Gas Accretion is Dominated by Warm Ionized Gas in Milky Way-Mass Galaxies at z ~ 0

We perform high-resolution hydrodynamic simulations of a Milky Way-mass galaxy in a fully cosmological setting using the adaptive mesh refinement code, Enzo, and study the kinematics of gas in the simulated galactic halo. We find that the gas inflow occurs mostly along filamentary structures in the halo. The warm-hot (10^5 K 10^6 K) ionized gases are found to dominate the overall mass accretion in the system (with dM/dt = 3-5 M_solar/yr) over a large range of distances, extending from the virial radius to the vicinity of the disk. Most of the inflowing gas (by mass) does not cool, and the small fraction that manages to cool does so primarily close to the galaxy (R <~ 20 kpc), perhaps comprising the neutral gas that may be detectable as, e.g., high-velocity clouds. The neutral clouds are embedded within larger, accreting filamentary flows, and represent only a small fraction of the total mass inflow rate. The inflowing gas has relatively low metallicity (Z/Z_solar < 0.2). The outer layers of the filamentary inflows are heated due to compression as they approach the disk. In addition to the inflow, we find high-velocity, metal-enriched outflows of hot gas driven by supernova feedback. Our results are consistent with observations of halo gas at low z.Comment: 10 pages including 5 figures, submitted to Ap

The Origin and Distribution of Cold Gas in the Halo of a Milky Way-Mass Galaxy

We analyze an adaptive mesh refinement hydrodynamic cosmological simulation of a Milky Way-sized galaxy to study the cold gas in the halo. HI observations of the Milky Way and other nearby spirals have revealed the presence of such gas in the form of clouds and other extended structures, which indicates on-going accretion. We use a high-resolution simulation (136-272 pc throughout) to study the distribution of cold gas in the halo, compare it with observations, and examine its origin. The amount (10^8 Msun in HI), covering fraction, and spatial distribution of the cold halo gas around the simulated galaxy at z=0 are consistent with existing observations. At z=0 the HI mass accretion rate onto the disk is 0.2 Msun/yr. We track the histories of the 20 satellites that are detected in HI in the redshift interval 0.5>z>0 and find that most of them are losing gas, with a median mass loss rate per satellite of 3.1 x 10^{-3} Msun/yr. This stripped gas is a significant component of the HI gas seen in the simulation. In addition, we see filamentary material coming into the halo from the IGM at all redshifts. Most of this gas does not make it directly to the disk, but part of the gas in these structures is able to cool and form clouds. The metallicity of the gas allows us to distinguish between filamentary flows and satellite gas. We find that the former accounts for at least 25-75% of the cold gas in the halo seen at any redshift analyzed here. Placing constraints on cloud formation mechanisms allows us to better understand how galaxies accrete gas and fuel star formation at z=0.Comment: 13 pages, 8 figures. Accepted for publication in Ap

Gas Condensation in the Galactic Halo

Using adaptive mesh refinement (AMR) hydrodynamic simulations of vertically stratified hot halo gas, we examine the conditions under which clouds can form and condense out of the hot halo medium to potentially fuel star formation in the gaseous disk. We find that halo clouds do not develop from linear isobaric perturbations. This is a regime where the cooling time is longer than the Brunt-Vaisala time, confirming previous linear analysis. We extend the analysis into the nonlinear regime by considering mildly or strongly nonlinear perturbations with overdensities up to 100, also varying the initial height, the cloud size, and the metallicity of the gas. Here, the result depends on the ratio of cooling time to the time required to accelerate the cloud to the sound speed (similar to the dynamical time). If the ratio exceeds a critical value near unity, the cloud is accelerated without further cooling and gets disrupted by Kelvin-Helmholtz and/or Rayleigh-Taylor instabilities. If it is less than the critical value, the cloud cools and condenses before disruption. Accreting gas with overdensities of 10-20 is expected to be marginally unstable; the cooling fraction will depend on the metallicity, the size of the incoming cloud, and the distance to the galaxy. Locally enhanced overdensities within cold streams have a higher likelihood of cooling out. Our results have implications on the evolution of clouds seeded by cold accretion that are barely resolved in current cosmological hydrodynamic simulations and absorption line systems detected in galaxy halos.Comment: 13 pages, 8 figures, submitted to Ap

