The VMC Survey -- XLIX. Discovery of a population of quasars dominated by nuclear dust emission behind the Magellanic Clouds

Abstract

Following the discovery of SAGE0536AGN ($z\sim$ 0.14), with the strongest 10-$\mu$m silicate emission ever observed for an Active Galactic Nucleus (AGN), we discovered SAGE0534AGN ($z\sim$ 1.01), a similar AGN but with less extreme silicate emission. Both were originally mistaken as evolved stars in the Magellanic Clouds. Lack of far-infrared emission, and therefore star-formation, implies we are seeing the central engine of the AGN without contribution from the host galaxy. They could be a key link in galaxy evolution. We used a dimensionality reduction algorithm, t-SNE (t-distributed Stochastic Neighbourhood Embedding) with multi-wavelength data from Gaia EDR3, VISTA survey of the Magellanic Clouds, AllWISE and the Australian SKA Pathfinder to find these two unusual AGN are grouped with 16 other objects separated from the rest, suggesting a rare class. Our spectroscopy at SAAO/SALT and literature data confirm at least 14 of these objects are extragalactic ($0.13<z<1.23$), all hosting AGN. Using spectral energy distribution fitter CIGALE we find that the majority of dust emission ($>70\%$) in these sources is due to the AGN. Host galaxies appear to be either in or transitioning into the green valley. There is a trend of a thinning torus, increasing X-ray luminosity and decreasing Eddington ratio as the AGN transition through the green valley, implying that as the accretion supply depletes, the torus depletes and the column density reduces. Also, the near-infrared variability amplitude of these sources correlates with attenuation by the torus, implying the torus plays a role in the variability.

accepted for publication in MNRAS

References in corpus (30)

• AGN Dusty Tori: I. Handling of Clumpy Media
• The XMM-Newton Serendipitous Survey. V. The Second XMM-Newton Serendipitous Source Catalogue
• The XMM-Newton serendipitous survey IX. The fourth XMM-Newton serendipitous source catalogue
• X-CIGALE: fitting AGN/galaxy SEDs from X-ray to infrared
• Resolving the obscuring torus in NGC 1068 with the power of infrared interferometry: Revealing the inner funnel of dust
• Fitting AGN/galaxy X-ray-to-radio SEDs with CIGALE and improvement of the code
• The distribution of silicate strength in Spitzer spectra of AGNs and ULIRGs
• The Half Million Quasars (HMQ) Catalogue
• Green Valley Galaxies
• The characteristic blue spectra of accretion disks in quasars as uncovered in the infrared
• 9.7 um Silicate Features in AGNs: New Insights into Unification Models
• Optically visible post-AGB/RGB stars and young stellar objects in the Small Magellanic Cloud: candidate selection, spectral energy distributions and spectroscopic examination
• Molecules and dust production in the Magellanic Clouds
• The host galaxies of X-ray selected Active Galactic Nuclei to z=2.5: Structure, star-formation and their relationships from CANDELS and Herschel/PACS
• Time-resolved infrared emission from radiation-driven central obscuring structures in Active Galactic Nuclei
• Black hole mass estimation for Active Galactic Nuclei from a new angle
• The growth of the central region by acquisition of counter-rotating gas in star-forming galaxies
• A complete census of silicate features in the mid-infrared spectra of active galaxies
• Spitzer Mid-IR Spectroscopy of Powerful 2Jy and 3CRR Radio Galaxies. II. AGN Power Indicators and Unification
• Polar dust obscuration in broad-line active galaxies from the XMM-XXL field
• Supermassive black holes in disk-dominated galaxies outgrow their bulges and co-evolve with their host galaxies
• The ASKAP-EMU Early Science Project: 888 MHz Radio Continuum Survey of the Large Magellanic Cloud
• Powerful t-SNE technique leading to clear separation of type-2 AGN and HII galaxies in BPT diagrams
• The ASKAP-EMU Early Science Project:Radio Continuum Survey of the Small Magellanic Cloud
• A Method to Distinguish Quiescent and Dusty Star-forming Galaxies with Machine Learning
• High-resolution, 3D radiative transfer modelling IV. AGN-powered dust heating in NGC 1068
• Dust Destruction by Drift-Induced Sputtering in Active Galactic Nuclei
• Modelling the strongest silicate emission features of local type 1 AGN
• The VMC Survey -- XXXVII. Pulsation periods of dust enshrouded AGB stars in the Magellanic Clouds
• Decoupled Black Hole Accretion and Quenching: The Relationship Between BHAR, SFR, and Quenching in Milky Way and Andromeda-mass Progenitors Since z = 2.5

Cited by in corpus (4)

• The intense production of silicates during the final AGB phases of intermediate mass stars
• Massive young stellar objects in the Local Group spiral galaxy M33 identified using machine learning
• Self-supervised contrastive learning of radio data for source detection, classification and peculiar object discovery
• The VMC survey -- LIII. Data release #7. Complete survey data and data from additional programmes