ORCID Profile
0000-0002-1975-4449
Current Organisations
University of Canterbury
,
Simons Foundation
,
George Mason University
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Publisher: American Meteorological Society
Date: 2016
DOI: 10.1175/WCAS-D-14-00037.1
Abstract: Research on adaptive capacity often focuses on economics and technology, despite evidence from the social sciences finding that socially shared beliefs, norms, and networks are critical in increasing in iduals’ and communities’ adaptive capacity. Drawing upon social cognitive theory, this paper builds on the first author’s Ph.D. dissertation and examines the role of collective efficacy—people’s shared beliefs about their group’s capabilities to accomplish collective tasks—in influencing Indians’ capacity to adapt to drinking water scarcity, a condition likely to be exacerbated by future climate change. Using data from a national survey (N = 4031), in iduals with robust collective efficacy beliefs were found to be more likely to participate in community activities intended to ensure the adequacy of water supplies, and this relationship was found to be stronger in communities with high levels of community collective efficacy compared to communities with low levels of community collective efficacy. In addition, community collective efficacy was positively associated with self-reported community adaptation responses. Public education c aigns aimed at increasing collective efficacy beliefs are likely to increase adaptive capacity.
Publisher: Oxford University Press (OUP)
Date: 26-03-2021
Abstract: In addition to the well-known gas phase mass–metallicity relation (MZR), recent spatially resolved observations have shown that local galaxies also obey a mass–metallicity gradient relation (MZGR), whereby metallicity gradients can vary systematically with galaxy mass. In this work, we use our recently developed analytic model for metallicity distributions in galactic discs, which includes a wide range of physical processes – radial advection, metal diffusion, cosmological accretion, and metal-enriched outflows – to simultaneously analyse the MZR and MZGR. We show that the same physical principles govern the shape of both: centrally peaked metal production favours steeper gradients, and this steepening is diluted by the addition of metal-poor gas, which is supplied by inward advection for low-mass galaxies and by cosmological accretion for massive galaxies. The MZR and the MZGR both bend at galaxy stellar mass $\\sim 10^{10}{-}10^{10.5}\\, \\rm {M_{\\odot }}$, and we show that this feature corresponds to the transition of galaxies from the advection-dominated to the accretion-dominated regime. We also find that both the MZR and MZGR strongly suggest that low-mass galaxies preferentially lose metals entrained in their galactic winds. While this metal-enrichment of the galactic outflows is crucial for reproducing both the MZR and the MZGR at the low-mass end, we show that the flattening of gradients in massive galaxies is expected regardless of the nature of their winds.
Publisher: Elsevier BV
Date: 08-2006
Publisher: American Astronomical Society
Date: 05-2023
Abstract: The driving of turbulence in galaxies is deeply connected with the physics of feedback, star formation, outflows, accretion, and radial transport in disks. The velocity dispersion of gas in galaxies therefore offers a promising observational window into these processes. However, the relative importance of each of these mechanisms remains controversial. In this work we revisit the possibility that turbulence on galactic scales is driven by the direct impact of accreting gaseous material on the disk. We measure this effect in a disk-like star-forming galaxy in IllustrisTNG, using the high-resolution cosmological magnetohydrodynamical simulation TNG50. We employ Lagrangian tracer particles with a high time cadence of only a few million years to identify accretion and other events. The energies of particles are measured by stacking the events in bins of time around the event. The average effect of each event is measured by fitting explicit models for the kinetic and turbulent energies as a function of time. These measurements are corroborated by cross-correlating the turbulent energy with other time series and searching for signals of causality, i.e., asymmetries across zero time lag. We find that accretion contributes to the large-scale turbulent kinetic energy even if it does not dominate in this ∼5 × 10 9 M ⊙ stellar mass galaxy. Extrapolating this finding to a range of galaxy masses, we find that there are regimes where energy from direct accretion may dominate the turbulent energy budget, particularly in disk outskirts, galaxies less massive than the Milky Way, and at redshift ∼2.