Variable Sodium Absorption in a Low-Extinction Type Ia Supernova

Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable Na I D absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova progenitors. We present the third detection of such variable absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from Keck and the HET. The data span ~3 months, from 5 days before maximum light to 90 days after maximum. We find that one component of the Na D absorption lines strengthened significantly with time, indicating a total column density increase of ~2.5 x 10^12 cm^-2. The changes are most prominent after maximum light rather than at earlier times when the UV flux from the SN peaks. As with SN 2006X, we detect no change in the Ca II H&K lines over the same time period, rendering line-of-sight effects improbable and suggesting a circumstellar origin for the absorbing material. Unlike the previous two SNe exhibiting variable absorption, SN 2007le is not highly reddened (E_B-V = 0.27 mag), also pointing toward circumstellar rather than interstellar absorption. Photoionization models show that the data are consistent with a dense (10^7 cm^-3) cloud or clouds of gas located ~0.1 pc from the explosion. These results broadly support the single-degenerate scenario previously proposed to explain the variable absorption, with mass loss from a nondegenerate companion star responsible for providing the circumstellar gas. We also present tentative evidence for narrow Halpha emission associated with the SN, which will require followup observations at late times to confirm. [abridged]Comment: 16 pages, 10 figures (8 in color), 5 tables. Accepted for publication in Ap

Infall Times for Milky Way Satellites From Their Present-Day Kinematics

We analyze subhalos in the Via Lactea II (VL2) cosmological simulation to look for correlations among their infall times and z = 0 dynamical properties. We find that the present day orbital energy is tightly correlated with the time at which subhalos last crossed into the virial radius. This energy-infall correlation provides a means to infer infall times for Milky Way satellite galaxies. Assuming that the Milky Way's assembly can be modeled by VL2, we show that the infall times of some satellites are well constrained given only their Galactocentric positions and line-of-sight velocities. The constraints sharpen for satellites with proper motion measurements. We find that Carina, Ursa Minor, and Sculptor were all accreted early, more than 8 Gyr ago. Five other dwarfs, including Sextans and Segue 1, are also probable early accreters, though with larger uncertainties. On the other extreme, Leo T is just falling into the Milky Way for the first time while Leo I fell in \sim 2 Gyr ago and is now climbing out of the Milky Way's potential after its first perigalacticon. The energies of several other dwarfs, including Fornax and Hercules, point to intermediate infall times, 2 - 8 Gyr ago. We compare our infall time estimates to published star formation histories and find hints of a dichotomy between ultrafaint and classical dwarfs. The classical dwarfs appear to have quenched star formation after infall but the ultrafaint dwarfs tend to be quenched long before infall, at least for the cases in which our uncertainties allow us to discern differences. Our analysis suggests that the Large Magellanic Cloud crossed inside the Milky Way virial radius recently, within the last \sim 4 billion years.Comment: 15 pages, 7 figures, all figures include colors, submitted for publication in MNRA

Full Circle or Spiralling Out of Control?: State Violence and the Control of Urbanisation in Papua New Guinea

There is an administrative reluctance to recognise the permanency of urban settlement in Papua New Guinea. This reluctance, evident since the 1960s, has been characteristic of both the colonial and post-colonial administrations. Opposition to some facets of urbanisation continues today, despite growing population and land pressures in most rural areas and real problems of landlessness emerging in particular rural areas. Colonial control of urban populations has been replicated in contemporary times, often in more draconian form. Eviction of urban settlers has been tied to issues of crime and urban respectability, and lingering perceptions that Melanesians should be rural residents. The growth of informal settlements and urbanisation are not seen as issues of urban planning, nor is the context of urban migration linked to socioeconomic inequality, hence other forms of urban policy are largely absent. Strengthening alliances between land-owners and the state (especially police and provincial administrations) have thus emphasised intraurban inequality and hampered national development

