1. Fabrizio Nicastro (INAF-OAR/CfA)
Have we Detected the Missing Baryons? FUV and X-Ray Evidence of the WHIM
Fabrizio Nicastro (INAF-OAR/CfA)
Collaborators: S. Mathur (OSU), R. Williams (OSU), M. Elvis (CfA), J. Drake (CfA), F. Fiore (INAF-OAR), Y. Krongold (IA-UNAM)
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

2. Outline The Missing Baryons problem and N-body simulations solution
The WHIM in the UV-FUV
The Controversial X-Ray Detections(?)
The Way Forward: Short- & Long-Term Prospects
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

3. (59 ± 9) % of Baryons are Missing
(Nicastro et al., 2005, Nature, 433, 495)
>76
5.7
1.7
4.6 29
4.8 46 54
% of b
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

4. Warm-Hot gas dominates Mass at low z
The Solution:WHIM ?
Warm-Hot gas dominates Mass at low z
Find the ‘Missing Baryons’ and
verify theory
Ecology of the Universe: dZ/dz
- Absolute (needs UV) and Relative
Metallicities.
- Galaxy Superwinds (SN) vs AGN
winds, jets
- Nucleosynthesis
Heating History of the Universe:
dT/dz
Cosmological parameters > 103 systems needed
LG-WHIM is a biased measure - Need z>0 WHIM absorbers to measure Wb
Local Group WHIM and Galaxy formation
Read WHIM Science goals; Why is the WHIM important
(Cen & Ostriker, 2006)
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

5. WHIM Strength & Detectability
Pure Collisional
Coll. + Phot (z=1, =5)
Size: R ~ 1 Mpc, Density: nb ~ cm-3, Temperature: T ~ K,
Ion Fraction: ξOVII ~ 1, ξOVI < 0.2, Metallicity: Z ~ 0.1 Z๏
=> NOVII ~ nbξOVIIZOR ~ 2x( ) cm-2 => WOVII ~ (1+z) mA
=> NOVI ~ nbξOVIZOR < 5x( ) cm-2 => WOVI < (1+z) mA
Contrast: FUV: 1032/( ) ~ ~ (0.1-1) x RFUSE/HST-STIS
X-Rays: 22/( ) ~ ~ (10-100) x RChandra/XMM
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

6. The WHIM in the FUV: 10-20 % of the Missing Mass
Cen & Fang, 2006
b(OVI) = 0.22 %, i.e. ~ 10 % Missing Baryons
(with ZO ~ 0.1 Z)
Also: BLAs (Richter et al., 2006): btherm(HI) > 45 km/s
(Cf b(HI) ~ km/s in Ly-Forest)
b(BLA) = 0.27 %, i.e. ~ 10 % Missing Baryons
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

7. The WHIM in X-Rays: 80-90 % of the Missing Mass?
Local Group
WHIM?
<z>=0.011
WHIM
<z>=0.027
Chandra TOOs:
F(0.5-2)=2x10-4 erg s-1
CPREs=5300
(Nicastro et al., 2005, Nature, 433,495; Nicastro et al., 2005, ApJ; Williams et al., 2005, ApJ, in press)
0.8 mA
8 mA
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

8. dNWHIM(OVII)/dz & bWHIM(OVII)
Cen & Fang, 2006
Fang et al., 2002
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

9. The Controversy (1) Differences are due to different assumptions
Nicastro et al., 2005a,b claim statistical significances of 3.5 and 4.8 for the two systems, based on F-tests (that do not properly account for the number of trial redshifts).
Kaastra et al., 2006 perform MonteCarlo tests and conclude that: P=40 % and P=6 % of falsely detect the two systems.
Nicastro et al., 2007 perform new MonteCarlo and confirm P=0.05 % and P < 0.01 % for the two systems (i.e. 3.5 and > 3.9 respectively).
Differences are due to different assumptions
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

