Using Galaxy Clusters for Cosmology and the XCS

1. Using Galaxy Clusters forCosmology and the XCS Ben Hoyle, Bob Nichol, David Bacon, Ed Lloyd-Davies, Kathy Romer & the XCS Cape Town April ‘08

2. Overview • Clusters • Clusters & Cosmology • Cluster collapse; cosmology • Cluster surveys • X-ray cluster catalogues • The XMM Cluster Survey [XCS] • Detecting clusters • Cluster classification • Redshift estimates • High redshift cluster • Mass estimate 1; Scaling relations • Mass estimate 2; Weak lensing • The magnification bias • The future

3. Clusters Properties of clusters of galaxies: • Size ~ few Mpc • Mass Emit broad range of EM • Galaxies -> optical • ICM -> X-rays

4. Clusters & cosmology Press & Schechter, spherical collapse The number density and mass of clusters, the mass function, n(M,z), are related to by: • Sheth & Tormen, ellipsoidal collapse

5. Cluster collapse; cosmology Spherical collapse Ellipsodial collapse Vary matter content Vary w=const Schaefer & Koyama Modify Gravity

6. Cluster surveys Cluster cosmology checklist: • Lots of clusters • Broad redshift range • Mass estimates Optical cluster catalogues • Large numbers • Redshifts • No masses X-ray cluster catalogues • Mass estimates: Cavaliere & Fusco-Femiano ’78, Dai et al ’06 • Small numbers • Redshifts difficult

7. X-ray cluster catalogues X-ray identified cluster catalogues are mainly taken from the literature.

8. Overview • Clusters • Clusters & Cosmology • Cluster collapse; cosmology • Cluster surveys • X-ray cluster catalogues • The XMM cluster survey [XCS] • Detecting clusters • Cluster classification • Redshift estimates • High redshift cluster • Mass estimate 1; Scaling relations • Mass estimate 2; Weak lensing • The magnification bias • The future

9. XMM Cluster Survey [XCS] The XCS: • Archival pointings • Serendipitous detections • 170 sq. deg. Present • 500 sq. deg. Total • 0.1<z<2 • Currently 1847 • Expect ~ 2000

10. Detecting clusters Color key • Extended sources, Green ellipses • Point sources, red circles • Unsure, Pink circles Simulated clusters Extended sources From simulations we can recover our selection function.

11. Cluster classification Cluster zoo • SDSS optical images • Centered on X-ray ra,dec • Optical & X-ray overlays • X-ray photon density contours • 610 XCS extended sources • 7 classification types • 9+ classifications

12. Cluster classification Results: • Gold sample • High Z • False detections • Cuts improve sample

13. Redshift estimates Empirically, see LRGs inhabit the central regions of clusters. Look along line of sight of the cluster, encounter an clump of LRGs. Assign LRG redshift to cluster • Test on ROSAT 400 sq. deg • Spectroscopic redshifts SDSS LRGs • Spec and Photo redshifts • Good Agreement

14. Redshift estimates Apply the LRG redshift estimate technique to the XCS 193 free cluster redshifts

15. Redshift estimates More than 300 redshifts Dedicated XCS photometric follow up NOAO + XCS -> NXS 136 for

16. High redshift cluster The most distant spectroscopically confirmed cluster of galaxies found to date. XMM-XCS J2215.9-1738 or J2215. • 5 pointings of a z=2.215 quasar • Cluster redshift 1.45 • Temp > 6KeV Standford et al astro-ph/0606075 Hilton et al astro-ph/0708.3258

17. High redshift cluster The most distant spectroscopically confirmed cluster of galaxies found to date. XMM-XCS J2215.9-1738 or J2215. • 5 pointings of a z=2.215 quasar • Cluster redshift 1.45 • Temp > 6KeV Standford et al astro-ph/0606075 Hilton et al astro-ph/0708.3258

18. Overview • Clusters • Clusters & Cosmology • Cluster collapse; cosmology • Cluster surveys • X-ray cluster catalogues • The XMM Cluster Survey [XCS] • Detecting clusters • Cluster classification • Redshift estimates • High redshift cluster • Mass estimates 1; Scaling relations • Mass estimate 2; Weak lensing • The magnification bias • The future

19. Mass estimate 1: Scaling relations Examine properties of X-ray clusters with a counter part in SDSS Combining optical [large numbers, no masses] and X-ray [small numbers, masses] cluster catalogues to obtain a mass proxy applicable to optically selected clusters. • X-ray clusters • eBCs,BCS,R400d,XCS • Reprocessed equally • [Dai et al ‘06] Empirical Relationship • Optical Clusters • Mass estimates • Constrain cosmology

20. Mass estimates 2: Weak lensing The Sloan has enabled the creation of two massive optical catalogues: MaxBCG clusters [Koester et al ’07] • ~13.10^3 • 0.1<z<0.3 volume limited • Well determined redshifts • Number of galaxies • Lack mass estimates • Member Galaxy luminosity DR4 Quasars [Richards et al] • ~3.10^5 • 0.5<z<2.25 • 5-band SDSS magnitudes We can follow Scranton et al ’05, and use a weak lensing mass measurement, called magnification bias.

21. The magnification bias The QSO unlensed source density:

22. The magnification bias Lensing changes the measured source density, by stretching the solid angle

23. The magnification bias Lensing magnifies the source flux

24. The magnification bias The cross correlation, is a function of bias, b, the weak lensing departure from unity, ,and the line of sight integrated density contrast, • The sign of the correlation • The signal strength Schnieder & Bartelmann astro-ph/9912508 Where alpha is the gradient of the QSO distribution, multiplied by 2.5 There is a change of sign of

25. The magnification bias, results We find [preliminary results]: Expect a strong correlation Expect a weak anti-correlation Stack similar clusters, expect the signal strength to increase with cluster mass.

26. The future Weak Lensing • SDSS DR6 QSO • 1 million QSO’s • Redo with full MaxBCG • Check systematics Mass estimates • Compare X-ray & weak lensing mass measurements • Assign MaxBCG clusters masses Cosmology • Assume LCDM constrain cosmological parameters • Constrain modified gravity models [Schaefer & Koyama ‘07]