SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES

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SYSTEMATICS ON SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATESCHANDRA X-RAY MASS ESTIMATES

Elena RasiaElena RasiaDipartimento di Dipartimento di

Astronomia, Astronomia, Padova,ItalyPadova,Italy

(rasia@pd.astro.it)(rasia@pd.astro.it)

Lauro MoscardiniLauro Moscardini

Giuseppe TormenGiuseppe Tormen

Stefano Ettori Stefano Ettori

Stefano Borgani Stefano Borgani

Pasquale Mazzotta Pasquale Mazzotta

Klaus DolagKlaus Dolag

Massimo MeneghettiMassimo Meneghetti

& Key-Project team& Key-Project team

CLUSTERS OF GALAXIES CLUSTERS OF GALAXIES && COSMOLOGYCOSMOLOGY

Clusters are rich sources of information about the underlying cosmological model :

According to the concordance model, clusters are the LARGEST LARGEST and MOST RECENT gravitationally-boundand MOST RECENT gravitationally-bound objects to form because structure grows hierarchically

Methods: Number countsNumber counts: the mass function : the mass function (PS 1974, ST 1999 SMT (PS 1974, ST 1999 SMT

2001, Jenkins etal 2001)2001, Jenkins etal 2001) Scaling relationsScaling relations: : M-LM-LXX , ,M-M-vvM-TM-T Barionic fractionBarionic fraction (Ettori et al 2003, Allen et al 2004, Vikhlinin et (Ettori et al 2003, Allen et al 2004, Vikhlinin et

al. 2003, Voevodkin & Vikhlinin 2004)al. 2003, Voevodkin & Vikhlinin 2004) Other methods:Other methods: arc statistics, SZ effect, LSS methods arc statistics, SZ effect, LSS methods

(correlation function, power spectrum..)(correlation function, power spectrum..)

Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

MASS is a FUNDAMENTAL quantity MASS is a FUNDAMENTAL quantity

for cosmological studiesfor cosmological studies

CLUSTERS OF GALAXIES CLUSTERS OF GALAXIES && COSMOLOGYCOSMOLOGY

=> NEED FOR SIMULATIONS=> NEED FOR SIMULATIONSThe comparison between observations and simulations is not always trivial. To

overcome the problem we built:

X-MAS: X-MAS:

X-RAY MAP X-RAY MAP SIMULATORSIMULATOR

a software package devoted to simulate X-ray observations of galaxy clusters obtained from hydro-simulations

Gardini et al. 04, Rasia et al. in prep.

X-MASX-MAS

HYDRO- DINAMICAL

SIMULATIONS

X-RAY EVENT FILE

As the object is the same…

comparing

quantities defined in simulations the same of those defined in observations?

What are the systematics errors affecting the X-ray analysis?

SYSTEMATICS ON X-RAY SYSTEMATICS ON X-RAY MASS ESTIMATEMASS ESTIMATE

Simulations:

high resolution resimulations of clusters extracted from the cosmological box (4 at z=0.175 + 1 at z=0.28)

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/100Ringberg, 24/28 October 2005 – Distant Clusters

of Galaxies

Borgani et al. ’05, Dolag et al. in prep

Rasia et al. ’05, submitted

STEP BY STEPSTEP BY STEPSoft 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.

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

MASS ESTIMATEMASS ESTIMATE model + politropic index : M

isothermal -model ( =1 and T0=T2500): M

hydrostatic equilibrium: MHE

hydrostatic equilibrium + velocities (Rasia et al. ‘04)

analytic formulae (NFW & RTM) (NFW ’97, Rasia et al. ‘04)

115.12

)/(3)(

)1/()1ln(

cxcxcxMM virNFW

2)1/()2(

2)1/()2(2/1

cxcxMM virRTM

RRvirvir= 1662 kpc= 1662 kpc

RR25002500=365 kpc=365 kpc

MMvirvir= 2.9 10= 2.9 101414 M Msunsun/h/h

TTvirvir=3.5 keV=3.5 keV

Bkg/100Bkg/100

A= (TA= (Tss-T-Txx)/)/TT

B= (TB= (Txx-T-Tss)/T)/Tssz=0.1

[0.5-5.] keV

INFLUENCE OF THE

BACKGROUND

bkg/100

bkg subtracted

CMERGBkg/100Bkg/100

20%40%

Mass are recovered…

but this is an effect of the background

RR25002500=355 kpc=355 kpc

RR25002500=316 kpc=316 kpc

TTvirvir= 2.7 keV= 2.7 keV

Bkg/100Bkg/100

A= (TA= (Tss-T-TXX)/)/TT

B= (TB= (Txx-T-Tss)/T)/Tss

Bkg/100Bkg/100

• “ 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 T>2-3 keV”

• “In the real world things may be different as observed spectra are affected by the following factors:

i. Convolution with the instrumental response;

ii. Poisson noise;

iii. Instrumental and cosmic backgrounds”

Mazzotta et al. 04

Bkg/100Bkg/100

CHOTz=

RRvirvir= kpc= kpc

RR25002500= kpc= kpc

MMvirvir= 10 M= 10 Msunsun/h/h

RRvirvir= kpc= kpc

RR25002500= kpc= kpc

MMvirvir= 10= 101414 M Msunsun/h/h

TTvirvir= keV= keV

Bkg/100Bkg/100

Z=0.175

Bkg/100Bkg/100

Bkg/100Bkg/100CHOTz=

z=0.28

Bkg/100Bkg/100

CHOT Bkg/100Bkg/100

Many cold blobs are still present in the ICM due to the no-

solved-yet overcooling problem

SYSTEMSYSTEMATICS ATICS

RR25002500 RR25002500 RR500500

MMHEHE-9%-9% 21% 21% 21% 21%

MM34% 34% 24% 24% 21% 21%

MM34% 34% 35% 35% 39% 39%

MMNFWNFW-2.4% -2.4% 17% 17% 20% 20%

MMRTMRTM-9.6% -9.6% 15% 15% 11% 11%

bkg/100

CCREL1REL1 CCREL2REL2 CCHOTHOT CCHOT,zHOT,z CCMERGMERG

MMHEHE 3030%%

28%28% 14%14% 28%28% 29%29%

vel.vel. 1212%%

11%11% 4%4% 26%26% 5%5%

Temp.Temp. 8%8% 11%11% 16%16% 11%11% 2%2%

SYSTEMSYSTEMATICS ATICS RR25002500, ,

bkg/100bkg/100

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

SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES

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