Crop Updates 2009 - Genetically Modified Crops, Nutrition, Soils, & Others

This session covers fifteen papers from different authors: 1. Performance of Canola Breeders Roundup Ready® canola hybrid CHYB-166 in 2008, Wallace Cowling, Canola Breeders Western Australia Pty Ltd 2. The implications of GM glyphosate resistant lupin, Art Diggle, Caroline Peek, Frank D’Emden, Fiona Evans, Bob French, Rob Grima, Sam Harburg, Abul Hashem,, John Holmes, Jeremy Lemon, Peter Newman, Janet Paterson, Steve Penny,Department of Agriculture and Food, Peter Portmann, Agriconnect 3. Nufarm Roundup Ready® Canola Systems Trials— 2008 Mark Slatter, Research and Development Officer, Victoria, Nufarm (0438 064 845) Angus MacLennan, Business Development Manager, New South Wales, Nufarm (0408 358 024) Cooperators: Monsanto, Nuseed, Pacific Seeds, Pioneer Seeds 4. Roundup Ready® canola—2008 Limited Commercial Release. Getting the system right, Andrew Wells and Mark Slatter, Nufarm Australia Limited (Reprint from 2008 GRDC Cropping Updates with Introductory note) NUTRITION 5. Fertilising in a changing price environment, Bill Bowden1, Wayne Pluske2 and Jeremy Lemon1, 1Department of Agriculture and Food, 2Back Paddock Company 6. Making better fertiliser for Western Australian cropping systems, Wen Chen1 2, Geoff Anderson1, Ross Brennan1and Richard Bell2 1Department of Agriculture and Food, 2School of Environmental Science, Murdoch University 7. The nitrogen fertiliser replacement value of biosolids from wastewater treatment, Hannah Rigby1, Deborah Pritchard1, David Collins1, Katrina Walton2, David Allen2 and Nancy Penney31School of Agriculture and Environment,Curtin University of Technology, Muresk Campus, 2Chemistry Centre of Western Australia 3Water Corporation of Western Australia 8. Fertilising to soil type (usually) pays, Michael Robertson, Bill Bowden and Roger Lawes, CSIRO, Floreat and Department of Agriculture and Food SOILS 9. Management of subsoil acidity and compaction using a combination of lime, deep ripping and controlled traffic, Stephen Davies, Chris Gazey, Breanne Best and David Gartner, Department of Agriculture and Food 10. Optimising gypsum applications through remote sensing and Variable Rate Technology, Frank D’Emden, Department of Agriculture and Food and Quenten Knight,Precision Agronomics Australia 11. Case study of a 17 year agricultural lime trial, Chris Gazey1, Joel Andrew2and Ryan Pearce3 1Department of Agriculture and Food; 2Precision SoilTech; 3ConsultAg 12. Soil organic carbon in WA agricultural soils, FC Hoyle and A Bennett, Department of Agriculture and Food OTHER 13. Is the no-till revolution complete in WA? Frank D’Emden1, Rick Llewellyn2 and Ken Flower3 1Department of Agriculture and Food, 2CSIRO Sustainable Ecosystems, 3University of Western Australia 14. Progression Planning (The Concept), Julian Krieg and Owen Catto, Wheatbelt Men’s Health 15. Is the Department of Agriculture and Food still a primary source of cropping information? Cindy Parsons, Department of Agriculture and Foo

