X-RAY BRIGHT GALAXY GROUPS AS COSMOLOGICAL TOOLS FABIO GASTALDELLO UNIVERSITY OF CALIFORNIA IRVINE D. BUOTE P. HUMPHREY L. ZAPPACOSTA J. BULLOCK W. MATHEWS UCSC F. BRIGHENTI BOLOGNA

OUTLINE 1.INTRODUCTION 2.RESULTS AND c-M PLOT FOR X-RAY GROUPS 3.COSMOLOGICAL IMPLICATIONS OF THE c-M PLOT OF THE EXTENDED SAMPLE 4.CONCLUSIONS

THE COSMOLOGICAL MODEL Allen et al. 2004

DM DENSITY PROFILE Navarro et al The concentration parameter c do not depend strongly on the innermost data points, r < 0.05 r vir (Bullock et al. 2001, B01; Dolag et al. 2004, D04).

c-M RELATION Bullock et al c slowly declines as M increases (slope of -0.1) Constant scatter (σ logc ≈ 0.14) the normalization depends sensitively on the cosmological parameters, in particular σ 8 and w (D04,Kuhlen et al. 2005).

c-M RELATION Kuhlen et al. 2005

c-M RELATION The median c-M relation for CDM halos is well described by the semi-analytic model proposed by B01, with 2 adjustable constants the c-M relation is adequately parameterized by a power law over a large range in mass (D04, Shaw et al. 2006)

Concentrations for relaxed halos are larger by 10% compared to the whole population (Jing 2000, Wechsler 2002, Maccio’ 2006). They show also smaller scatter (σ logc ≈ 0.10) Wechsler et al Selection Effects

OBSERVATIONS: METHODS Stellar/Galaxy Dynamics: –Advantages: can apply to most Es and many clusters –Disadvantages: velocity dispersion anisotropy, limited galaxy numbers in cluster cores, equilibrium Gravitational Lensing: –Advantages: applicable to most clusters (z~0.2-1), no assumption about equilibrium required –Disadvantages: projection effects and substructure (esp. strong lensing), limited number of background galaxies for analysis of core (weak lensing), only statistical information in outskirts of galaxies/groups X-Rays: –Advantages: isotropic pressure tensor, gas fills 3D potential well, data quality not limited by finite number of group/cluster galaxies, results for single objects –Disadvantages: hydrostatic equilibrium …

X-RAY SYSTEMATICS 1.HYDROSTATIC EQUILIBRIUM 2.MULTIPHASE GAS/PROJECTION EFFECTS IN CORES 3.DISCRETE SOURCES IN Es 4.BKG SUBTRACTION 5.DEPROJECTION AND FITTING PROCEDURES

X-RAY MASS DETERMINATION Spectra averaged within circular annuli Normalization / shape of spectrum gives gas density / temperature

X-RAY MASS DETERMINATION 1. Assume spherical symmetry 2. Fit spectra with coronal plasma models and obtain (deprojected) spectral quantities 3. Fit parameterized functions to radial profiles of gas density and temperature 4. Assume hydrostatic equilibrium 5. Calculate the radial mass profile

A SPECIAL ERA IN X-RAY ASTRONOMY ChandraXMM-Newton 1 arcsec resolution High sensitivity due to high effective area, i.e. more photons

NFW a good fit to the mass profile c-M relation is consistent with no variation in c and with the gentle decline with increasing M expected from CDM ( α =  0.03, P05). Vikhlinin et al Pointecouteau et al Clusters X-ray results

c-M relation obtained using different techniques, e.g., redshift-space caustics (Rines & Diaferio 2006), weak gravitational lensing (Mandelbaum et al. 2006) are all consistent with no variation in c Rines & Diaferio (2006) Mandelbaum et al. (2006)

THE PROJECT Improve significantly the constraints on the c-M relation by analyzing a wider mass range with many more systems, in particular obtaining accurate mass constraints on relaxed systems with ≤ M ≤ M sun First study of the mass profiles of 7 early type galaxies with Chandra (Humphrey et al. 2006)

HIGHLIGHTS ON THE GALAXY SCALE … Humphrey et al. 2006

The contribution of the stellar mass Huge c > 30 in some previous X-ray studies (NGC 6482, Khosroshahi et al. 2004) Baryons (stars) and DM different distributions Fitting an NFW model to DM NFW + stellar component can bias high c (Mamon & Lokas 2005)

Interaction of DM and Baryons In addition adiabatic contraction (AC) 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). Gnedin et al. 2006

HIGHLIGHTS ON THE GALAXY SCALE … Humphrey et al NFW+stars best fit AC leads to more discrepant stellar M/L c-M relation in agreement with ΛCDM

THE PROJECT Improve significantly the constraints on the c-M relation by analyzing a wider mass range with many more systems, in particular obtaining accurate mass constraints on relaxed systems with ≤ M ≤ M sun Our recent study of the mass profiles of 7 early type galaxies with Chandra indicates c-M values consistent with ΛCDM (Humphrey et al. 2006) There are very few constraints on groups scale (10 13 ≤ M ≤ M sun ), where numerical predictions are more accurate because a large number of halo can be simulated.

