JWST Catches a Strongly Gravitationally Lensed AGN In Transition from Type II to Type I

TL;DR

The paper investigates whether high-redshift AGN follow an evolutionary path from obscured Type II to unobscured Type I, leveraging JWST/NIRCam imaging of a strongly lensed AGN SDSSJ2222+2745 at $z=2.801$. By combining archival HST data, PSF-constrained GALFIT decomposition, and Prospector-based SED fitting, the authors isolate the host galaxy and infer its star-formation history. They find a mildly disturbed, dusty host with a clear color gradient and an SFH showing a burst around $200-500\, \mathrm{Myr}$ ago, consistent with merger-triggered activity leading toward a transitionary AGN. The results provide observational support for the evolutionary link between AGN classes at cosmic noon and demonstrate the unique insights afforded by gravitational lensing with JWST for studying AGN feedback and host-galaxy coevolution at ≈$20$ pc scales ($z=2.801$).

Abstract

JWST has enabled the discovery of a statistical sample of obscured (type II) active galactic nuclei (AGN) at cosmic noon. Studies comparing those type II AGN with type I AGN at that epoch have reinforced the long-standing idea of an evolutionary link between those classes of objects. Mergers, the idea goes, disturb the morphologies and angular momentum of galaxies. The disruption of angular momentum allows material to be funneled toward galactic cores, sparking AGN activity and potentially also a burst of star-formation. That material enshrouds the galactic nucleus, leading to a type II AGN. Later, AGN feedback clears the circumnuclear dust, leading to a transition into a type I AGN, and also quenches star formation. If this is a common outcome, a class of intermediate objects should exist. Such objects would be somewhat disturbed and dusty and sit below the star-forming galaxy main sequence, and their star-formation histories would show an increase in star-formation at around the time of the suspected merger. We present new JWST observations of SDSSJ2222+2745, a strongly lensed AGN at z=2.801. The lensing magnification enables a detailed study of the host galaxy spanning the rest-ultraviolet through near infrared. JWST and HST photometry, morphological models, and models of the host's spectral energy distribution reveal that SDSSJ2222+2745 is actively transitioning from a type II to type I AGN. Catching a lensed AGN at this special evolutionary phase makes SDSSJ2222+2745 a unique laboratory to study the physical processes involved in the transition and their relationships to the AGN and the host galaxy at incredible spatial-resolution down to about 20pc at z=2.801.

Figures (8)

• Figure 1: SDSSJ2222+2745 NIRCam data. R/G/B = F444W/F150W/F115W. The labeling scheme, A-F, for the 6 images of the lensed AGN follows the labels of sharon17. Images E and F are not visible above the light of the cluster galaxies at this scaling, but are well-detected in the NIRCam imaging. Inset panels show F444W imaging, the deepest imaging we obtained, zoomed in and stretched to emphasize clumpy substructures, particularly in images A and B. The red inset box shows images A and B, while the yellow inset box shows image C.
• Figure 2: From left to right, images A, B, and C of the lensed AGN and host galaxy, with R/G/B=F444W/F150W/F115W. Images of two distinct clumps are each marked by white and yellow arrows. Clumps as large as these would show up even if they were on the other, less magnified, side of images A or B, where the magnification is a factor of $\sim2$ lower given that they show up in image C where the magnification is $\sim5\times$ lower. These are real, though minor, asymmetries and not just a matter of differential magnification.
• Figure 3: From left to right: Image, GALFIT model, and residual for image A and other nearby sources, with the same scaling and contrast in each panel. Each row contains an image, model and residual for a single filter. The top row is F115W, the middle row is F150W, and the bottom row is F444W.
• Figure 4: Same as Fig. \ref{['fig:quasarA']}, but for image B.
• Figure 5: Images of SDSSSJ2222+2745 image A in F115W, F150W, and F444W (from left to right) after subtracting the best-fit model of the AGN and matching to the F444W PSF. The light profile along the red line plotted over each image, crossing over the central AGN, is shown in the corresponding panel in the bottom row. Generally, these show relatively smooth profiles for the host galaxy, with little evidence of significant under or over subtraction of the AGN in our decompositions.