13 research outputs found
The Evolution of X-ray Clusters of Galaxies
Considerable progress has been made over the last decade in the study of the
evolutionary trends of the population of galaxy clusters in the Universe. In
this review we focus on observations in the X-ray band. X-ray surveys with the
ROSAT satellite, supplemented by follow-up studies with ASCA and Beppo-SAX,
have allowed an assessment of the evolution of the space density of clusters
out to z~1, and the evolution of the physical properties of the intra-cluster
medium out to z~0.5. With the advent of Chandra and Newton-XMM, and their
unprecedented sensitivity and angular resolution, these studies have been
extended beyond redshift unity and have revealed the complexity of the
thermodynamical structure of clusters. The properties of the intra-cluster gas
are significantly affected by non-gravitational processes including star
formation and Active Galactic Nucleus (AGN) activity. Convincing evidence has
emerged for modest evolution of both the bulk of the X-ray cluster population
and their thermodynamical properties since redshift unity. Such an
observational scenario is consistent with hierarchical models of structure
formation in a flat low density universe with Omega_m=0.3 and sigma_8=0.7-0.8
for the normalization of the power spectrum. Basic methodologies for
construction of X-ray-selected cluster samples are reviewed and implications of
cluster evolution for cosmological models are discussed.Comment: 40 pages, 15 figures. Full resolution figures can be downloaded from
http://www.eso.org/~prosati/ARAA
The establishment of the Standard Cosmological Model through observations
Over the last decades, observations with increasing quality have
revolutionized our understanding of the general properties of the Universe.
Questions posed for millenia by mankind about the origin, evolution and
structure of the cosmos have found an answer. This has been possible mainly
thanks to observations of the Cosmic Microwave Background, of the large-scale
distribution of matter structure in the local Universe, and of type Ia
supernovae that have revealed the accelerated expansion of the Universe. All
these observations have successfully converged into the so-called "concordance
model". In spite of all these observational successes, there are still some
important open problems, the most obvious of which are what generated the
initial matter inhomogeneities that led to the structure observable in today's
Universe, and what is the nature of dark matter, and of the dark energy that
drives the accelerated expansion. In this chapter I will expand on the previous
aspects. I will present a general description of the Standard Cosmological
Model of the Universe, with special emphasis on the most recent observations
that have us allowed to consolidate this model. I will also discuss the
shortfalls of this model, its most pressing open questions, and will briefly
describe the observational programmes that are being planned to tackle these
issues.Comment: Accepted for publication in the book "Reviews in Frontiers of Modern
Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka;
publisher Springer Nature) funded by the European Union Erasmus+ Strategic
Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556