K+A Galaxies as the Aftermath of Gas-Rich Mergers: Simulating the Evolution of Galaxies as Seen by Spectroscopic Surveys

Models of poststarburst (or "K+A") galaxies are constructed by combining fully three-dimensional hydrodynamic simulations of galaxy mergers with radiative transfer calculations of dust attenuation. Spectral line catalogs are generated automatically from moderate-resolution optical spectra calculated as a function of merger progress in each of a large suite of simulations. The mass, gas fraction, orbital parameters, and mass ratio of the merging galaxies are varied systematically, showing that the lifetime and properties of the K+A phase are strong functions of merger scenario. K+A durations are generally less than ~0.1-0.3 Gyr, significantly shorter than the commonly assumed 1 Gyr, which is obtained only in rare cases, owing to a wide variation in star formation histories resulting from different orbital and progenitor configurations. Combined with empirical merger rates, the model lifetimes predict rapidly-rising K+A fractions as a function of redshift that are consistent with results of large spectroscopic surveys, resolving tension between the observed K+A abundance and that predicted when one assumes the K+A duration is the lifetime of A stars (~1 Gyr). The effects of dust attenuation, viewing angle, and aperture bias on our models are analyzed. In some cases, the K+A features are longer-lived and more pronounced when AGN feedback removes dust from the center, uncovering the young stars formed during the burst. In this picture, the K+A phase begins during or shortly after the bright starburst/AGN phase in violent mergers, and thus offers a unique opportunity to study the effects of quasar and star formation feedback on the gas reservoir and evolution of the remnant. Analytic fitting formulae are provided for the estimates of K+A incidence as a function of merger scenario.Comment: 26 pages, 13 figures; ApJ; minor changes to reflect accepted versio

Quasars Are Not Light-Bulbs: Testing Models of Quasar Lifetimes with the Observed Eddington Ratio Distribution

We use the observed distribution of Eddington ratios as a function of supermassive black hole (BH) mass to constrain models of AGN lifetimes and lightcurves. Given the observed AGN luminosity function, a model for AGN lifetimes (time above a given luminosity) translates directly to a predicted Eddington ratio distribution. Models for self-regulated BH growth, in which feedback produces a 'blowout' decay phase after some peak luminosity (shutting down accretion) make specific predictions for the lifetimes distinct from those expected if AGN are simply gas starved (without feedback) and very different from simple phenomenological 'light bulb' models. Present observations of the Eddington ratio distribution, spanning 5 decades in Eddington ratio, 3 in BH mass, and redshifts z=0-1, agree with the predictions of self-regulated models, and rule out 'light-bulb', pure exponential, and gas starvation models at high significance. We compare the Eddington ratio distributions at fixed BH mass and fixed luminosity (both are consistent, but the latter are much less constraining). We present empirical fits to the lifetime distribution and show how the Eddington ratio distributions place tight limits on AGN lifetimes at various luminosities. We use this to constrain the shape of the typical AGN lightcurve, and provide simple analytic fits. Given independent constraints on episodic lifetimes, most local BHs must have gained their mass in no more than a couple of bright episodes, in agreement with merger-driven fueling models.Comment: 21 pages, 13 figures, accepted to ApJ (revised to match accepted version; modeling and tests of redshift evolution added

September 11: Symbolism And Responses To 9/11

Professors Hopkins and Hopkins review the impact of 9/11 as a symbol in American politics. Following the terrorist attacks, 9/11 became a simple reference condensing wide-ranging events and emotions. Various interpretations emerged about what caused 9/11 and enabled the attacks. The authors claim that 9/11 allowed US leaders to pursue certain policy prescriptions that otherwise would have been blocked. Among four possible prescriptions for responding to the attacks, the Bush administration chose a praetorian policy of preventive war, with Iraq as its first example. In the authors’ view, by pursuing an expansive but highly militarized response, the US has overlooked the need to alleviate the conditions that made 9/11 possible. The authors recommend that the US, as part of a multilateral effort, allocate major resources to expanding global public goods, including measures that strengthen barriers to proliferation, enhance fighting of global crime, and reduce incentives for terrorism, especially ones arising in failing states where distorted education and weak protection of human rights encourage organized terrorism

The Spectator in the Picture

This paper considers whether pictures ever implicitly represent internal spectators of the scenes they depict, and what theoretical construal to offer of their doing so. Richard Wollheim's discussion (Painting as an Art, ch.3) is taken as the most sophisticated attempt to answer these questions. I argue that Wollheim does not provide convincing argument for his claim that some pictures implicitly represent an internal spectator with whom the viewer of the picture is to imaginatively identify. instead, I defend a view on which the external spectator simply imagines herself interacting, psychologically and otherwise, with the depicted scene. I explore some of the consequences of the two positions for pictorial aesthetics, arguing that the view I favour is at least as competent as Wollheim's at accommodating those phenomena we have any reason to think hold

Sculpture and Space

What is distinctive about sculpture as an artform? I argue that it is related to the space around it as painting and the other pictorial arts are not. I expound and develop Langer's suggestive comments on this issue, before asking what the major strengths and weaknesses of that position might be

The effect of public communication campaigns on family communication and behaviour : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Business Studies in Communication Management at Massey University

This thesis examines how mass communicated messages from a public communication campaign affect interpersonal communication within families. It also considers how interpersonal communication among family members flows on to affect behaviours in the family. The study uses McDevitt and Chaffee's five-stage sequence of behavioural activation within families to examine two pro-environmental campaigns: the Big Clean Up and Clean Up NZ. Seven families exposed to the messages of the communication campaigns were interviewed to gain an understanding of what communication process occurred as a result of these interventions. "Downward" (parent to child), and "upward" (child to parent) flows of communication were examined. The results suggest that communication among family members has a substantial bearing on a family's behavioural response to campaign messages. However, the person who engenders the discussions also plays a major role in the success or otherwise of the communication outcomes. The campaign messages had different effects on children than they did on parents. There were no significant behaviour changes in families where the parent was the initial message receiver; however where the child provided the initial intervention behaviour changes tended to occur. While children received new information, and developed new behaviours based on the campaign messages, parents tended to have existing beliefs and patterns of behaviour endorsed. The relationship between interpersonal family communication, campaign messages and changes in behaviour has implications for communicators developing campaigns that aim to change behaviour