x-ray bright galaxy groups as cosmological tools fabio gastaldello university of california irvine...

X-RAY BRIGHT X-RAY BRIGHT GALAXY GROUPS AS GALAXY GROUPS AS

COSMOLOGICAL TOOLSCOSMOLOGICAL TOOLSFABIO GASTALDELLO

UNIVERSITY OF CALIFORNIA IRVINED. BUOTE

P. HUMPHREY

L. ZAPPACOSTA

J. BULLOCK

W. MATHEWS UCSC

F. BRIGHENTI BOLOGNA

OUTLINEOUTLINE

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 MODELTHE COSMOLOGICAL MODEL

Allen et al. 2004

DM DENSITY PROFILEDM DENSITY PROFILE

Navarro et al. 2004

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

c-M RELATIONc-M RELATION

Bullock et al. 2001

•c slowly declines as M increases (slope of -0.1)

•Constant scatter (σlogc ≈ 0.14)

•the normalization depends sensitively on the cosmological parameters, in particular σ8 and w (D04,Kuhlen et al. 2005).

c-M RELATIONc-M RELATION

Kuhlen et al. 2005

c-M RELATIONc-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 (σlogc ≈ 0.10)

Wechsler et al. 2002

Selection EffectsSelection Effects

OBSERVATIONS: METHODSOBSERVATIONS: METHODSStellar/Galaxy Dynamics:

– Advantages: can apply to most Es and many clusters– Disadvantages: velocity dispersion anisotropy, limited

galaxy numbers in cluster cores, equilibriumGravitational 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 SYSTEMATICSX-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 DETERMINATIONX-RAY MASS DETERMINATION

• Spectra averaged within circular annuli• Normalization / shape of spectrum gives gas density

/ temperature

X-RAY MASS DETERMINATIONX-RAY MASS DETERMINATION1. Assume spherical symmetry2. Fit spectra with coronal plasma models and

obtain (deprojected) spectral quantities3. Fit parameterized functions to radial profiles of

gas density and temperature4. Assume hydrostatic equilibrium5. Calculate the radial mass profile

A SPECIAL ERA IN X-RAY ASTRONOMY

Chandra XMM-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 = -0.040.03, P05).

Vikhlinin et al. 2006Pointecouteau et al. 2005

Clusters X-ray resultsClusters 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 PROJECTTHE 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 1012 ≤ M ≤ 1014 Msun

•First study of the mass profiles of 7 early type galaxies with Chandra (Humphrey et al. 2006)

HIGHLIGHTS ON THE GALAXY SCALE …HIGHLIGHTS ON THE GALAXY SCALE …

Humphrey et al. 2006

The contribution of the stellar The contribution of the stellar massmass

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 BaryonsInteraction 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 …HIGHLIGHTS ON THE GALAXY SCALE …

Humphrey et al. 2006

•NFW+stars best fit

•AC leads to more discrepant stellar M/L

•c-M relation in agreement with ΛCDM

THE PROJECTTHE 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 1012 ≤ M ≤ 1014 Msun

•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 (1013 ≤ M ≤ 1014 Msun) , where numerical predictions are more accurate because a large number of halo can be simulated.

In Gastaldello et al. 2006 (astro-ph 0610134) 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 SAMPLESELECTION OF THE SAMPLE

•Chandra inner regions

XMM outer regions

•Accurate bkg subtraction by modeling all components

NGC 533

DATA ANALYSYSDATA ANALYSYS

DATA ANALYSYSDATA ANALYSYS

•Fit gas density and temperature Fit gas density and temperature simultaneously assuming only simultaneously assuming only parameterizations for temperature and mass.parameterizations for temperature and mass.Advantages:Advantages:

•better constraints on Mbetter constraints on M•easy to interpret goodness of fiteasy to interpret goodness of fit

DATA ANALYSISDATA 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,ZFe).

•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

RESULTSRESULTS•After accounting for the mass of the hot gas, NFW + stars is the best fit model

MKW 4

NGC 533

RESULTSRESULTS•No detection of stellar mass due to poor sampling in the inner 20 kpc or localized AGN disturbance

A 2717

RESULTSRESULTS•No detection of stellar mass due to poor sampling in the inner 20 kpc or localized AGN disturbance

NGC 5044

Buote et al. 2002

RESULTSRESULTS

•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 0.570.21, 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. 2006

Stellar M/L 0.760.24

c-M relation for groupsc-M relation for groups

We obtain a slope α=-0.2260.076, c decreases with M at the 3σ level

THE X-RAY c-M RELATION THE X-RAY c-M RELATION • Buote et al. 2006

(astro-ph 0610135) c-M relation for 39 systems ranging in mass from ellipticals to the most massive galaxy clusters (0.06-20) x 1014 Msun.

• 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 THE X-RAY c-M RELATION

WMAP 1 yr Spergel et al. 2003

THE X-RAY c-M RELATION 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 σ8 (0.74), combined with the action of the tilt of the power spectrum and the lower value of Ωm.

Novel evidence of dark energy using only observations in local universe

O

D

1

Q

3

CAVEATS/FUTURE WORKCAVEATS/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)

CONCLUSIONSCONCLUSIONS

•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