Prof. Dr. Philipp Richter
Project Draft UV-Spectroscopy
Baryons in the metal-enriched warm-hot intergalactic medium
A significant fraction of the baryonic mass in the Universe is believed to be contained in the so-called warm-hot intergalactic medium (WHIM), a diffuse intergalactic gas phase that is heated
to temperatures beyond 100.000 K from the gravitational collapse of large-scale filaments. The FUV and EUV range contains several transitions from highly-ionized metals (e.g., CIV, OVI, NeVIII, MgX) that can be used to traced the WHIM at low and intermediate redshifts by way of QSO absorption spectroscopy and to determine its distribution, physical nature, and - in particular – its cosmological mass density. However, an accurate estimate of the gas mass in WHIM requires a detailed modeling of the ionization conditions in the gas, which in turn requires knowledge about the multiphase-characteristics of the absorbing WHIM gas structures.
Only with a spectral resolution R>45,000 (and high S/N) it is possible to identify possible velocity-offsets in the line centroids of the above mentioned high ions that would indicate multiple gas phases in the WHIM and that need to be taken into account for a realistic estimate of the gas mass in the WHIM. Note that such velocity offsets are commonly seen in high-ions absorbers at high redshift using optical spectrographs (such as VLT/UVES) that have R>45,000.
We will re-observe a selected sample of QSO sightlines with known WHIM absorption features (e.g., OVI, NeVIII) at high spectral resolution to characterize the kinematic sub-structure in the WHIM absorbers. The velocity information in the in the different high-ion phases will be used to constrain ionization models of the WHIM that then can be compared to cosmological simulations.
High-resolution observations of OVI, NeVIII, and MgX absorbers at high S/N (>50) in the FUV and UV range will be essential to improve our understanding of the WHIM at z<1, its physical properties and its baryon budget.
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