Dust rotational dynamics in non-stationary shock: rotational disruption of nanoparticles by stochastic mechanical torques and spinning dust emission

Abstract

In a previous work, Hoang and Tram discovered a new mechanism for destruction of nanoparticles due to suprathermal rotation of grains in stationary C-shocks, which is termed rotational disruption. In this paper, we extend our previous study for non-stationary shocks driven by outflows and young supernovae remnants that have dynamical ages shorter than the time required to establish a stationary C-shock, which is composed of a C-shock and a J-shock tail (referred as CJ-shock). For the C-shock component, we find that smallest nanoparticles (size $\lesssim 1$ nm) of weak materials (i.e., tensile strength $S_{\rm max} \lesssim 10^{9}\ \rm erg\ cm^{-3}$) can be rotationally disrupted due to suprathermal rotation induced by supersonic neutral drift. For the J-shock component, although nanoparticles are rotating thermally, the smallest ones can still be disrupted because the gas is heated to higher temperatures by J-shocks. We then model microwave emission from rapidly spinning nanoparticles where the grain size distribution has the lower cutoff determined by rotational disruption for the different shock models. We also calculate the spectral flux of microwave emission from a shocked region at distance of 100 pc from the observer for the different gas density, shock age, and shock velocities. We suggest that microwave emission from spinning dust can be used to trace nanoparticles and shock velocities in dense molecular outflows. Finally, we discuss a new way that can release molecules from the nanoparticle surface into the gas in the shocked regions, which we name rotational desorption.