Transcript Slide 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
OUTLINE
•INTRODUCTION
•SELECTION OF THE SAMPLE
•DATA ANALYSIS
•RESULTS AND c-M PLOT
•CONCLUSIONS
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
NFW PROFILE
c = rvir/rs with virial radius corresponding to overdensity of 100
for this talk and Mvir 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
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
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
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).
Wu & Xue 2000
Lower concentration predicted
by simulations (e.g. Bullock et
al. 2001)
High c as seen in X-rays for
M < 1014 solar masses
Good quality Chandra data show
similar results (NGC 6482,
Khosroshahi et al. 2004)
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)
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) ?
SELECTION OF THE SAMPLE
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 1014 solar masses
• objects in our own attempt of an X-ray flux limited sample taken from
NORAS (Bohringer et al. 2000)
IC 1860
MKW 4
NGC 533
NGC 1550
SELECTION OF THE SAMPLE
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 1014 solar masses
• objects in our own attempt of an X-ray flux limited sample taken from
NORAS (Bohringer et al. 2000)
NGC 5044 Buote et al.2003
NGC 1132
ESO 3060170
MS 0116
SELECTION OF THE SAMPLE
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 1014 solar masses
• objects in our own attempt of an X-ray flux limited sample taken from
NORAS (Bohringer et al. 2000)
A 262
A 2717
AWM 4
A 1991
SELECTION OF THE SAMPLE
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 1014 solar masses
• objects in our own attempt of an X-ray flux limited sample taken from
NORAS (Bohringer et al. 2000)
A 1314
NGC 5129
RGH 80
NGC 4325
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 !
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
DATA ANALYSIS
NGC 5044 offset
Buote et al. 2004
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,ZFe). 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.
… 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
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)
T PROFILES
MKW 4
NGC 533
A 262
NGC 2563
IC 1860
AWM 4
SCALED T PROFILES
SCALED T PROFILES
Vikhlinin et al. 2005
Sun et al. 2003
Stellar mass or not ?
NGC 4325
NGC 5129
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/LB
are in the range 2-7. We can not discriminate between
these two latter models.
c vs. M
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