JWST Confirms the Nature of CID-42

TL;DR

JWST imaging conclusively identified the active galactic nucleus in CID-42, ruling out previous hypotheses of a recoiling or slingshot SMBH, and confirmed it as a merging galaxy pair with only one active SMBH.

Contribution

This study demonstrates JWST's superior imaging capabilities in resolving galaxy cores and clarifying the nature of SMBH activity in merging galaxies.

Findings

Only the SE core hosts an unobscured AGN

The NW core shows no evidence of AGN activity

CID-42 is a merging galaxy pair with a single active SMBH

Abstract

The galaxy CID-42 (CXOC J100043.1+020637.2) at z=0.359 has been proposed to contain a promising candidate for a gravitational wave (GW) recoiling supermassive black hole (SMBH), a slingshot SMBH from a triple-SMBH interaction, or a kpc-scale dual Active Galactic Nuclei (AGN). These claims were primarily based on a pair of bright cores separated by $\sim 0.''5$ resolved in optical HST imaging. Existing HST, Chandra and ground-based imaging and spectroscopy are unable to confirm either scenario. With improved spatial resolution, depth, and IR wavelength coverage, NIRCam multi-band imaging from the COSMOS-Web JWST treasury program well resolved the two cores in CID-42, revealing a significant stellar bulge for both cores (with stellar masses of $\sim 10^{10}\,M_\odot$ for both). JWST imaging further revealed that only the SE core contains an unobscured AGN point source, based on both image decomposition and spectral energy distribution fitting. There is no evidence for AGN activity in the NW core. These new observations unambiguously rule out the GW-recoiling and slingshot SMBH scenarios, and establish CID-42 as a low-redshift merging pair of galaxies, with only one active AGN in the system. These results demonstrate the unparalleled capabilities of JWST (even with imaging alone) in studying the galactic-scale environment of merging galaxies and SMBHs.