Scattering from dust in molecular clouds: Constraining the dust grain
  size distribution through near-infrared cloudshine and infrared coreshine
  Context. The largest grains (0.5-1 micron) in the interstellar size
distribution are efficient in scattering near- and mid-infrared radiation.
These wavelengths are therefore particularly well suited to probe the still
uncertain high-end of the size distribution. Aims. We investigate the change in
appearance of a typical low-mass molecular core from the Ks (2.2 micron) band
to the Spitzer IRAC 3.6 and 8 micron bands, and compare with model
calculations, which include variations of the grain size distribution. Methods.
We combine Spitzer IRAC and ground-based near-infrared observations to
characterize the scattered light observed at the near- and mid-infrared
wavelengths from the core L260. Using a spherical symmetric model core, we
perform radiative transfer calculations to study the impact of various dust
size distributions on the intensity profiles across the core. Results. The
observed scattered light patterns in the Ks and 3.6 micron bands are found to
be similar. By comparison with radiative transfer models the two profiles place
constraints on the relative abundance of small and large (more than 0.25
micron) dust grains. The scattered light profiles are found to be inconsistent
with an interstellar silicate grain distribution extending only to 0.25 micron
and large grains are needed to reach the observed fluxes and the flux ratios.
The shape of the Ks band surface brightness profile limits the largest grains
to 1-1.5 micron. Conclusions. In addition to observing coreshine in the Spitzer
IRAC channels, the combination with ground-based near-infrared observations are
suited to constrain the properties of large grains in cores.
