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Efrain Gatuzz


Warm-Hot Intergalactic Medium
Matter detected in form of ISM, stars, galaxies and intra-cluster medium adds up to 50% of the estimated baryonic density in the nearby universe. Cosmological simulations indicate that most of the "missing baryons" reside in the form of warm-hot intergalactic medium (WHIM) filamentary hot structures among galaxies with temperatures T ~ 10⁵ – 10⁷ K, which can be analyzed in the X-ray wavelength region. In that sense, absorption lines detected in the Intergalactic Medium (IGM) due to high-ionization states (e.g. O VII and O VIII) are good indicators of the presence of the WHIM. I am developing a high-ionized X-ray absorption model in order to analyze the physical conditions of this environment.

X-ray absorption in the ISM
The Interstellar Medium (ISM), gas and dust between stars, is an important component in the stellar formation and stellar evolution processes. I have studied this environment in detail through the high-resolution X-ray spectroscopy. Using Chandra and XMM-Newton X-ray spectra, I measured reliable values of its abundance, column densities, and ionization fractions, finding that the predominant component of the ISM is the neutral gas (~ 90%).

I developed a new X-ray absorption model called ISMabs that takes into account both neutral and ionized species from H, He, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni and Zn. This model is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS, and Sherpa.