ESTREMO/WFXRT Project. WHIM Working Group. Report

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ESTREMO/WFXRT Project. WHIM Working Group.Report
Enzo Branchini Univ. Roma TRE On behalf of
the WHIM WG Alessandra Corsi
INAF/IASF Massimiliano Galeazzi Univ. of
Miami Melania Del Santo
INAF/IASF Fabrizio Fiore
INAF/OAR Pasquale Mazzotta Univ. Tor
Vergata Silvano Molendi
INAF/IASF Lauro Moscardini Univ.
Bologna Fabrizio Nicastro
INAF/OAR Luigi Piro
INAF/IASF Mauro Roncarelli Univ.
Bologna Eugenio Ursino Univ. of
Miami Matteo Viel INAF/OAT

• Roma.
• Area del CNR.
• 12/09/2006

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Outline of the Talk
Goal Assess the possibility of detecting the
WHIM both in absorption and in emission with
ESTREMO/WFXRT, characterize its physical state,
trace its evolution and estimate the local mean
baryon density. - Uncertainties in WHIM
modeling - Absorption. Updates. Analysis of new
synthetic spectra (A. Corsi) - Emission. State
of the art. Emission analysis with WFXRT -
Work in progress.
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RandomSystematic Errors
Large scatter in dg(d) T(d) Z(d) relations does
not Precision Cosmology. Need to assess
how well can we measure WWHIM
WHIM models rely on several assumptions (e.g. IGM
metallicity, the ionization state of the various
metals etc) that may result in systematic errors
when comparing models with observations. We
have considered several different WHIM to account
for model
uncertainties
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Publicly available models
Absorption Spectra

• Semi analytic model (Viel et al. 2003) _at_
  http//www.rm.iasf.cnr.it/Estremo.html
• Montecarlo model (Nicastro 2006) _at_
  http//hea-www.harvard.edu/nicastro/Estremo/
• Hydrodynamical model (Viel 2006) _at_
  http//www.rm.iasf.cnr.it/Estremo.html

And tranformed in Xspec-format by Melania Del
Santo and Alessandra Corsi
Surface Brightness Maps
Hydrodynamical model ( Borgani et al. 2005,
Galeazzi - Ursino 2006)
Almost Ready
Joint Emission Absorption Spectra
Hydrodynamical model ( Borgani et al. 2005,
Galeazzi-Ursino 2006)
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The WHIM in Absorption

• Alessandra Corsi
• Fabrizio Nicastro
• Luigi Piro
• Matteo Viel

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Synthetic Absorption Spectra Hydro-model

• Hydro simulation (Viel 2006) Stacking outputs _at_
  z0.0/0.1/0.2/0.3/0.4/0.5 Box 60 Mpc/h. 4003 DM
  4003 GAS Softening 2.5 Kpc/h comoving. Star
  formation. No Feedback. UV background (QSO
  galaxies). No X-ray background. No Radiative
  transport. No metal cooling. 7 independent line
  of sights out to z0.5. T, r, Z as a function of
  redshift. OVI, OVII, OVII Kb, OVIII, CV, NeIX,
  MgXI, FeXVII optical depth

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Detecting WHIM in AbsorptionMinimum flux
(fluence) of background sources
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20
OVII absorbers per unit redshift
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OVII absorbers per unit redshift
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3
3
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Detecting WHIM in Absorption Which background
sources

• There are several classes of luminous background
  objects that are bright enough
• For OVII absorption lines to be detected with
  ESTREMO/WFXRT
• Bright Blazars with fluence of 2.5?10-5 erg
  cm-2 in 70 ks observation
• during the outburst phase ( e.g. PKS2155-304.
  Nicastro et al. 2002).
• Pros Very Bright.
  Cons Very Few.
• Bright QSOs with fluxesgt 510-12 erg cm-2 s 1
  keV 1
• Pros Not too Rare. Cons Very Nearby. Faint
  (Exposure times 1 Msec required)
• GRB afterglows with fluence of 3?10-6 erg
  cm-2 (tgt60s) in 60 ks observation
• Pros Fast Pointing required. Cons Bright.
  Not too rare (10 per year).
• (More in Alessandra Corsi Talk)

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The WHIM in emission.

