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 $r_{\rm c}\simeq1.03$ kpc. The dark-to-luminous mass ratio is $(M_{\rm dm}/M_{\star})|_{R_{\rm eff}}\simeq9.6$ within the effective radius $R_{\rm eff} \simeq 0.62\,$kpc and $(M_{\rm dm}/M_{\star})|_{3 {\rm kpc}} \simeq 144$ 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 $J$-factor and decay $D$-factor are, respectively, $\log_{10}(J$ $[$GeV$^2$ cm$^{-5}])\simeq18.34$ and $\log_{10}(D$ $[$GeV cm$^{-2}])\simeq18.55$, for integration angle $\theta = 0.5^{\circ}$. 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 $z \gtrsim 2$ than at $z\simeq 0$, 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 ($\sigma_0$) and half-mass radius ($r_{\rm h}$) as functions of halo mass $M$ and redshift $z$, in a cosmological $\Lambda$-CDM $N$-body simulation. In the range $0\lesssim z\lesssim 2.5$, we find $\sigma_0\propto M^{0.31-0.37}$ and $r_{\rm h}\propto M^{0.28-0.32}$, close to the values expected for homologous virialized systems. At fixed $M$ in the range $10^{11} M_\odot \lesssim M\lesssim 5.5 \times 10^{14} M_\odot$ we find $\sigma_0\propto(1+z)^{0.35}$ and $r_{\rm h}\propto(1+z)^{-0.7}$. We show that such evolution of the halo scaling laws is driven by individual haloes growing in mass following the evolutionary tracks $\sigma_0\propto M^{0.2}$ and $r_{\rm h}\propto M^{0.6}$, consistent with simple dissipationless merging models in which the encounter orbital energy is accounted for. We compare the $N$-body data with ETGs observed at $0\lesssim z\lesssim3$ by populating the haloes with a stellar component under simple but justified assumptions: the resulting galaxies evolve consistently with the observed ETGs up to $z \simeq 2$, but the model has difficulty reproducing the fast evolution observed at $z\gtrsim 2$. 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 $\Lambda$CDM Universe, the specific stellar angular momentum ($j_\ast$) and stellar mass ($M_\ast$) of a galaxy are correlated as a consequence of the scaling existing for dark matter haloes ($j_{\rm h}\propto M_{\rm h}^{2/3}$). 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 $j_\ast-M_\ast$ 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 $7 \lesssim \log M_\ast/M_\odot \lesssim 11.5$. We significantly improve all previous estimates of the Fall relation by determining $j_\ast$ profiles homogeneously for all galaxies, using extended HI rotation curves, and selecting only galaxies for which a robust $j_\ast$ could be measured (converged $j_\ast(<R)$ radial profile). We find the relation to be well described by a single, unbroken power-law $j_\ast\propto M_\ast^\alpha$ over the entire mass range, with $\alpha=0.55\pm 0.02$ and orthogonal intrinsic scatter of $0.17\pm 0.01$ 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