High-Resolution X-ray Spectroscopy of the Interstellar Medium

TL;DR

This study uses high-resolution X-ray spectroscopy of the low-mass X-ray binary GS 1826-238 to analyze the multiphase interstellar medium, revealing elemental abundances, dust contributions, and ionization states with unprecedented detail.

Contribution

It provides a detailed analysis of the ISM's phases, dust, and elemental abundances using high-quality X-ray spectra, highlighting deviations from proto-Solar values and the role of dust.

Findings

Oxygen over-abundant by 1.23 times proto-Solar

Neon over-abundant by 1.75 times proto-Solar

Most iron bound in dust grains

Abstract

The interstellar medium (ISM) has a multiphase structure characterized by gas, dust and molecules. The gas can be found in different charge states: neutral, low-ionized (warm) and high-ionized (hot). It is possible to probe the multiphase ISM through the observation of its absorption lines and edges in the X-ray spectra of background sources. We present a high-quality RGS spectrum of the low-mass X-ray binary GS 1826-238 with an unprecedent detailed treatment of the absorption features due to the dust and both the neutral and ionized gas of the ISM. We constrain the column density ratios within the different phases of the ISM and measure the abundances of elements such as O, Ne, Fe and Mg. We found significant deviations from the proto-Solar abundances: oxygen is over-abundant by a factor 1.23 +/- 0.05, neon 1.75 +/- 0.11, iron 1.37 +/- 0.17 and magnesium 2.45 +/- 0.35. The abundances are consistent with the measured metallicity gradient in our Galaxy: the ISM appears to be metal-rich in the inner regions. The spectrum also shows the presence of warm/hot ionized gas. The gas column has a total ionization degree less than 10%. We also show that dust plays an important role as expected from the position of GS 1826-238: most iron appears to be bound in dust grains, while 10-40% of oxygen consists of a mixture of dust and molecules.