Simulations of Dwarf Galaxy Formation

Dwarf galaxies are related to important cosmological questions, and central to our understanding of the physics of galaxy formation. In this thesis, I present the results of cosmological, hydrodynamical simulations of the formation and evolution of dwarf galaxies. I compare the simulation results with observations, and interpret them in the context of a Lambda-CDM cosmology. In high resolution simulations of isolated dwarf galaxies, I show that a combination of supernova feedback and the cosmic UV background results in the formation of galaxies with properties similar to the Local Group dwarf spheroidals, and that both effects are strongly moderated by the depth of the gravitational potential. The simulations naturally reproduce the observed scaling relations between luminosity and mass-to-light ratio, and between total stellar mass and metallicities. The final objects have halo masses between 2.3 x 10^8 and 1.1 x 10^9 solar masses, mean velocity dispersions between 6.5 and 9.7 kms^-1, stellar masses ranging from 5 x 10^5 to 1.2 x 10^7 solar masses, median metallicities between [Fe/H]=-1.8 and -1.1, and half-light radii of the order of 200 to 300 pc, all comparable with Local Group dwarf spheroidals. The simulations also indicate that the dwarf spheroidal galaxies observed today lie near a mass threshold around 10^9 solar masses, in agreement with stellar kinematic data, where supernova feedback not only suffices to completely expel the interstellar medium and leave the residual gas-free, but where the combination of feedback, UV radiation and self-shielding establishes a dichotomy of age distributions similar to that observed in the Milky Way and M31 satellites. A second line of work has been the analysis of the dwarf galaxy population resulting from the Aquila simulation. By simultaneously including the formation of a Milky Way type galaxy along with ~500 dwarf-sized haloes in the mass range of ~10^8 - 10^10 solar masses, this simulation allows a study of the effect of the environment on dwarf galaxy evolution. I study the relative importance, and interplay, of the different mechanisms for gas loss, and compare the properties of the satellites with those of isolated dwarf galaxies. A third set of simulations focuses on the formation of dwarf galaxies in a representative sample of haloes extracted from the Millennium-II simulation. The six haloes in these simulations all have a z=0 mass of ~10^10 solar masses and show different mass assembly histories, which are reflected in different star formation histories. The galaxies reach final stellar masses in the range of 5 x 10^7 - 10^8 solar masses, consistent with other published simulations of galaxy formation in similar mass haloes. The resulting objects have structures and stellar populations consistent with dwarf elliptical and dwarf irregular galaxies. However, in a Lambda-CDM universe, 10^10 solar mass haloes must typically contain galaxies with much lower stellar mass than these simulations predict, if they are to match observed galaxy abundances. The dwarf galaxies formed in my own and all other current hydrodynamical simulations are more than an order of magnitude more luminous than expected for haloes of this mass. I discuss the significance and possible implications of this result for cosmological models, and for the assumptions about the physics of galaxy formation. Finally, I present preliminary results of a direct comparison between hydrodynamical simulations and semi-analytical models for the formation of dwarf galaxies. Current semi-analytical models, which are tuned to match the statistical properties of galaxies, do not agree with the predictions of hydrodynamical simulations for individual objects. Conversely, when tuned to accurately reproduce the simulations, semi-analytical models can give a more qualitative interpretation of the simulation results, in terms of equations of galaxy formation. The combination of the two methods allows an extrapolation from individual cases to cosmological volumes, not currently attainable with direct simulations alone

The Local Group's mass: probably no more than the sum of its parts

The total mass of the Local Group (LG) and the masses of its primary constituents, the Milky Way and M31, are important anchors for several cosmological questions. In recent years, independent measurements have consistently yielded halo masses close to $10^{12} \mathrm{M_\odot}$ for the MW, and $1-2 \times 10^{12} \mathrm{M_\odot}$ for M31, while estimates derived from the pair's kinematics via the `timing argument' have yielded a combined mass of around $5 \times 10^{12} \mathrm{M_\odot}$. Here, we analyse the extremely large Uchuu simulation to constrain the mass of the Local Group and its two most massive members. First, we demonstrate the importance of selecting LG analogues whose kinematics are dominated by mutual interactions to a similar extent as the LG. Adopting the observed separation and radial velocity, we obtain a weighted posterior of $75_{-40}^{+65}$ kms$^{-1}$ for the uncertain transverse velocity. Via Gaussian process regression, we infer a total mass of $3.2^{+1.2}_{-0.9} \times 10^{12} \mathrm{M_\odot}$, significantly below the timing argument prediction. Importantly, we show that the remaining uncertainty is not rooted in the analysis or observational errors, but in the irreducible scatter in the kinematics-mass relation. We further find a mass for the less massive halo of $0.9_{-0.3}^{+0.6} \times 10^{12} \mathrm{M_\odot}$ and for the more massive halo of $2.3_{-0.9}^{+1.0} \times 10^{12} \mathrm{M_\odot}$, consistent with independent measurements of the masses of MW and M31, respectively. Incorporating the mass of the MW as an additional prior allows us to further constrain all measurements and determine that the MW is very likely to be the lower mass object of the two.Comment: 15 pages, submitted to MNRAS. Full source code provided, comments are welcom

