Magnesium and silicon in interstellar dust: an X-ray overview

Abstract

The dense Galactic environment is a large reservoir of interstellar dust. Therefore, this region represents a perfect laboratory to study the properties of the cosmic dust grains. X-rays are the most direct way to detect the interaction of light with dust present in these dense environments. The interaction between the radiation and the interstellar matter imprints specific absorption features in the X-ray spectrum. We study them with the aim of defining the chemical composition, the crystallinity and structure of the dust grains which populate the inner regions of the Galaxy. We investigate the magnesium and the silicon K-edges detected in the Chandra/HETG spectra of eight bright X-ray binaries, distributed in the neighbourhood of the Galactic centre. We model the two spectral features using accurate extinction cross sections of silicates, that we have measured at the synchrotron facility Soleil, France. Near the Galactic centre magnesium and silicon show abundances similar to the solar ones and they are highly depleted from the gas phase (${\delta }_{\mathrm{Mg}}>0.90$ and ${\delta }_{\mathrm{Si}}>0.96$). We find that amorphous olivine with a composition of $\mathrm{MgFeSi}{\mathrm{O}}_4$ is the most representative compound along all lines of sight according to our fits. The contribution of Mg-rich silicates and quartz is low (less than $10\%$). On average we observe a percentage of crystalline dust equal to $11\%$. For the extragalactic source LMC X-1, we find a preference for forsterite, a magnesium-rich olivine. Along this line of sight we also observe an underabundance of silicon $A_{\mathrm{Si}}/A_{\mathrm{LMC}}=0.5\pm 0.2$.

16 pages, 7 figures, recommended for publication in Astronomy and Astrophysics

References in corpus (21)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
• On the use of C-stat in testing models for X-ray spectra
• 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)
• Systematic comparison of photoionised plasma codes with application to spectroscopic studies of AGN in X-rays
• Silica in Protoplanetary Disks
• Dust-depletion sequences in damped Lyman-α absorbers: a unified picture from low-metallicity systems to the Galaxy
• On the Crystallinity of Silicate Dust in the Interstellar Medium
• Detailed Abundances for the Old Population near the Galactic Center: I. Metallicity distribution of the Nuclear Star Cluster
• The inner two degrees of the Milky Way. Evidence of a chemical difference between the Galactic Center and the surrounding inner bulge stellar populations
• Oxygen, α-element and iron abundance distributions in the inner part of the Galactic thin disc
• Silicate Composition of the Interstellar Medium
• Dust absorption and scattering in the silicon K-edge
• Absorption and scattering by interstellar dust in the silicon K-edge of GX 5-1
• Investigating the interstellar dust through the Fe K-edge
• The Evolution of Dust Opacity in Core Collapse Supernovae and the Rapid Formation of Dust in Their Ejecta
• Missing Fe: hydrogenated iron nanoparticles
• Dust-depletion sequences in damped Ly-α absorbers II. The composition of cosmic dust, from low-metallicity systems to the Galaxy

Cited by in corpus (2)

• The hot interstellar medium towards 4U 1820-30: a Bayesian analysis
• Near K-Edge Photoionization and Photoabsorption of Singly, Doubly, and Triply Charged Silicon Ions