In Gastaldello et al (astro-ph ) we selected a sample of 16 objects from the XMM and Chandra archives with the best available data with no obvious disturbance, with a dominant elliptical galaxy at the center The best we can do to ensure hydrostatic equilibrium and recover mass from X-rays. SELECTION OF THE SAMPLE

Chandra inner regions XMM outer regions Accurate bkg subtraction by modeling all components NGC 533 DATA ANALYSYS

Fit gas density and temperature simultaneously assuming only parameterizations for temperature and mass.Fit gas density and temperature simultaneously assuming only parameterizations for temperature and mass.Advantages: better constraints on Mbetter constraints on M easy to interpret goodness of fiteasy to interpret goodness of fit

DATA ANALYSIS NGC 1550 Projection of the 3D ρ and T thus obtained to the results from spectral analysis, including the radial variation of the plasma emissivity  (T,Z Fe ). Using an onion peeling deprojection (e.g., Fabian et al. 1981) gives consistent results with the above method Spectroscopic like T problem (e.g., Vikhlinin et al. 2005). Folding through responses : no change in the case of NGC 5044

RESULTS After accounting for the mass of the hot gas, NFW + stars is the best fit model MKW 4 NGC 533

RESULTS No detection of stellar mass due to poor sampling in the inner 20 kpc or localized AGN disturbance A 2717

RESULTS No detection of stellar mass due to poor sampling in the inner 20 kpc or localized AGN disturbance NGC 5044 Buote et al. 2002

RESULTS NFW + stars best fit model Not all the objects require stellar mass, due to poor sampling in the inner 20 kpc or localized AGN disturbance. Stellar M/L in K band for the objects with best available data is 0.57  0.21, in reasonable agreement with SP synthesis models (≈ 1) Adopting more complicated models, like introducing AC or N04 did not improve the fits. AC produces too low stellar mass-to- light ratios

Humphrey et al Stellar M/L 0.76  0.24

c-M relation for groups We obtain a slope α=  0.076, c decreases with M at the 3σ level

THE X-RAY c-M RELATION Buote et al (astro-ph ) c-M relation for 39 systems ranging in mass from ellipticals to the most massive galaxy clusters ( ) x M sun. A power law fit requires at high significance (6.6σ) that c decreases with increasing M Normalization and scatter consistent with relaxed objects

THE X-RAY c-M RELATION WMAP 1 yr Spergel et al. 2003

THE X-RAY c-M RELATION WMAP 3yr Spergel et al. 2006

The WMAP 3 yr model is rejected at > 99.99% and the reason of its poor performance is the low value of σ 8 (0.74), combined with the action of the tilt of the power spectrum and the lower value of Ω m.

Novel evidence of dark energy using only observations in local universe O D 1 Q 3

CAVEATS/FUTURE WORK HE (10% from simulations, e.g. Nagai et al. 2006) Early formation bias Semi-analytic model prediction of c-M Gas physics and AC (problems also with rotation curves of spirals: Kassim et al. 2006, Gnedin et al. 2006)

CONCLUSIONS Mass constraints for X-ray bright groups derived from good quality Chandra and XMM data can be of the same quality as obtained for hot, massive clusters. This crucial mass regime has provided the crucial evidence of the decrease of c with increasing M c-M relation offers interesting and novel approach to potentially constrain cosmological parameters

WHAT SIMULATIONS TELL US Basic theory for the buildup of structure in the universe and the evolution of properties of gravitationally bound structures is well developed, it has been extensively simulated at increasingly high resolution and analytic formulations have been developed to describe their behavior (e.g., mass function: Jenkins et al. 2001). Density profiles of dark matter halos on all scales can be well approximated by a universal profile (Navarro, Frenk & White 1995, 1997)

BKG SUBTRACTION 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

BKG MODELLING NGC 5044 offset Buote et al. 2004

BKG MODELLING MKW 4

DATA ANALYSIS Chandra is crucial in the inner region where a steep temperature gradient is present When data are available, we use Chandra in the core and XMM in the outer regions

Mass Models For the mass models (applied to the gravitating matter) we consider NFW NFW + stars, modeled with a de Vaucolueurs model with effective radius measured in the K band by 2MASS (Jarrett et al. 2000) NFW +stars adiabatically contracted (AC) using code by O. Gnedin (Gnedin et al. 2004)

DATA ANALYSYS “Parametric mass method” is the principal approach of the study: we assume parameterizations for the temperature and mass profiles to calculate the gas density assuming HE Gas density solution We considered also the temperature solution

Schmidt & Allen 2006 results c  M a (1+z) -b with a =  0.11 and b = 0.54  0.47