An inner ring and the micro lensing toward the Bulge

All current Bulge-Disk models for the inner Galaxy fall short of reproducing self-consistently the observed micro-lensing optical depth by a factor of two ($> 2\sigma$). We show that the least mass-consuming way to increase the optical depth is to add density roughly half-way the observer and the highest micro-lensing-source density. We present evidence for the existence of such a density structure in the Galaxy: an inner ring, a standard feature of barred galaxies. Judging from data on similar rings in external galaxies, an inner ring can contribute more than 50% of a pure Bulge-Disk model to the micro-lensing optical depth. We may thus eliminate the need for a small viewing angle of the Bar. The influence of an inner ring on the event-duration distribution, for realistic viewing angles, would be to increase the fraction of long-duration events toward Baade's window. The longest events are expected toward the negative-longitude tangent point at $\ell\sim$ -22\degr . A properly sampled event-duration distribution toward this tangent point would provide essential information about viewing angle and elongation of the over-all density distribution in the inner Galaxy.Comment: 9 pages, 7(15) figs, LaTeX, AJ (accepted

Equilibrium Disk-Bulge-Halo Models for the Milky Way and Andromeda Galaxies

We describe a new set of self-consistent, equilibrium disk galaxy models that incorporate an exponential disk, a Hernquist model bulge, an NFW halo and a central supermassive black hole. The models are derived from explicit distribution functions for each component and the large number of parameters permit detailed modeling of actual galaxies. We present techniques that use structural and kinematic data such as radial surface brightness profiles, rotation curves and bulge velocity dispersion profiles to find the best-fit models for the Milky Way and M31. Through N-body realizations of these models we explore their stability against the formation of bars. The models permit the study of a wide range of dynamical phenomenon with a high degree of realism.Comment: 58 pages, 20 figures, submitted to the Astrophysical Journa

Can We Reduce Negative Blood Cultures With Clinical Scores and Blood Markers? Results From an Observational Cohort Study

Only a small proportion of blood cultures routinely performed in emergency department (ED) patients is positive. Multiple clinical scores and biomarkers have previously been examined for their ability to predict bacteremia. Conclusive clinical validation of these scores and biomarkers is essential.This observational cohort study included patients with suspected infection who had blood culture sampling at ED admission. We assessed 5 clinical scores and admission concentrations of procalcitonin (PCT), C-reactive protein (CRP), lymphocyte and white blood cell counts, the neutrophil-lymphocyte count ratio (NLCR), and the red blood cell distribution width (RDW). Two independent physicians assessed true blood culture positivity. We used logistic regression models with area under the curve (AUC) analysis.Of 1083 patients, 104 (9.6%) had positive blood cultures. Of the clinical scores, the Shapiro score performed best (AUC 0.729). The best biomarkers were PCT (AUC 0.803) and NLCR (AUC 0.700). Combining the Shapiro score with PCT levels significantly increased the AUC to 0.827. Limiting blood cultures only to patients with either a Shapiro score of </=4 or PCT < 0.1 mug/L would reduce negative sampling by 20.2% while still identifying 100% of positive cultures. Similarly, a Shapiro score </=3 or PCT <0.25 mug/L would reduce cultures by 41.7% and still identify 96.1% of positive blood cultures.Combination of the Shapiro score with admission levels of PCT can help reduce unnecessary blood cultures with minimal false negative rates.The study was registered on January 9, 2013 at the 'ClinicalTrials.gov' registration web site (NCT01768494)

