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SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES

This study investigates the systematic errors affecting X-ray mass estimates of distant galaxy clusters using data from the Chandra X-ray Observatory. It introduces X-MAS, a software package designed to simulate X-ray observations derived from hydrodynamical simulations. The research aims to compare observational data with simulations to understand the key factors influencing mass estimates, such as background contamination and spectral properties. Our findings reveal critical insights into structure formation within cosmological models, emphasizing the importance of precise mass estimations for advancing cosmology.

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SYSTEMATICS ON CHANDRA X-RAY MASS ESTIMATES

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  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

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