Skip to main content
SearchLoginLogin or Signup

The composition of solid phase Fe in the interstellar medium

Presentation #104.13 in the session ISM/Galaxies - Poster Session.

Published onMay 03, 2024
The composition of solid phase Fe in the interstellar medium

Understanding the composition of interstellar Fe, suspected to condense into solid dust grains within the diffuse interstellar medium (ISM), remains a challenge. We use the XMM Reflection Grating Spectrometer to conduct a high-resolution spectral analysis of Fe L shell absorption in the ISM toward the X-ray binaries Cygnus X-1 and GX 339-4. Meteoritic studies of suspected interstellar grain analogs and computational simulations hint that metallic Fe nanoparticles or Fe-rich sulfides could dominate. Using cross-sections from Lee et al. (2009) and Kortright & Kim (2000), we model the absorption and scattering profiles of metallic Fe, fayalite, ferrous sulfate, hematite, and lepidocrocite using a power-law distribution of grain sizes. We also include gas-phase Fe oxidation states from neutral to Fe3+. We find that gas-phase Fe accounts for a small fraction of total interstellar Fe in these sight lines. The observed dust absorption in the Fe L spectral features are offset from the laboratory cross-sections we examined, indicating discrepancies in the energy scale calibration. To address this, we search for the best fitting extinction cross-sections together with shifts in their energy scale. Based on our analysis, we suggest iron oxides in the Fe3+ oxidation state as the prime candidates for Fe-bearing dust in these sight lines. To confirm this, further laboratory assessments of energy calibration for suspected interstellar compounds is required.

No comments here