Structure formation with two periods of inflation : beyond PLaln Lambda CDM

We discuss structure formation in models with a spectator field in small-field inflation which accommodate a secondary period of inflation. In such models, subgalactic scale primordial fluctuations can be much suppressed in comparison to the usual power-law Lambda CDM model while the large scale fluctuations remain consistent with current observations. We discuss how a secondary inflationary epoch may give rise to observable features in the small scale power spectrum and hence be tested by the structures in the Local Universe.Peer reviewe

The intimidated bodies: The somatic consequences of state terrorism in Mario Vargas Llosa’s novel The Feast of the Goat

This paper argues that Mario Vargas Llosa’s novel The Feast of the Goat (2000) uses the images of the bodies of three of its characters (Urania Cabral, Trujillo and Agustín Cabral) to represent the mechanisms of state terrorism at the time of Trujillo’s dictatorship in the Dominican Republic. It is a traumatizing system, which leaves somatic marks in all the actors involved. We analyze the manners in which the Peruvian author uses the images of protagonists’ organic processes to sketch the psychical, emotional and ideological processes and states, linked to or generated by the policies of intimidation.This paper argues that Mario Vargas Llosa’s novel The Feast of the Goat (2000) uses the images of the bodies of three of its characters (Urania Cabral, Trujillo and Agustín Cabral) to represent the mechanisms of state terrorism at the time of Trujillo’s dictatorship in the Dominican Republic. It is a traumatizing system, which leaves somatic marks in all the actors involved. We analyze the manners in which the Peruvian author uses the images of protagonists’ organic processes to sketch the psychical, emotional and ideological processes and states, linked to or generated by the policies of intimidation

Biopolitique et autobiographisme. Les deux malades de Franz Joseph Gall

The aim of this article is, on the one hand, to show Franz Joseph Gall as an important figure for setting up the ideological framework for modern biopolitics and, on the other, to look at the literary traces of his personal engagement in this endeavour. In the first part, we place his thought in the ideological context of the 18th and 19th century; the second one analyses the images of the patients created by the author, in order to show their different configurations: while some appear as reduced to the role of homo sacer (Giorgio Agamben’s term), others are inscribed in a dignifying discourse. We look at the political implications of this situation.The aim of this article is, on the one hand, to show Franz Joseph Gall as an important figure for setting up the ideological framework for modern biopolitics and, on the other, to look at the literary traces of his personal engagement in this endeavour. In the first part, we place his thought in the ideological context of the 18th and 19th century; the second one analyses the images of the patients created by the author, in order to show their different configurations: while some appear as reduced to the role of homo sacer (Giorgio Agamben’s term), others are inscribed in a dignifying discourse. We look at the political implications of this situation

Lispector y Borges. Los teólogos Clarice Lispector and Jorge Luis Borges. The theologians.

Este artículo constituye un ejercicio de aproximación dialéctica entre Clarice Lispector y Jorge Luis Borges, considerando el contenido filosófico de sus escritos, específicamente en lo referido al cuestionamiento de la subjetividad individual. Las principales diferencias entre los dos autores (lo racional frente a lo intuitivo, la intertextualidad frente a la introspección, la erudición frente al misticismo) se deconstruyen de tal forma que ambos proyectos literarios resultan complementarios o incluso reductibles a un denominador común.

The Timeless Timing Argument and the Mass of the Local Group

The Timing Argument connects the motion of a two-body system to its mass in an expanding Universe with a finite age, under the assumption that it has evolved on a self-gravitating orbit. It is commonly applied to the present-day Milky Way-M31 system in order to infer its unknown mass from the measured kinematics. We use a set of Local Group analogues from the Uchuu simulation to investigate the Timing Argument over cosmic time. We find that the median inferred mass remains almost constant over the past 12 Gyr, even while the haloes themselves grew in mass by more than an order of magnitude. By contrast, we find a closer, and nearly time-invariant agreement between the Timing Argument value and the mass within a sphere of radius equal to the MW-M31 separation, and we identify this as the total mass of the system. We conclude that the comparatively close present-day agreement between the Timing Argument and the sum of the halo masses reflects no underlying relation, but merely echoes the fact that the MW and M31 now contain most (but not all) of the mass of the Local Group system.Comment: 6 pages, 4 figures, this version accepted to MNRAS Letter