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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
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).
Navarro et al. 2004
c-M RELATION
•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).
Bullock et al. 2001
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)
Selection Effects
Wechsler et al. 2002
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)
OBSERVATIONS: METHODS
–
–
–
–
–
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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.
2.
3.
4.
5.
Assume spherical symmetry
Fit spectra with coronal plasma models and obtain
(deprojected) spectral quantities
Fit parameterized functions to radial profiles of gas
density and temperature
Assume hydrostatic equilibrium
Calculate the radial mass profile
A SPECIAL ERA IN X-RAY ASTRONOMY
Chandra
•1 arcsec resolution
XMM-Newton
•High sensitivity due to high
effective area, i.e. more
photons
Clusters X-ray results
Pointecouteau et al. 2005
Vikhlinin et al. 2006
• 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 = -0.040.03, P05).
Rines & Diaferio (2006)
Mandelbaum et al. (2006)
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
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 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 …
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. 2006
•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 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.
SELECTION OF THE SAMPLE
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.
DATA ANALYSYS
•Accurate bkg subtraction by modeling all components
•Chandra inner regions
XMM outer regions
NGC 533
DATA ANALYSYS
•Fit gas density and temperature simultaneously
assuming only parameterizations for temperature
and mass.
Advantages:
•better constraints on M
•easy 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,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
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
Buote et al. 2002
NGC 5044
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-tolight ratios
Humphrey et al. 2006
Stellar M/L 0.760.24
c-M relation for groups
We obtain a slope α=-0.2260.076, c decreases with M at the 3σ level
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 (0.0620) 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
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 σ8 (0.74), combined with the
action of the tilt of the power spectrum and the lower value of Ωm.
O
D
1
Q
3
Novel evidence of dark
energy using only
observations in local
universe
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