The Astrophysical Journal · 2024

A Candidate Dual Active Galactic Nucleus in MCG-03-34-64

Resolving a Candidate Dual Active Galactic Nucleus with ∼100 pc Separation in MCG-03-34-64

Anna Trindade Falcão, T. J. Turner, S. B. Kraemer, J. Reeves, V. Braito, H. R. Schmitt, L. Feuillet

ApJ 972, 185 (2024)

**Artist concept of a candidate pair of actively accreting supermassive black holes.** NASA, ESA, Joseph Olmsted (STScI).

Scientific summary

A Candidate Dual Active Galactic Nucleus

New Hubble and Chandra observations, together with archival XMM-Newton, NuSTAR, and VLA data, resolve compact optical, X-ray, and radio structures in the central region of MCG-03-34-64. Hubble imaging reveals three compact [O III] and F814W emission regions. Chandra resolves two nearly equal-luminosity Fe Kα peaks, while the VLA image contains two radio peaks at consistent locations. The measurements favor a candidate dual active galactic nucleus separated by approximately 100 pc, although the paper cannot definitively exclude a single active nucleus interacting with the surrounding interstellar medium.

Key results

Measurements and physical implications

Hubble imaging resolves three compact [O III] and F814W emission regions. The northern-to-central and central-to-southern [O III] separations are 79 ± 8 pc and 76 ± 8 pc, respectively.

Chandra resolves two 6.2-6.6 keV Fe Kα peaks separated by 125 ± 21 pc. Each is detected at approximately 6σ and has a luminosity of (3.2 ± 0.6) × 10⁴⁰ erg s⁻¹.

The VLA 8.46 GHz image contains two radio peaks separated by 116 ± 14 pc and spatially colocated with the northern and central Fe Kα and [O III] regions.

Joint XMM-Newton and NuSTAR modeling gives an integrated Fe Kα luminosity of 1.0 × 10⁴¹ erg s⁻¹ and a scattering-corrected intrinsic 2-10 keV luminosity of 1.5 × 10⁴³ erg s⁻¹.

The multiwavelength centroids and high Fe Kα luminosities support a candidate dual active galactic nucleus, but the data do not definitively exclude a single active nucleus plus shocked interstellar gas. Deeper Chandra imaging and spatially resolved gas kinematics are required to distinguish the scenarios.

Figures from the study

Original-publication Hubble [O III] image of the nucleus of MCG-03-34-64. — **HST [O III]**Continuum-subtracted Hubble [O III] imaging resolves three compact emission regions in the nucleus of MCG-03-34-64.Trindade Falcão et al. 2024, ApJ 972, 185 (CC BY 4.0).

VLA 8.46 GHz radio-continuum image of the compact nucleus of MCG-03-34-64. — **VLA 8.46 GHz**VLA-A 8.46 GHz radio-continuum imaging resolves two peaks separated by 116 ± 14 pc.Trindade Falcão et al. 2024, ApJ 972, 185 (CC BY 4.0).

Chandra 6-7 keV image of MCG-03-34-64 with the compact Fe K alpha peaks and comparison centroids marked. — **Multiwavelength nuclear centroids**The continuum-subtracted Hubble [O III] image is compared with the two VLA radio peaks and the two Chandra Fe Kα peaks.Trindade Falcão et al. 2024, ApJ 972, 185 (CC BY 4.0).

Chandra images of MCG-03-34-64 in four X-ray energy bands, with the two compact Fe K alpha peaks marked in the 6.2-6.6 keV panel. — **Energy-resolved Chandra imaging**Chandra imaging across four energy bands isolates two compact Fe Kα peaks in the 6.2-6.6 keV band.Trindade Falcão et al. 2024, ApJ 972, 185 (CC BY 4.0).

Chandra X-ray spectrum of MCG-03-34-64 with the Fe K alpha complex and best-fit spectral model. — **X-ray spectroscopy and MYTorus modeling**The Chandra spectrum isolates the Fe Kα complex, while the joint XMM-Newton and NuSTAR spectrum constrains the transmitted, reflected, line-emitting, and soft X-ray components.Trindade Falcão et al. 2024, ApJ 972, 185 (CC BY 4.0).