MIDIS: Quantifying the AGN component of X-ray-detected galaxies

Steven Gillman, John P. Pye, Almudena Alonso-Herrero, Martin J. Ward, Leindert Boogaard, Tuomo V. Tikkanen, Luis Colina, G. Östlin, Pablo G. Pérez-González, Luca Costantin, Edoardo Iani, Pierluigi Rinaldi, Javier Álvarez-Márquez, A. Bik, Sarah E. I. Bosman, Alejandro Crespo Gómez, Andreas Eckart, Macarena García-Marín, Thomas R. Greve, Jens Hjorth, A. Labiano, Danial Langeroodi, J. Melinder, Florian Peißker, Fabian Walter, M. Güdel, Thomas Henning, P. -O. Lagage, Thomas P. Ray

First listed 2025-01-20 | Last updated 2025-01-20

Abstract

We combine the deepest X-ray survey from the Chandra Deep Field-South (CDF-S) `7-Ms' survey with the deepest mid-infrared (5.6$ μm$) image from the JWST/MIRI Deep Imaging Survey (MIDIS) in the Hubble Ultra-Deep Field (HUDF) to study the infrared counterparts and point-source emission of 31 X-ray sources with a median, intrinsic, rest-frame X-ray luminosity of $\log_{10}(L_{\rm Xc}^{\rm 0.5-7keV})$=42.04$\pm$0.22 erg $\rm s^{-1}$. The sample includes 24 AGN with a redshift range, as set by the X-ray detectability, of $z \simeq 0.5-3$. Through a multi-wavelength morphological decomposition, employing three separate classifications (visual, parametric and non-parametric) we separate (where present) the luminosity of the point-like AGN component from the remainder of the host-galaxy emission. The unprecedented mid-infrared sensitivity and imaging resolution of MIRI allows, in many cases, the direct characterisation of point-like (i.e. unresolved) components in the galaxies' emission. We establish a broad agreement between the three morphological classifications. At least 70% of the X-ray sources, including some classified as galaxies, show unresolved emission in the MIRI images, with the unresolved-to-total flux fraction at rest-frame 2$μm$ ranging from $\sim$0.2 to $\sim$0.9. At high X-ray luminosities ($\log_{10}(L_{\rm Xc}$)>43 erg $\rm s^{-1}$) we derive a consistent rest-frame near-infrared 2$ μm$ point-source luminosity to that derived for local AGN, whilst at lower X-ray luminosity we identify an excess in the 2$ μm$ emission compared to pre-JWST studies. We speculate this offset may be driven by a combination of Compton-thick AGN components and nuclear starburst, merger driven activity. Our observations highlight the complex nature of X-ray sources in the distant Universe and demonstrate the power of JWST/MIRI in quantifying their nuclear infrared emission. (Abridged)

Short digest

Using MIDIS MIRI 5.6 μm imaging in the HUDF cross-matched to the CDF-S 7 Ms catalog, the authors morphologically decompose 31 X-ray sources (24 AGN; z≈0.5–3) with visual, Sérsic+PSF, and non-parametric classifiers to isolate unresolved nuclear emission at rest-frame ~2 μm. They find ≥70% show an unresolved MIRI component with unresolved-to-total 2 μm flux fractions spanning ~0.2–0.9, and at Lx>10^43 erg s^-1 the 2 μm point-source luminosities align with local AGN relations. At lower X-ray luminosities, they report an excess 2 μm nuclear component relative to pre-JWST expectations, plausibly linked to Compton-thick AGN and/or compact nuclear starburst/merger activity. The work demonstrates that MIRI can robustly quantify nuclear IR emission in faint X-ray sources and clarifies the AGN/host balance across Cosmic Noon.

Key figures to inspect

• Figure 1: Use the MIDIS false-color cutouts (F1000W/F770W/F560W) to verify which CDF-S XIDs exhibit red, compact MIR cores and to cross-check each target’s z and Lx; note IDs 695 and 758 lack reliable F1000W, affecting color inference.
• Figure 2: Inspect Lx versus redshift with N_H coloring to see the flux-limited locus of the MIDIS subsample and where obscured systems sit relative to the full 7 Ms population.
• Figure 3: Examine F210M/F560W and F480M/F560W color maps to identify centrally peaked red colors that betray unresolved hot-dust emission; compare with the PSF FWHM circles to judge true compactness.
• Figure 4: Read off Sérsic+PSF fits at rest-frame ~2 μm (PSF and host magnitudes, Sérsic n, Gini–M20, residuals) to assess the measured PSF fractions and the diversity of host morphologies across representative XIDs.