• Massimiliano Galeazzi
• Eugenio Ursino
• Stefano Borgani
• Massimo Roncarelli
• Lauro Moscardini.

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Cosmological hydrodynamic simulation (Borgani et
al. 2004)
Cosmological parameters
Physical parameters

1. Intrinsic Metallicity (Gadget)
2. Croft Model (PAr)
3. Cen (Cen) Scatter

3 Different Metallicity Models
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Project Si.Li.Cone
Simulating high-resolution spectroscopic X-ray
observations of the WHIM

1. Field 1 deg2 x 40
2. 0 z 2
3. Ang. resolution 14 arcsec
4. Redshift sampling 51 snaps
5. Spectral resolution (1 eV)
6. 3 phases Hot Diffuse Dense
7. 3 metallicity models

1. Choice of the right output
2. Randomization
3. Calculating X-ray spectrum (1000 bins)
4. Smoothing into the map (SPH)

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Phase diagram
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DENSE 5ltLog(T)lt7 Log r gt3
DIFFUSE 5ltLog(T)lt7 Log r lt3
HOT Log(T)gt7
DIFFUSE Phase - Surface Brightness in the 0.5-2
KeV Band (Metallicity Model3) 10-12
erg/cm2/s/deg2 10 of the CXB
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Detecting WHIM in Emission
A dedicated analysis of S. Borgani et al hydro
simulation is currently being performed by M.
Galeazzi, L. Moscardini, M. Roncarelli and E.
Ursino to assess the possibility of detecting
WHIM in emission.

• Extrapolating Yoshikawa et al. 2003 and our study
  show that OVII (triplet)
• OVIII from diffuse WHIM can be detected by
  ESTREMO/WFXRT at S/Ngt3 in a
• texp106 sec exposure.
• Diffuse WHIM emission (mostly OVII line) account
  for 10 of the total
• CXB in the energy band 0.5-2.0 KeV.
• Most of the signal is produced between 0.1ltzlt0.5
• In 1-3 of the cases in a FOV of 3 the flux is
  above 10 of the CXB
• In 10-20 of the cases the flux comes from a
  single filament, making it easier
• unambiguous identification of X-ray emission
  lines.
• Energy resolution of ESTREMO/WFXRT good enough.
  Angular resolution
• 1-3. Very good background subtraction is
  mandatory.

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What fraction of WHIM can we reveal in emission ?
Cen simulation cube
OVII Flux in a 3 (1.5 Mpc) cube. WHIM
densediffuse
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Can we identify WHIM ?
WHIM
Total 0ltzlt2
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Spectrum vs. FOV
FOV3 A filament is in the FOV and O lines are
clearly present
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Spectrum vs. FOV
FOV6 The DXB count rate increases with the FOV,
but the filament count rate does not increase
appreaciably. Moreover, more filaments get in the
FOV, making the identification more difficult.
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Spectrum vs. FOV
FOV15 The DXB flux is too high and completely
covers the filament lines. Moreover, too many
lines due to different filament are in the FOV,
making the identification impossible.
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Measuring WHIM angular clustering
with WFXRT

• We consider 10 different FOV of 60 X 60
  observed for 1 Ms
• each and obtain 256x256 pixel surface brightness
  maps The pixel
• size of 23x23 is chosen to meet instrument
  requirements.
• We quantify the clustering using the angular two
  point correlation
• function that we measure through Davis and
  Peebles (82) estimator.
• Flux is estimated in the 0.28-0.65 KeV band to
  maximize the OVII and OVIII line contributions
  from WHIM out to z0.5

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• Correlation signal is dominated by Hot and Dense
  phases and
• attributed to the intrinsic autocorrelation of
  extended sources.
• Signal from the diffuse phase small but
  significantly nonzero.
• Field-to-field variation dominate over Poisson
  noise (exposure
• time could be reduced or less fields need to be
  observed).

