Cosmology with galaxy clusters?

Cosmology with galaxy clusters? Cosmology with the cluster mass fct. Piero Rosati (ESO, Garching) Paolo Tozzi (INAF-OAT, Trieste) Colin Norman (JHU, Baltimora) Elena Pierpaoli (Princeton Univ.) Douglas Scott (UBC, Vancouver) Martin White (UC Berkley) Cosmological hydro simulations: Giuseppe Murante (INAF, Torino) Klaus Dolag (DAUP, PAdova) Luca Tornatore (DAUT, Trieste) Volker Springel (MPA, Garching) Lauro Moscardini (DAUB, Bologna) Giuseppe Tormen (DAUP, Padova) Paolo Tozzi (INAF-OAT, Trieste) Antonaldo Diaferio (Phys. Dept., Torino) (a) Why clusters as cosmological probes? (b) Understanding the systematics: What's the correct value of σ8? Why do we need to understand cluster physics? (c) How hydrodynamical simulations of clusters can help? Stefano Borgani (DAUT, Trieste) Talk @SAIt-2003, Trieste, April 17th 2003

Evolution of hot (T> 3 kev) clusters SB & Guzzo 2001

Distant (z>0.7) clusters in the Chandra archive (Rosati, SB & Norman 2002, ARAA) Redshift Luminosity 0.75 Mpc

What's needed for cosmology with clusters? (a) An efficient method to find clusters: sensitivity to detect clusters at high redshift negligible impact of false and spurious detections. (b) A precise knowledge of the selection function searching volume within which a cluster is found. : sky-coverage : luminosity distance : flux : max. z for the given flim (c) A reliable method to measure cluster masses better if given by the observable on which cluster selection is based.

Why X-ray clusters? (SB & Guzzo, 2001) (1) They are sharply defined in the X-ray: LX ρg2 T1/2 (2) LX closely related to mass: LX from XBACs (Ebeling et al. 1997). Masses from virial analysis (Girardi et al. 1998). (3) Flux-limit establishes a precisecriterion for sample completeness and searching volume.

The Cluster X-ray LF Remarkable agreement among all the local surveys (unlike for the galaxy LF) Bulk of cluster population already in place at z 1. Moderate negative evolution in the bright-end. Robust reference for the evolution of the cluster population!

The observed LX-TX relation SB, Rosati et al. (2001) Rosati, SB & Norman (2002) Holden et al. (2002) Steepening below T~1 kev. No evidence for evol. out to z ~1 (cf. Vikhlinin et al. 2002) see also talk by S. Ettori

The mass-temperature relation Isothermal gas + β-model (Finoguenov, Reiprich & Boehringer '01) Resolved TX profiles with Beppo-SAX (Ettori, De Grandi & Molendi '02) 40% lower normalization than expected. Possibly steeper for groups. Nature of the scatter: (a) intrinsic vs. observational (b) how is it distributed? Need to be extended to distant clusters (Ettori et al., in prep)

The observed M-LX relation Reiprich & Boehringer 02 ROSAT + ASCA Hydrostatic equil. + isothermal β-model Resolved TX profiles with Beppo-SAX (Ettori, De Grandi & Molendi '02) Well-defined relation with ~20-40% scatter! To be extended at high z with Chandra/XMM data (Ettori et al., in prep)

Changing the ICM physics (Rosati, SB, Norman 2002, ARAA) Results dependent on ICM physics... Ωm<0.6 at >3σ! σ8 lower that expected.

Which is the correct value of σ8? (Pierpaoli, SB, Scott & White 2003)

Intrinsic scatter in the M-LX relation Convolution with intrinsic (log-normal) scatter inflates the predicted XLF Lower σ8 required to fit the observed XLF No scatter 20% 40%

Statistical errors in the M-LX relation Statistical errors in the M-LX relation widen the confidence contours. Important question: Error marginal. No error What's the prior for the error distribution?

Conclusions on cosmology (a) Galaxy clusters ARE cosmological probes: 0.2 < Ωm < 0.5 σ8 = 0.75 +/- 0.05 (b) What's needed to reduce uncertainties? Systematics need to be taken under much better control... LX-T-M relations need to be improved for distant clusters! How well do we know cluster astrophysics?

A Tree+SPH high-res. Simulation of the cosmic web Collab. with A. Diaferio, K. Dolag, L. Moscardini, G. Murante, V. Springel, G. Tormen, L.Tornatore, P.Tozzi Code: Tree + SPH GADGET (Springel et al. 2001, 2002) www.mpa-garching.mpg.de/gadget Radiative cool.+uv backgr. Multiphase model for star-formation and model galactic winds. ΛCDM cosmology: Ωm= 1-ΩΛ=0.3, Ωbar 0.02h-2, h=0.7, σ8=0.8 L = 192 h-1 Mpc ; Ngas=NDM= 4803 εpl= 7.5 h-1 kpc ; mgas= 6.9 108 h-1 M 40,000 CPU hours and 100 Gb RAM, using 64 processors of IBM-SP4 in CINECA (INAF grant); about 1.2 Tb of data produced.

400 clusters with > 104 particles. X-ray cluster scaling properties and nature of their scatter. Contribution of diffuse gas to the soft X-ray background. SZ effect from clumped and diffuse gas. Comparing cluster masses: X-ray, lensing, optical and SZ. Diffuse intracluster light on a statistical basis. Ζoom-in simulations of clusters and other interesting regions. Populate the box with simulated and SAM galaxies.

The LX-TX Relation at z=0 The observed LX-TX is reproduced at the cluster scale, TX>2 kev. Up-scattered points due to the contribution of ''cooling cores''. No bending at the scale of groups, TX<1 kev. Need to increase the feedback efficiency? Account for the contribution from cooling cores.

The mass-temperature relation Normalization ~30% higher than observed. No much effect of cooling in increasing TX in central regions... Open questions: (a) Effect of different feedback prescriptions? (b) Lacking physics? (c) Comparing to better data sets (i.e. resolving TX profiles).

The entropy excess in groups/poor clusters Entropy excess at T<2 kev well reproduced! Data still based on ROSAT/ASCA observations... Chandra and XMM data may substantially change this picture! Trace entropy evolution (see talk by S. Ettori).

The fraction of cold gas in clusters From observations: fcold~ 10% No trend with TX Balogh et al. '01 Larger fcold for groups Lin, Mohr & Stanford '03 From simulations: fcold~ 15-20% for clusters fcold~ 20-25% for groups Feedback is not strong enough to prevent overcooling!

What's next? Understand how much intrensic scatter is generated by dynamics: calibrating cosmological constraints with simulations. Do we need more resolution until more physics is included? Re-simulate a few objects at much better resolution to understand: (a) The effect of increasing the feedback strength: what's required to bring the star fraction down to the observed value? (b) Improved feedback schemes and metal enrichment.

Cosmology with galaxy clusters borgani@ts.astro.it

Comparing REFLEX and RDCS 90% c.l. contours for REFLEX (solid line) RDCS (dotted line) LX-T-Mvir relations: LX-T from observations T-Mvir from simulations (β=1.15) 45% log-normal overall scatter assumed!