Accretion Disc Particle Accretion in Major Merger Simulations

A recent approach to simulating localized feedback from active galactic nuclei by Power et al. (2011) uses an accretion disc particle to represent both the black hole and its accretion disc. We have extrapolated and adapted this approach to simulations of Milky Way-sized galaxy mergers containing black holes and explored the impact of the various parameters in this model as well as its resolution dependence. The two key parameters in the model are an effective accretion radius, which determines the radius within which gas particles are added to the accretion disc, and a viscous time-scale which determines how long it takes for material in the accretion disc to accrete on to the black hole itself. We find that there is a limited range of permitted accretion radii and viscous time-scales, with unphysical results produced outside this range. For permitted model parameters, the nuclear regions of simulations with the same resolution follow similar evolutionary paths, producing final black hole masses that are consistent within a factor of two. When comparing the resolution dependence of the model, there is a trend towards higher resolution producing slightly lower mass black holes, but values for the two resolutions studied again agree within a factor of two. We also compare these results to two other AGN feedback algorithms found in the literature. While the evolution of the systems vary, most notably the intermediate total black hole mass, the final black hole masses differ by less than a factor of five amongst all of our models, and the remnants exhibit similar structural parameters. The implication of this accretion model is that, unlike most accretion algorithms, a decoupling of the accretion rate on to the black hole and the local gas properties is permitted and obtained; this allows for black hole growth even after feedback has prevented additional accretion events on to the disc.Comment: 17 pages, accepted to MNRA

On the Spatial Correlations of Lyman Break Galaxies

Motivated by the observed discrepancy between the strong spatial correlations of Lyman break galaxies (LBGs) and their velocity dispersions, we consider a theoretical model in which these starbursting galaxies are associated with dark matter halos that experience appreciable infall of material. We show using numerical simulation that selecting halos that substantially increase in mass within a fixed time interval introduces a ``temporal bias'' which boosts their clustering above that of the underlying population. If time intervals consistent with the observed LBGs star formation rates of 50 solar masses per year are chosen, then spatial correlations are enhanced by up to a factor of two. These values roughly correspond to the geometrical bias of objects three times as massive. Thus, it is clear that temporal biasing must be taken into account when interpreting the properties of Lyman break galaxies.Comment: 5 Pages, 2 Figures, Accepted for Publication in ApJ Letter

AGN Feedback models: Correlations with star formation and observational implications of time evolution

We examine the correlation between the star formation rate (SFR) and black hole accretion rate (BHAR) across a suite of different AGN feedback models, using the time evolution of a merger simulation. By considering three different stages of evolution, and a distinction between the nuclear and outer regions of star formation, we consider 63 different cases. Despite many of the feedback models fitting the M-\sigma\ relationship well, there are often distinct differences in the SFR-BHAR correlations, with close to linear trends only being present after the merger. Some of the models also show evolution in the SFR-BHAR parameter space that is at times directly across the long-term averaged SFR-BHAR correlation. This suggests that the observational SFR-BHAR correlation found for ensembles of galaxies is an approximate statistical trend, as suggested by Hickox et al. Decomposing the SFR into nuclear and outer components also highlights notable differences between models and there is only modest agreement with observational studies examining this in Seyfert galaxies. For the fraction of the black hole mass growth from the merger event relative to the final black hole mass, we find as much as a factor of three variation among models. This also translates into a similar variation in the post-starburst black hole mass growth. Overall, we find that while qualitative features are often similar amongst models, precise quantitative analysis shows there can be quite distinct differences.Comment: Accepted to MNRAS. Comments welcom

Does suspicion of motives mediate the relationship between social exclusion and smile discrimination? : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Psychology at Massey University, Manawatu, New Zealand

Individuals who are socially excluded or suspicious of other’s motives show increased sensitivity to social cues signalling positive affect. Facial expressions such as smiles are cues that signal affiliative intent. They may occur in the presence or absence of positive felt emotion, creating uncertainty for perceivers about affiliative motives underlying the expression. Excluded or suspicious individuals are better able to determine authenticity of such expressions and use the information to guide their social interactions with others. Despite shared theoretical frameworks, no research has examined a potential relationship between social exclusion and suspicion of motives themselves. Sample frames used have also lacked cultural diversity, inhibiting ability to generalise findings beyond Western European or American populations. The current study seeks to address both issues. This study predicted that feelings of social exclusion would make a person more suspicious of others’ social motives and that changes in levels of suspicion would mediate the relationship between a person’s feelings of exclusion and their ability to differentiate the social content of smiles. One hundred and eleven students of East and Southeast Asian origin, aged 18 to 50 years, were recruited to participate in the study from Massey University in Palmerston North, New Zealand. They completed an online survey where they were randomly assigned to one of two experimental social pain conditions (exclusion or inclusion). Cyberball was used to manipulate feelings of social pain, before participants were administered the Suspicion of Motive Index, a smile discrimination task, and the Needs Threat Scale. Results indicated that Cyberball reliably elicited feelings of exclusion and inclusion but found no significant evidence to support the hypothesised relationships between social exclusion, suspicion of motive and smile discrimination. The findings indicate that effects measured in previous research cannot be generalised to the present sample frame in the New Zealand context. The current study raises questions about the theoretical and methodological universality of the constructs and how they may be influenced by underlying cultural differences in intergroup relations, situational context, emotion expression, perception and recognition