XMM-Newton observation of the relaxed cluster A478: Gas and dark matter distribution from 0.01R
to 0.5R
1
Service d'Astrophysique du CEA, L'Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette, France e-mail: pointeco@discovery.saclay.cea.fr
2
SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
Received:
12
December
2003
Accepted:
5
March
2004
We present an
mosaic observation of the hot (
keV) and nearby (
)
relaxed cluster of galaxies A478. We derive precise gas density, gas
temperature, gas mass
and total mass profiles up to 
(about half of the virial
radius R200). The gas density profile is highly peaked towards
the center and the surface brightness profile is well fitted by a sum
of three β-models.
The derived gas density profile is in excellent agreement, both in
shape and in normalization, with the published Chandra density
profile (measured
within 
of the center). Projection
and PSF effects on the temperature profile determination are thoroughly
investigated.
The derived radial temperature structure is as expected for a cluster
hosting a cooling core, with a
strong negative gradient at the cluster center. The temperature rises
from ~2 keV up to a plateau of ~6.5 keV beyond 
(i.e.
, 
Mpc being the virial radius).
From the temperature profile
and the density profile and on the hypothesis of hydrostatic
equilibrium, we derived the total mass profile of A478 down to 0.01 and
up to 0.5 times the virial radius. We tested different dark matter
models against the observed mass profile. The Navarro et al.
([CITE]) model is significantly preferred to other models.
It leads to a total mass of 
for
a concentration parameter of 
. The gas mass
fraction increases slightly with radius. The gas mass fraction at a
density contrast of 
is 
, consistent
with
previous results on similar hot and massive clusters. We confirm the
excess of absorption in the direction of A478. The derived absorbing
column density exceeds the 21 cm measurement by a factor of ~2,
this excess extending well beyond the cool core region. Through the
study of this absorbing component and a cross
correlation with infrared data, we argue that the absorption excess
is of Galactic origin, rather than intrinsic to the cluster.
Key words: galaxies: clusters: individual: A478 / galaxies: intergalacic medium / cosmology: observations / cosmology: dark matter / X-rays: galaxies: clusters
© ESO, 2004