Crop Updates 2009 - Farming Systems

This session covers nineteen papers from different authors: Decision support technology 1. The use of high resolution imagery in broad acre cropping, Derk Bakker and Grey Poulish, Department of Agriculture and Food 2. Spraywise decisions – online spray applicatiors planning tool, Steve Lacy, Nufarm Australia Ltd 3. Testing for redlegged earthmite resistance in Western Australia, Svetlana Micic, Peter Mangano, Tony Dore and Alan Lord, Department of Agriculture and Food 4. Screening cereal, canola and pasture cultivars for Root Lesion Nematode (Pratylenchus neglectus), Vivien Vanstone, Helen Hunter and Sean Kelly,Department of Agriculture and Food Farming Systems Research 5. Lessons from five years of cropping systems research, WK Anderson, Department of Agriculture and Food 6. Facey Group rotations for profit: Five years on and where to next? Gary Lang and David McCarthy, Facey Group, Wickepin, WA Mixed Farming 7. Saline groundwater use by Lucerne and its biomass production in relation to groundwater salinity, Ruhi Ferdowsian, Ian Roseand Andrew Van Burgel, Department of Agriculture and Food 8. Autumn cleaning yellow serradella pastures with broad spectrum herbicides – a novel weed control strategy that exploits delayed germination, Dr David Ferris, Department of Agriculture and Food 9. Decimating weed seed banks within non-crop phases for the benefit of subsequent crops, Dr David Ferris, Department of Agriculture and Food 10. Making seasonal variability easier to deal with in a mixed farming enterprise! Rob Grima,Department of Agriculture and Food 11. How widely have new annual legume pastures been adopted in the low to medium rainfall zones of Western Australia? Natalie Hogg, Department of Agriculture and Food, John Davis, Institute for Sustainability and Technology Policy, Murdoch University 12. Economic evaluation of dual purpose cereal in the Central wheatbelt of Western Australia, Jarrad Martin, Pippa Michael and Robert Belford, School of Agriculture and Environment, CurtinUniversity of Technology, Muresk Campus 13. A system for improving the fit of annual pasture legumes under Western Australian farming systems, Kawsar P Salam1,2, Roy Murray-Prior1, David Bowran2and Moin U. Salam2, 1Curtin University of Technology; 2Department of Agriculture and Food 14. Perception versus reality: why we should measure our pasture, Tim Scanlon, Department of Agriculture and Food, Len Wade, Charles Sturt University, Megan Ryan, University of Western Australia Modelling 15. Potential impact of climate changes on the profitability of cropping systems in the medium and high rainfall areas of the northern wheatbelt, Megan Abrahams, Chad Reynolds, Caroline Peek, Dennis van Gool, Kari-Lee Falconer and Daniel Gardiner, Department of Agriculture and Food 16. Prediction of wheat grain yield using Yield Prophet®, Geoff Anderson and Siva Sivapalan, Department of Agriculture and Food 17. Using Yield Prophet® to determine the likely impacts of climate change on wheat production, Tim McClelland1, James Hunt1, Zvi Hochman2, Bill Long3, Dean Holzworth4, Anthony Whitbread5, Stephen van Rees1and Peter DeVoil6 1 Birchip Cropping Group, Birchip, Vic, 2Agricultural Production Systems Research Unit (APSRU), CSIRO Sustainable Ecosystems, Climate Adaptation Flagship, Qld, 3 AgConsulting, SA 4 Agricultural Production Systems Research Unit (APSRU), CSIRO Sustainable Ecosystems, Toowoomba Qld, 5 CSIRO Sustainable Ecosystems, SA, 6 Agricultural Production Systems Research Unit (APSRU), Department of Agriculture and Fisheries, Queensland 18. Simple methods to predict yield potential: Improvements to the French and Schultz formula to account for soil type and within-season rainfall, Yvette Oliver, Michael Robertson and Peter Stone, CSIRO Sustainable Ecosystems 19. Ability of various yield forecasting models to estimate soil water at the start of the growing season, Siva Sivapalan, Kari-Lee Falconer and Geoff Anderson, Department of Agriculture and Foo