Panchromatic radiative transfer modelling of stars and dust in the Sombrero galaxy

Abstract

We present a detailed study of the dust energy balance in the Sombrero galaxy M104. From a full radiative transfer analysis, including scattering, absorption and thermal re-emission, we construct models that can reproduce images at optical/near-infrared (near-IR) wavelengths, the observed stellar spectral energy distribution and the minor axis extinction profiles in theVandRC band. A standard model, which contains only an old stellar population to heat the dust, underestimates the observations of dust emission at IR wavelengths by a factor of ~3. Supplementing this basic model with a young stellar component of low star formation activity in both the inner disc (star formation rate, SFR ~0.21M⊙yr-1) and dust ring (SFR ~0.05M⊙yr-1), we are capable of solving the discrepancy in the dust energy budget of the Sombrero galaxy at wavelengths shortwards of 100μm. To account for the increased far-IR/submm emission beyond 100μm, we propose an additional dust component distributed in quiescent clumps. This model with a clumpy dust structure predicts three-quarters of the total dust content (~2.8 × 107M⊙) to reside in compact dust clouds with no associated embedded sources. Although the assumption of a clumpy dust structure in the Sombrero galaxy is supported by high-resolution optical data, we cannot rule out the possibility that dust grains with a higher dust emissivity account for part of the discrepancy in the energy budget at submm wavelengths. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.