Probing the history of galaxy clusters with metallicity and entropy measurements
PhDT(2012)
Abstract
Galaxy clusters are the largest gravitationally
bound objects found today in our Universe. The gas they contain,
the intra-cluster medium (ICM), is heated to temperatures in the
approximate range of 1 to 10 keV, and thus emits X-ray radiation.
Studying the ICM through the spatial and spectral analysis of its
emission returns the richest information about both the overall
cosmological context which governs the formation of clusters, as
well as the physical processes occurring within. The aim of this
thesis is to learn about the history of the physical processes that
drive the evolution of galaxy clusters, through careful, spatially
resolved measurements of their metallicity and entropy content. A
sample of 45 nearby clusters observed with Chandra is analyzed to
produce radial density, temperature, entropy and metallicity
profiles. The entropy profiles are computed to larger radial
extents than in previous Chandra analyses. The results of this
analysis are made available to the scientific community in an
electronic database. Comparing metallicity and entropy in the
outskirts of clusters, we find no signature on the entropy profiles
of the ensemble of supernovae that produced the observed metals. In
the centers of clusters, we find that the metallicities of
high-mass clusters are much less dispersed than those of low-mass
clusters. A comparison of metallicity with the regularity of the
X-ray emission morphology suggests that metallicities in low-mass
clusters are more susceptible to increase from violent events such
as mergers. We also find that the variation in the stellar-to-gas
mass ratio as a function of cluster mass can explain the variation
of central metallicity with cluster mass, only if we assume that
there is a constant level of metallicity for clusters of all
masses, above which the observed galaxies add more metals in
proportion to their mass.
MoreTranslated text
Key words
galaxy clusters,metallicity
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