Infrared emission from dust in shocked gas

Abstract

The cooling effects of dust in a shock-heated gas and the resulting infrared emission spectra of the dust are considered for a two-component model of interstellar dust. An expression is obtained for the fraction of plasma ion and electron impact energy deposited in a grain of given radius and applied to the model of the interstellar dust proposed by Mathis, Rumpl and Nordsieck (1977), which is characterized by a power-law size distribution of bare silicate and graphite grains. Infrared emissivities are consistent with a conventional opacity curve for the silicates; however, unusual infrared properties are obtained for the carbon grains. Planck-averaged emissivities are also computed. Initial cooling rates of gas in fast shock waves due to the dust model are then calculated, and dust emission is computed taking into account the effects of sputtering and other grain destruction processes. The resulting emission spectra are presented for selected densities and shock speeds, and it is noted that current instrumentation is capable of measuring the infrared spectra of supernova remnants for shock speeds greater than 200 km/sec and preshock H densities greater than or equal to 100/sq cm.