# Presentation: 568043

## Zappacosta Luca (INAF-OATS/UC Irvine)

**Zappacosta Luca (INAF-OATS/UC Irvine)**

## The baryon history from simulations

- From cosmological simulations
*Cen & Ostriker 2006*

- Missing
- baryons

## The Warm-Hot Intergalactic Medium (WHIM)

- Located in the non-virialized filamentary large-scale structure of the local (z<1) cosmic web
- Gas shock-heated during its infall in the large-scale structure gravitational potential
- Filaments size: 25-5  3-5 Mpc
- Warm-hot T  105-107 K
- Low density: 10-20b
- The bulk at overdensities  1-1000b
- Cen & Ostriker 1999, Davé et al. 2001,
- Dolag et al. 2006, Cen & Ostriker 2006

- Cen & Ostriker 2006

## WHIM in superstructures

- Large amounts of warm-hot
- gas distributed in filaments
- in  supercluster sized
- large-scale  structures
- E.g.
- Metal mass (MZ) contribution
- 300-103b  ~20% of MZWHIM
- 600-103b  ~10% of MZWHIM
- (Cen & Ostriker 2006)

## How to detect the WHIM

- Mainly in the Far UV/soft X-rays
- Soft X-ray (< 1 keV) imaging  ROSAT, XMM
- FarUV/X-ray absorption lines from the most abundant ions (oxygen: OVI, OVII, OVIII, Ne ions, ... ) in the spectrum of bright background sources (the *X-ray forest*; Hellsten et al. 1998)  Chandra and XMM gratings, FUSE, HST-STIS
- X-ray direct spectroscopy:
- Line emission from the ions  XMM, Suzaku
- cluster soft excesses  ROSAT, XMM, Suzaku

## Detecting WHIM in emission

- Emission studies can probe the hotter (T > 106 K) and
- denser (>100b ) WHIM phase
- Problems to deal with:
- Low surface brightness regions emitting in the soft X-ray energies (< 1 keV)
- Galactic NH  (need low NH regions)
- Lots of Galactic foregrounds and extragalactic backgrounds
- Large field of view (e.g. 3Mpc @ z=0.1  27 arcmin)

## WHIM and galaxies in filaments

- The dark matter large-scale structure gathers galaxies and gas
- Gas and galaxies trace
- each others in filaments

## WHIM in emission studies

- Few claims of WHIM filamentary X-ray emission correlated with galaxy/clusters distribution
- (E.g. Kull & Boehringer 1999, Scharf et al. 2000, Tittley & Enriksen 2001, Werner et al. 2008)
- Low/mid resolution detectors ROSAT, ASCA, XMM
- temperature  1 keV
- High dense regions (inter-cluster regions)
- Pollution by intracluster medium outskirts
- Sometimes no clear redshift determination from galaxies

## WHIM in the Warwick fieldZappacosta et al. 2002

- Low NH  field (~<1020 cm-2)
- _Warwick et al. 1998_  detection of diffuse filamentary emission on several partially overlapping ROSAT PSPC pointings
- Re-analysis of one of the ROSAT fields
- Aims:
- Correlate diffuse emission with galaxy overdensity
- Redshift of the correlated structures
- Measure flux and spectral shape

## Diffuse emission in the soft X-rays

- 20ks ROSAT PSPC field (**1/4 keV band**) after point source removal
**Extended structures detected**
- Structures in common  **5******** significant**
- ISM absorption correction from 21cm map do not affect the morphologies

## Galaxy/X-ray distribution

- Galaxy distribution
- optical observations obtained at Isaac Newton Telescope (Canary Islands)
- central region of PSPC field of view
- 5 photometric bands   photo-z
- Correlation X-ray/galaxies
- Projected galaxy overdensity coincident with the structure

## The redshift of the overdensity

- galaxy overdensity significant at 6 in the range 0.3 < zphot < 0.6.
- A later spectroscopic survey  (161 obj)
- zspec=0.40  (20 obj)
-   (Mannucci, Bonnoli, LZ et al. 2007)

## Spectral shape of the structure

**spectrum consistent with  WHIM:**
**T~3-6·10****6 ****K**
- (assumed Z=0.05-0.3Zsun)
- group and clusters are too hot (T>107K)
- unresolved type I AGNs are 3 inconsistent (=2)