10. No conclusive evidence, yet, for X-Ray WHIM
The Controversy (2)
Rasmussen et al., 2006 show no evidence of the absorption lines seen by Chandra in a high S/N XMM-Newton RGS spectrum of Mkn 421
RLETG ~ 2.4 x RRGS
Bottom Line:
No conclusive evidence, yet, for X-Ray WHIM
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

11. The Way Forward: Short-Term
FUV:
Systematic search of BLAs and OVI on archival STIS and archival and new FUSE
KOS in 2009: deep observations of BLAs and moderate-to-high-z OVI
X-Rays:
Only pursuable way with Chandra and XMM: Multi-Ms observations of higher-z, strategically selected (i.e. BLAs, OVI, or pilot X-ray spectra) bright targets
On quiescent targets RGS slightly better than Chandra whwre both RGSs are present, because of high LETG background
LETG is the only instrument at > 40 A: sensitivity at C 4 times better than at O
ES: 1ES (z=0.361: 10x Mkn 421)
Approved 100 ks FUSE
Proposed 300 ks Chandra
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

12. Long-Term Prospects & high spectral resolution
Long Term: mapping the WHIM up to z~1: Needs large throughput
& high spectral resolution
Tens to hundreds systems would enable:
b ® and dN/dz to better than few/tens %
WHIM density in galaxy voids vs galaxy overdensities
Multi-phase studies ® ® ®
Hundreds to Thousands of Systems would enable:
b ® and dN/dz to better than few tenth of %
Cosmological Parameters
Dark-Matter Maps
Metallicity History: dZ/dz (Ecology of the Universe) (needs UV) ®
IGM/galaxy/AGN Feedback
Heating History of the Universe (dT/dz) ®
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

13. Pharos distant beacons as cosmological probes
A GRB MIDEX mission concept
R > 0.5 keV (RLETG=400)
Aeff > 0.5 keV (ALETG=20 cm2)
1 arcmin ASM localization
Slew in s
‘The “Pharos” of Alexandria, one
of the Seven Wonders of the
ancient world, was the tallest
building on Earth (120m). Its
mysterious mirror, whose reflection
could be seen more than 55 km
off-shore fascinated scientists for
centuries.’
Fast on this; Read ‘Pharos’ of Alexandria
Fabrizio Nicastro & Martin Elvis
On behalf of the Pharos Team (CfA, MIT, GSFC, MSFC, OAR-INAF, IASF-INAF)
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

14. EDGE Explorer of the Diffuse emission and GRB Explosions
Piro, L., Den Herder, J.W. & Ohashi, T., for the Edge collaboration
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

15. WHIM Absorption: Pharos vs Edge
Fluence(0.3-2 keV) = 10-5 ergs cm-2
~ 2-17/year
Fluence(0.3-2 keV) = 10-6 ergs cm-2
~ 10-70/year
Stress that even at 1e-6 we do a lot! And a lot better than with the best calorimeter
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

16. WHIM in Emission: Edge FOV=3’
A filament is in the FOV and O lines are clearly present
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)

17. High-z Galaxy ISM GRB Redshifts in X-Rays
F= z=1, NH=1E21, NeII and OI, dz/z=10-4 !
“Edge”
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)
Talk by Nicastro

18. Conclusions
Up to % of the Missing Baryons Mass has been found in the FUV: OVI & BLAs
The only two tentative X-Ray (Chandra) detections of WHIM (+ possibly the LG-WHIM) give a cosmological mass density of WHIM consistent with expectations (within large errors due to low number statistics)
However, such detections are controversial ==> no conclusive evidence, yet, for the bulk of the Missing Baryons mass
Only way forward with current facilities is long integrations of, smartly selected, targets: bright in soft X, low Galactic NH, presence of BLAs, or OVI, galaxies concentrations, pilot X-ray observations
Long-Term Prospects: Need Large Throughput & high Spectral Resolution in the Soft X-Ray: PHAROS & EDGE
12/8/2018
Oustanding Questions for the Santandard Cosmological Model (IC, London)