Characterisation of vertical BrO distribution during events of enhanced tropospheric BrO in Antarctica, from combined remote and in-situ measurements

Tropospheric BrO was measured by a ground-based remote-sensing spectrometer at Halley in Antarctica in spring 2007, and BrO was measured by satellite-borne remote-sensing spectrometers using similar spectral regions and similar Differential Optical Absorption Spectroscopy (DOAS) analyses. Near-surface BrO was simultaneously measured in situ at Halley by Chemical Ionisation Mass Spectrometer (CIMS), and in an earlier year near-surface BrO was measured at Halley over a long path by a ground-based DOAS spectrometer. During enhancement episodes, total amounts of tropospheric BrO from the ground-based remote-sensor were similar to those from space, but if we assume that the BrO was confined to the mixed layer they were very much larger than values measured by either near-surface technique. This large apparent discrepancy can be resolved if substantial amounts of BrO were in the free troposphere during most enhancement episodes. Amounts observed by the ground-based remote sensor at different elevation angles, and their formal inversions to vertical profiles, demonstrate that much of the BrO was indeed often in the free troposphere. This is consistent with the ~5 day lifetime of Bry and with the enhanced BrO observed during some Antarctic blizzards

The SAMI Galaxy Survey: Stellar population radial gradients in early-type galaxies

We study the internal radial gradients of the stellar populations in a sample comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney- AAO Multi-object Integral field spectrograph) Galaxy Survey. We stack the spectra of individual spaxels in radial bins, and derive basic stellar population properties: total metallicity ([Z/H]), [Mg/Fe], [C/Fe] and age. The radial gradient ($\nabla$) and central value of the fits (evaluated at R$_e$/4) are compared against a set of six possible drivers of the trends. We find that velocity dispersion ($\sigma$) - or, equivalently gravitational potential - is the dominant driver of the chemical composition gradients. Surface mass density is also correlated with the trends, especially with stellar age. The decrease of $\nabla$[Mg/Fe] with increasing $\sigma$ is contrasted by a rather shallow dependence of $\nabla$[Z/H] with $\sigma$ (although this radial gradient is overall rather steep). This result, along with a shallow age slope at the massive end, imposes stringent constraints on the progenitors of the populations that contribute to the formation of the outer envelopes of ETGs. The SAMI sample is split between a 'field' sample and a cluster sample. Only weak environment-related differences are found, most notably a stronger dependence of central total metallicity ([Z/H]$_{e4}$) with $\sigma$, along with a marginal trend of $\nabla$[Z/H] to steepen in cluster galaxies, a result that is not followed by [Mg/Fe]. The results presented here serve as constraints on numerical models of the formation and evolution of ETGs.Comment: 14 pages, 9 figures, 3 tables. Submitted to MNRA

On the global hydration kinetics of tricalcium silicate cement

We reconsider a number of measurements for the overall hydration kinetics of tricalcium silicate pastes having an initial water to cement weight ratio close to 0.5. We find that the time dependent ratio of hydrated and unhydrated silica mole numbers can be well characterized by two power-laws in time, $x/(1-x)\sim (t/t_x)^\psi$. For early times $t < t_x$ we find an `accelerated' hydration ($\psi = 5/2$) and for later times $t > t_x$ a `deaccelerated' behavior ($\psi = 1/2$). The crossover time is estimated as $t_x \approx 16 hours$. We interpret these results in terms of a global second order rate equation indicating that (a) hydrates catalyse the hydration process for $t<t_x$, (b) they inhibit further hydration for $t > t_x$ and (c) the value of the associated second order rate constant is of magnitude 6x10^{-7} - 7x10^{-6} liter mol^{-1} s^{-1}. We argue, by considering the hydration process actually being furnished as a diffusion limited precipitation that the exponents $\psi = 5/2$ and $\psi = 1/2$ directly indicate a preferentially `plate' like hydrate microstructure. This is essentially in agreement with experimental observations of cellular hydrate microstructures for this class of materials.Comment: RevTeX macros, 6 pages, 4 postscript figure

The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies

Using the stellar kinematic maps and ancillary imaging data from the Sydney AAO Multi Integral field (SAMI) Galaxy Survey, the intrinsic shape of kinematically-selected samples of galaxies is inferred. We implement an efficient and optimised algorithm to fit the intrinsic shape of galaxies using an established method to simultaneously invert the distributions of apparent ellipticities and kinematic misalignments. The algorithm output compares favourably with previous studies of the intrinsic shape of galaxies based on imaging alone and our re-analysis of the ATLAS3D data. Our results indicate that most galaxies are oblate axisymmetric. We show empirically that the intrinsic shape of galaxies varies as a function of their rotational support as measured by the "spin" parameter proxy Lambda_Re. In particular, low spin systems have a higher occurrence of triaxiality, while high spin systems are more intrinsically flattened and axisymmetric. The intrinsic shape of galaxies is linked to their formation and merger histories. Galaxies with high spin values have intrinsic shapes consistent with dissipational minor mergers, while the intrinsic shape of low-spin systems is consistent with dissipationless multi-merger assembly histories. This range in assembly histories inferred from intrinsic shapes is broadly consistent with expectations from cosmological simulations.Comment: 15 pages, 11 figures, MNRAS in prin

The SAMI Galaxy Survey: gravitational potential and surface density drive stellar populations -- I. early-type galaxies

