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We present a new version of the GalactICS code that can generate self-consistent equilibrium galaxy models with a two-component stellar disc and a gas disc as well as a centrally-concentrated bulge and extended dark halo. The models can serve as initial conditions for simulations of isolated galaxies that include both hydrodynamics and collisionless dynamics. We test the code by evolving a pair of simple gas disc-halo models, which differ only in the initial temperature of the gas component. The models are similar to the ones considered in the Wang et al. except that here, the halo is live whereas they included the halo as a fixed potential. We find that the basic structural properties of the models, such as the rotation curve and surface density profiles, are well-preserved over 1.5 Gyr. We also construct a Milky Way model that includes thin and thick stellar disc components, a gas disc, a bulge, and a dark halo. Bar formation occurs in all disc-like components at about 1 Gyr. The bar is strongest in the thin disc while the gas disc contains the most prominent spiral features. The length of the bar in our model is comparable to what has been inferred for the Galactic bar., Comment: 10 pages, 13 figures, accepted to MNRAS

We present a two-step method to simulate and study non-circular motions in strongly barred galaxies. The first step is to constrain the initial parameters using a Bayesian analysis of each galaxy's azimuthally averaged rotation curve, the 3.6 $\rm \mu m$ surface brightness, and the gas surface density. The second step is to generate equilibrium models using the GalactICS code and evolve them via GADGET-2. The bar strengths and mock velocity maps of the resulting snapshots are compared to observations in order to determine the best representation of the galaxy. We test our method on the unbarred galaxy NGC 3621 and the barred galaxies NGC 1300 and NGC 1530. NGC 3621 provides a validation of our method of generating initial conditions. NGC 1530 has an intermediate bar orientation that allows for a comparison to DiskFit. Finally NGC 1300 has a bar oriented parallel to the galaxy's major axis, where other algorithms tend to fail. Our models for NGC 3621 and NGC 1530 are comparable to those obtained using commonly available algorithms. Moreover, we have produced one of the first mass distribution models for NGC 1300., Comment: 19 pages, 15 figures, 5 tables, accepted for publication in A&A

Galaxy masses play a fundamental role in our understanding of structure formation models. This review addresses the variety and reliability of mass estimators that pertain to stars, gas, and dark matter. The different sections on masses from stellar populations, dynamical masses of gas-rich and gas-poor galaxies, with some attention paid to our Milky Way, and masses from weak and strong lensing methods, all provide review material on galaxy masses in a self-consistent manner., Comment: 145 pages, 28 figures, to appear in Reviews of Modern Physics. Figure 22 is missing here, and Figs. 15, 26-28 are at low resolution. This version has a slightly different title and some typos fixed in Chapter 5. For the full review with figures, please consult: http://www.astro.queensu.ca/~courteau/GalaxyMasses_28apr2014.pdf

Recently, ATIC and PAMELA measured an anomalously large flux of leptonic cosmic rays which may arise from dark matter self-annihilation. While the annihilation signal predicted for a smooth halo is 10^2-10^3 times smaller than the measured excess, the signal can be boosted by the presence of subhalos. We investigate the feasibility of large boost factors using a new Monte Carlo calculation technique that is constrained by previous simulation work on halo substructure. The model accounts for the observed decrease in the amount of substructure with decreasing halo mass and the scatter in halo structural parameters such as the density concentration parameter. Our results suggest that boost factors of the order of 10^2 are ruled out at more than 14 sigma. We conclude that substructure alone, at least with commonly assumed annihilation cross-sections, cannot explain the anomalous flux measured by ATIC and PAMELA., Comment: 6 pages, 2 figures, submitted to Phys Rev D

We explore the dependence of the subhalo mass function on the spectral index n of the linear matter power spectrum using scale-free Einstein-de Sitter simulations with n=-1 and n=-2.5. We carefully consider finite volume effects that may call into question previous simulations of n<-2 power spectra. Subhaloes are found using a 6D friends-of-friends algorithm in all haloes originating from high-sigma peaks. For n=-1, we find that the cumulative subhalo mass function is independent of the parameters used in the subhalo finding algorithm and is consistent with the subhalo mass function found in LCDM simulations. In particular, the subhalo mass function is well fit by a power-law with an index of alpha=-0.9, that is the mass function has roughly equal mass in subhaloes per logarithmic interval in subhalo mass. Conversely, for n=-2.5, the algorithm parameters affect the subhalo mass function since subhaloes are more triaxial with less well defined boundaries. We find that the index alpha is generally larger with alpha>=-0.75. We infer that although the subhalo mass function appears to be independent of n so long as n>=-2, it begins to flatten as n->-3. Thus, the common practice of using alpha=-1.0 may greatly overestimate the number of subhaloes at the smallest scales in the CDM hierarchy., Comment: 13 pages, 8 figures, to be published in MNRAS

In the cold dark matter model of structure formation, galaxies are assembled hierarchically from mergers and the accretion of subclumps. This process is expected to leave residual substructure in the Galactic dark halo, including partially disrupted clumps and their associated tidal debris. We develop a model for such halo substructure and study its implications for dark matter (WIMP and axion) detection experiments. We combine the Press-Schechter model for the distribution of halo subclump masses with N-body simulations of the evolution and disruption of individual clumps as they orbit through the evolving Galaxy to derive the probability that the Earth is passing through a subclump or stream of a given density. Our results suggest that it is likely that the local complement of dark matter particles includes a 1-5% contribution from a single clump. The implications for dark matter detection experiments are significant, since the disrupted clump is composed of a `cold' flow of high-velocity particles. We describe the distinctive features due to halo clumps that would be seen in the energy and angular spectra of detection experiments. The annual modulation of these features would have a different signature and phase from that for a smooth halo and, in principle, would allow one to discern the direction of motion of the clump relative to the Galactic center., Comment: 26 pages, 18 figures