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

Abstract

The nuclear region of Type 1 active galactic nuclei (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 NGC 4151 at long baselines of ∼250 m using the CHARA Array, reaching structures at hundred microarcsecond 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 the equatorial plane in a ring-like geometry, viewed at an inclination angle of ∼40°. The 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 Hubble Space Telescope, 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 led to an effectively flaring geometry as we observe.

Polarimetric Reverberation Mapping in Medium-Band Filters

“…Appendix A Table A1. Observed values of nonpolarized continuum and nonpolarized and polarized broad line flux for Mrk 335, Mrk 509 and Mrk 817 : (1) date of observations (dd/mm/yyyy), (2) the same in Julian form JD-2450000, (3) continuum flux in mJy, (4) the Stokes Q parameters of the continuum flux in %, (5) the Stokes U parameters of the continuum flux in %, (6) broad Hα line flux with subtracted continuum, in mJy, (7) the Stokes Q parameters of the line flux with subtracted continuum, in %, (8) the Stokes U parameters of the line flux with subtracted continuum, in %, (9) polarized broad Hα line flux with subtracted continuum, in mJy. For Mrk 817, the upper values of I line , Q line , U line and I p line are for the "blue" line profile wing and the bottom values are for the "red" wing.…”

“…its location and chemical composition determine the accretion properties of the AGN. Thanks to high-angular-resolution observations of local active galaxies in the infrared (IR) (e.g., [4][5][6][7][8]) and molecular lines (e.g., [9,10]) now it becomes possible to obtain direct images of the dusty region, while in the optical range, this structure is still unresolvable. The development of observational capabilities made it possible to determine the geometry of the dusty region, which turned out to be different from the toroidal (see [11] for a review), and also to move from the simple models of a clumpy [12] and smooth-distributed [13] dusty "torus" to more complex ones ( [7,14,15] etc.…”

Polarimetric Reverberation Mapping in Medium-Band Filters

“…Appendix A Table A1. Observed values of nonpolarized continuum and nonpolarized and polarized broad line flux for Mrk 335, Mrk 509 and Mrk 817 : (1) date of observations (dd/mm/yyyy), (2) the same in Julian form JD-2450000, (3) continuum flux in mJy, (4) the Stokes Q parameters of the continuum flux in %, (5) the Stokes U parameters of the continuum flux in %, (6) broad Hα line flux with subtracted continuum, in mJy, (7) the Stokes Q parameters of the line flux with subtracted continuum, in %, (8) the Stokes U parameters of the line flux with subtracted continuum, in %, (9) polarized broad Hα line flux with subtracted continuum, in mJy. For Mrk 817, the upper values of I line , Q line , U line and I p line are for the "blue" line profile wing and the bottom values are for the "red" wing.…”

“…its location and chemical composition determine the accretion properties of the AGN. Thanks to highangular-resolution observations of local active galaxies in the infrared (IR) (e.g., [4][5][6][7][8]) and molecular lines (e.g., [9,10]) now it becomes possible to obtain direct images of the dusty region, while in the optical range, this structure is still unresolvable. The development of observational capabilities made it possible to determine the geometry of the dusty region, which turned out to be different from the toroidal (see [11] for a review), and also to move from the simple models of a clumpy [12] and smooth-distributed [13] dusty "torus" to more complex ones ( [7,14,15] etc.…”

LeMMINGs

“…The inner disc-like component is likely due to the gaseous response to the primary bar Asif et al 2005). Inside this inner gaseous feature is an outflowing ionised gas from the AGN (Kishimoto et al 2022). Wang et al (2010) reported that the galaxy might have experienced an Eddington-rate outburst ∼ 10,000 yrs ago.…”