Vast planes of satellites in a high resolution simulation of the Local Group: comparison to Andromeda

We search for vast planes of satellites (VPoS) in a high resolution simulation of the Local Group performed by the CLUES project, which improves significantly the resolution of former similar studies. We use a simple method for detecting planar configurations of satellites, and validate it on the known plane of M31. We implement a range of prescriptions for modelling the satellite populations, roughly reproducing the variety of recipes used in the literature, and investigate the occurence and properties of planar structures in these populations. The structure of the simulated satellite systems is strongly non-random and contains planes of satellites, predominantly co-rotating, with, in some cases, sizes comparable to the plane observed in M31 by Ibata et al.. However the latter is slightly richer in satellites, slightly thinner and has stronger co-rotation, which makes it stand out as overall more exceptional than the simulated planes, when compared to a random population. Although the simulated planes we find are generally dominated by one real structure, forming its backbone, they are also partly fortuitous and are thus not kinematically coherent structures as a whole. Provided that the simulated and observed planes of satellites are indeed of the same nature, our results suggest that the VPoS of M31 is not a coherent disc and that one third to one half of its satellites must have large proper motions perpendicular to the plane

High resolution simulations of the reionization of an isolated Milky Way - M31 galaxy pair

We present the results of a set of numerical simulations aimed at studying reionization at galactic scale. We use a high resolution simulation of the formation of the Milky Way-M31 system to simulate the reionization of the local group. The reionization calculation was performed with the post-processing radiative transfer code ATON and the underlying cosmological simulation was performed as part of the CLUES project. We vary the source models to bracket the range of source properties used in the literature. We investigate the structure and propagation of the galatic ionization fronts by a visual examination of our reionization maps. Within the progenitors we find that reionization is patchy, and proceeds locally inside out. The process becomes patchier with decreasing source photon output. It is generally dominated by one major HII region and 1-4 additional isolated smaller bubbles, which eventually overlap. Higher emissivity results in faster and earlier local reionization. In all models, the reionization of the Milky Way and M31 are similar in duration, i.e. between 203 Myr and 22 Myr depending on the source model, placing their zreion between 8.4 and 13.7. In all models except the most extreme, the MW and M31 progenitors reionize internally, ignoring each other, despite being relatively close to each other even during the epoch of reionization. Only in the case of strong supernova feedback suppressing star formation in haloes less massive than 10^9 M_sun, and using our highest emissivity, we find that the MW is reionized by M31.Comment: Accepted for publication in ApJ. 14 pages, 4 figures, 1 tabl

Breaking Boundaries in Computing in Undergraduate Courses

An important question in undergraduate curricula is that of incorporating computing into STEM courses for majors and non-majors alike. What does it mean to teach “computing” in this context? What are some of the benefits and challenges for students and instructors in such courses? This paper contributes to this important dialog by describing three undergraduate courses that have been developed and taught at Harvey Mudd College and Loyola Marymount University. Each case study describes the course objectives, implementation challenges, and assessments

The orbital poles of Milky Way satellite galaxies: a rotationally supported disc-of-satellites

Available proper motion measurements of Milky Way (MW) satellite galaxies are used to calculate their orbital poles and projected uncertainties. These are compared to a set of recent cold dark-matter (CDM) simulations, tailored specifically to solve the MW satellite problem. We show that the CDM satellite orbital poles are fully consistent with being drawn from a random distribution, while the MW satellite orbital poles indicate that the disc-of-satellites of the Milky Way is rotationally supported. Furthermore, the bootstrapping analysis of the spatial distribution of theoretical CDM satellites also shows that they are consistent with being randomly drawn. The theoretical CDM satellite population thus shows a significantly different orbital and spatial distribution than the MW satellites, most probably indicating that the majority of the latter are of tidal origin rather than being DM dominated sub-structures. A statistic is presented that can be used to test a possible correlation of satellite galaxy orbits with their spatial distribution.Comment: Accepted for publication in Ap

Galaxy subgroups in galaxy clusters

Galaxies which fall into clusters as part of the same infall halo can retain correlations due to their shared origin. N-body simulations are used to study properties of such galaxy subgroups within clusters, including their richnesses and prevalence. The sizes, densities and velocity dispersions of all subgroups with >= 8 galaxies are found and compared to those of the host clusters. The largest galaxy subgroup provides a preferred direction in the cluster and is compared to other preferred directions in the cluster. Scatter in cluster mass measurements (via five observables), along ~ 96 lines of sight, is compared to the relation of the line of sight to this preferred direction: scatter in cluster velocity dispersion measurements show the strongest correlation. The Dressler-Shectman test (Dressler & Shectman 1988), is applied to these clusters, to see whether the substructure it identifies is related to these subgroups. The results for any specific line of sight seem noisy; however, clusters with large subgroups tend to have a higher fraction of lines of sight where the test detects substructure.Comment: 12 pages, final version for publication with helpful comments from referee and others include

Bayesian physical reconstruction of initial conditions from large scale structure surveys

We present a fully probabilistic, physical model of the non-linearly evolved density field, as probed by realistic galaxy surveys. Our model is valid in the linear and mildly non-linear regimes and uses second order Lagrangian perturbation theory to connect the initial conditions with the final density field. Our parameter space consists of the 3D initial density field and our method allows a fully Bayesian exploration of the sets of initial conditions that are consistent with the galaxy distribution sampling the final density field. A natural byproduct of this technique is an optimal non-linear reconstruction of the present density and velocity fields, including a full propagation of the observational uncertainties. A test of these methods on simulated data mimicking the survey mask, selection function and galaxy number of the SDSS DR7 main sample shows that this physical model gives accurate reconstructions of the underlying present-day density and velocity fields on scales larger than ~6 Mpc/h. Our method naturally and accurately reconstructs non-linear features corresponding to three-point and higher order correlation functions such as walls and filaments. Simple tests of the reconstructed initial conditions show statistical consistency with the Gaussian simulation inputs. Our test demonstrates that statistical approaches based on physical models of the large scale structure distribution are now becoming feasible for realistic current and future surveys.Comment: 20 pages, 8 figure

Cosmic queuing: galaxy satellites, building blocks and the hierarchical clustering paradigm

We study the properties of building blocks (BBs, i.e. accreted satellites) and surviving satellites of present-day galaxies using the SAG semi-analytic model of galaxy formation in the context of a concordance Lambda Cold Dark Matter (LCDM) cosmology. We consider large numbers of DM halo merger trees spanning a wide range of masses (~1x10^10 - 2.14x10^15 Msun). We find higher metallicities for BBs with respect to surviving satellites, an effect produced by the same processes behind the build-up of the mass-metallicity relation. We prove that these metallicity differences arise from the higher peak height in the density fluctuation field occupied by BBs and central galaxies which have collapsed into a single object earlier than surviving satellites. BBs start to form stars earlier, during the peak of the merger activity in LCDM, and build-up half of their final stellar mass (measured at the moment of disruption) up to four times faster than surviving satellites. Surviving satellites keep increasing their stellar masses rather quiescently down to z~1. The difference between the metallicities of satellites, BBs and central galaxies depends on the host DM halo mass, in a way that can be used as a further test for the concordance cosmology.Comment: 5 pages, 4 figures. Accepted for publication in MNRAS Letter