The Galactic Bar

The Milky Way's bar dominates the orbits of stars and the flow of cold gas in the inner Galaxy, and is therefore of major importance for Milky Way dynamical studies in the Gaia era. Here we discuss the pronounced peanut shape of the Galactic bulge that has resulted from recent star count analysis, in particular from the VVV survey. We also discuss the question whether the Milky Way has an inner disky pseudo-bulge, and show preliminary evidence for a continuous transition in vertical scale-height from the peanut bulge-bar to the planar long bar.Comment: Invited talk, 10pp, 4 figures. To be published in "Lessons from the Local Group - a conference in honour of David Block and Bruce Elmegreen", May 2014, eds. Freeman, K.C., Elmegreen, B.G., Block, D.L. and Woolway, M. (SPRINGER: NEW YORK

The Structure of the Milky Way's Bar Outside the Bulge

While it is incontrovertible that the inner Galaxy contains a bar, its structure near the Galactic plane has remained uncertain, where extinction from intervening dust is greatest. We investigate here the Galactic bar outside the bulge, the long bar, using red clump giant (RCG) stars from UKIDSS, 2MASS, VVV, and GLIMPSE. We match and combine these surveys to investigate a wide area in latitude and longitude, |b|<9deg and |l|<40deg. We find: (1) The bar extends to l~25deg at |b|~5deg from the Galactic plane, and to l~30deg at lower latitudes. (2) The long bar has an angle to the line-of-sight in the range (28-33)deg, consistent with studies of the bulge at |l|<10deg. (3) The scale-height of RCG stars smoothly transitions from the bulge to the thinner long bar. (4) There is evidence for two scale heights in the long bar. We find a ~180pc thin bar component reminiscent of the old thin disk near the sun, and a ~45pc super-thin bar component which exists predominantly towards the bar end. (5) Constructing parametric models for the RC magnitude distributions, we find a bar half length of 5.0+-0.2kpc for the 2-component bar, and 4.6+-0.3kpc for the thin bar component alone. We conclude that the Milky Way contains a central box/peanut bulge which is the vertical extension of a longer, flatter bar, similar as seen in both external galaxies and N-body models.Comment: Accepted for publication by MNRA

The Initial Mass Function of the Inner Galaxy Measured From OGLE-III Microlensing Timescales

We use the timescale distribution of ~3000 microlensing events measured by the OGLE-III survey, together with accurate new made-to-measure dynamical models of the Galactic bulge/bar region, to measure the IMF in the inner Milky Way. The timescale of each event depends on the mass of the lensing object, together with the relative distances and velocities of the lens and source. The dynamical model provides statistically these distances and velocities allowing us to constrain the lens mass function, and from this to infer the IMF. Parameterising the IMF as a broken power-law, we find slopes in the main sequence $\alpha_{\rm ms}=1.31\pm0.10|_{\rm stat}\pm0.10|_{\rm sys}$ and brown dwarf region $\alpha_{\rm bd}=-0.7\pm0.9|_{\rm stat}\pm0.8|_{\rm sys}$ where we use a fiducial 50% binary fraction, and the systematic uncertainty covers the range of binary fractions 0-100%. Similarly for a log-normal IMF we conclude $M_c=(0.17\pm0.02|_{\rm stat}\pm0.01|_{\rm sys})M_\odot$ and $\sigma_m=0.49\pm0.07|_{\rm stat}\pm0.06|_{\rm sys}$. These values are very similar to a Kroupa or Chabrier IMF respectively, showing that the IMF in the bulge is indistinguishable from that measured locally, despite the lenses lying in the inner Milky Way where the stars are mostly ~10Gyr old and formed on a fast $\alpha$-element enhanced timescale. This therefore constrains models of IMF variation that depend on the properties of the collapsing gas cloud.Comment: 6 pages, 3 figures. Accepted by ApJ

MOA-II Galactic Microlensing Constraints: The Inner Milky Way has a Low Dark Matter Fraction and a Near Maximal Disk

