130 research outputs found
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
INTEGRAL observations of the Crab pulsar
The paper presents the timing and spectral analysis of several observations
of the Crab pulsar performed with INTEGRAL in the energy range 3-500 keV. All
these observations, when summed together provide a high statistics data set
which can be used for accurate phase resolved spectroscopy. A detailed study of
the pulsed emission at different phase intervals is performed. The spectral
distribution changes with phase showing a characteristic reverse S shape of the
photon index. Moreover the spectrum softens with energy, in each phase
interval, and this behavior is adequately modeled over the whole energy range
3-500 keV with a single curved law with a slope variable with Log(E),
confirming the BeppoSAX results on the curvature of the pulsed emission. The
bending parameter of the log-parabolic model is compatible with a single value
of 0.14+/-0.02 over all phase intervals. Results are discussed within the
three-dimensional outer gap model.Comment: 10 pages, 7 figures, accepted by Astronomy and Astrophysic
The Circumgalactic Medium in Massive Halos
This chapter presents a review of the current state of knowledge on the cool
(T ~ 1e4 K) halo gas content around massive galaxies at z ~ 0.2-2. Over the
last decade, significant progress has been made in characterizing the cool
circumgalactic gas in massive halos of Mh ~ 1e12-1e14 Msun at intermediate
redshifts using absorption spectroscopy. Systematic studies of halo gas around
massive galaxies beyond the nearby universe are made possible by large
spectroscopic samples of galaxies and quasars in public archives. In addition
to accurate and precise constraints for the incidence of cool gas in massive
halos, detailed characterizations of gas kinematics and chemical compositions
around massive quiescent galaxies at z ~ 0.5 have also been obtained. Combining
all available measurements shows that infalling clouds from external sources
are likely the primary source of cool gas detected at d >~ 100 kpc from massive
quiescent galaxies. The origin of the gas closer in is currently less certain,
but SNe Ia driven winds appear to contribute significantly to cool gas found at
d < 100 kpc. In contrast, cool gas observed at d <~ 200 kpc from luminous
quasars appears to be intimately connected to quasar activities on parsec
scales. The observed strong correlation between cool gas covering fraction in
quasar host halos and quasar bolometric luminosity remains a puzzle. Combining
absorption-line studies with spatially-resolved emission measurements of both
gas and galaxies is the necessary next step to address remaining questions.Comment: 29 pages, 7 figures, invited review to appear in "Gas Accretion onto
Galaxies", Astrophysics and Space Science Library, eds. A. Fox & R. Dave, to
be published by Springe
The optical light curve of the LMC pulsar B0540-69 in 2009
This paper reports a detailed analysis of the optical light curve of PSR
B0540-69, the second brightest pulsar in the visible band, obtained in 2009
(Jan. 18 and 20, and Dec. 14, 15, 16, 18) with the very high speed photon
counting photometer Iqueye mounted at the ESO 3.6-m NTT in La Silla (Chile).
The optical light curve derived by Iqueye shows a double structure in the main
peak, with a raising edge steeper than the trailing edge. The double peak can
be fitted by two Gaussians with the same height and FWHM of 13.3 and 15.5 ms
respectively. Our new values of spin frequencies allow to extend by 3.5 years
the time interval over which a reliable estimate of frequency first and second
derivatives can be performed. A discussion of implications on the braking index
and age of the pulsar is carried out. A value of n = 2.087 +/- 0.007 for the
overall braking index from 1987 to 2009 is derived. The braking index corrected
age is confirmed around 1700 years.Comment: Accepted for publication in MNRA
Chemodynamics of a simulated disc galaxy: initial mass functions and Type Ia supernova progenitors
We trace the formation and advection of several elements within a cosmological adaptive mesh refinement simulation of an L� galaxy. We use nine realizations of the same initial conditions with different stellar initial mass functions (IMFs), mass limits for Type II and Type Ia supernovae (SNII, SNIa) and stellar lifetimes to constrain these subgrid phenomena. Our code includes self-gravity, hydrodynamics, star formation, radiative cooling and feedback from multiple sources within a cosmological framework. Under our assumptions of nucleosynthesis we find that SNII with progenitor masses of up to 100 M� are required to match low-metallicity gas oxygen abundances. Tardy SNIa are necessary to reproduce the classical chemical evolution ‘knee’ in [O/Fe]–[Fe/H]: more prompt SNIa delayed time distributions do not reproduce this feature. Within our framework of hydrodynamical mixing of metals and galaxy mergers we find that chemical evolution is sensitive to the shape of the IMF and that there exists a degeneracy with the mass range of SNII. We look at the abundance plane and present the properties of different regions of the plot, noting the distinct chemical properties of satellites and a series of nested discs that have greater velocity dispersions are more α-rich and metal poor with age
