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arXiv · 2610.02465

Separating the Optical to Near-Infrared Light of AGN and Their Host Galaxies

Callum Dewsnap·Pauline Barmby·Sarah C. Gallagher
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Abstract

The properties of galaxies that host active galactic nuclei (AGNs) offer clues to the conditions that enable accretion onto supermassive black holes. A galaxy's morphology can provide significant information on the evolutionary processes underway. By modeling the surface-brightness profiles of galaxies that host AGN, we can characterize physical properties of the host galaxy. With a sample of sources across a wide range of redshifts, we can investigate how both the supermassive black hole and galaxy evolve over time. Applying the best practices from previous work, we perform Sersic + point source fits of 96 X-ray-selected AGN in the Extended Groth Strip across up to 13 bands of James Webb Space Telescope and Hubble Space Telescope imaging using AstroPhot. We examine both parametric (Sersic) and nonparametric methods in tandem to best determine the physical properties of the host galaxy. After separating the light of the host galaxy and the AGN, we perform independent CIGALE model fits to photometric spectral energy distributions to estimate physical properties including the host galaxy stellar mass and star formation rate, and AGN disk luminosity. In the stellar-mass/star-formation-rate plane, the AGN host galaxies align with the population of massive non-AGN galaxies in the control sample across all redshifts. The AGN disk luminosities result in ratios of bolometric to X-ray flux within the expected range, 5-20:1. We provide an evaluation of the limitations of Sersic modeling to obtain galaxy properties and provide recommendations on best practices for multi-band AGN+host galaxy image decomposition with James Webb Space Telescope imaging.

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Callum Dewsnap, Pauline Barmby, Sarah C. Gallagher. 2026-10-01. Separating the Optical to Near-Infrared Light of AGN and Their Host Galaxies. https://doi.org/10.1088/1538-3873%2Faea2cf

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