Observing galaxy cluster
simulations with an X-ray
telescope
Elena Rasia
Department of Physics,
University of Michigan
Chandra Fellows Symposium
Harvard-Smithsonian Center for Astrophysics
October 13, 2006
COSMOLOGY
From:
From:
WMAP
(3rd year)
•H0=73 +/- 3 km/s/Mpc
WMAP(1st year)
•H0=71 +/- 2 km/s/Mpc
•8=0.74 +/- 0.05
SDSS
•8=0.9 +/- 0.03
•n = 0.951 +0.01/-0.02
2dF
•B h2=0.0223 +/-0.0008
weak lensing
•n = 0.98 +/- 0.02
• =0.72 +/-0.02
•DM h2=0.127 +0.007/0.013
SNe Ia
•B =0.024 +/-0.003
Ly- forest
•DM h2=0.115+/-0.013
• =0.09 +/- 0.03
Age of G.C.
(Spergel et al. 2006)
Plank
SNAP
(Seljak et al. 2005)
DUNE (Dark Universe Explorer)
DES (Dark Energy Survey)
clusters
XEUS (X-ray Evolving Universe Spectroscopy mission)
Constellation-X
(Haiman et al 2005)
SIMULATIONS:
GADGET/GADGET2 Tree +
SPH
(Springel et al .’01; Springel
‘05)
CMD
(M  0.27,    0.7, 8
=0.8/0.9, h=0.70)
Explicit entropy conservation
(Springel & Hernquist ‘02)
Radiative cooling + uniform
evolving UV background
Multiphase model for starformation + galactic winds
(Springel & Hernquist ‘03)
Thermal conduction (Jubelgas
et al. ‘04; Dolag et al. ‘04)
Chemical enrichment from
Sn-Ia and II (Tornatore et al.
’04, ‘06)
Reduced-viscosity SPH
scheme (Dolag et al. ‘05)
X-MAS
X-ray Map
Simulator
(Gardini et al 2004, Rasia et al. 2006)
First part:
Second part:
Depend on the
Selection of los +
characteristics of
projection into the
the X-ray telescope
sky, is quite
and detector
general+
(Chandra ACIS-S,
computation of the
Chandra ACIS-I,
spectral emissivity
XMM-Newton EPICMOS1&2 XMMNewton EPIC-PN)
X-RAY EVENT FILES
which can be analyzed
using the X-ray tools
X-ray Map
Simulator
Main Results
Contrast between temperature definitions in simulations
and observations: TEW is not a good description of the Xray spectroscopic temperature (Gardini et al. 2004)
Temperature to use in simulations TSL ->cosmological
consequence for M-T (Mazzotta et al 2004, Rasia et al.
2005)
Study of systematics bias of mass measurement (Rasia
et al. 2006) and metallicity measurement (Rasia et al. in
prep.)
TEMPERATURES
simulation
X-ray observation
The different degree of
thermal homogeneity has
strong implications on the
temperature profiles:
for the perturbed systems the
spectral and emissionweighted temperature
profiles are not in good
agreement (Gardini et al.
2004)
TEMPERATURES
Emission-Weighted
W ew  (T)n 2
Shock front


T
 WTdV
 WdV

Spectroscopic-Like
W sl  n 2 /T 0.75
No Shock front
beside being biased toward densest regions the spectroscopic temperature
is also biased toward the coolest regions (Mazzotta et al. 2004)
Mazzotta et al. 2004, see also Vikhlinin 2006
COSMOLOGICAL IMPLICATIONS
Simple theoretical
arguments supported by
hydro N-body simulations
suggest the existence for
virialized gravitational
systems of a tight relation
between M-T:
M500=M0(kT500/1keV)
TSL=(0.70±0.01)TEW+(0.29±0.05)
Rasia et al .2005, Kawahara et al. in prep
MASS-TEMPERATURE RELATION
M0 is higher using Tsl instead of Tew
T_EW (Borgani et al.2004)
Msim
T_SL (Rasia et al. 2005)
M,
MASS BIAS
• Hydrostatic equilibrium
equation
Gap explained by the
velocity motions of the gas
the is not completely at rest
even in the center of the
cluster
• Hydro(dynamic?) equilibrium
equation
(Rasia et al. 2004, see also Kay
et al. 2004, Faltenbacher et al.
2005, Lau et al. 2006, Nagai
et al. 2006)
MASS BIAS
The mass recovered through
the HE equation are
underestimated by 20%, half or
more of which solved by
including the kinetic pressure
term (Rasia et al. 2006, see
also Nagai et al. 2006).
The mass measurements
reconstructed via the -model
show a systematic
underestimate, with typical
deviation of about 40% at R2500
and R500.
SUMMARY





Clusters are good probe to extract cosmological
parameters
To study systematics bias, to verify models and
hypothesis and to test (X-ray, but not only…) methods
we need SIMULATIONS
We built X-MAS that allow us to make proper
comparison between simulations and observations
TEW is not a good description of Tspec -> we propose
another formulation TSL -> this has relevant
cosmological consequence for M-T
X-ray mass estimates present systematic bias due to
different reasons -> this has to be taken into account
in comparing different M-T relation present in literature