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 wavelengths, the observed stellar SED and the minor axis
extinction profiles in the V and R_C band. A standard model, that contains only
an old stellar population to heat the dust, underestimates the observations of
dust emission at infrared wavelengths by a factor of ~ 3. Supplementing this
basic model with a young stellar component of low star formation activity in
both the inner disk (SFR ~ 0.21 Msun/yr) and dust ring (SFR ~ 0.05 Msun/yr), we
are capable of solving the discrepancy in the dust energy budget of the
Sombrero galaxy at wavelengths shortwards of 100 \mum. To account for the
increased FIR/submm emission beyond 100 \mum, we propose a additional dust
component distributed in quiescent clumps. This model with a clumpy dust
structure predicts three-quarters of the total dust content (~ 2.8 x 10^7 Msun)
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.Comment: 10 pages, 5 figures, accepted for publication in MNRA
