Recent studies suggest a population of dust grains exceeding the classical maximum grain size of 0.25 µm to be present in the denser regions of the interstellar medium. In this study, we examine the possibility of using scattered near- and mid-infrared light as an instrument to determine the properties of interstellar dust grains.
We will be utilizing observations of the filament TMC-1N located in the Taurus molecular cloud complex with a wavelength coverage from 1.25 µm to 8.0 µm. The observations were made with the United Kingdom infrared telescopes (UKIRT) wide-field infrared camera (WFCAM), and with Spitzer space telescopes IRAC instrument. We have also used the COBE satellites DIRBE instrument, and observations from the WISE satellite to determine the strength of the background intensity towards our source.
To analyse the observations, we use radiative-transfer calculations and Markov chain Monte Carlo computations on several different dust models with varying grain-size distributions and chemical compositions. The optical properties of the dust grains are based on the computations made by Li and Draine (The Astrophysical Journal, vol. 554, p. 778, 2001). The parameters we are studying are the maximum grain size of the dust grains, the size distribution of the grains, the strength of the radiation field towards the Taurus molecular cloud complex, and the optical depth of the TMC-1N filament.
Comparing our simulations with the observations, a dust grain population with maximum grain sizes exceeding the classical 0.25 µm seems most probable. Our simulations also indicate that the grain size distribution favours smaller grains over the large ones, although the larger grains contribute a significant portion of the total dust mass. These changes in the grain population should also be seen in the observed thermal emission. Thus, for further studies on the topic, we would suggest methods that combine information gathered from infrared light scattering and emission studies.
