Accuracy of core mass estimates in simulated observations of dust emission

摘要

We study the reliability of mass estimates obtained for molecular cloud coresusing sub-millimetre and infrared dust emission. We use magnetohydrodynamicsimulations and radiative transfer to produce synthetic observations withspatial resolution and noise levels typical of Herschel surveys. We estimatedust colour temperatures using different pairs of intensities, calculate columndensities and compare the estimated masses with the true values. We comparethese results to the case when all five Herschel wavelengths are available. Weinvestigate the effects of spatial variations of dust properties and theinfluence of embedded heating sources. Wrong assumptions of dust opacity andits spectral index beta can cause significant systematic errors in massestimates. These are mainly multiplicative and leave the slope of the massspectrum intact, unless cores with very high optical depth are included.Temperature variations bias colour temperature estimates and, in quiescentcores with optical depths higher than for normal stable cores, masses can beunderestimated by up to one order of magnitude. When heated by internalradiation sources the observations recover the true mass spectra. The shape,although not the position, of the mass spectrum is reliable againstobservational errors and biases introduced in the analysis. This changes onlyif the cores have optical depths much higher than expected for basichydrostatic equilibrium conditions. Observations underestimate the value ofbeta whenever there are temperature variations along the line of sight. A biascan also be observed when the true beta varies with wavelength. Internalheating sources produce an inverse correlation between colour temperature andbeta that may be difficult to separate from any intrinsic beta(T) relation ofthe dust grains. This suggests caution when interpreting the observed massspectra and the spectral indices.