Accuracy of core mass estimates in simulated observations of dust
  emission
  We study the reliability of mass estimates obtained for molecular cloud cores
using sub-millimetre and infrared dust emission. We use magnetohydrodynamic
simulations and radiative transfer to produce synthetic observations with
spatial resolution and noise levels typical of Herschel surveys. We estimate
dust colour temperatures using different pairs of intensities, calculate column
densities and compare the estimated masses with the true values. We compare
these results to the case when all five Herschel wavelengths are available. We
investigate the effects of spatial variations of dust properties and the
influence of embedded heating sources. Wrong assumptions of dust opacity and
its spectral index beta can cause significant systematic errors in mass
estimates. These are mainly multiplicative and leave the slope of the mass
spectrum intact, unless cores with very high optical depth are included.
Temperature variations bias colour temperature estimates and, in quiescent
cores with optical depths higher than for normal stable cores, masses can be
underestimated by up to one order of magnitude. When heated by internal
radiation sources the observations recover the true mass spectra. The shape,
although not the position, of the mass spectrum is reliable against
observational errors and biases introduced in the analysis. This changes only
if the cores have optical depths much higher than expected for basic
hydrostatic equilibrium conditions. Observations underestimate the value of
beta whenever there are temperature variations along the line of sight. A bias
can also be observed when the true beta varies with wavelength. Internal
heating sources produce an inverse correlation between colour temperature and
beta that may be difficult to separate from any intrinsic beta(T) relation of
the dust grains. This suggests caution when interpreting the observed mass
spectra and the spectral indices.
