The WHIM - inaf iasf bologna

The WHIM - inaf iasf bologna

Advanced Telescope for High Energy Astrophysics

Missing baryons with ATHENA

3/23/12 F, Nicastro (Athena Na?onal Mee?ng)

F. Nicastro (INAF-OAR)

L. Piro, X. Barcons, E. Branchini, J.

Bregman, J. Kaastra, T. Ohashi, J.

Nevalainen, Y. Takei, E. Ursino



The Missing Baryon Problem:

Baryon Budget at z

Ω b


h -2 = 0.0226 h -2 = 0.0456

Ω b


The WHIM in Hydro-­‐dynamical simula?ons

3/23/12 F, Nicastro (Athena National Meeting)

Britton+12, in prep.


The WHIM in Hydro-­‐dynamical simula?ons


Cool-Phase: ~20%


Warm-Phase: ~60%

Hot-Phase: ~20%

3/23/12 F, Nicastro (Athena National Meeting)


The WHIM (???) in OVI (Danforth&Shull08)

Ω b


= 0.0038 ± 0.0004

down to N OVI >10 13 cm -2

i.e. (8.6±0.8)% of Ω b


New Baryon Budget @z

The Astrophysical Journal, 641:217–228, 2006 April 10

# 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A.

The Galaxy-­‐OVI Correla?on (Stocke+06)


John T. Stocke, Steven V. Penton, Charles W. Danforth, J. Michael Shull, Jason Tumlinson, 1 and Kevin M. McLin 2

Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, Box 389, University of Colorado,

Boulder, CO 80309;,,,,,

Received 2005 July 28; accepted 2005 December 9


We combine a FUSE sample of O vi absorbers (z < 0:15) with a database of 1.07 million galaxy redshifts to

explore the relationship between absorbers and galaxy environments. All 37 absorbers with N O vi 10 13:2 cm 2 lie

within 800 h70 1 kpc of the nearest galaxy, with no compelling evidence for O vi absorbers in voids. The O vi absorbers

often appear to be associated with environments of individual galaxies. Gas with 10% 5% solar metallicity (O vi

and C iii) has a median spread in distance of 350–500 h70 1 kpc around L? galaxies and 200–270 h70 1 kpc around 0.1L?

galaxies (ranges reflect uncertain metallicities of gas undetected in Ly absorption). In order to match the O vi line

frequency, (dN /dz) 20 for N O vi 10 13:2 cm 2 , galaxies with L 0:1L ? must contribute to the cross section. Ly

absorbers with N H i 10 13:2 cm 2 cover 50% of the surface area of typical galaxy filaments. Two-thirds of these

show O vi and/or C iii absorption, corresponding to a 33%–50% covering factor at 0.1 Z and suggesting that metals

are spread to a maximum distance of 800 h70 1 kpc, within typical galaxy supercluster filaments. Approximately 50%

of the O vi absorbers have associated Ly line pairs with separations (v) Ly ¼ 50 200 km s 1 . These pairs could

represent shocks at the speeds necessary to create copious O vi, located within 100 h70 1 kpc of the nearest galaxy and

accounting for much of the two-point correlation function of low-z Ly forest absorbers.

Subject headings: galaxies: dwarf — galaxies: starburst — intergalactic medium — quasars: absorption lines —

ultraviolet: galaxies


Warm, photoionized gas in the intergalactic medium (IGM)

contains virtually all the baryons in the universe at z > 2. With

the growth of large-scale structure at later cosmic times, much of

this gas cools into clumps and galaxies, while other gas is shock

heated to temperatures of 10 5 –10 7 K (Cen & Ostriker 1999; Davé

et al. 1999). Even at z 0, approximately 30% of all baryons still

reside in the warm (T 10 4 K) photoionized Ly forest (Penton

et al. 2004, hereafter Paper IV). Another 30%–40% of the baryons

may reside in even hotter gas (T ¼ 10 5 10 7 K), the ‘‘warm-hot

IGM’’ or WHIM (Cen & Ostriker 1999; Davé et al. 1999; Nicastro

et al. 2005).

