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

August 30 – 31, 2018

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




Abstract list for FM2
Poster list for FM2

Thursday, 30. Aug.

Census of cosmic baryons
room: F2
08:30 - Fabrizio Nicastro (The Missing Baryons in the Warm-Hot Intergalactic Medium)
08:55 - Chen, Hsiao-Wen (Cosmic Ultraviolet Baryon Survey)
09:15 - Artale, Maria Celeste (Large-scale mass distribution in the IllustrisTNG simulation)
09:30 - Ma, Yin-Zhe (Detection of missing baryons with thermal and kinetic Sunyaev-Zeldovich effect)
09:45 - Klitsch, Anne (A survey of moclecular gas in HI-Absorption-Selected Systems)

Baryons in the intergalactic medium
room: F2
10:30 - Borgani, Stefano (Simulating hot diffuse baryons: from cluster outskirts to proto-clusters)
10:55 - Fang, Taotao (Observing the Warm and Hot Baryons at Low Redshift)
11:15 - Cai, Yan-Chuan (A search for warm-hot baryons in the cosmic web using Sunyaev-Zel’dovich effect)
11:30 - Tanimura, Hideki (Unbound warm/hot gas in filaments and superclusters)
11:45 - Gallego, Sofia (Connecting the Dots: Stacking the Cosmic Web in Ly a emission with MUSE and EAGLE)

Baryons in the intergalactic and circumgalactic medium
room: F2
13:30 - Peeples, Molly (The Multiphase Circumgalactic Medium)
13:55 - Massimiliano Galeazzi (Studying the WHIM through X-ray emission)
14:15 - Davies, Jonathan (Origin and evolution of the X-ray luminous circumgalactic medium)
14:30 - Choi, Ena (The signature of AGN feedback on CGM properties)
14:45 - Young-Soo Jo (Global distribution of far-ultraviolet emission from the highly ionized gas in the Milky Way)


Friday, 31. Aug.

Baryons in the circumgalactic medium
room: M
08:30 - Joel Bregman (The Baryon and Metal Content of Halos of Galaxies)
08:55 - Mathur, Smita (The warn-hot circumgalactic medium of galaxies: clues from the Milky Way)
09:15 - Augustin, Ramona (CGM emission predictions from cosmological zoom-in simulations)
09:30 - Li, Miao (How Supernovae-driven Hot Outflows Regulate Circumgalactic Medium)
09:45 - Jones, Amy (Studying extra-planar, ionized gas with stacked MaNGA galaxies)

Soft Diffuse X-ray background
room: M
10:30 - Shelton, Robin (Review of the Diffuse Soft X-ray Background)
10:55 - Dan McCammon (What we don’t know about hot gas in the Galaxy, and how X-ray observations might help)
11:15 - Li, Jiang-Tao (The Hot Baryons in the Circum-Galactic Medium Around Massive Isolated Spiral Galaxies)
11:30 - Bogdan, Akos (Hot X-ray halos as probes of galaxy formation)
11:45 - Gupta, Anjali (Missing baryons and the warm-hot circumgalactic medium of a late type galaxy NGC3221)

Future X-ray missions
room: F2
15:30 - Tashiro, Makoto (XARM ability for the distant warm hot plasmas)
15:45 - Jan-Willem den Herder (Detection of the WHIM: prospects for Athena)
16:00 - Joel Bregman (Arcus: Exploring the Formation and Evolution of Structure in the Universe)
16:15 - Ohashi, Takaya (Super DIOS mission)
16:30 - Cui, Wei (HUBS: Hot Universe Baryon Surveyor)
16:45 - Vikhlinin, Alexey (Revealing the Invisible Drivers of Galaxy and Structure Formation with Lynx)



  • 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



Wei Cui 


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XXX IAU General Assembly | ACV - Austria Center Vienna  | Bruno-Kreisky-Platz 1  | 1220 Vienna