Speaker
Description
Cosmic rays (CRs) have a large effect on the physical and chemical evolution of star-forming material. One particular aspect of this is desorption; CRs that impact dust grains deposit energy along their track, heating the grain transiently to a higher temperature. The grain then sheds the deposited energy via (partial) desorption of the ice mantle. This mechanism is arguably the most important means of desorbing icy material in regions well shielded from the interstellar radiation field.
Earlier numerical models of CR-induced desorption have assumed that the grains are always heated to a transient maximum temperature of 70 K, stemming from the assumption that the CRs are iron nuclei and that the radius of the (spherical) grain is fixed at 0.1 microns. In reality, there is a spectrum of CRs, consisting of different particles coming in with a range of energies. This means that dust grains can be transiently heated to temperatures of a few tens of K, which is enough to desorb H2 for example, and in fact such heating events occur much more often than those heating the grains to 70 K.
We present the results of revised CR-induced desorption models where the effect of “weak heating events”, that is, those heating the grains to a few tens of K, on gas-phase and ice abundances in star-forming regions is examined. We direct particular attention to H2 ice, which is notorious for appearing in unrealistic amounts in chemical simulations. Surprisingly, we find that even the weak heating events are not enough to remove large quantities of H2 from the grains. The abundances of species other than H2 are however affected by the revision of the CR desorption model to various degrees depending on the physical conditions. We discuss the implications of our results on the understanding of (ice) chemistry in the interstellar medium.
