SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES Elena Rasia Dipartimento di Astronomia, Padova,Italy Lauro Moscardini Giuseppe Tormen Stefano Ettori Stefano Borgani Pasquale Mazzotta Klaus Dolag Massimo Meneghetti & Key-Project team
CLUSTERS OF GALAXIES & COSMOLOGY Clusters are rich sources of information about the underlying cosmological model : LARGEST and MOST RECENT gravitationally-bound 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-L X,M- v M-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..) Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies MASS is a FUNDAMENTAL quantity for cosmological studies
CLUSTERS OF GALAXIES & COSMOLOGY => 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 X-RAY MAP SIMULATOR 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-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 MASS ESTIMATE Simulations: high resolution resimulations of clusters extracted from the cosmological box (4 at z= 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/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies Borgani et al. ’05, Dolag et al. in prep Rasia et al. ’05, submitted
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. Deprojection: the 3D gas density and the 3D temperature profiles. Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies , r c HE
MASS ESTIMATE model + politropic index : M isothermal -model ( =1 and T 0 =T 2500 ): M hydrostatic equilibrium: M HE 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
C MERG R vir = 1662 kpc R vir = 1662 kpc R 2500 =365 kpc R 2500 =365 kpc M vir = M sun /h M vir = M sun /h T vir =3.5 keV T vir =3.5 keV Bkg/100 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies A= (T s -T x )/ T B= (T x -T s )/T s z=0.175 [0.5-5.] keV
INFLUENCE OF THE BACKGROUND DATA bkg DATA bkg/100 bkg subtracted Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
C MERG Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies 20% 40% Mass are recovered… but this is an effect of the background
C REL1 C REL2 R vir = 1567 kpc R vir = 1567 kpc R 2500 =355 kpc R 2500 =355 kpc M vir = M sun /h M vir = M sun /h T vir =3.5 keV T vir =3.5 keV R vir = 1368 kpc R vir = 1368 kpc R 2500 =316 kpc R 2500 =316 kpc M vir = M sun /h M vir = M sun /h T vir = 2.7 keV T vir = 2.7 keV Bkg/100 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
C REL2 C REL1 Bkg/100 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies A= (T s -T X )/ T B= (T x -T s )/T s
C REL2 Bkg/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” “T spec 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
C REL1 C REL2 Bkg/100 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
C HOT C HOT z=0.28 R vir = kpc R vir = kpc R 2500 = kpc R 2500 = kpc M vir = 10 M sun /h M vir = 10 M sun /h T vir =3.5 keV T vir =3.5 keV R vir = kpc R vir = kpc R 2500 = kpc R 2500 = kpc M vir = M sun /h M vir = M sun /h T vir = keV T vir = keV Bkg/100 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
C HOT Z=0.175 Bkg/100 Bkg/100 C HOT z=0.28 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
C HOT z=0.28 Bkg/100 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies
C HOT Bkg/100 Many cold blobs are still present in the ICM due to the no-solved- yet overcooling problem
SYSTEMATI CS R 2500 R 500 M HE -9%21%21% MMMM34%24%21% M 34%35%39% M NFW -2.4%17%20% M RTM -9.6%15%11% bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies C REL1 C REL2 C HOT C HOT,z C MERG M HE 30%28%14%28%29% vel. vel.12%11%4%26%5% Temp.8%11%16%11%2% SYSTEMATI CS R 2500, bkg/100
Ringberg, 24/28 October 2005 – Distant Clusters of GalaxiesConclusions 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