In a series of papers using moderate-resolution spectrographs

aboard the Hubble Space Telescope (HST ), the Colorado group

has identified a sample of nearly 200 Ly absorbers (Penton et al.

2000b, hereafter Paper I; Penton et al. 2000a, hereafter Paper II;

Paper IV). The Ly absorption line is sensitive to warm, photoionized

gas, and high-sensitivity HST spectra with 10–20 km s 1

resolution can detect absorbers with N H i 10 12:5 cm 2 . Hotter,

shock-heated gas is less easily detected because the Lyman lines

become weak and broad with increasing temperatures, while

higher ionization metal lines (C iii,Civ,Ovi, Ne viii) require gas

3/23/12 F,

ofNicastro significant metallicity


(3% solar


metallicity) in


order to be


The search for the WHIM has now begun, both in the soft

as described by Danforth & Shull (2005, hereafter DS05). At the

present time, the HST and FUSE approaches have each netted

40 O vi absorbers. An analysis (DS05) of the absorber frequency

per unit redshift suggests that 5% of all local baryonic

mass is in WHIM at 10 5 –10 6 K, assuming that 20% of the oxygen

is in O vi and that ½O/HŠ 1. This baryon assessment assumes

that all O vi absorbers are formed in collisionally ionized gas

(Danforth & Shull 2005; Savage et al. 2005), although photoionization

models can reproduce some of the observed line strengths,

widths, and ratios (Tripp et al. 2001). For a few O vi absorbers,

photoionization of gas with very low density (10 5 cm 3 ) and

large sizes (1 Mpc) can provide a match to the observables

(Prochaska et al. 2004; Savage et al. 2002; Tripp et al. 2001).

Thus, while the O vi systems account for 5% of baryons, not all

of them are necessarily at temperatures identified as WHIM (10 5 –

10 7 K). The hotter WHIM is detectable only through weak X-ray

absorption lines from highly ionized species such as O vii,Oviii,

N vi, and N vii (Nicastro et al. 2005) or possibly very broad Ly

lines. The O vii X-ray detections are still too few to establish an

accurate line density and baryon fraction, although it could be as

large as suggested by simulations (Cen & Ostriker 1999; Davé

et al. 1999, 2001).

The simulations have proven fairly accurate in predicting the

“All OVI Absorbers with N OVI >10 13.2 cm -2

lie within 800 h -1 kpc from L* galaxies, with no

evidence for OVI absorbers in voids”.


baryon content of the warm, photoionized IGM. Some 30% of all

baryons were predicted by Davé et al. (1999) to be in the 10 4 K

The Galaxy-­‐BLA Correla?on (Danforth+10)

The strong advantage of BLA vs OVI is that they trace baryons independently on metals.

So, in principle, BLAs could be found farther from galaxies, where metallicity is lower.

Danforth, Shull & Stocke (2010) find:



3/23/12 F, Nicastro (Athena National Meeting)


Why in X-Rays: WHIM Warm…and Cool Phases

f 12

= g 2

g 1


2πe 2 ν 2 A 21

Ion Transition Wavelength (Å) Energy (eV) f

OI Kα 23.52 527.1 0.118

OII Kα 23.29 532.3 0.198

OIII Kα 23.01-23.08 538.8-537.2 0.292

OIV Kα 22.76 544.7 0.409

OV Kα 22.37 554.2 0.533

OVI Kα 22.03 562.8 0.538

OVII Kα 21.60 574.0 0.696

OVII Kβ 18.63 665.5 0.146

OVIII Kα 18.97 653.6 0.416

3/23/12 F, Nicastro (Athena National Meeting)


Galaxy concentrations as WHIM tracers

Right Ascension



3/23/12 F, Nicastro (Athena National Meeting)


A Serendipitous hot X-Ray/BLA

Filament at z=0.118?

