Probing Heavily Obscured AGN in Major Galaxy Mergers Using the mm-X-ray Correlation

Abstract

The study of heavily obscured supermassive black hole (SMBH) growth in late-stage galaxy mergers is challenging: column densities $N_{\mathrm{H}}>10^{24},{\mathrm{cm}}^{-2}$ can block most nuclear emission, leaving significant gaps in the SMBH growth census. Millimeter-wave continuum emission offers a potential window into this obscured phase, as it can trace Active Galactic Nuclei (AGN) activity through mechanisms less affected by dust extinction. In this work, we test whether the observed correlation between millimeter ($\sim 200,\mathrm{GHz}$) and hard X-ray (14 - 150,keV) luminosities can be used to plausibly identify hidden AGN in local (Ultra)Luminous Infrared Galaxies (U)LIRGs, including systems hosting confirmed dual AGN. We identify three sources -- one confirmed AGN and two strong candidates -- presenting significant evidence of AGN activity. The confirmed dual AGN lie within $\sim 3\sigma$ of the mm--X-ray correlation, suggesting this relation can be used to identify hidden pairs. By combining the position of each source relative to this correlation with independent star formation rate constraints, we propose a method to disentangle AGN and star formation contributions for sources with measured column densities. While our analysis is based on a small, heterogeneous local sample and relies on empirical scaling relations, these results indicate that millimeter continuum emission may provide a useful complementary diagnostic for obscured SMBH growth. ALMA observations at high angular resolutions are particularly valuable for this approach, while future facilities such as the ngVLA will be essential to test its robustness in larger and more distant samples.

References in corpus (30)

• Array Programming with NumPy
• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• Modelling the behaviour of accretion flows in X-ray binaries
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• BAT AGN Spectroscopic Survey - V. X-ray properties of the Swift/BAT 70-month AGN catalog
• BAT AGN Spectroscopic Survey I: Spectral Measurements, Derived Quantities, and AGN Demographics
• Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured
• Merging and Clustering of the Swift BAT AGN Sample
• An Exploratory Chandra Survey of a Well-Defined Sample of 35 Large Bright Quasar Survey Broad Absorption Line Quasars
• Chandra unveils a binary Active Galactic Nucleus in Mrk463
• The X-ray and Radio Connection in Low-luminosity Active Nuclei
• Chandra Discovery of a Binary Active Galactic Nucleus in Mrk 739
• High-Resolution Radio Continuum Measurements of the Nuclear Disks of Arp 220
• Galaxy gas as obscurer: II. Separating the galaxy-scale and nuclear obscurers of Active Galactic Nuclei
• A hard X-ray view of Luminous and Ultra-luminous Infrared Galaxies in GOALS: I - AGN obscuration along the merger sequence
• The black hole fundamental plane from a uniform sample of radio and X-ray emitting broad line AGNs
• Comprehensive Broadband X-ray and Multiwavelength Study of Active Galactic Nuclei in Local 57 Ultra/luminous Infrared Galaxies Observed with NuSTAR and/or Swift/BAT
• BASS XXXII: Studying the Nuclear Mm-wave Continuum Emission of AGNs with ALMA at Scales $\lesssim$ 100-200 pc
• The properties of the AGN torus as revealed from a set of unbiased NuSTAR observations
• A Tight Correlation Between Millimeter and X-ray Emission in Accreting Massive Black Holes from <100 Milliarcsecond-resolution ALMA Observations
• UGC 4211: A Confirmed Dual Active Galactic Nucleus in the Local Universe at 230 pc Nuclear Separation
• The Molecular Gas in the NGC 6240 Merging Galaxy System at the Highest Spatial Resolution
• Radio continuum properties of luminous infrared galaxies. Identifying the presence of an AGN in the radio
• X-ray emission from the nuclear region of Arp 220
• Characterizing Compact 15-33 GHz Radio Continuum Sources in Local U/LIRGs
• Chasing Super-Massive Black Hole merging events with $Athena$ and LISA
• No evidence of AGN features in the nuclei of Arp 220 from JWST/NIRSpec IFS
• Candidate high-redshift protoclusters and lensed galaxies in the Planck list of high-z sources overlapping with Herschel-SPIRE imaging
• Accretion and Obscuration in Merger-Dominated Luminous Red Quasars
• Millimeter emission from supermassive black hole coronae