Modelling dust rings in early-type galaxies through a sequence of radiative transfer simulations and 2D image fitting

TL;DR

This paper introduces 'Lord Of The Rings' (LOTR), a new method combining radiative transfer simulations and 2D image fitting to model dust rings in early-type galaxies, revealing their impact on surface brightness and AGN activity.

Contribution

The paper presents a novel pipeline integrating GALFIT and SKIRT to accurately model dust extinction in galaxy surface brightness profiles, accounting for dust rings.

Findings

Dust rings can mimic central point sources in brightness profiles.

Proper dust modeling is crucial for accurate flux and AGN characterization.

Dust mass in rings may be linked to AGN activity.

Abstract

A large fraction of early-type galaxies (ETGs) host prominent dust features, and central dust rings are arguably the most interesting among them. We present here `Lord Of The Rings' (LOTR), a new methodology which allows to integrate the extinction by dust rings in a 2D fitting modelling of the surface brightness distribution. Our pipeline acts in two steps, first using the surface fitting software GALFIT to determine the unabsorbed stellar emission, and then adopting the radiative transfer code SKIRT to apply dust extinction. We apply our technique to NGC 4552 and NGC 4494, two nearby ETGs. We show that the extinction by a dust ring can mimic, in a surface brightness profile, a central point source (e.g. an unresolved nuclear stellar cluster or an active galactic nucleus; AGN) superimposed to a `core' (i.e. a central flattening of the stellar light commonly observed in massive ETGs). We discuss how properly accounting for dust features is of paramount importance to derive correct fluxes especially for low luminosity AGNs (LLAGNs). We suggest that the geometries of dust features are strictly connected with how relaxed is the gravitational potential, i.e. with the evolutionary stage of the host galaxy. Additionally, we find hints that the dust mass contained in the ring relates to the AGN activity.