Depletion Study of Si And Fe with Mid- and Far-Infrared Imaging Spectroscopy with SPICA

Abstract

Ionic emission lines, such as [Si II] 35 μm, [Fe II] 26 μm, and [Fe III] 23 μm, can be used to investigate the gas-phase abundance of Si and Fe, which are key elements of the constituents of interstellar dust grains. The depletion study of Si and Fe provides crucial information on the chemical composition of dust. The investigation of the spatial distribution and the correlation with the physical properties of the environment in active regions is important for the understanding of the evolution of the interstellar matter. Previous studies showed that the gas-phase Si abundance is much larger than that in cool interstellar clouds and much less depleted than Fe. However, the depletion of these metals in active regions still has large uncertainties due to the varying physical properties in the large aperture as well as the insufficient sensitivity. We explore the strategy to estimate the physical properties using midand far-infrared emission lines that SPICA can observe.