Dust emission from a parsec-scale structure in the Seyfert 1 nucleus of NGC 4151

TL;DR

This study uses mid-infrared interferometry to measure the size and temperature of warm dust in the nucleus of NGC 4151, providing new insights into the structure of Seyfert galaxy nuclei and supporting the unified model.

Contribution

First direct size and temperature measurements of nuclear warm dust in a Seyfert 1 galaxy using mid-IR interferometry.

Findings

Dust emission region diameter ~2.0 pc

Warm dust temperature ~285 K

Extended silicate emission possibly on parsec scale

Abstract

We report mid-IR interferometric measurements with \sim 10 mas resolution, which resolve the warm (T = 285 +25 / -50 K) thermal emission at the center of NGC 4151. Using pairs of VLT 8.2 m telescopes with MIDI and by comparing the data to a Gaussian model, we determined the diameter of the dust emission region, albeit only along one position angle, to be 2.0 +/- 0.4 pc (FWHM). This is the first size and temperature estimate for the nuclear warm dust distribution in a Seyfert 1 galaxy. The parameters found are comparable to those in Seyfert 2 galaxies, thus providing direct support for the unified model. Using simple analytic temperature distributions, we find that the mid-infrared emission is probably not the smooth continuation of the hot nuclear source that is marginally resolved with K band interferometry. We also detected weak excess emission around 10.5 micron in our shorter baseline observation, possibly indicating that silicate emission is extended to the parsec scale.