SYSTEMATICS ON SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATESCHANDRA X-RAY MASS ESTIMATES
Elena RasiaElena RasiaDipartimento di Dipartimento di
Astronomia, Astronomia, Padova,ItalyPadova,Italy
([email protected])([email protected])
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
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
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?
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
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.
35.02
0 1)(
cr
rSrS
Deprojection: the 3D gas density and the 3D temperature profiles.
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
, rc
HE
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)
sun
c
cc
p
Mrr
rrrT
mGrM
115.12
3
0)/(1
)/(3)(
rd
d
rd
Td
mG
TrkrM
p
b
ln
ln
ln
ln2
)1/()1ln(
)1/()1ln(
ccc
cxcxcxMM virNFW
2)1/()2(
2)1/()2(2/1
2/1
cc
cxcxMM virRTM
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
CMERG
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
Bkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
A= (TA= (Tss-T-Txx)/)/TT
B= (TB= (Txx-T-Tss)/T)/Tssz=0.1
75
[0.5-5.] keV
INFLUENCE OF THE
BACKGROUND
DATA
bkg
DATA
bkg/100
bkg subtracted
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
CMERGBkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
20%40%
Mass are recovered…
but this is an effect of the background
CREL1
CREL2
RRvirvir= 1567 kpc= 1567 kpc
RR25002500=355 kpc=355 kpc
MMvirvir= 2.5 10= 2.5 101414 M Msunsun/h/h
TTvirvir=3.5 keV=3.5 keV
RRvirvir= 1368 kpc= 1368 kpc
RR25002500=316 kpc=316 kpc
MMvirvir= 1.6 10= 1.6 101414 M Msunsun/h/h
TTvirvir= 2.7 keV= 2.7 keV
Bkg/100Bkg/100
Bkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
CREL2
CREL1
Bkg/100Bkg/100
Bkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
A= (TA= (Tss-T-TXX)/)/TT
B= (TB= (Txx-T-Tss)/T)/Tss
CREL2
Bkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
• “ 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
CREL1
CREL2
Bkg/100Bkg/100
Bkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
CHOT
CHOTz=
0.28
RRvirvir= kpc= kpc
RR25002500= kpc= kpc
MMvirvir= 10 M= 10 Msunsun/h/h
TTvirvir=3.5 keV=3.5 keV
RRvirvir= kpc= kpc
RR25002500= kpc= kpc
MMvirvir= 10= 101414 M Msunsun/h/h
TTvirvir= keV= keV
Bkg/100Bkg/100
Bkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
CHOT
Z=0.175
Bkg/100Bkg/100
Bkg/100Bkg/100CHOTz=
0.28
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
CHOT
CHOT
z=0.28
Bkg/100Bkg/100
Bkg/100Bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
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
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
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
Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
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