Microlensing provides a unique tool to break the stellar to dark matter degeneracy in the inner Milky Way. We combine N-body dynamical models fitted to the Milky Way's Boxy/Peanut bulge with exponential disk models outside this, and compute the microlensing properties. Considering the range of models consistent with the revised MOA-II data, we find low dark matter fractions in the inner Galaxy: at the peak of their stellar rotation curve a fraction $f_v=(0.88\pm0.07)$ of the circular velocity is baryonic (at $1\sigma$, $f_v > 0.72$ at $2\sigma$). These results are in agreement with constraints from the EROS-II microlensing survey of brighter resolved stars, where we find $f_v=(0.9\pm0.1)$ at $1\sigma$. Our fiducial model of a disk with scale length 2.6kpc, and a bulge with a low dark matter fraction of 12%, agrees with both the revised MOA-II and EROS-II microlensing data. The required baryonic fractions, and the resultant low contribution from dark matter, are consistent with the NFW profiles produced by dissipationless cosmological simulations in Milky Way mass galaxies. They are also consistent with recent prescriptions for the mild adiabatic contraction of Milky Way mass haloes without the need for strong feedback, but there is some tension with recent measurements of the local dark matter density. Microlensing optical depths from the larger OGLE-III sample could improve these constraints further when available.Comment: 14 pages, 13 figures, submitted to MNRA

Pseudo-Newtonian Potentials for Nearly Parabolic Orbits

We describe a pseudo-Newtonian potential which, to within 1% error at all angular momenta, reproduces the precession due to general relativity of particles whose specific orbital energy is small compared to c^2 in the Schwarzschild metric. For bound orbits the constraint of low energy is equivalent to requiring the apoapsis of a particle to be large compared to the Schwarzschild radius. Such low energy orbits are ubiquitous close to supermassive black holes in galactic nuclei, but the potential is relevant in any context containing particles on low energy orbits. Like the more complex post-Newtonian expressions, the potential correctly reproduces the precession in the far-field, but also correctly reproduces the position and magnitude of the logarithmic divergence in precession for low angular momentum orbits. An additional advantage lies in its simplicity, both in computation and implementation. We also provide two simpler, but less accurate potentials, for cases where orbits always remain at large angular momenta, or when the extra accuracy is not needed. In all of the presented cases the accuracy in precession in low energy orbits exceeds that of the well known potential of Paczynski & Wiita (1980), which has ~30% error in the precession at all angular momenta.Comment: 4 pages, 1 figure. Accepted by Ap

Just Biofuels? Mapping dimensions of energy justice in relation to an international liquid biofuel supply chain

Abstract It is argued in this thesis that it is morally right to identify and address matters of energy justice associated with renewable energy technologies - and thus biofuels. Equity appraisals, as defined in this thesis, can help to identify social and environmental burdens caused by the implementation of these technologies and where they exist, thus helping to understand the extent to which global sustainable development ideals to reduce inequalities are being achieved. This study is the first equity appraisal of an internationally-traded (Brazil-UK) liquid biofuel (sugarcane bioethanol), across both sites of production and consumption, conducted in a manner advocated by energy justice and environmental justice theories. Furthermore, this study provides the first empirical insights in this context of the ways that principal dimensions of energy justice can interrelate and specifically how matters of procedural justice and recognition can drive distributional changes in outcomes amongst people connected and affected to a transnational liquid biofuel supply chain. Primary qualitative data collected from people living in producer and consumption localities revealed that the nature and geographical patterning of issues differed from the views of transnational governance actors and experts. Rather than the majority of burdens lying with those living in Brazil, and UK-based consumers largely indifferent and unaffected, this research found both positive and negative equity issues affecting people at both ends of the supply chain. Matters of recognition and procedural injustice were found to be affecting consumers, affecting their abilities to engage effectively with their liquid biofuels purchases that could help drive the consumption of more sustainable, just and socially acceptable biofuels. Conversely, higher levels of recognition of local communities and associated impacts in this particular Brazilian production locality were found to be improving social and environmental outcomes for residents. This research highlights the importance of situated, contextual, primary qualitative data for equity appraisals of liquid biofuels and other renewable technologies. It is argued that these types of appraisals should be conducted more systematically in the field to supplement existing forms of appraisals, support decision-making processes and improve the chances of achieving energy justice in relation to renewable energy technologies

