1. TEMPERATURE AND DARK MATTER PROFILES OF AN X-RAY GROUP SAMPLE FABIO GASTALDELLO UNIVERSITY OF CALIFORNIA IRVINE D. BUOTE P. HUMPHREY L. ZAPPACOSTA J. BULLOCK A. COORAY W. MATHEWS UCSC F. BRIGHENTI BOLOGNA

2. OUTLINE INTRODUCTION SELECTION OF THE SAMPLE DATA ANALYSIS RESULTS AND c-M PLOT CONCLUSIONS

3. DARK MATTER IN GROUPS The nature of DM is one of the fundamental problems in astrophysics. Crucial is the comparison with N-body simulations predicting a universal profile (NFW, Navarro et al. 1997) for DM halos This prediction is starting to be extensively tested at the scale of massive clusters (Pointecouteau et al. 2005, Vikhlinin et al. 2005) both in term of the shape of the DM profile and the relation between the concentration parameter c and the virial mass M There are very few constraints on groups scale, where numerical predictions are more accurate because a large number of halo can be simulated

4. NFW PROFILE c = r vir /r s with virial radius corresponding to overdensity of 100 for this talk and M vir characterize the profile c-M correlation: at fixed z low mass haloes shows higher c because they collapse earlier, when universe was denser We are also testing other profiles, in particular NFW2 (Navarro et al. 2004), but in this talk only NFW

5. DARK MATTER IN GROUPS The nature of DM is one of the fundamental problems in astrophysics. Crucial is the comparison with N-body simulations predicting a universal profile (NFW, Navarro et al. 1997) for DM halos This prediction is starting to be extensively tested at the scale of massive clusters (Pointecouteau et al. 2005, Vikhlinin et al. 2005) both in term of the shape of the DM profile and the relation between the concentration parameter c and the virial mass M There are very few constraints on groups scale, where numerical predictions are more accurate because a large number of halo can be simulated

6. NFW a good fit to the mass profile (Pointecouteau et al. 2005) Good agreement with the predicted c-M relation (Vikhlinin et al. 2005) Measurements slightly higher than average: highly relaxed cluster

7. DARK MATTER IN GROUPS The nature of DM is one of the fundamental problems in astrophysics. Crucial is the comparison with N-body simulations predicting a universal profile (NFW, Navarro et al. 1997) for DM halos This prediction is starting to be extensively tested at the scale of massive clusters (Pointecouteau et al. 2005, Vikhlinin et al. 2005) both in term of the shape of the DM profile and the relation between the concentration parameter c and the virial mass M There are very few constraints on groups scale, where numerical predictions are more accurate because a large number of halo can be simulated. Mostly overlooked discrepancy with old ROSAT and ASCA DATA (Sato et al. 2000, Wu & Xue 2000).

8. High c as seen in X-rays for M < 10 14 solar masses Lower concentration predicted by simulations (e.g. Bullock et al. 2001) Good quality Chandra data show similar results (NGC 6482, Khosroshahi et al. 2004) Wu & Xue 2000

9. Possible explanations … NFW distribution apply only to the dark matter component and the baryons have a different distribution dominating the mass profile in the inner regions. Fitting an NFW model to DM NFW + stellar component can bias the result (Mamon & Lokas 2005)

10. Possible explanations … In addition adiabatic contraction could play a role i.e. DM halo responds to condensations of baryons into stars, which should cause the DM profile to contract adiabatically in the center (Blumenthal et al. 1986). Key is the increasing importance of stars for systems with mass lower than rich clusters. Some other biases in our measurements (the objects we are looking at) ?

11. In stark contrast with the situation for clusters, there is no X-ray selected, flux limitated sample to derive statistical constraints We selected a sample from the XMM and Chandra archives with the best available data with no obvious disturbance (exceptions like A 262) with a dominant elliptical galaxy at the center (only exception RGH 80) The best we can do to ensure hydrostatic equilibrium and recover mass from X-rays: Brightest 1 keV groups assembled by catalogs like Mulchaey et al. 2003 or O’Sullivan 2001 Fossil groups 2-3 keV Poor clusters to cover the mass range near 10 14 solar masses objects in our own attempt of an X-ray flux limited sample taken from NORAS (Bohringer et al. 2000) SELECTION OF THE SAMPLE

12. IC 1860NGC 533 MKW 4 NGC 1550

13. In stark contrast with the situation for clusters, there is no X-ray selected, flux limitated sample to derive statistical constraints We selected a sample from the XMM and Chandra archives with the best available data with no obvious disturbance (exceptions like A 262) with a dominant elliptical galaxy at the center (only exception RGH 80) The best we can do to ensure hydrostatic equilibrium and recover mass from X-rays: Brightest 1 keV groups assembled by catalogs like Mulchaey et al. 2003 or O’Sullivan 2001 Fossil groups 2-3 keV Poor clusters to cover the mass range near 10 14 solar masses objects in our own attempt of an X-ray flux limited sample taken from NORAS (Bohringer et al. 2000) SELECTION OF THE SAMPLE

