Missing Baryons and the WHIM: First Combined XrayFUV Detection and Metallicity Estimate

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Missing Baryons and the WHIMFirst Combined
X-ray/FUV Detection and Metallicity Estimate
Fabrizio Nicastro (FORTH/SAO/INAF-OAR) M.
Conciatore (SAO), L. Zappacosta (SAO), Y.
Krongold (IA-UNAM)
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Outline

• WHIM Observables and Diagnostics
• the FUV/X-ray Synergy
• Current Evidence FUV and X-rays
• The Line of Sight to PKS 0558-504
• the First WHIM Filament with HI and Metal
• Conclusions

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Where are the Baryons?
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WHIM Baryon Fraction vs T
Transitions ?(HIa)1215.7 A (UV) ?(HIß)1025.7 A
(UV) ?(OVI)1031.9 A (UV) ?(OVIIa)21.6 A
(X) ?(OVIIIa)18.97 A (X) ?(CVa)40.2 A (X)
Cf. with R(COS)15 km s-1
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FUV Evidence lt 10-20 of the Missing Mass
Uncertain Ionization Correction
Cen Fang, 2006
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X-Rays Evidence 80 of the Missing MassFew and
controversial Unknown Metallicity Correction
(Nicastro09, Submitted)
10000 CPRES !!!
Chandra-LETG XMM-RGS (N08) XMM-RGS (R07)
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Galaxy Halo or Local Group
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Mass and Metal Content
Ionization Correction from same-element ion line
ratios
Metallicity Correction from HI to Metal line
ratios
Observable
FUV X
FUV X
X Radio
Both FUV and X-ray are Essential
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OVIII Absorption in the XMM-RGS Spectrum of PKS
0558-504
2.7s
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The Best-Fitting WHIM Model
LogT6.56-0.170.19 LogNH19.50.3 (Z/Z?)-1
z0.1170.001
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BLB BLA in FUSE and IUE
1.7s
4.1s
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BLB FWHM consistent with thermal broadening at
logT6.6
For logT6.6
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The WHIM Filament at z0.118
From HI and T ? Z (1-4) Z?
From lack of OVI ? logT gt 6.52
From X-rays ? logT lt 6.75
logNH 21.50.3 (Z/Z0.01?)-1
From Z and T ? d 300 and Theory
From d and NH ? D4-7 Mpc
Combined Statistical Significance 5.2s
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Future Prospects the optimal X-ray/FUV sample

• Requires (S/N)RE 50 60 in COS G130M G160M
• Requires (S/N)RE 15 in IXO gratings
• Doable for 18 lines of sight at zgt0.3, with COS
  and IXO/Pharos
• Expected 80 systems with accurate Z and T
  estimates
• ? build empirical relationship between WHIM
  parameters
• Additional 100 lines of sight, i.e. 400 systems
  for X-ray only

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Conclusions

• The FUV probes the 20 low-temperature end of
  the WHIM distribution
• ionization (and so metallicity) corrections is
  highly uncertain
• The X-rays probe the bulk of the WHIM mass, but
  only relative metallicities and ionization
  correction
• without HI no metallicity correction and so
  estimate is possible
• Both FUV and X-rays are essential
• First FUV/X-ray detection of a possible WHIM
  filament along the line of sight to PKS 0558-504
  
• we estimate Z 1-4 Z?, in good agreement with
  expectations
• COS can now build the BLA/BLB database for future
  X-ray follow-ups, for 18 sightlines
• unique possibility to calibrate empirical
  relationship between WHIM physical parameters