Artist’s depiction of two active black holes in merging galaxies, with a smaller distant black hole at upper left and a larger foreground black hole at lower right, each surrounded by a hot accretion disk and launching a narrow blue jet.

The Astrophysical Journal · 2024

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

Multiwavelength observations identify a candidate dual active galactic nucleus in MCG-03-34-64 on an approximately 100 pc scale; the current data do not yet uniquely exclude a single-AGN plus shocked-gas interpretation.

Artist’s concept: Artist’s depiction of two active black holes in merging galaxies, each surrounded by a hot accretion disk and launching a narrow jet. The illustration represents the candidate dual-AGN interpretation; it is not an observation of MCG-03-34-64.

NASA, ESA, Joseph Olmsted (STScI)

Paper

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

Scientific overview

New HST/ACS and Chandra/ACIS-S observations, combined with archival HST, VLA-A, XMM-Newton, and NuSTAR data, reveal three compact optical emission regions, two spatially resolved 6.2–6.6 keV Fe Kα peaks separated by 125 ± 21 pc, and two 8.46 GHz radio centroids separated by 116 ± 14 pc. The multiwavelength centroids and Fe Kα energetics support a candidate dual-AGN interpretation, but the paper also retains a single-AGN plus shocked-interstellar-medium scenario. Deeper Chandra imaging and resolved nuclear gas kinematics are required for confirmation.

Main findings

HST/ACS imaging resolves three compact [O III] and F814W emission regions; adjacent [O III] separations are 79 ± 8 pc and 76 ± 8 pc.

Chandra resolves two 6.2–6.6 keV Fe Kα peaks separated by 125 ± 21 pc. The peaks are present in each individual observation and in the merged image; their luminosities and the derived intrinsic nuclear luminosity depend on calibration and spectral modeling.

VLA-A imaging shows two 8.46 GHz radio centroids separated by 116 ± 14 pc. Their correspondence with the northern and central optical and Fe Kα centroids supports, but does not confirm, the candidate dual-AGN interpretation.

Observational evidence

Continuum-subtracted HST/ACS [O III] image of the central region of MCG-03-34-64, showing three compact emission peaks, diffraction spikes, a color scale, and a 340 pc scale bar. — **HST [O III]**Cropped [O III] panel from HST/ACS Figure 1. The continuum-subtracted narrow-band image shows three compact emission regions in the nucleus of MCG-03-34-64; the scale bar represents 340 pc.Trindade Falcão et al. 2024, ApJ 972, 185, DOI: 10.3847/1538-4357/ad6b91, CC BY 4.0. Cropped and/or resized for web presentation.

VLA-A 8.46 GHz radio-continuum image of MCG-03-34-64 with two radio centroids marked by white circles, three HST [O III] centroids marked in green, and a 170 pc scale bar. — **VLA 8.46 GHz**Cropped VLA-A 8.46 GHz radio-continuum image shown on a logarithmic color scale. White circles mark the two radio centroids, green circles mark the three HST [O III] centroids, and the scale bar represents 170 pc.Trindade Falcão et al. 2024, ApJ 972, 185, DOI: 10.3847/1538-4357/ad6b91, CC BY 4.0. Cropped and/or resized for web presentation.

Merged Chandra/ACIS-S 6.2–6.6 keV Fe K alpha image of MCG-03-34-64 with HST [O III] centroids in red, VLA 8.46 GHz centroids in white, Chandra Fe K alpha centroids in blue, and a 170 pc scale bar. — **Chandra 6.2–6.6 keV Fe Kα**Merged Chandra/ACIS-S 6.2–6.6 keV Fe Kα image, binned to one-eighth of the native pixel and Gaussian smoothed. Red circles mark HST [O III] centroids, white circles mark VLA 8.46 GHz centroids, blue circles mark Chandra Fe Kα centroids, and the scale bar represents 170 pc.Trindade Falcão et al. 2024, ApJ 972, 185, DOI: 10.3847/1538-4357/ad6b91, CC BY 4.0. Cropped and/or resized for web presentation.

Analysis and modeling

Four merged Chandra/ACIS-S images of the inner approximately 200 pc of MCG-03-34-64 in the 0.3–3, 3–5, 6.2–6.6, and 6–7 keV bands, with two Fe K alpha centroids marked in blue in the 6.2–6.6 keV panel and 170 pc scale bars. — **Energy-resolved Chandra imaging**Merged Chandra/ACIS-S images of the inner approximately 200 pc in the 0.3–3, 3–5, 6.2–6.6, and 6–7 keV bands. The images use one-eighth subpixel binning and Gaussian smoothing; blue circles mark the two Fe Kα centroids in the 6.2–6.6 keV panel.Trindade Falcão et al. 2024, ApJ 972, 185, DOI: 10.3847/1538-4357/ad6b91, CC BY 4.0. Cropped and/or resized for web presentation.

Three-panel X-ray spectroscopy figure for MCG-03-34-64 showing the combined Chandra/ACIS-S spectrum and Fe K alpha band at left, joint XMM-Newton and NuSTAR data with MYTorus components at center, and the best-fit model with residuals at right. — **Chandra, XMM-Newton, and NuSTAR spectroscopy**Left: combined Chandra/ACIS-S spectrum with the Fe Kα line measured at 6.39 ± 0.01 keV and the 6.2–6.6 keV band marked. Center and right: joint XMM-Newton/EPIC-pn and NuSTAR spectrum, MYTorus components, best-fit model, and residuals. The inferred absorption and intrinsic luminosities are model dependent.Trindade Falcão et al. 2024, ApJ 972, 185, DOI: 10.3847/1538-4357/ad6b91, CC BY 4.0. Cropped and/or resized for web presentation.