Publisher: Springer Science and Business Media LLC
Date: 27-06-2016
DOI: 10.1038/NATURE18292
Abstract: Photoelectric heating--heating of dust grains by far-ultraviolet photons--has long been recognized as the primary source of heating for the neutral interstellar medium. Simulations of spiral galaxies have shown some indication that photoelectric heating could suppress star formation however, simulations that include photoelectric heating have typically shown that it has little effect on the rate of star formation in either spiral galaxies or dwarf galaxies, which suggests that supernovae are responsible for setting the gas depletion time in galaxies. This result is in contrast with recent work indicating that a star formation law that depends on galaxy metallicity--as is expected with photoelectric heating,but not with supernovae--reproduces the present-day galaxy population better than does a metallicity-independent one. Here we report a series of simulations of dwarf galaxies, the class of galaxy in which the effects of both photoelectric heating and supernovae are expected to be strongest. We simultaneously include space and time-dependent photoelectric heating in our simulations, and we resolve the energy-conserving phase of every supernova blast wave, which allows us to directly measure the relative importance of feedback by supernovae and photoelectric heating in suppressing star formation. We find that supernovae are unable to account for the observed large gas depletion times in dwarf galaxies. Instead, photoelectric heating is the dominant means by which dwarf galaxies regulate their star formation rate at any given time,suppressing the rate by more than an order of magnitude relative to simulations with only supernovae.
Publisher: American Astronomical Society
Date: 05-07-2012
Publisher: Oxford University Press (OUP)
Date: 29-01-2021
Abstract: We present a new model for the evolution of gas phase metallicity gradients in galaxies from first principles. We show that metallicity gradients depend on four ratios that collectively describe the metal equilibration time-scale, production, transport, consumption, and loss. Our model finds that most galaxy metallicity gradients are in equilibrium at all redshifts. When normalized by metal diffusion, metallicity gradients are governed by the competition between radial advection, metal production, and accretion of metal-poor gas from the cosmic web. The model naturally explains the varying gradients measured in local spirals, local dwarfs, and high-redshift star-forming galaxies. We use the model to study the cosmic evolution of gradients across redshift, showing that the gradient in Milky Way-like galaxies has steepened over time, in good agreement with both observations and simulations. We also predict the evolution of metallicity gradients with redshift in galaxy s les constructed using both matched stellar masses and matched abundances. Our model shows that massive galaxies transition from the advection-dominated to the accretion-dominated regime from high to low redshifts, which mirrors the transition from gravity-driven to star formation feedback-driven turbulence. Lastly, we show that gradients in local ultraluminous infrared galaxies (major mergers) and inverted gradients seen both in the local and high-redshift galaxies may not be in equilibrium. In subsequent papers in this series, we show that the model also explains the observed relationship between galaxy mass and metallicity gradients, and between metallicity gradients and galaxy kinematics.
Publisher: Oxford University Press (OUP)
Date: 09-07-2014
Publisher: Oxford University Press (OUP)
Date: 21-12-2013
Publisher: Springer Science and Business Media LLC
Date: 20-11-2011
DOI: 10.1038/NCLIMATE1295
Publisher: Oxford University Press (OUP)
Date: 10-06-2019
Abstract: We present a flexible, detailed model for the evolution of galactic discs in a cosmological context since z ≈ 4, including a physically motivated model for radial transport of gas and stars within galactic discs. This expansion beyond traditional semi-analytic models that do not include radial structure, or include only a prescribed radial structure, enables us to study the internal structure of disc galaxies and the processes that drive it. In order to efficiently explore the large parameter space allowed by this model, we construct a neural-network-based emulator that can quickly return a reasonable approximation for many observables we can extract from the model, e.g. the star formation rate or the half-mass stellar radius, at different redshifts. We employ the emulator to constrain the model parameters with Bayesian inference by comparing its predictions to 11 observed galaxy scaling relations at a variety of redshifts. The constrained models agree well with observations, both those used to fit the data and those not included in the fitting procedure. These models will be useful theoretical tools for understanding the increasingly detailed observational data sets from Integral Field Units (IFUs).
Location: United States of America
No related grants have been discovered for John Forbes.