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The Stellar Morphology & Size of X-ray-selected Active Galactic Nuclei Host Galaxies Revealed by JWST

Bovornpratch Vijarnwannaluk, Zhen-Kai Gao, Wei-Hao Wang, Chian-Chou Chen, Abdurrahman Naufal, Adarsh Ranjan, Bau-Ching Hsieh, Chayan Mondal, Chayan Mondal, Chih-Yuan Chang, Hiddo S. B. Algera, Li-Wen Liao, Masayuki Akiyama, Seong Jin Kim, Shoichiro Mizukoshi, Tomotsugo Goto, Yu-Yen Chang, Caitlin Casey, Jeyhan S. Kartaltepe, Hollis B. Akins, Marko Shuntov, Maximilien Franco, Santosh Harish

TL;DR

This study probes the stellar morphology and size evolution of X-ray–selected AGN host galaxies using JWST COSMOS-Web near-infrared imaging. By combining high-resolution rest-frame $1\,\mu$m morphology measurements with detailed AGN-host decomposition and non-parametric diagnostics, it finds AGN hosts have effective radii in the range $R_e\sim 1$–$5$ kpc, situated between star-forming and quiescent galaxies at fixed stellar mass and exhibiting a steeper size-mass slope than SFGs. The rest-frame morphology indicates a substantial spheroidal component, while a low merger fraction (~6%) and residual disk–like substructures suggest that major mergers are not the dominant AGN triggering path, pointing to a more nuanced interplay of secular processes and timescales. Overall, the work demonstrates that AGN activity can occur in relatively compact, spheroid-dominated hosts and that mergers may operate on longer or different timescales than AGN episodes, with implications for models of galaxy evolution and quenching.

Abstract

We investigate the stellar shape and size-mass relationship of X-ray selected Active Galactic Nuclei (AGN) host galaxies using the high-angular resolution and deep sensitivity in the near-infrared of the COSMOS-Web JWST survey field. We present the rest-frame 1-$μm$ size, stellar mass, Sersic index, axis-ratio, Gini-$M_{20}$ parameters of 690 moderate luminosity AGNs between redshift 0-3 and with stellar mass $\log M_s\sim 10.75$. We find that AGN host galaxies have an effective radius of 1-5 kpc, which is between star-forming (SFG) and quiescent galaxies (QGs) of the same stellar mass. AGN hosts have similar size-mass trends as SFG and QGs, being smaller at higher redshift for the same stellar mass. The slope of the size-mass relationship of AGN host galaxies is steeper than that of star-forming galaxies. Their rest-frame 1$μm$ stellar morphology indicates a significant spheroidal component. We observed a low merger fraction (6%) in our sample as well as substructures similar to disks, bars, and spiral arms in the residual images, which are in tension with evolutionary pathways that require major mergers. However, it may also be due to the different timescales between mergers and AGN activity.

The Stellar Morphology & Size of X-ray-selected Active Galactic Nuclei Host Galaxies Revealed by JWST

TL;DR

This study probes the stellar morphology and size evolution of X-ray–selected AGN host galaxies using JWST COSMOS-Web near-infrared imaging. By combining high-resolution rest-frame m morphology measurements with detailed AGN-host decomposition and non-parametric diagnostics, it finds AGN hosts have effective radii in the range – kpc, situated between star-forming and quiescent galaxies at fixed stellar mass and exhibiting a steeper size-mass slope than SFGs. The rest-frame morphology indicates a substantial spheroidal component, while a low merger fraction (~6%) and residual disk–like substructures suggest that major mergers are not the dominant AGN triggering path, pointing to a more nuanced interplay of secular processes and timescales. Overall, the work demonstrates that AGN activity can occur in relatively compact, spheroid-dominated hosts and that mergers may operate on longer or different timescales than AGN episodes, with implications for models of galaxy evolution and quenching.

Abstract

We investigate the stellar shape and size-mass relationship of X-ray selected Active Galactic Nuclei (AGN) host galaxies using the high-angular resolution and deep sensitivity in the near-infrared of the COSMOS-Web JWST survey field. We present the rest-frame 1- size, stellar mass, Sersic index, axis-ratio, Gini- parameters of 690 moderate luminosity AGNs between redshift 0-3 and with stellar mass . We find that AGN host galaxies have an effective radius of 1-5 kpc, which is between star-forming (SFG) and quiescent galaxies (QGs) of the same stellar mass. AGN hosts have similar size-mass trends as SFG and QGs, being smaller at higher redshift for the same stellar mass. The slope of the size-mass relationship of AGN host galaxies is steeper than that of star-forming galaxies. Their rest-frame 1 stellar morphology indicates a significant spheroidal component. We observed a low merger fraction (6%) in our sample as well as substructures similar to disks, bars, and spiral arms in the residual images, which are in tension with evolutionary pathways that require major mergers. However, it may also be due to the different timescales between mergers and AGN activity.
Paper Structure (6 sections, 2 figures)

This paper contains 6 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Data
  3. NIRCam Imaging Data
  4. Pipeline Stages
  5. Wisp Removal
  6. Point Spread Function (PSF) Model Construction

Figures (2)

  • Figure 1: Deviation in the RA and declination of the JWST detected galaxies against the coordinates presented in the HSC-PDR3 catalogs. The red dashed lines show the 1$\sigma$ deviation, while the cyan cross shows the median shift from 0. The red circle shows 1 pixel size (0.03"). The numbers in parentheses show the median absolute deviation (MAD) in RA and declination.
  • Figure 2: Measured FWHM of each NIRCam band in our mosaic compared with the empirical FWHM and recent analysis of NIRCam data from other studies. The horizontal dashed lines show steps of 1 pixel. The diagonal line shows the diffraction limit FWHM.