The well-established correlations between the mass of a galaxy and the properties of its stars are considered evidence for mass driving the evolution of the stellar population. However, for early-type galaxies (ETGs), we find that $g-i$ color and stellar metallicity [Z/H] correlate more strongly with gravitational potential $\Phi$ than with mass $M$, whereas stellar population age correlates best with surface density $\Sigma$. Specifically, for our sample of 625 ETGs with integral-field spectroscopy from the SAMI Galaxy Survey, compared to correlations with mass, the color--$\Phi$, [Z/H]--$\Phi$, and age--$\Sigma$ relations show both smaller scatter and less residual trend with galaxy size. For the star formation duration proxy [$\alpha$/Fe], we find comparable results for trends with $\Phi$ and $\Sigma$, with both being significantly stronger than the [$\alpha$/Fe]-$M$ relation. In determining the strength of a trend, we analyze both the overall scatter, and the observational uncertainty on the parameters, in order to compare the intrinsic scatter in each correlation. These results lead us to the following inferences and interpretations: (1) the color--$\Phi$ diagram is a more precise tool for determining the developmental stage of the stellar population than the conventional color--mass diagram; and (2) gravitational potential is the primary regulator of global stellar metallicity, via its relation to the gas escape velocity. Furthermore, we propose the following two mechanisms for the age and [$\alpha$/Fe] relations with $\Sigma$: (a) the age--$\Sigma$ and [$\alpha$/Fe]--$\Sigma$ correlations arise as results of compactness driven quenching mechanisms; and/or (b) as fossil records of the $\Sigma_{SFR}\propto\Sigma_{gas}$ relation in their disk-dominated progenitors.Comment: 9 pages, 4 figures, 1 table Accepted to Ap

The SAMI Galaxy Survey: energy sources of the turbulent velocity dispersion in spatially-resolved local star-forming galaxies

We investigate the energy sources of random turbulent motions of ionised gas from H$\alpha$ emission in eight local star-forming galaxies from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. These galaxies satisfy strict pure star-forming selection criteria to avoid contamination from active galactic nuclei (AGN) or strong shocks/outflows. Using the relatively high spatial and spectral resolution of SAMI, we find that -- on sub-kpc scales our galaxies display a flat distribution of ionised gas velocity dispersion as a function of star formation rate (SFR) surface density. A major fraction of our SAMI galaxies shows higher velocity dispersion than predictions by feedback-driven models, especially at the low SFR surface density end. Our results suggest that additional sources beyond star formation feedback contribute to driving random motions of the interstellar medium (ISM) in star-forming galaxies. We speculate that gravity, galactic shear, and/or magnetorotational instability (MRI) may be additional driving sources of turbulence in these galaxies.Comment: 11 pages, 5 figures, 3 tables. Accepted by MNRA

The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry

In order to determine the causes of kinematic asymmetry in the H$\alpha$ gas in the SAMI Galaxy Survey sample, we investigate the comparative influences of environment and intrinsic properties of galaxies on perturbation. We use spatially resolved H$\alpha$ velocity fields from the SAMI Galaxy Survey to quantify kinematic asymmetry ($\overline{v_{asym}}$) in nearby galaxies and environmental and stellar mass data from the GAMA survey. {We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetry for galaxies with $\mathrm{\log(M_*/M_\odot)}>10.0$, but there is no significant correlation for galaxies with $\mathrm{\log(M_*/M_\odot)}<10.0$. Moreover, low mass galaxies ($\mathrm{\log(M_*/M_\odot)}<9.0$) have greater kinematic asymmetry at all separations, suggesting a different physical source of asymmetry is important in low mass galaxies.} We propose that secular effects derived from gas fraction and gas mass may be the primary causes of asymmetry in low mass galaxies. High gas fraction is linked to high $\frac{\sigma_{m}}{V}$ (where $\sigma_m$ is H$\alpha$ velocity dispersion and $V$ the rotation velocity), which is strongly correlated with $\overline{v_{asym}}$, and galaxies with $\log(M_*/M_\odot)<9.0$ have offset $\overline{\frac{\sigma_{m}}{V}}$ from the rest of the sample. Further, asymmetry as a fraction of dispersion decreases for galaxies with $\log(M_*/M_\odot)<9.0$. Gas mass and asymmetry are also inversely correlated in our sample. We propose that low gas masses in dwarf galaxies may lead to asymmetric distribution of gas clouds, leading to increased relative turbulence.Comment: 15 pages, 20 figure

Increasing conspicuity on night-time roads : Perspectives from cyclists and runners

Pedestrians and cyclists are at significant risk of being killed as a result of a collision with a vehicle at night-time because of their poor conspicuity. Retroreflective strips positioned on the moveable joints, in a biological motion configuration (biomotion), greatly enhance the night-time conspicuity of pedestrians and cyclists, but it is not clear how widely this strategy is adopted among those running and cycling under low light levels (dawn and dusk or at night). This study explored runners’ and cyclists’ beliefs about their own conspicuity, and the strategies they use to increase their conspicuity and safety under low light levels. Nine focus groups involving 50 participants (mean age = 39.5 ± 13.9 years) were held with individuals who ran and/or cycled under low light conditions or at night-time. The strategies that participants used to increase their conspicuity and enhance their personal safety, and the importance they placed on increased conspicuity to other road users at night was explored. Data were analysed thematically, with two main themes identified. Strategies describes the different approaches used to increase conspicuity when running or cycling in low light, some of which are ineffective. Importance describes how conspicuity relates to other considerations that influence cyclists and runners. While they may believe that conspicuity is essential for their safety, they may compromise their own conspicuity by prioritising style or comfort, or because they believe that being more conspicuous is of limited value because it cannot compensate for the behaviour of other road users. In summary, cyclists and runners are largely unaware of effective strategies to increase their night-time conspicuity, particularly the use of biomotion reflective strips. Garment manufacturers should ensure that conspicuity features (with supporting educative product information on labels) are incorporated into cyclists’ and runners’ clothing or accessories to improve wearer conspicuity and hence safety in low light conditions.</p