SYSTEMATICS ON CHANDRA XRAY MASS ESTIMATES

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SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES
Elena Rasia Dipartimento di Astronomia,
Padova,Italy (rasia_at_pd.astro.it)

• Lauro Moscardini
• Giuseppe Tormen
• Stefano Ettori
• Stefano Borgani
• Pasquale Mazzotta
• Klaus Dolag
• Massimo Meneghetti
• Key-Project team

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CLUSTERS OF GALAXIES COSMOLOGY

• Clusters are rich sources of information about
  the underlying cosmological model
• According to the concordance model, clusters are
  the LARGEST and MOST RECENT gravitationally-bound
  objects to form because structure grows
  hierarchically
• Methods

• Number counts the mass function (PS 1974, ST
  1999 SMT 2001, Jenkins etal 2001)
• Scaling relations M-LX ,M-?vM-T
• Barionic fraction (Ettori et al 2003, Allen et al
  2004, Vikhlinin et al. 2003, Voevodkin
  Vikhlinin 2004)
• Other methods arc statistics, SZ effect, LSS
  methods (correlation function, power spectrum..)

MASS is a FUNDAMENTAL quantity for cosmological
studies
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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CLUSTERS OF GALAXIES COSMOLOGYgt NEED FOR
SIMULATIONS
The comparison between observations and
simulations is not always trivial. To overcome
the problem we built
X-MAS X-RAY MAP SIMULATOR
Gardini et al. 04, Rasia et al. in prep.
a software package devoted to simulate X-ray
observations of galaxy clusters obtained from
hydro-simulations
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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X-MAS
As the object is the same comparing
HYDRO- DINAMICAL SIMULATIONS
X-RAY EVENT FILE

• quantities defined in simulations the same of
  those defined in observations?
• What are the systematics errors affecting the
  X-ray analysis?

Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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SYSTEMATICS ON X-RAY MASS ESTIMATE
Rasia et al. 05, submitted

• Simulations
• high resolution resimulations of clusters
  extracted from the cosmological box (4 at z0.175
  1 at z0.28)
• Physics radiative cooling, the effect of a
  uniform time-dependet UV background, a
  sub-resolution model for star formation from a
  multiphase interstellar medium, as well as
  galactic winds powered by SN explosions (Springel
  Hernquist 2003), suppressed thermal conduction
• Mock observation with X-MAS to produce long
  exposure Chandra-like observations
• Normal bkg bkg/100

Borgani et al. 05, Dolag et al. in prep
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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STEP BY STEP
Soft energy band images 0.2-2 keV in order
to recognize and exclude cold regions. Spatial
analysis the surface brightness
is extracted in the 0.5-5 keV
energy band from
concentric annuli Spectral analysis spectra are
extracted by using CIAO tools in the 0.5-8 keV
band in PI channels and fitted within XSPEC
package with a single thermal model using ?2
statistic.
?, rc

• Deprojection
• the 3D gas density and
• the 3D temperature profiles.

? HE
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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MASS ESTIMATE

• ? model politropic index ? M??
• isothermal ?-model (? 1 and T0T2500) M?
• hydrostatic equilibrium MHE
• hydrostatic equilibrium velocities (Rasia et
  al. 04)
• analytic formulae (NFW RTM) (NFW 97, Rasia et
  al. 04)

Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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0.5-5. keV
Bkg/100

• Rvir 1662 kpc
• R2500365 kpc
• Mvir 2.9 1014 Msun/h
• Tvir3.5 keV

CMERG
A (Ts-Tx)/?T B (Tx-Ts)/Ts
Bkg/100
z0.175
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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DATA
bkg
DATA
bkg/100
INFLUENCE OF THE BACKGROUND
bkg subtracted
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of Galaxies
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Mass are recovered but this is an effect of the
background
CMERG
Bkg/100
20
40
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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Bkg/100
CREL1

• Rvir 1567 kpc
• R2500355 kpc
• Mvir 2.5 1014 Msun/h
• Tvir3.5 keV

CREL2
Bkg/100

• Rvir 1368 kpc
• R2500316 kpc
• Mvir 1.6 1014 Msun/h
• Tvir 2.7 keV

Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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Bkg/100
CREL1
A (Ts-TX)/?T B (Tx-Ts)/Ts
Bkg/100
CREL2
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of Galaxies
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• The spectrum of any single-temperature model
  cannot completely reproduce the spectral
  properties of a multi- temperature source
• Tspec can be properly defined only for spectra
  with Tgt2-3 keV
• In the real world things may be different as
  observed spectra are affected by the following
  factors
• Convolution with the instrumental response
• Poisson noise
• Instrumental and cosmic backgrounds

Mazzotta et al. 04
Bkg/100
CREL2
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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Bkg/100
CREL1
CREL2
Bkg/100
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of Galaxies
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Bkg/100
CHOT

• Rvir kpc
• R2500 kpc
• Mvir 10 Msun/h
• Tvir3.5 keV

Bkg/100
CHOTz0.28

• Rvir kpc
• R2500 kpc
• Mvir 1014 Msun/h
• Tvir keV

Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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Bkg/100
CHOT Z0.175
CHOTz0.28
Bkg/100
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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Bkg/100
CHOT
Bkg/100
CHOT z0.28
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of Galaxies
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CHOT
Bkg/100
Many cold blobs are still present in the ICM due
to the no-solved-yet overcooling problem
Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies
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bkg/100
SYSTEMATICS
SYSTEMATICS R2500, bkg/100
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of Galaxies
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Conclusions

• The true mass of a galaxy cluster can be
  recovered by using HE or analytic formulae only
  because of some conspirancy
• ?-models are ALWAYS understimates
• Reducing drastically the influence of the bkg all
  the mass estimates are an UNDERESTIMATE of the
  true mass (being worse the ?-models and better
  the analytic functions)
• Main sources of discrepancy
• temperature bias measurements
• neglected contribution of the velocity field

Ringberg, 24/28 October 2005 Distant Clusters
of Galaxies