Revisiting the Tale of Hercules: how stars orbiting the Lagrange points visit the Sun

We propose a novel explanation for the Hercules stream consistent with recent measurements of the extent and pattern speed of the Galactic bar. We have adapted a made-to-measure dynamical model tailored for the Milky Way to investigate the kinematics of the solar neighborhood (SNd). The model matches the 3D density of the red clump giant stars (RCGs) in the bulge and bar as well as stellar kinematics in the inner Galaxy, with a pattern speed of 39 km s$^{-1}$ kpc$^{-1}$. Cross-matching this model with the $Gaia$ DR1 TGAS data combined with RAVE and LAMOST radial velocities, we find that the model naturally predicts a bimodality in the $U\!-\!V$-velocity distribution for nearby stars which is in good agreement with the Hercules stream. In the model, the Hercules stream is made of stars orbiting the Lagrange points of the bar which move outward from the bar's corotation radius to visit the SNd. While the model is not yet a quantitative fit of the velocity distribution, the new picture naturally predicts that the Hercules stream is more prominent inward from the Sun and nearly absent only a few $100$ pc outward of the Sun, and plausibly explains that Hercules is prominent in old and metal-rich stars.Comment: 7 pages, 5 figures. ApJ Letters, in pres

Solubility Studies of the Nafion ® perfluorosulfonated ionomer

This thesis describes an investigation into routes for the solubilisation of Nafion® membrane. Nafion® membrane in the protonated, lithium, sodium and potassium cation forms has been dissolved at high temperature and pressure in an autoclave. Solvent blends of water and either methanol, ethanol, 1-propanol or 1-butanol were used and solution concentrations of up to 15 wt% were achieved. The effect of temperature and time at temperature have been investigated for this autoclave method. Solutions made in this way have been concentrated by solvent evaporation to yield solutions of about 30 wt% Nation®. A promising method to dissolve Nafion® in a microwave acid digestion bomb in water/ alcohol blends has also been developed. Reflux dissolution has also been used to produce Nafion® solutions. Swelling experiments have been undertaken to help establish optimum solvent blends for the solubilisation process. A solubility parameter is proposed from a swelling study and is further investigated by a new procedure involving contact angle measurements. The properties of films cast from resulting Nafion® solutions and the melt flow properties of Nafion® powders in the protonated and tetrabutylammonium cation forms are also reported. The technological target of this work was to establish the ideal route for the dissolution of Nafion® membrane and the optimisation of high concentration solutions, which has been achieved

Made-to-Measure models of the Galactic Box/Peanut bulge: stellar and total mass in the bulge region

We construct dynamical models of the Milky Way's Box/Peanut (B/P) bulge, using the recently measured 3D density of Red Clump Giants (RCGs) as well as kinematic data from the BRAVA survey. We match these data using the NMAGIC Made-to-Measure method, starting with N-body models for barred discs in different dark matter haloes. We determine the total mass in the bulge volume of the RCGs measurement (+-2.2 x +- 1.4 x +- 1.2 kpc) with unprecedented accuracy and robustness to be 1.84 +- 0.07 x10^10 Msun. The stellar mass in this volume varies between 1.25-1.6 x10^10 Msun, depending on the amount of dark matter in the bulge. We evaluate the mass-to-light and mass-to-clump ratios in the bulge and compare them to theoretical predictions from population synthesis models. We find a mass-to-light ratio in the K-band in the range 0.8-1.1. The models are consistent with a Kroupa or Chabrier IMF, but a Salpeter IMF is ruled out for stellar ages of 10 Gyr. To match predictions from the Zoccali IMF derived from the bulge stellar luminosity function requires about 40% or 0.7 x10^10 Msun dark matter in the bulge region. The BRAVA data together with the RCGs 3D density imply a low pattern speed for the Galactic B/P bulge of 25-30 km.s-1.kpc-1. This would place the Galaxy among the slow rotators (R >= 1.5). Finally, we show that the Milky Way's B/P bulge has an off-centred X structure, and that the stellar mass involved in the peanut shape accounts for at least 20% of the stellar mass of the bulge, significantly larger than previously thought.Comment: Accepted for publication in MNRA