IAU Focus Meeting FM2:
Warm and Hot Baryonic Matter in the Cosmos

August 30 – 31, 2018



  • Wei Cui (chair) - Purdue University, West Lafayette, USA
  • Jan-Willem den Herder - SRON, Utrecht, the Netherlands
  • Alexis Finoguenov - University of Helsinki, Helsinki, Finland
  • Takaya Ohashi - Tokyo Metropolitan University, Tokyo, Japan
  • Randall Smith - SAO/CfA, Boston, USA
  • Romeel Dave - University of the Western Cape, Cape Town, South Africa
  • Taotao Fang - Xiamen University, Xiamen, China
  • Li Ji - Purple Mountain Observatory, Nanjing, China
  • Smita Mathur - Ohio State University, Columbus, USA
  • Kyoko Matsushita - Tokyo University of Science, Tokyo, Japan
  • Fabrizio Nicastro - INAF-OAR, Rome, Italy
  • Naomi Ota - Nara Women’s University, Nara, Japan
  • Frits Paerels - Columbia University, New York, USA
  • Joop Schaye - Leiden University, Leiden, the Netherlands
  • Robin Shelton - University of Georgia, Athens, USA
  • Norbert Werner - Eötvös Loránd University, Budapest, Hungary

Scientific Rationale:

One of the triumphs of the Big Bang Nucleosynthesis theory is that its predicted abundances of primordial isotopes are in good agreement with the measured values. Moreover, the predicted baryonic mass is accounted for at high redshifts observationally. Going towards low redshifts, however, only a fraction of the BBN baryons are detected; this is the “missing baryon problem”. The common wisdom is that those baryons are not missing, but are hidden in warm-hot gas of very low density in the cosmic web or circumgalactic medium; cosmological hydrodynamic simulations support this view. Such gas may be “seen” through the emission and absorption lines of its highly ionized constituents. For that, dedicated high-throughput, high-resolution spectroscopic missions at FUV/EUV and soft X-ray wavelengths would be required. The proposed Focus Meeting will gather observers, theorists, and experimentalists to discuss topics related to the “missing baryon problem” and other important issues (such as the origin of the soft diffuse X-ray background) that can be addressed with such missions. A number of mission concepts will also be presented. The scope of the meeting goes much beyond that of any one Division.


  • Census of cosmic baryons 
  • Baryons in the intergalactic medium 
  • Baryons in the circumgalactic medium and galactic halos 
  • Soft diffuse X-ray background 
  • Future prospects for dedicated spectroscopic missions at FUV/EUV and soft X-ray wavelengths

Link to External Website:


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