Outskirts of Distant Galaxies In Absorption

QSO absorption spectroscopy provides a sensitive probe of both the neutral medium and diffuse ionized gas in the distant Universe. It extends 21cm maps of gaseous structures around low-redshift galaxies both to lower gas column densities and to higher redshifts. Combining galaxy surveys with absorption-line observations of gas around galaxies enables comprehensive studies of baryon cycles in galaxy outskirts over cosmic time. This Chapter presents a review of the empirical understanding of the cosmic neutral gas reservoir from studies of damped Lya absorbers (DLAs). It describes the constraints on the star formation relation and chemical enrichment history in the outskirts of distant galaxies from DLA studies. A brief discussion of available constraints on the ionized circumgalactic gas from studies of lower column density Lya absorbers and associated ionic absorption transitions is presented at the end.Comment: 45 pages, 7 figures, invited review, Book chapter in "Outskirts of Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library, Springer, in pres

The role of endothelial cilia in post-embryonic vascular development

BACKGROUND: Cilia are essential for morphogenesis and maintenance of many tissues. Loss-of-function of cilia in early zebrafish development causes a range of vascular defects including cerebral haemorrhage and reduced arterial vascular mural cell coverage. In contrast, loss of endothelial cilia in mice has little effect on vascular development. We therefore used a conditional rescue approach to induce endothelial cilia ablation after early embryonic development and examined the effect on vascular development and mural cell development in post-embryonic, juvenile and adult zebrafish. RESULTS: ift54(elipsa) mutant zebrafish are unable to form cilia. We rescued cilia formation and ameliorated the phenotype of ift54 mutants using a novel Tg(ubi:loxP-ift54-loxP-myr-mcherry,myl7:EGFP)sh488 transgene expressing wildtype ift54 flanked by recombinase sites, then used a Tg(kdrl:cre)s898 transgene to induce endothelial-specific inactivation of ift54 at post-embryonic ages. Fish without endothelial ift54 function could survive to adulthood and exhibited no vascular defects. Endothelial inactivation of ift54 did not affect development of tagln-positive vascular mural cells around either the aorta or the caudal fin vessels, nor formation of vessels after tailfin resection in adult animals. CONCLUSIONS: Endothelial cilia are not essential for development and remodelling of the vasculature in juvenile and adult zebrafish when inactivated after embryogenesis

Prospects For Identifying Dark Matter With CoGeNT

It has previously been shown that the excess of events reported by the CoGeNT collaboration could be generated by elastically scattering dark matter particles with a mass of approximately 5-15 GeV. This mass range is very similar to that required to generate the annual modulation observed by DAMA/LIBRA and the gamma rays from the region surrounding the Galactic Center identified within the data of the Fermi Gamma Ray Space Telescope. To confidently conclude that CoGeNT's excess is the result of dark matter, however, further data will likely be needed. In this paper, we make projections for the first full year of CoGeNT data, and for its planned upgrade. Not only will this body of data more accurately constrain the spectrum of nuclear recoil events, and corresponding dark matter parameter space, but will also make it possible to identify seasonal variations in the rate. In particular, if the CoGeNT excess is the product of dark matter, then one year of CoGeNT data will likely reveal an annual modulation with a significance of 2-3$\sigma$. The planned CoGeNT upgrade will not only detect such an annual modulation with high significance, but will be capable of measuring the energy spectrum of the modulation amplitude. These measurements will be essential to irrefutably confirming a dark matter origin of these events.Comment: 6 pages, 6 figure

Dependence of direct detection signals on the WIMP velocity distribution

The signals expected in WIMP direct detection experiments depend on the ultra-local dark matter distribution. Observations probe the local density, circular speed and escape speed, while simulations find velocity distributions that deviate significantly from the standard Maxwellian distribution. We calculate the energy, time and direction dependence of the event rate for a range of velocity distributions motivated by recent observations and simulations, and also investigate the uncertainty in the determination of WIMP parameters. The dominant uncertainties are the systematic error in the local circular speed and whether or not the MW has a high density dark disc. In both cases there are substantial changes in the mean differential event rate and the annual modulation signal, and hence exclusion limits and determinations of the WIMP mass. The uncertainty in the shape of the halo velocity distribution is less important, however it leads to a 5% systematic error in the WIMP mass. The detailed direction dependence of the event rate is sensitive to the velocity distribution. However the numbers of events required to detect anisotropy and confirm the median recoil direction do not change substantially.Comment: 21 pages, 7 figures, v2 version to appear in JCAP, minor change

Spin-independent elastic WIMP scattering and the DAMA annual modulation signal

We discuss the interpretation of the annual modulation signal seen in the DAMA experiment in terms of spin-independent elastic WIMP scattering. Taking into account channeling in the crystal as well as the spectral signature of the modulation signal we find that the low-mass WIMP region consistent with DAMA data is confined to WIMP masses close to $m_\chi \simeq 12$ GeV, in disagreement with the constraints from CDMS and XENON. We conclude that even if channeling is taken into account this interpretation of the DAMA modulation signal is disfavoured. There are no overlap regions in the parameter space at 90% CL and a consistency test gives the probability of $1.2\times 10^{-5}$. We study the robustness of this result with respect to variations of the WIMP velocity distribution in our galaxy, by changing various parameters of the distribution function, and by using the results of a realistic N-body dark matter simulation. We find that only by making rather extreme assumptions regarding halo properties can we obtain agreement between DAMA and CDMS/XENON.Comment: 21 pages, 12 figures, matches version accepted in JCA

