844 research outputs found
Action-based dynamical models of dwarf spheroidal galaxies: application to Fornax
We present new dynamical models of dwarf spheroidal galaxies (dSphs) in which
both the stellar component and the dark halo are described by analytic
distribution functions that depend on the action integrals. In their most
general form these distribution functions can represent axisymmetric and
possibly rotating stellar systems. Here, as a first application, we model the
Fornax dSph, limiting ourselves, for simplicity, to the non rotating, spherical
case. The models are compared with state-of-the-art spectroscopic and
photometric observations of Fornax, exploiting the knowledge of the
line-of-sight velocity distribution of the models and accounting for the
foreground contamination from the Milky Way. The model that best fits the
structural and kinematic properties of Fornax has a cored dark halo, with core
size kpc. The dark-to-luminous mass ratio is within the effective radius kpc and
within 3 kpc. The stellar velocity distribution is isotropic almost over the
full radial range covered by the spectroscopic data and slightly radially
anisotropic in the outskirts of the stellar distribution. The dark-matter
annihilation -factor and decay -factor are, respectively,
GeV cm and GeV
cm, for integration angle . This
cored halo model of Fornax is preferred, with high statistical significance, to
both models with a Navarro, Frenk and White dark halo and simple
mass-follows-light models.Comment: Accepted 2018 July 6; Received 2018 June 1; Submitted in original to
MNRAS form 2018 February
The imprint of dark matter haloes on the size and velocity dispersion evolution of early-type galaxies
Early-type galaxies (ETGs) are observed to be more compact, on average, at than at , at fixed stellar mass. Recent observational
works suggest that such size evolution could reflect the similar evolution of
the host dark matter halo density as a function of the time of galaxy
quenching. We explore this hypothesis by studying the distribution of halo
central velocity dispersion () and half-mass radius () as
functions of halo mass and redshift , in a cosmological -CDM
-body simulation. In the range , we find
and , close to
the values expected for homologous virialized systems. At fixed in the
range we find
and . We show that
such evolution of the halo scaling laws is driven by individual haloes growing
in mass following the evolutionary tracks and , consistent with simple dissipationless merging models in
which the encounter orbital energy is accounted for. We compare the -body
data with ETGs observed at by populating the haloes with
a stellar component under simple but justified assumptions: the resulting
galaxies evolve consistently with the observed ETGs up to , but the
model has difficulty reproducing the fast evolution observed at .
We conclude that a substantial fraction of the size evolution of ETGs can be
ascribed to a systematic dependence on redshift of the dark matter haloes
structural properties.Comment: 15 pages, 14 figures, 1 table. Matches the Accepted version from
MNRA
Magnetorotational instability in cool cores of galaxy clusters
Clusters of galaxies are embedded in halos of optically thin, gravitationally
stratified, weakly magnetized plasma at the system's virial temperature. Due to
radiative cooling and anisotropic heat conduction, such intracluster medium
(ICM) is subject to local instabilities, which are combinations of the thermal,
magnetothermal and heat-flux-driven buoyancy instabilities. If the ICM rotates
significantly, its stability properties are substantially modified and, in
particular, also the magnetorotational instability (MRI) can play an important
role. We study simple models of rotating cool-core clusters and we demonstrate
that the MRI can be the dominant instability over significant portions of the
clusters, with possible implications for the dynamics and evolution of the cool
cores. Our results give further motivation for measuring the rotation of the
ICM with future X-ray missions such as ASTRO-H and ATHENA.Comment: 17 pages, 10 figures, accepted for publication in Journal of Plasma
Physics, Special Issue "Complex Plasma Phenomena in the Laboratory and in the
Universe
Máquinas Rising from the Trucks against the Coming of Planes : A Posthumanist Reading of Ernest Hemingway’s For Whom the Bell Tolls
In this thesis, I study American author Ernest Hemingway’s critically and commercially successful novel For Whom the Bell Tolls (1940) through the theoretical framework of posthumanism. The novel tells the story of an American volunteer in the Spanish Civil War, who is tasked to blow up a bridge with the help of local rebels. My aim is to demonstrate that there is a clear posthumanist consciousness at play in the novel and that it is possible and valuable to study classic literature through this branch of literary criticism.
Although posthumanism is a rather new theory, there are already multiple different definitions for it. At its largest scope it is interested in all things beyond humans, despite at times being narrowed down to only concern machines. For the purpose of this thesis, my main focus is on the portrayal of machines, but for a full view of the posthumanist consciousness, I also discuss other manifestations of posthumanism, namely nature and beliefs.
My analysis of the novel delineates an abundance of posthuman entities in the prose. I discuss their meaning individually and collectively in detail. In the end, it is apparent that the novel displays a distinct posthuman consciousness on which this study shed new light on, although the book has already been studied extensively. The novel has various dimensions of posthumanism that provide much material for further studies in the future
The angular momentum-mass relation: a fundamental law from dwarf irregulars to massive spirals
In a CDM Universe, the specific stellar angular momentum ()
and stellar mass () of a galaxy are correlated as a consequence of the
scaling existing for dark matter haloes ().
The shape of this law is crucial to test galaxy formation models, which are
currently discrepant especially at the lowest masses, allowing to constrain
fundamental parameters, e.g. the retained fraction of angular momentum. In this
study, we accurately determine the empirical relation (Fall
relation) for 92 nearby spiral galaxies (from S0 to Irr) selected from the
Spitzer Photometry and Accurate Rotation Curves (SPARC) sample in the
unprecedented mass range . We
significantly improve all previous estimates of the Fall relation by
determining profiles homogeneously for all galaxies, using extended HI
rotation curves, and selecting only galaxies for which a robust could
be measured (converged radial profile). We find the relation to be
well described by a single, unbroken power-law
over the entire mass range, with and orthogonal intrinsic
scatter of dex. We finally discuss some implications for galaxy
formation models of this fundamental scaling law and, in particular, the fact
that it excludes models in which discs of all masses retain the same fraction
of the halo angular momentum.Comment: A&A Letters, accepte
Empathy-based stories capturing the voice of female secondary school students in Tanzania
Tanzania, like many other African countries, has experienced a rapid expansion of its secondary education sector. This has resulted in large numbers of secondary school graduates struggling to build a future through continuing education or finding employment. 1 Students are faced with the difficult task of assessing their opportunities in the face of various challenges and making plans to build a better life. The presented research uses empathy-based stories to identify which elements were considered to be important by students in determining their success in education. The analysis of narrative data represents a shared cultural meaning on the social and cultural support available to students. The findings suggest that using empathy-based stories as a methodological tool can provide valuable insights for culture-sensitive and intercultural research through its ability to widen the context of discovery.Peer reviewe
Henry of Ghent on the Siege of Acre : Magnanimity, Suicide and the Role of God
This article deals with some key ideas found in Henry of Ghent’s Quodlibet XV, question 16, which is concerned with the actions of a Christian knight during the siege of Acre that took place in 1291. In answering the question of whether the soldier acted magnanimously on the battlefield, Henry provides a rich discussion of magnanimity and the ethics of suicide. Despite his status as one of the leading minds of the later 13th century, Henry’s ideas on magnanimity have received little attention in previous scholarship. On my reading, Henry’s understanding of magnanimity is reminiscent of the Christian view of magnanimity before the assimilation of Aristotle into the university curriculum. Furthermore, Henry allows God’s causality a more central role in his discussion of warfare than most 13th-century theologians and canon lawyers.Peer reviewe
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