Collimation and scattering of the active galactic nucleus emission in the Sombrero galaxy

TL;DR

This study analyzes the central region of the Sombrero galaxy using IFU data, revealing collimation and scattering of AGN emission, consistent with the Unified Model, and demonstrating a method to detect scattered light in low-luminosity AGNs.

Contribution

It provides new evidence of AGN emission collimation and scattering in the Sombrero galaxy, supporting the Unified Model and showcasing an effective analysis technique.

Findings

Detection of collimated and scattered AGN emission.

Identification of a dusty torus/disk structure.

Confirmation of the edge-on orientation of the torus/disk.

Abstract

We present an analysis of a data cube of the central region of M104, the Sombrero galaxy, obtained with the GMOS-IFU of the Gemini-South telescope, and report the discovery of collimation and scattering of the active galactic nucleus (AGN) emission in the circumnuclear region of this galaxy. Analysis with PCA Tomography and spectral synthesis revealed the existence of collimation and scattering of the AGN featureless continuum and also of a broad component of the H{\alpha} emission line. The collimation and scattering of this broad H{\alpha} component was also revealed by fitting the [NII] {\lambda}{\lambda}6548,6583 and H{\alpha} emission lines as a sum of Gaussian functions. The spectral synthesis, together with a V-I image obtained with the Hubble Space Telescope, showed the existence of circumnuclear dust, which may cause the light scattering. We also identify a dusty feature that may be interpreted as a torus/disk structure. The existence of two opposite regions with featureless continuum (P.A. = -18{\deg} +/- 13{\deg} and P.A. = 162{\deg} +/- 13{\deg}) along a direction perpendicular to the torus/disk (P.A. = 72{\deg} +/- 14{\deg}) suggests that this structure is approximately edge-on and collimates the AGN emission. The edge-on torus/disk also hides the broad-line region. The proposed scenario is compatible with the Unified Model and explains why only a weak broad component of the H{\alpha} emission line is visible and also why many previous studies detected no broad H\alpha. The technique used here proved to be an efficient method not only for detecting scattered light but also for testing the Unified Model in low luminosity AGNs.