An Atom Laser Based on Raman Transitions

In this paper we present an atom laser scheme using a Raman transition for the output coupling of atoms. A beam of thermal atoms (bosons) in a metastable atomic state $|1 >$ are pumped into a multimode atomic cavity. This cavity is coupled through spontaneous emission to a single mode of another cavity for the ground atomic state, $|2 >$. Above a certain threshold pumping rate a large number of atoms, $N_2$, builds up in this single quantum state and transitions to the ground state of the cavity become enhanced by a factor $(N_2 + 1)$. Atoms in this state are then coupled to the outside of the cavity with a Raman transition. This changes the internal state of the atom and imparts a momentum kick, allowing the atoms to leave the system.Comment: 8 pages, 4 postscript figures, uses RevTex, home page at http://online.anu.edu.au/Physics/Welcome.html (Some aspects of the exact physical model have changed from original version. Other general improvements included

Diffusion as mixing mechanism in granular materials

We present several numerical results on granular mixtures. In particular, we examine the efficiency of diffusion as a mixing mechanism in these systems. The collisions are inelastic and to compensate the energy loss, we thermalize the grains by adding a random force. Starting with a segregated system, we show that uniform agitation (heating) leads to a uniform mixture of grains of different sizes. We define a characteristic mixing time, $\tau_{mix}$, and study theoretically and numerically its dependence on other parameters like the density. We examine a model for bidisperse systems for which we can calculate some physical quantities. We also examine the effect of a temperature gradient and demonstrate the appearance of an expected segregation.Comment: 15 eps figures, include

A Bayesian view of the current status of dark matter direct searches

Bayesian statistical methods offer a simple and consistent framework for incorporating uncertainties into a multi-parameter inference problem. In this work we apply these methods to a selection of current direct dark matter searches. We consider the simplest scenario of spin-independent elastic WIMP scattering, and infer the WIMP mass and cross-section from the experimental data with the essential systematic uncertainties folded into the analysis. We find that when uncertainties in the scintillation efficiency of Xenon100 have been accounted for, the resulting exclusion limit is not sufficiently constraining to rule out the CoGeNT preferred parameter region, contrary to previous claims. In the same vein, we also investigate the impact of astrophysical uncertainties on the preferred WIMP parameters. We find that within the class of smooth and isotropic WIMP velocity distributions, it is difficult to reconcile the DAMA and the CoGeNT preferred regions by tweaking the astrophysics parameters alone. If we demand compatibility between these experiments, then the inference process naturally concludes that a high value for the sodium quenching factor for DAMA is preferred.Comment: 37 pages, 14 figures and 7 tables. Replacement for matching the version accepted for publicatio

Cerebrovascular endothelial cells form transient Notch‐dependent cystic structures in zebrafish

We identify a novel endothelial membrane behaviour in transgenic zebrafish. Cerebral blood vessels extrude large transient spherical structures that persist for an average of 23 min before regressing into the parent vessel. We term these structures “kugeln”, after the German for sphere. Kugeln are only observed arising from the cerebral vessels and are present as late as 28 days post fertilization. Kugeln do not communicate with the vessel lumen and can form in the absence of blood flow. They contain little or no cytoplasm, but the majority are highly positive for nitric oxide reactivity. Kugeln do not interact with brain lymphatic endothelial cells (BLECs) and can form in their absence, nor do they perform a scavenging role or interact with macrophages. Inhibition of actin polymerization, Myosin II, or Notch signalling reduces kugel formation, while inhibition of VEGF or Wnt dysregulation (either inhibition or activation) increases kugel formation. Kugeln represent a novel Notch‐dependent NO‐containing endothelial organelle restricted to the cerebral vessels, of currently unknown function

Ice sheet model dependency of the simulated Greenland Ice Sheet in the mid-Pliocene

The understanding of the nature and behavior of ice sheets in past warm periods is important for constraining the potential impacts of future climate change. The Pliocene warm period (between 3.264 and 3.025 Ma) saw global temperatures similar to those projected for future climates; nevertheless, Pliocene ice locations and extents are still poorly constrained. We present results from the efforts to simulate mid-Pliocene Greenland Ice Sheets by means of the international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP). We compare the performance of existing numerical ice sheet models in simulating modern control and mid-Pliocene ice sheets with a suite of sensitivity experiments guided by available proxy records. We quantify equilibrated ice sheet volume on Greenland, identifying a potential range in sea level contributions from warm Pliocene scenarios. A series of statistical measures are performed to quantify the confidence of simulations with focus on inter-model and inter-scenario differences. We find that Pliocene Greenland Ice Sheets are less sensitive to differences in ice sheet model configurations and internal physical quantities than to changes in imposed climate forcing. We conclude that Pliocene ice was most likely to be limited to the highest elevations in eastern and southern Greenland as simulated with the highest confidence and by synthesizing available regional proxies; however, the extent of those ice caps needs to be further constrained by using a range of general circulation model (GCM) climate forcings