Investigating the interstellar dust through the Fe K-edge

Abstract

The chemical and physical properties of interstellar dust in the densest regions of the Galaxy are still not well understood. X-rays provide a powerful probe since they can penetrate gas and dust over a wide range of column densities (up to $10^{24}{\mathrm{cm}}^{-2}$). The interaction (scattering and absorption) with the medium imprints spectral signatures that reflect the individual atoms which constitute the gas, molecule, or solid. In this work we investigate the ability of high resolution X-ray spectroscopy to probe the properties of cosmic grains containing iron. Although iron is heavily depleted into interstellar dust, the nature of the Fe-bearing grains is still largely uncertain. In our analysis we use iron K-edge synchrotron data of minerals likely present in the ISM dust taken at the European Synchrotron Radiation Facility. We explore the prospects of determining the chemical composition and the size of astrophysical dust in the Galactic centre and in molecular clouds with future X-ray missions. The energy resolution and the effective area of the present X-ray telescopes are not sufficient to detect and study the Fe K-edge, even for bright X-ray sources. From the analysis of the extinction cross sections of our dust models implemented in the spectral fitting program SPEX, the Fe K-edge is promising for investigating both the chemistry and the size distribution of the interstellar dust. We find that the chemical composition regulates the X-ray absorption fine structures in the post edge region, whereas the scattering feature in the pre-edge is sensitive to the mean grain size. Finally, we note that the Fe K-edge is insensitive to other dust properties, such as the porosity and the geometry of the dust.

11 pages, 10 figures. Accepted for publication in Astronomy and Astrophysics

References in corpus (9)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point
• The shape and composition of interstellar silicate grains
• On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk
• The Athena X-ray Integral Field Unit (X-IFU)
• Galactic abundance gradients from Cepheids : On the iron abundance gradient around 10-12 kpc
• A hidden reservoir of Fe/FeS in interstellar silicates?
• The Composition of Interstellar Grains Toward Zeta Ophiuchi: Constraining the Elemental Budget Near the Diffuse-Dense Cloud Transition
• Absorption and scattering by interstellar dust in the silicon K-edge of GX 5-1

Cited by in corpus (3)

• Dust absorption and scattering in the silicon K-edge
• Magnesium and silicon in interstellar dust: an X-ray overview
• The hot interstellar medium towards 4U 1820-30: a Bayesian analysis