43 research outputs found
Forward modeling populations of flares from tidal disruptions of stars by supermassive black holes
High Energy Astrophysic
Observations of metals in the intra-cluster medium
Because of their deep gravitational potential wells, clusters of galaxies
retain all the metals produced by the stellar populations of the member
galaxies. Most of these metals reside in the hot plasma which dominates the
baryon content of clusters. This makes them excellent laboratories for the
study of the nucleosynthesis and chemical enrichment history of the Universe.
Here we review the history, current possibilities and limitations of the
abundance studies, and the present observational status of X-ray measurements
of the chemical composition of the intra-cluster medium. We summarise the
latest progress in using the abundance patterns in clusters to put constraints
on theoretical models of supernovae and we show how cluster abundances provide
new insights into the star-formation history of the Universe.Comment: 28 pages, 12 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 16; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
The chemical enrichment of the ICM from hydrodynamical simulations
The study of the metal enrichment of the intra-cluster and inter-galactic
media (ICM and IGM) represents a direct means to reconstruct the past history
of star formation, the role of feedback processes and the gas-dynamical
processes which determine the evolution of the cosmic baryons. In this paper we
review the approaches that have been followed so far to model the enrichment of
the ICM in a cosmological context. While our presentation will be focused on
the role played by hydrodynamical simulations, we will also discuss other
approaches based on semi-analytical models of galaxy formation, also critically
discussing pros and cons of the different methods. We will first review the
concept of the model of chemical evolution to be implemented in any
chemo-dynamical description. We will emphasise how the predictions of this
model critically depend on the choice of the stellar initial mass function, on
the stellar life-times and on the stellar yields. We will then overview the
comparisons presented so far between X-ray observations of the ICM enrichment
and model predictions. We will show how the most recent chemo-dynamical models
are able to capture the basic features of the observed metal content of the ICM
and its evolution. We will conclude by highlighting the open questions in this
study and the direction of improvements for cosmological chemo-dynamical models
of the next generation.Comment: 25 pages, 11 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 18; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
X-ray Survey Results on Active Galaxy Physics and Evolution
This "pedagogical" review describes the key Chandra and XMM-Newton
extragalactic surveys to date and details some of their implications for AGN
physics and evolution. We additionally highlight two topics of current
widespread interest: (1) X-ray constraints on the AGN content of luminous
submillimeter galaxies, and (2) the demography and physics of high-redshift (z
> 4) AGN as revealed by X-ray observations. Finally, we discuss prospects for
future X-ray surveys with Chandra, XMM-Newton, and upcoming missions.Comment: 26 pages, in Physics of Active Galactic Nuclei at All Scales, eds.
Alloin D., Johnson R., Lira P. (Springer-Verlag, Berlin), version with all
figures at http://www.astro.psu.edu/users/niel/papers/papers.htm