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• Unlike for the dense and hot phases
• the correlation signal of the diffuse phase
• hardly depends on the model assume for
• the IGM metallicity of the IGM in the
  hydro-dynamical simulation

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• Hot and dense phase
• are dominated by
• extended sources that
• should be easy to
• remove. A simple
• 3s-clipping procedure
• allows to remove all
• correlation but that of
• the diffuse WHIM.

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• The possibility of detecting WHIM through its
  angular correlation
• properties relies on EXTREMO/WFXRT ability of
  resolving discrete sources. As AGNs are the main
  contributors of the soft-X-ray sky
• we construct mock surface brightness maps of
  unresolved AGNs and compute the angular
  correlation function of the signal.

0.5-2 KeV Band Detection Limit 10-16
erg/cm2/sec (Molendi 2006) At this limit 10-20
of the CXB is resolved. (Marchetti et al.
2003)
(Molendi 2006)

• Take a LogN-LogS model for unresolved AGN
  assuming that they contribute 5-10 to the CXB
• Assume a N(z) distribution for unresolved AGNs
• Assume that AGNs are hosted in Dark Matter halos
• Extract a sample of mock AGNs by assigning an
  x-ray flux to DM halos extracted from N-body
  simulations.

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AGN LogN-LogS Two Models
1 Marchetti et al 2003 extrapolated below
CHANDRA limit. Stot5 CXB
Log N
Euclidean
2 Euclidean extrapolation below CHANDRA limit.
Stot10 CXB
CHANDRA Det. Limit
Marchetti et al 2003 Extrapolated
ESTREMO Det. Limit
Marchetti et al 2003
Log S
erg/cm2/s/deg2
1E-16
3E-17
7E-18
3E-19
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Flux in the 0.38-0.65 KeV band extrapolated
assuming sources with power law spectra with G1.2

• GIF Simulation of a
• LCDM model
• Stacking 10-simulation
• cubes at different epochs
• L-Cube 479 Mpc.h
• Only DM halos with
• Mgt5x1011 solar
• considered.

LogN-LogS

• Field 1 deg2
• 0 z 2
• iii Dq 23 arcsec
• iv z-sampling 8 snaps

N(z) of resolved AGNs from Hopkins (2006)
bolometric LF.
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Unresolved AGN-correlation function is
consistent with zero and significantly below that
of Diffuse WHIM. (see Croft et al. 2000) This
result is robust as it does not depend
significantly on the models assumed for the AGNs
LogN-LogS and N(z) functions.
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Detecting WHIM in Absorption and Emission

• Is there any benefit in detecting WHIM absorption
  AND Emission ?
• In principle YES since in this case one could
  estimate Tgas by
• comparing different absorption lines of the same
  ion ad rgas by
• comparing emission AND absorption features. This
  allows to
• estimate rgas and Tgas without a-priori knowledge
  of Zgas.

However, one has to account for the multiphase
nature of the WHIM. Also, according to Kawahara
et al. (2005) only 20 of WHIM OVII absorption
systems are also detected in emission in a t300
Ks observation (scaling from DIOS results). We
are currently producing mock emission and
absorption spectra for the same FOV to perform a
dedicated analysis.
Kawahara et al. 2005
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To summarize.

• WHIM. Absorption. ESTREMO/WFXRT should allow
  unambiguous detection of WHIM in absorption using
  bright GRB afterglows, Blazars or bright AGNs.
  10-20 detections per year looks like a realistic
  goal. Whether this will allow to estimate Wb
  (z0) to within 10 remains to be seen.
• WHIM Emission 1 Detecting WHIM seems to be
  possible but with 1 Msec exposure time. Angular
  res of 1 would improve subtraction of the dense
  WHIM component. A sizable (mass) fraction of the
  total WHIM could be probed
• WHIM emission 2. Thanks to the good angular
  resolution of WFXRT the indirect detection of
  WHIM through its autocorrelation in the surface
  brightness maps is a realistic goal.