From X-rays è logT < 6.75;

logN H =21.5±0.3 (Z/Z 0.01¤ ) -1

From lack of OVI è logT > 6.52

From HI and T

è Z = (1-4)% Z ¤

From Z and T è δ ≈ 300

and Theory

From δ and N H

è D=4-7 Mpc

Combined Statistical Significance = 5.2σ

(5σ if FUSE systematics are included)


3/23/12 F, Nicastro (Athena National Meeting)


0.5 Ms Chandra on 1ES 1553+113

(z>0.4)LETG LSF-Smoothed Residuals

4 WHIM + 1 Photoionized Systems



O z=0.044


4 C z=0.044 O z=0.153

C z=0.153

C z=0.100

O z=0.100







O z=0.124

O z=0.132




C z=0.132

C z=0.124



O z=0.044

O z=0.100

O z=0.153

4 C z=0.044 C z=0.100


C z=0.153




O z=0.132

O z=0.124


22 23 24 25 26




C z=0.132

C z=0.124

43 44 45 46 47

3/23/12 F, Nicastro (Athena National Meeting)


Physical Properties and Metallicities










5 10 15

5 10 15

3/23/12 F, Nicastro (Athena National Meeting)


Athena Breaks Det. Limit

by an order of magnitude

5.0 5.5 6.0








50 100 150 200 250 300

3/23/12 F, Nicastro (Athena National Meeting)


The WHIM with Athena: Absorption











0.2 0.3 0.4 0.5


0.2 0.3 0.4 0.5


1 Ms for F 0.5-2 = 1 mCrab along a random WHIM LOS from Cen & Ostriker, 2006

Detects 5 Systems with logT = 5.2-6.4 K, logN H = 18.7-19.4 (Z/Z ¤ ) -1 cm -2 at z

Athena AGN Targets for Abs. WHIM

+ ~ 6 GRB/yr

z > 0.4

1ES 1553+115

Up to 100 filaments can be measured by ATHENA in 5 yrs by observing AGN (closer

filaments) and bright GRB aaerglows (most distant filaments) down to δ ~ 20

3/23/12 F, Nicastro (Athena National Meeting)


Athena Absorption and Emission spectra

3/23/12 F, Nicastro (Athena National Meeting)


Observing Programme (5yrs)

WHIM in absorption: about 80 filaments probing

overdensities down to ~20

• Follow up of AGN (z>0.3) selected to show OVI

systems: 11 obiects with F>7e-12 c.g.s 4.5Msec

• 2 AGNs (not specifically UV selected) with similar z

and fluxes : 0.8 Msec (or free from AGN obs.)

• AGN (z>0.2) in outburst: 1 per year: 1 Msec

• 30 bright GRB afterglows (TOO in ~12 hrs): 4.5


3/23/12 F, Nicastro (Athena National Meeting)


Observing Programme (II)

WHIM in emission (+ joint absorption/emission studies):

About 300 systems with overdensity >100:

• About 1/3 of the absorption systems detected in emission

providing an independent density measurement

• Serendipitous survey of about 300 systems from the use of

full data base of XMS observations with t>100 ksec: no

additional time requested

• Observations of 2 selected sites where the presence of a

filament is expected, like regions bridging cluster of

galaxies and/or identified e.g. by the 3D distribution of

galaxies (e.g Sculptor wall or alike) for a total of 2 Msec.

3/23/12 F, Nicastro (Athena National Meeting)



• Athena will enable the detection and study of the, still elusive,

largest reservoir of baryons in the local Universe.

The integral field spectroscopy delivered by XMS allows to

characterize both absorption and emission properties, to reveal

all phases of warm-hot baryons, and so to:

– Measure the cosmological mass density of baryons in the WHIM to

better than 5\%

– Measure WHIM physical properties, i.e. temperature, volume and

column densities, to better than 1%, 10%, 1% respectively

– Measure the WHIM metal abundance as a function of WHIM physical

properties and redshift, and so study the IGM enrichment processes as

a function of the environmental conditions (feedback)

– Discriminate between different models for the formation and evolution

3/23/12 of WHIM filaments in F, the Nicastro local (Athena Universe. National Meeting) 20

Whereabouts, Physical State and

Metallicity of the Missing Baryons

in the Local Universe


Cervia-Milano Marittima


3/23/12 F, Nicastro (Athena Na?onal Mee?ng) 21

Thursday, February 2, 12

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