Virial Sequences for Thick Discs and Haloes: Flattening and Global Anisotropy

The virial theorem prescribes the ratio of the globally-averaged equatorial to vertical velocity dispersion of a tracer population in spherical and flattened dark haloes. This gives sequences of physical models in the plane of global anisotropy and flattening. The tracer may have any density, though there are particularly simple results for power-laws and exponentials. We prove the flattening theorem: for a spheroidally stratified tracer density with axis ratio q in a dark density potential with axis ratio g, the ratio of globally averaged equatorial to vertical velocity dispersion depends only on q/g. As the stellar halo density and velocity dispersion of the Milky Way are accessible to observations, this provides a new method for measuring the flattening of the dark matter. If the kinematics of the local halo subdwarfs are representative, then the Milky Way's dark halo is oblate with a flattening in the potential of g ~ 0.85, corresponding to a flattening in the dark matter density of ~ 0.7. The fractional pressure excess for power-law populations is roughly proportional to both the ellipticity and the fall-off exponent. Given the same pressure excess, if the density profile of one stellar population declines more quickly than that of another, then it must be rounder. This implies that the dual halo structure claimed by Carollo et al. (2007) for the Galaxy, a flatter inner halo and a rounder outer halo, is inconsistent with the virial theorem. For the thick disc, we provide formulae for the virial sequences of double-exponential discs in logarithmic and Navarro-Frenk-White (NFW) haloes. There are good matches to the observational data on the flattening and anisotropy of the thick disc if the thin disc is exponential with a short scalelength ~ 2.6 kpc and normalisation of 56 solar masses per square parsec, together with a logarithmic dark halo.Comment: MNRAS, submitted, 13 pages, 7 figures, small changes to made to correspond to final accepted versio

Dynamics of Gaseous Disks in a Non-axisymmetric Dark Halo

The dynamics of a galactic disk in a non-axisymmetric (triaxial) dark halo is studied in detail using high-resolution, numerical, hydrodynamical models. A long-lived, two-armed spiral pattern is generated for a wide range of parameters. The spiral structure is global, and the number of turns can be two or three, depending on the model parameters. The morphology and kinematics of the spiral pattern are studied as functions of the halo and disk parameters. The spiral structure rotates slowly, and its angular velocity varies quasi-periodically. Models with differing relative halo masses, halo semi-axis ratios, distributions of matter in the disk, Mach numbers in the gaseous component, and angular rotational velocities of their halos are considered.Comment: 22 pages, 11 figure

Bar Diagnostics in Edge-On Spiral Galaxies. I. The Periodic Orbits Approach

We develop diagnostics to detect the presence and orientation of a bar in an edge-on disk, using its kinematical signature in the position-velocity diagram (PVD) of a spiral galaxy observed edge-on. Using a well-studied barred spiral galaxy mass model, we briefly review the orbital properties of two-dimensional non-axisymmetric disks and identify the main families of periodic orbits. We use those families as building blocks to model real galaxies and calculate the PVDs obtained for various realistic combinations of periodic orbit families and for a number of viewing angles with respect to the bar. We show that the global structure of the PVD is a reliable bar diagnostic in edge-on disks. Specifically, the presence of a gap between the signatures of the families of periodic orbits in the PVD follows directly from the non-homogeneous distribution of the orbits in a barred galaxy. Similarly, material in the two so-called forbidden quadrants of the PVD results from the elongated shape of the orbits. We show how the shape of the signatures of the dominant x1 and x2 families of periodic orbits in the PVD can be used efficiently to determine the viewing angle with respect to the bar and, to a lesser extent, to constrain the mass distribution of an observed galaxy. We also address the limitations of the models when interpreting observational data.Comment: 22 pages, 9 figures (AASTeX, aaspp4.sty). Accepted for publication in The Astrophysical Journa

The MACHO project: Microlensing Optical Depth towards the Galactic Bulge from Difference Image Analysis

