Simulating the Warm-Hot Intergalactic Medium (WHIM)

How does the Universe evolve from the highly uniform medium measured by WMAP at high redshift to the highly discrete assembly of clusters, groups, galaxies and stars that we observe nowadays? Moreover, the number of baryons in the current Universe seems to be less than half that measured at high redshift by WMAP, standard big bang nucleosynthesis, and by the detailed observation of the Lyman alpha forest. What happened to the missing baryons?

We expect a significant part of the baryons (up to 50%) in the near universe to be collected in the so called Warm Hot Intergalactic Medium (WHIM), a filamentary gas at temperatures in the range of 105-107 K. However, very little is known about the properties of this gas. Hydrodynamic simulations predict that the gas in the WHIM is in the form of high temperature, highly ionized plasma, emitting and absorbing primarily in soft X-ray. It is currently believed that a significant fraction of the diffuse x-ray background below 1 keV may be due to thermal emission from the Warm Hot Intergalactic Medium (WHIM). Its signature should be observable in red-shifted soft x-ray emission and absorption lines from highly ionized elements.

Based on the output of a large scale hydrodynamic SPH simulations we studiy the WHIM emission and absorption in the soft X-ray band. Our simulations try to answer three primary questions:

  1. What are the properties of the WHIM?
  2. How can we study and detect the WHIM with existing and/or approved missions?
  3. How can we design a mission optimized for the detection and characterization of the WHIM?


For an overview of our current effort you can review some of our publications:

Accordion Group

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  • Publications:

    "X-Ray and Sunyaev-Zel'dovich Properties of the Warm-hot Intergalactic Medium", E. Ursino, M. Galeazzi, K. Huffenberger, ApJ 789, 55 (2014)

    "Reconstructing the Shape of the Correlation Function", K. M. Huffenberger, M. Galeazzi, E. Ursino, ApJS 206, 23 (2013).

    "The Hot and Energetic Universe: The missing baryons and the warm-hot intergalactic medium", J. Kaastra, et al., arXiv:1306.2324

    "The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission", K. Nandra, et al., arXiv:1306.2307

    "ORIGIN: Metal Creation and Evolution from the Cosmic Dawn", J. W. den Herder et al., Exp. Astron. 34, 519 (2012).

    "The Extreme Physics Explorer", M. Garcia, M. Elvis, J. Bookbinder, L. Brenneman, E. Bulbul, P. Nulsen, D. Patnaude, R. Smith, S. Bandler, T. Okajima, A. Ptak, E. Figueroa-Feliciano, D. Chakrabarty, R. Danner, D. Daily, G. Fraser, R. Willingale, J. Miller, T. J., Turner, G. Risalti, M. Galeazzi, arXiv:1112.1327 (2011).

    "Studying the Warm-hot Intergalactic Medium in Emission", Y. Takei, E. Ursino, E. Branchini, T. Ohashi, H. Kawahara, K. Mitsuda, L. Piro, A. Corsi, L. Amati, J. W. den Herder, M. Galeazzi, J. Kaastra, L. Moscardini, F. Nicastro, F. Paerels, M. Roncarelli, and M. Viel, ApJ 734, 91 (2011).

    "Expected properties of the two-point autocorrelation function of the intergalactic medium", E. Ursino, E. Branchini, M. Galeazzi, F. Marulli, L. Moscardini, L. Piro, M. Roncarelli, and Y. Takei, MNRAS 414, 2970 (2011).

    "Effect of Metallicity on X-ray Emission from the Warm-Hot Intergalactic Medium", E. Ursino, M. Galeazzi, and M. Roncarelli, ApJ 721, 46 (2010).

    "Studying the Warm Hot Intergalactic Medium with Gamma-Ray Bursts", E. Branchini, E. Ursino, A. Corsi, D. Martizzi, L. Amati, J. W. den Herder, M. Galeazzi, B. Gendre, J. Kaastra, L. Moscardini, F. Nicastro, T. Ohashi, F. Paerels, L. Piro, M. Roncarelli, Y. Takei, M. Viel, ApJ 697, 328 (2009).

    "EDGE: Explorer of diffuse emission and gamma-ray burst explosions", L. Piro, et al. (M. Galeazzi), Exp. Astron. 23, 67 (2009).

    "X-ray Flux from the Warm-Hot Intergalactic Medium", E. Ursino and M. Galeazzi, ApJ, 652, 1085 (2006).