Magnesium and silicon in interstellar dust: X-ray overview
Abstract
Context. The dense Galactic environment is a large reservoir of interstellar dust. Therefore, this region represents a perfect laboratory to study the properties of cosmic dust grains. X-rays are the most direct way to detect the interaction of light with dust present in these dense environments.
Aims: The interaction between the radiation and the interstellar matter imprints specific absorption features on the X-ray spectrum. We study them with the aim of defining the chemical composition, the crystallinity, and structure of the dust grains that populate the inner regions of the Galaxy.
Methods: We investigated 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 modelled the two spectral features using accurate extinction cross-sections of silicates, which we measured at the synchrotron facility Soleil, France.
Results: Near the Galactic centre, magnesium and silicon show abundances similar to the solar ones and they are highly depleted from the gas phase (δMg > 0.90 and δSi > 0.96). We find that amorphous olivine with a composition of MgFeSiO4 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 under-abundance of silicon ASi/ALMC = 0.5 ± 0.2.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 2020
- DOI:
- 10.1051/0004-6361/201936805
- arXiv:
- arXiv:2007.03329
- Bibcode:
- 2020A&A...641A.149R
- Keywords:
-
- astrochemistry;
- X-rays: binaries;
- X-rays: ISM;
- dust;
- extinction;
- ISM: abundances;
- X-rays: individuals: LMC X-1;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies;
- Condensed Matter - Materials Science
- E-Print:
- 16 pages, 7 figures, recommended for publication in Astronomy and Astrophysics