NGC 147, NGC 185 and CassII: a genetic approach to orbital properties, star formation and tidal debris

NGC147, NGC185 and CassiopeiaII (CassII) have similar positions in the sky, distances and measured line of sight velocities. This proximity in phase space suggests that these three satellites of M31 form a subgroup within the Local Group. Nevertheless, the differences in their star formation history and interstellar medium, and the recent discovery of a stellar stream in NGC~147, combined with the lack of tidal features in the other two satellites, are all indications of complex and diverse interactions between M31 and these three satellites. We use a genetic algorithm to explore the different orbits that these satellites can have and select six sets of orbits that could best explain the observational features of the NGC147, NGC185 and CassII satellites. The parameters of these orbits are then used as a starting point for N-body simulations. We present models for which NGC147, NGC185 and CassII are a bound group for a total time of at least one Gyr but still undergo different interactions with M31 and as a result NGC147 has a clear stellar stream whereas the other two satellites have no significant tidal features. This result shows that it is possible to find solutions that reproduce the contrasting properties of the satellites and for which NGC147-NGC185-CassII have been gravitationally bound.Comment: Accepted for publication on MNRAS. 12 pages, 9 figure

The Dynamics of Satellite Galaxy Planes

First created to explain the discrepancies between the predictions and observations, dark matter makes up around 25% of the universe’s energy budget. Λ Cold Dark Matter (ΛCDM) cosmology accurately represents the large scale structure of the current universe, but shows significant variation in the small ℨscale structure. The recently discovered planes of dwarf satellite galaxies orbiting the Milky Way and M31 adds to the mystery of the small scale distribution of the Local Group. Though similar planar structures are seemingly rare occurrences in ΛCDM cosmological simulations, they could shed light on the dark matter environment of their host galaxies. This thesis explores the factors that affect the stability and longevity of a plane of satellite galaxies in a M31-like system, with numerical simulations. The most influential factors are the shape of the host dark matter distribution, and the plane’s inclination to the axes of the dark halo. For the M31 plane to be older than 4 Gyrs, it either needs to exist in a near spherical dark halo, or be aligned with the dark halo axes. Lifetimes of planar formations inclined to the halo axes, in a prolate/ oblate halo are limited to ≤3 Gyrs, and a populous environment of dark subhalos disperse the planar formation by increasing its thickness over 3 Gyrs. As the fraction of total dark matter mass that is included in the subhalo population reaches ∼40%, the overall shape of the dark matter distribution also becomes unstable over ≥5 Gyrs. Massive, non-planar, interloping galaxies have a notable effect on planes only when their mass is ≥ 1010 M, and any orbital plane misalignments exaggerate this effect. The shape of the M31 host halo also exerts a significant influence on the orbit of M33. In conclusion, planes of satellites are generally short lived in ΛCDM cosmology, and hence we must be located at a special time in the evolution of the M31 plane, and are lucky enough to see its coherent pattern

Stability of Satellite Planes in M31 II: Effects of the Dark Subhalo Population

International audienceThe planar arrangement of nearly half the satellite galaxies of M31 has been a source of mystery and speculation since it was discovered. With a growing number of other host galaxies showing these satellite galaxy planes, their stability and longevity have become central to the debate on whether the presence of satellite planes are a natural consequence of prevailing cosmological models, or represent a challenge. Given the dependence of their stability on host halo shape, we look into how a galaxy plane's dark matter environment influences its longevity. An increased number of dark matter subhaloes results in increased interactions that hasten the deterioration of an already-formed plane of satellite galaxies in spherical dark haloes. The role of total dark matter mass fraction held in subhaloes in dispersing a plane of galaxies presents non-trivial effects on plane longevity as well. But any misalignment of plane inclines to major axes of flattened dark matter haloes lead to their lifetimes being reduced to ≤3 Gyr. Distributing ≥40 per cent of total dark mass in subhaloes in the overall dark matter distribution results in a plane of satellite galaxies which is prone to change through the 5-Gyr integration time period

CodePlex: Software Complexity Measuring Tool based on ECB Measure

The surge in popularity of object-oriented programming as a predominant paradigm in software development has spurred numerous studies to introduce metrics for assessing the complexity of object-oriented programs. These metrics typically fall into two primary categories: those focusing on object-oriented aspects and those centered on cognitive aspects, delineating their principal areas of concern when evaluating program complexity. Within the realm of cognitive aspects, the majority of metrics have historically been confined to the consideration of no more than three complexity variables. However, the ECB (Enhanced Cognitive Based) measure stands as a notable exception, capable of encompassing and addressing four or more intricate facets in the assessment of software program intricacy and difficulty. This research paper undertakes the exploration of the incorporation of these multidimensional metrics as refinements to the existing weighted composite complexity CB measure, originally introduced by Chhillar and Bhasin. In doing so, it endeavors to furnish a more comprehensive and holistic framework for the evaluation of program complexity, accommodating both object-oriented and cognitive dimensions. Furthermore, the study assumes the pivotal role of empirically validating the practical effectiveness of the ECB measure, seeking to bridge the chasm between theoretical metrics and their tangible applicability in real-world settings. Such an endeavor holds profound significance for software developers and researchers, proffering invaluable insights that can advance our understanding and management of intricate object-oriented programs