, Seong Jin Kim, Chih-Teng Ling, Cossas C. -K Wu, Tetsuya Hashimoto, Simon C. -C. Ho, Amos Y. -A. Chen, Ersin Gogus

TL;DR

This work develops redshift-aware JWST/MIRI MIR color diagnostics by synthesizing Spitzer IDEOS spectra into MIRI photometry and using Gaussian Mixture Modeling to define class-specific color regions across $0.25 \le z \le 2.10$. Applying these colors to the SMILES survey yields 121 AGN, 154 SFGs, and 6 silicate-absorption-dominated galaxies up to $z \ge 2$, including the first high-$z$ deep Si absorption examples. SED fitting with CIGALE corroborates the physical interpretation of the MIR classifications, showing most $z \sim 1$ SFGs on the star formation main sequence and evidence for evolution at $z \sim 2$, while revealing contamination challenges from MIR-weak/dwarf systems. The authors provide the classification tool and Gaussian region files for public use, enabling scalable, spectroscopically informed population studies with current and upcoming JWST/MIRI data and enhancing our understanding of galaxy evolution during cosmic noon.

Abstract

We investigated the James Webb Space Telescope photometric color classification of mid-infrared (MIR) selected galaxies at high redshifts, toward cosmic noon. 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. 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 micron 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$\sim$2. We applied the photometric MIR colors to the largest ($\sim$34 arcmin square) 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 $10^{9.2} \sim 10^{11.9} L_{\odot}$ at 0.9 $\leq$z < 1.57. The majority of them are consistent with the z$\sim$1 main sequence. We also identified the first examples of z$\sim$1 galaxies with deep silicate absorption.

JWST MIRI color classification of mid-infrared selected galaxies: MIRI color classification toward cosmic noon

TL;DR

This work develops redshift-aware JWST/MIRI MIR color diagnostics by synthesizing Spitzer IDEOS spectra into MIRI photometry and using Gaussian Mixture Modeling to define class-specific color regions across . Applying these colors to the SMILES survey yields 121 AGN, 154 SFGs, and 6 silicate-absorption-dominated galaxies up to , including the first high- deep Si absorption examples. SED fitting with CIGALE corroborates the physical interpretation of the MIR classifications, showing most SFGs on the star formation main sequence and evidence for evolution at , while revealing contamination challenges from MIR-weak/dwarf systems. The authors provide the classification tool and Gaussian region files for public use, enabling scalable, spectroscopically informed population studies with current and upcoming JWST/MIRI data and enhancing our understanding of galaxy evolution during cosmic noon.

Abstract

We investigated the James Webb Space Telescope photometric color classification of mid-infrared (MIR) selected galaxies at high redshifts, toward cosmic noon. 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. 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 micron 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 z2. We applied the photometric MIR colors to the largest (34 arcmin square) 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 at 0.9 z < 1.57. The majority of them are consistent with the z1 main sequence. We also identified the first examples of z1 galaxies with deep silicate absorption.

Paper Structure

This paper contains 22 sections, 8 figures, 1 table.

Table of Contents

  1. Introduction
  2. Sample and analysis
  3. Spitzer IDEOS sample
  4. Color analysis
  5. Classification of each MIR class
  6. Classification of AGN, SFGs, and composite galaxies
  7. Comparison with MIRI color classifications in the literature
  8. MIR spectral classification of MIR detected galaxies in SMILES
  9. SMILES survey
  10. SMILES data
  11. MIRI color classification of SMILES sample
  12. SED analysis of the selected SFGs
  13. Results and discussion
  14. MIRI color selection
  15. MIRI selected AGN toward cosmic noon
  16. ...and 7 more sections

Figures (8)

  • Figure 1: MIRI colors of different MIR class IDEOS galaxies at $z=$ 0.25--0.30 (top left panel), $z=$ 0.58--0.65 (top right and middle left panels), $z=$ 0.90--0.92 (middle right panel), $z=$ 1.00--1.10 (bottom left panel), $z=$ 1.50--1.60 (bottom right panel). The MIR class symbol code is given in the legend. In each panel, the ellipses represent a 2D Gaussian component for the MIR class subregions.
  • Figure 2: Subregions obtained from the GMM analysis for AGN (1A-1B-2A combined) and SFGs (1C-2C combined). The regions of AGN and SFGs are shown as orange and green ellipses, respectively.
  • Figure 3: Left and middle panels: Color--color diagrams adopted from Kirkpatrick2017b. The solid cyan circles are their AGN, composite, and SFGs regions. Right panel: Color--color diagram Kirkpatrick2023. The cyan hexagon defines their AGN region. In all panels, the dark green and orange ellipses respectively represent the SFGs and AGN regions obtained by the GMM analysis.
  • Figure 4: MIRI colors of SMILES galaxies. The subregions obtained from the GMM analysis for AGN (1A-1B-2A combined), SFGs (1C-2C combined) are shown as the orange and dark green ellipses.
  • Figure 5: Two examples (SMILES IDs 1237 and 1479) of the best-fitting SEDs of the MIRI-selected SFGs candidates at $z\sim1.5$. The red and blue curves show the dust emission and the stellar emission, respectively. The purple circles show the observed photometric fluxes. The filled red circles are the model fluxes. The best model for 1479 requires an AGN component; in 1237 there is no AGN.
  • ...and 3 more figures