The x-ray microcalorimeter spectrometer onboard Athena
Trabajo presentado a la conferencia: "Space Telescopes and Instrumentation: Ultraviolet to Gamma Ray" celebrada en Amsterdam (Holanda) el 1 de julio de 2012.-- et al.One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena. In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given. © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.Peer Reviewe
The Hot and Energetic Universe: The evolution of galaxy groups and clusters
Major astrophysical questions related to the formation and evolution of
structures, and more specifically of galaxy groups and clusters, will still be
open in the coming decade and beyond: what is the interplay of galaxy,
supermassive black hole, and intergalactic gas evolution in the most massive
objects in the Universe - galaxy groups and clusters? What are the processes
driving the evolution of chemical enrichment of the hot diffuse gas in
large-scale structures? How and when did the first galaxy groups in the
Universe, massive enough to bind more than 10^7 K gas, form? Focussing on the
period when groups and clusters assembled (0.5<z<2.5), we show that, due to the
continuum and line emission of this hot intergalactic gas at X-ray wavelengths,
Athena+, combining high sensitivity with excellent spectral and spatial
resolution, will deliver breakthrough observations in view of the
aforementioned issues. Indeed, the physical and chemical properties of the hot
intra-cluster gas, and their evolution across time, are a key to understand the
co-evolution of galaxy and supermassive black hole within their environments.Comment: Supporting paper for the science theme The Hot and Energetic Universe
to be implemented by the Athena+ X-ray observatory
(http://www.the-athena-x-ray-observatory.eu). 10 pages, 4 figure
A faint type of supernova from a white dwarf with a helium-rich companion
Supernovae (SNe) are thought to arise from two different physical processes.
The cores of massive, short-lived stars undergo gravitational core collapse and
typically eject a few solar masses during their explosion. These are thought to
appear as as type Ib/c and II SNe, and are associated with young stellar
populations. A type Ia SN is thought to arise from the thermonuclear detonation
of a white dwarf star composed mainly of carbon and oxygen, whose mass
approaches the Chandrasekhar limit. Such SNe are observed in both young and old
stellar environments. Here we report our discovery of the faint type Ib SN
2005E in the halo of the nearby isolated galaxy, NGC 1032.
The lack of any trace of recent star formation near the SN location (Fig. 1),
and the very low derived ejected mass (~0.3 M_sun), argue strongly against a
core-collapse origin for this event. Spectroscopic observations and the derived
nucleosynthetic output show that the SN ejecta have high velocities and are
dominated by helium-burning products, indicating that SN 2005E was neither a
subluminous nor a regular SN Ia (Fig. 2). We have therefore found a new type of
stellar explosion, arising from a low-mass, old stellar system, likely
involving a binary with a primary white dwarf and a helium-rich secondary. The
SN ejecta contain more calcium than observed in any known type of SN and likely
additional large amounts of radioactive 44Ti. Such SNe may thus help resolve
fundamental physical puzzles, extending from the composition of the primitive
solar system and that of the oldest stars, to the Galactic production of
positrons.Comment: Revised to reflect published version in Nature, May 20th, 2010.
Additional data and analysis are include
The First Decade of Science with Chandra and XMM-Newton
NASA's Chandra X-ray Observatory and ESA's XMM-Newton made their first
observations one decade ago. The unprecedented and complementary capabilities
of these observatories to detect, image, and measure the energy of cosmic
X-rays, achieved less than 50 years after the first detection of an extra-solar
X-ray source, represent an increase in sensitivity comparable in going from
naked-eye observations to the most powerful optical telescopes over the past
400 years! In this review, we highlight some of the many discoveries made by
Chandra and XMM-Newton that have transformed 21st century astronomy and briefly
discuss prospects for future research.Comment: 8 pages, 10 figures, published in Natur
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