Entropy scaling in galaxy clusters: insights from an XMM-Newton observation of the poor cluster A1983

Entropy scaling in galaxy clusters: insights from an XMM-Newton
observation of the poor cluster A1983

Authors:
G.W. Pratt,
M. Arnaud (CEA-Saclay Service d’Astrophysique)

Comments: Submitted to A&A; Figs 2, 7, 11 and 12 are low res versions

An XMM-Newton observation of the cool (kT=2.1 keV) cluster A1983, at z=0.044,
is presented. Gas density and temperature profiles are calculated for the inner
500 h_{50}^{-1} kpc (~0.35 r_200). The outer regions of the surface brightness
profile are well described with a beta model with beta=0.74, but the central
regions require the introduction of a second component. The temperature profile
is flat at the exterior with a slight dip towards the centre. The total mass
profile, calculated assuming hydrostatic equilibrium, is consistent with an NFW
profile, but with a low concentration parameter c=3.75 +/- 0.74. The M/L_B
ratio profile shows that, at large scale, light traces mass to a reasonable
extent, and the M/L_B ratio at 0.35 r_200 is consistent with the trends with
mass observed in the optical. The M_Fe/L_B ratio is about two times less than
that observed for a cluster at 5 keV. The gas mass fraction rises rapidly to
level off at ~200 kpc; the value at 0.35 r_200 is ~8%. The scaling properties
of the emission measure profile are consistent with the empirical relation
mgas propto Tx^{1.94}, and not with the self-similar relation mgas propto
Tx^{1.5}. Comparison of the entropy profile of A1983 with that of the hot
cluster A1413 shows that the profiles are well scaled using the empirically
determined relation S propto Tx^{0.65}, suggesting that the slope of the S-T
relation is shallower than in the self-similar model. The form of the entropy
profiles is remarkably similar, and there is no sign of a larger isentropic
core in the cooler cluster. These data provide powerful agruments against
preheating models. In turn, there is now increasing observational support for a
trend of f_gas with system mass, which may go some way towards explaining the
observed scaling behaviour. (Abridged.)

References and citations for this submission:

SLAC-SPIRES HEP (refers to ,
cited by, arXiv reformatted)