- The flux (0.2-0.3 keV) is in good agreement (10-12 erg/s/cm2/deg2) with the simulations (*Croft et al. 2001*)

## Filament in a supercluster environment

- Size > 6 Mpc (@ z=0.4)
- Overdensity: ~600b with large uncertainties
- (outskirts of groups at r500~1000 b )
- 10 spectroscopically confirmed clusters/groups at  z0.3950.015
- Supercluster environment (100 Mpc)

## Sculptor Supercluster (z=0.1) , NH ~1.5 1020 cm-2       Zappacosta et al. 2005

- Sculptor Supercluster (z=0.1) , NH ~1.5 1020 cm-2       **Zappacosta et al. 2005**

## WHIM in the Sculptor Scl: color-color 

- WHIM in the Sculptor Scl: color-color

## Correlation coefficient

- 3/4 keV/ 1.5 keV

-              Hot      Medium             Cold

- Correlation (>3 significant) between galaxy distribution and regions of X-ray emission which correspond to plasma with T 5-6106 K
- Cannot be explained by correlations with:
-  unresolved AGNs
-  emission from group of galaxies or individual galaxies
**Evidence for warm-hot gas permeating the supercluster**

## X-ray absorption spectroscopy: no WHIM detection so far

- _Mkn 421 case_
- Among the most luminous and intensely studied blazars
- X-ray high resolution spectroscopy absorption studies with Chandra and XMM with high quality grating data

## X-ray absorption spectroscopy: no WHIM detection so far

- _PKS2155-304 case_
- Among the most luminous and intensely studied blazars
- X-ray high resolution spectroscopy absorption studies with Chandra and XMM with high quality grating data

## Why WHIM has yet to be detected in X-rays

- Different authors and different satellites have
- given controversial results so far
- Details of the data analysis and statistical assessment are crucial for weak lines detection

## Strategies for WHIM detection

- Blind searches
- Very bright AGNs
- Very long exposures
- Low density filaments
-       weak lines

- Distance from observer

## Strategies for WHIM detection

- Targeted searches
- Moderately bright AGNs behind superstructures
- Lower exposure times
- larger gas densities
*A priori *redshift knowledge
- Higher metallicities
-       stronger lines

- Distance from observer

## WHIM in filaments: our strategy

- Since 2005
- Proposing TOO observations of blazars during their outburst state located behind local known large-scale unvirialized filamentary structures traced by the galaxy distribution to obtain a firm detection (i.e. 5) of the WHIM.
- (approved in Chandra Cycle 7/8/9, XMM-AO6, PI: Zappacosta)

## The Sculptor Wall

- Blazar H2356-309 (z=0.165)
- Sculptor Wall z=0.03 (@blazar location)
- Observation triggered with both
- XMM and Chandra during two
- different short outbursts
- XMM observation (>40 hours after the request of observation)
- Chandra observation (~10 hours after the request of observation)
- Source flux 1.2-1.510-11 erg/s/cm2 (~quiescent state)
- Nonetheless...

## OVII WHIM evidence

**From both XMM and Chandra**
- Evidence of local and intervening OVII in **both** Chandra and XMM spectra
- The intervening OVII line is at the redshift of the Sculptor Wall (z=0.03)
- Joint OVII significance 3
- NOVII (z=0.03) = 941015 cm-2

- Black: XMM, Red: Chandra

- Zappacosta et al. 2008 in prep.

## The future:a benchmark observation of WHIM

- It will provide a 5 detection
- of OVII
- first firm WHIM
- detection
- A non detection will provide a
- strong upper limit
- Serious challenge
- for the theory
- (baryonic matter distribution, processes of metal enrichment)

- Simulated 500ks Chandra observation

## Conclusions

- WHIM is difficult to detect.... but we already knew that!
- WHIM in unvirialized structures can be detected in dense supercluster environment with data and satellites already available
- Soft X-ray diffuse emission (Warwick field, Sculptor Scl)
- X-ray absorption in background AGN spectra (Sculptor Wall)
- Galaxy distribution provides a valid signpost for the WHIM
- distribution in superclusters
- Characterization of supercluster enviroment more feasible than the bulk of ‘missing baryons’
- Useful to characterize future observatories which will target mainly these dense regions in line emission