The dusty heart of Circinus

Abstract

Context. Active galactic nuclei play a key role in the evolution of galaxies, but their inner workings and physical connection to the host are poorly understood due to a lack of angular resolution. Infrared interferometry makes it possible to resolve the circumnuclear dust in the nearby Seyfert 2 galaxy, the Circinus Galaxy. Previous observations have revealed complex structures and polar dust emission but interpretation was limited to simple models. The new Multi AperTure mid-Infrared Spectro-Scopic Experiment (MATISSE) makes it possible to image these structures for the first time. Aims. We aim to precisely map the morphology and temperature of the dust surrounding the supermassive black hole through interferometric imaging. Methods. We observed the Circinus Galaxy with MATISSE at the Very Large Telescope Interferometer (VLTI), producing 150 correlated flux spectra and 100 closure phase spectra. The novel inclusion of closure phases makes interferometric imaging possible for the first time. We reconstructed images in the N-band at ∼10 mas resolution. We fit blackbody functions with dust extinction to several aperture-extracted fluxes from the images to produce a temperature distribution of central dusty structures. Results. We find significant substructure in the circumnuclear dust: central unresolved flux of ∼0.5 Jy, a thin disk 1.9 pc in diameter oriented along ∼45°, and a ∼4 × 1.5 pc polar emission extending orthogonal to the disk. The polar emission exhibits patchiness, which we attribute to clumpy dust. Flux enhancements to the east and west of the disk are seen for the first time. We distinguish the temperature profiles of the disk and of the polar emission: the disk shows a steep temperature gradient indicative of denser material; the polar profile is flatter, indicating clumpiness and/or lower dust density. The unresolved flux is fitted with a high temperature, ∼370 K. The polar dust remains warm (∼200 K) out to 1.5 pc from the disk. We attribute approximately 60% of the 12 μm flux to the polar dust, 10% to the disk, and 6% is unresolved; the remaining flux was resolved out. The recovered morphology and temperature distribution resembles modeling of accretion disks with radiation-driven winds at large scales, but we placed new constraints on the subparsec dust. Conclusions. The spatially resolved subparsec features imaged here place new constraints on the physical modeling of circumnuclear dust in active galaxies; we show strong evidence that the polar emission consists of dust clumps or filaments. The dynamics of the structures and their role in the Unified Model remain to be explored.

ALMA imaging of the cold molecular and dusty disk in the type 2 active nucleus of the Circinus galaxy

“…In conclusion, we find the nuclear emission to be very compact, possibly elongated in the equatorial direction and with a size of ∼3 pc. This is not much larger than the emission by the dust at T ∼ 300 K traced by mid-infrared interferometry (Tristram et al 2014;Isbell et al 2022).…”

“…Figure 8 shows the λ = 11.8 µm warm dust emission obtained by Stalevski et al (2017) after subtracting the point spread function (PSF) of the strong unresolved core to better reveal the polar extension out to 20 pc. Also the core is to a large degree elongated in the polar direction, as revealed by higher resolution mid-infrared interferometric observations (Tristram et al 2014;Isbell et al 2022). The polar elongation of the dust emission can be explained by a dusty hollow cone illuminated by an inclined accretion disk (Stalevski et al 2017).…”

“…H 2 O masers at 22 GHz trace a thin, warped disk with a radius of r = 0.4 pc as well as a wide-angle outflow (Greenhill et al 2003). While the maser disk matches a dense, hot (T ∼ 300 K) dust disk, the majority of the thermal dust emission in the mid-infrared is extended in the polar direction on scales of ∼2.0 pc as revealed by mid-infrared interferometry (Tristram et al 2007(Tristram et al , 2014Isbell et al 2022). In fact the polar dust emission is visible out to ∼20 pc (e.g.…”

The Dust Sublimation Region of the Type 1 AGN NGC 4151 at a Hundred Microarcsecond Scale as Resolved by the CHARA Array Interferometer

“…On the other hand, the mid-IR interferometry for large angular size AGNs (i.e., NGC 1068 and Circinus galaxy) indicates an equatorial elongation in several R sub scales, embedded in the polar elongation at much larger scales of tens of R sub (Raban et al 2009;López-Gonzaga et al 2014;Tristram et al 2014). This has now even more clearly been shown by mid-IR interferometric imaging for NGC 1068 (Gámez Rosas et al 2022; see more below) and for Circinus (Isbell et al 2022). Since we are probing a few R sub scale for NGC 4151 here (λ/b ∼ 1.8 mas; R sub ∼ 0.3−0.5 mas for NGC 4151), our detection of the equatorial elongation seems geometrically consistent with such a structure being seen by the mid-IR interferometry.…”

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- IV. Aperture Masking Interferometry

“…Combining AMI with VLTI-MATISSE should advance the study of Active Galactic Nuclei (AGN). To date, VLTI-MATISSE has only been able to observe Circinus (Isbell et al 2022) and NGC 1068 (Gámez Rosas et al 2022) because other sources are too faint. AMI is expected to provide unique constraints on the morphology of AGN at scales of a few hundred mas, contributing data to further theoretical models and engender subsequent observations with improved capabilities on ground-based beamcombiners.…”