The dust sublimation region of the Type 1 AGN NGC4151 at a hundred micro-arcsecond scale as resolved by the CHARA Array interferometer

Makoto Kishimoto, Matt Anderson, Theo ten Brummelaar, Christopher Farrington, Robert Antonucci, Sebastian Hoenig, Florentin Millour, Konrad Tristram, Gerd Weigelt, Laszlo Sturmann, Judit Sturmann, Gail Schaefer, Nic Scott

Submitted on 13 September 2022


The nuclear region of Type 1 AGNs has only been partially resolved so far in the near-infrared (IR) where we expect to see the dust sublimation region and the nucleus directly without obscuration. Here we present the near-IR interferometric observation of the brightest Type 1 AGN NGC4151 at long baselines of ~250 m using the CHARA Array, reaching structures at hundred micro-arcsecond scales. The squared visibilities decrease down to as low as ~0.25, definitely showing that the structure is resolved. Furthermore, combining with the previous visibility measurements at shorter baselines but at different position angles, we show that the structure is elongated *perpendicular* to the polar axis of the nucleus, as defined by optical polarization and a linear radio jet. A thin-ring fit gives a minor/major axis ratio of ~0.7 at a radius ~0.5 mas (~0.03 pc). This is consistent with the case where the sublimating dust grains are distributed preferentially in an equatorial plane in a ring-like geometry, viewed at an inclination angle of ~40 deg. Recent mid-IR interferometric finding of polar-elongated geometry at a pc scale, together with a larger-scale polar outflow as spectrally resolved by the HST, would generally suggest a dusty, conical and hollow outflow being launched presumably in the dust sublimation region. This might potentially lead to a polar-elongated morphology in the near-IR, as opposed to the results here. We discuss a possible scenario where an episodic, one-off anisotropic acceleration formed a polar-fast and equatorially-slow velocity distribution, having lead to an effectively flaring geometry as we observe.


Comment: Accepted for publication in ApJ

Subject: Astrophysics - Astrophysics of Galaxies