SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES

1. SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES Elena Rasia Dipartimento di Astronomia, Padova,Italy (rasia@pd.astro.it) Lauro Moscardini Giuseppe Tormen Stefano Ettori Stefano Borgani Pasquale Mazzotta Klaus Dolag Massimo Meneghetti & Key-Project team

2. 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-boundobjects 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

3. 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 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

4. 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

5. SYSTEMATICS ON X-RAY MASS ESTIMATE Rasia et al. ’05, submitted • 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/100 Borgani et al. ’05, Dolag et al. in prep Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

6. 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 2statistic. , rc • Deprojection: • the 3D gas density and • the 3Dtemperature profiles.  HE Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

7. MASS 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) Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

8. [0.5-5.] keV Bkg/100 • Rvir= 1662 kpc • R2500=365 kpc • Mvir= 2.9 1014 Msun/h • Tvir=3.5 keV CMERG A= (Ts-Tx)/T B= (Tx-Ts)/Ts z=0.175 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

9. DATA bkg DATA bkg/100 INFLUENCE OF THE BACKGROUND bkg subtracted Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

10. 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

11. Bkg/100 CREL1 • Rvir= 1567 kpc • R2500=355 kpc • Mvir= 2.5 1014 Msun/h • Tvir=3.5 keV CREL2 Bkg/100 • Rvir= 1368 kpc • R2500=316 kpc • Mvir= 1.6 1014 Msun/h • Tvir= 2.7 keV Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

12. Bkg/100 CREL1 A= (Ts-TX)/T B= (Tx-Ts)/Ts Bkg/100 CREL2 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

13. “ 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: • 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

14. Bkg/100 CREL1 CREL2 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

15. Bkg/100 CHOT • Rvir= kpc • R2500= kpc • Mvir= 10 Msun/h • Tvir=3.5 keV Bkg/100 CHOTz=0.28 • Rvir= kpc • R2500= kpc • Mvir= 1014 Msun/h • Tvir= keV Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

16. Bkg/100 CHOT Z=0.175 CHOTz=0.28 Bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

17. Bkg/100 CHOT Bkg/100 CHOT z=0.28 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

18. 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

19. bkg/100 SYSTEMATICS SYSTEMATICS R2500, bkg/100 Ringberg, 24/28 October 2005 – Distant Clusters of Galaxies

20. 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