14. NGC 5044 Buote et al.2003NGC 1132 ESO 3060170 MS 0116

15. In stark contrast with the situation for clusters, there is no X-ray selected, flux limitated sample to derive statistical constraints We selected a sample from the XMM and Chandra archives with the best available data with no obvious disturbance (exceptions like A 262) with a dominant elliptical galaxy at the center (only exception RGH 80) The best we can do to ensure hydrostatic equilibrium and recover mass from X-rays: Brightest 1 keV groups assembled by catalogs like Mulchaey et al. 2003 or O’Sullivan 2001 Fossil groups 2-3 keV Poor clusters to cover the mass range near 10 14 solar masses objects in our own attempt of an X-ray flux limited sample taken from NORAS (Bohringer et al. 2000) SELECTION OF THE SAMPLE

16. A 262 A 1991 A 2717 AWM 4

17. In stark contrast with the situation for clusters, there is no X-ray selected, flux limitated sample to derive statistical constraints We selected a sample from the XMM and Chandra archives with the best available data with no obvious disturbance (exceptions like A 262) with a dominant elliptical galaxy at the center (only exception RGH 80) The best we can do to ensure hydrostatic equilibrium and recover mass from X-rays: Brightest 1 keV groups assembled by catalogs like GEMS (Osmond & Ponman 2004) or O’Sullivan 2001 Fossil groups 2-3 keV Poor clusters to cover the mass range near 10 14 solar masses objects in our own attempt of an X-ray flux limited sample taken from NORAS (Bohringer et al. 2000) SELECTION OF THE SAMPLE

18. A 1314RGH 80 NGC 5129 NGC 4325

20. DATA ANALYSIS We extracted concentric circular annuli located at the X-ray centroid and fitted 1T models (+ brem when needed) Bkg subtraction is crucial. Usual methods like simple use of bkg templates or double subtraction (Arnaud et al. 2002) are not enough MKW 4 annulus 12-14 arcmin There is still the source component !

21. DATA ANALYSIS We extracted concentric circular annuli located at the X-ray centroid and fitted 1T models (+ brem when needed) Bkg subtraction is crucial. Usual methods like simple use of bkg templates or double subtraction (Arnaud et al. 2002) have some flaws We completely model the various bkg components (Lumb et al. 2002), exploiting the fact that the source component, mainly characterized by the Fe-L shell, is clearly spectrally separated from the other bkg components

22. DATA ANALYSIS NGC 5044 offset Buote et al. 2004

23. From T and ρ profiles to mass profiles NGC 1550 We projected parameterized models of the 3D ρ and T to the result obtained from our spectral analysis (the projected gas mass density is derived from the norm of the thermal spectral model), including the radial variation of the plasma emissivity  (T,Z Fe ). Folding through response coming soon (e.g. Mazzotta et al. 2004). We use these models to evaluate the derivatives in the equation of HE, thus constructing the mass data points.

24. … but also exploring other methods Onion peeling deprojection Potential models: you assume NFW and a parameterization for one quantity and you solve for the other

25. From T and ρ profiles to mass profiles NGC 1550 For the mass models (applied to the gravitating - the mass of X-ray emitting gas) we consider NFW NFW + stars, modeled with an Hernquist profile (Hernquist 1990) NFW +stars adiabatically contracted (AC) using code by O. Gnedin (Gnedin et al. 2004)

26. T PROFILES MKW 4 A 262 IC 1860 NGC 533 NGC 2563 AWM 4

27. SCALED T PROFILES

28. Vikhlinin et al. 2005 Sun et al. 2003

29. Stellar mass or not ? Only some systems (8 out of 19) like NGC 1550 seems to need the introduction of the stellar component. When fitted with an NFW+Hernquist or AC model, with the stellar mass free to vary, the returned stellar M/L B are in the range 2-7. We can not discriminate between these two latter models. NGC 4325 NGC 5129

30. c vs. M

31. CONCLUSIONS The sample of groups show a similarity of temperature profiles, general agreement with an NFW profile (when accounting for the central galaxy in the inner region). Clearly the stellar component is biasing some of our results. This is more clear at the galaxy scale (Humphrey et al. 2005, astro-ph 0510819) c-M diagram is very interesting and we can possibly look at early forming groups (e.g. Zentner et al. 2005). Theoretical effort to reproduce our selection and first steps toward characterization of cosmological parameters