We present the microlensing optical depth towards the Galactic bulge based on the detection of 99 events found in our Difference Image Analysis (DIA) survey. This analysis encompasses three years of data, covering ~ 17 million stars in ~ 4 deg^2, to a source star baseline magnitude limit of V = 23. The DIA technique improves the quality of photometry in crowded fields, and allows us to detect more microlensing events with faint source stars. We find this method increases the number of detection events by 85% compared with the standard analysis technique. DIA light curves of the events are presented and the microlensing fit parameters are given. The total microlensing optical depth is estimated to be tau_(total)= 2.43^(+0.39/-0.38) x 10^(-6) averaged over 8 fields centered at l=2.68 and b=-3.35. For the bulge component we find tau_(bulge)=3.23^(+0.52/-0.50) x 10^(-6) assuming a 25% stellar contribution from disk sources. These optical depths are in good agreement with the past determinations of the MACHO Alcock et al. (1997) and OGLE Udalski et al. (1994) groups, and are higher than predicted by contemporary Galactic models. We show that our observed event timescale distribution is consistent with the distribution expected from normal mass stars, if we adopt the stellar mass function of Scalo (1986) as our lens mass function. However, we note that as there is still disagreement about the exact form of the stellar mass function, there is uncertainty in this conclusion. Based on our event timescale distribution we find no evidence for the existence of a large population of brown dwarfs in the direction of the Galactic bulge.Comment: Updated references and corrected optical depth values. tau_tot= [2.91(+0.47/-0.45) -> 2.43^(+0.39/-0.38)] x 10^(-6) tau_bul = [3.88(+0.63/-0.60) -> 3.23^(+0.52/-0.50)] x 10^(-6

Coupling the dynamics and the molecular chemistry in the Galactic center

The physical conditions of the Galactic center (GC) clouds moving with non-circular velocities are not well-known. We have studied the physical conditions of these clouds with the aim of better understanding the origin of the outstanding physical conditions of the GC molecular gas and the possible effect of the large scale dynamics on these physical conditions.Using published CO(1-0) data, we have selected a set of clouds belonging to all the kinematical components seen in the longitude-velocity diagram of the GC. We have done a survey of dense gas in all the components using the J=2-1 lines of CS and SiO as tracers of high density gas and shock chemistry. We have detected CS and SiO emission in all the kinematical components. The gas density and the SiO abundance of the clouds in non-circular orbits are similar those in the nuclear ring (GCR). Therefore, in all the kinematical components there are dense clouds that can withstand the tidal shear. However, there is no evidence of star formation outside the GCR. The high relative velocity and shear expected in the dust-lanes along the bar major axis could inhibit the star formation process, as observed in other galaxies. The high SiO abundances derived in the non-circular velocity clouds are likely due to the large-scale shocks that created the dust lanesComment: One figure as an independent PDF file. Accepted by A&

Staphylococcus epidermidis glucose uptake in biofilm versus planktonic cells

The aim of this work was to compare the glucose uptake of biofilms formed by four different Staphylococcus epidermidis strains as well as to compare between sessile and planktonic cells of the same strain. Biofilm cells showed a lower level of glucose uptake compared to planktonic cells. Moreover, glucose uptake by cells in the sessile form was strongly influenced by biofilm composition. Therefore, this work helps to confirm the phenotypic variability of S. epidermidis strains and the different behaviour patterns between sessile and free cells.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ESP/42688/2001; SFRH/BD/19265/2004

Analysis of Peculiarities of the Stellar Velocity Field in the Solar Neighborhood

Based on a new version of the Hipparcos catalogue and an updated Geneva-Copenhagen survey of F and G dwarfs, we analyze the space velocity field of about 17000 single stars in the solar neighborhood. The main known clumps, streams, and branches (Pleiades, Hyades, Sirius, Coma Berenices, Hercules, Wolf 630-alpha Ceti, and Arcturus) have been identified using various approaches. The evolution of the space velocity field for F and G dwarfs has been traced as a function of the stellar age. We have managed to confirm the existence of the recently discovered KFR08 stream. We have found 19 Hipparcos stars, candidates for membership in the KFR08 stream, and obtained an isochrone age estimate for the stream, 13 Gyr. The mean stellar ages of the Wolf 630-alpha Ceti and Hercules streams are shown to be comparable, 4--6 Gyr. No significant differences in the metallicities of stars belonging to these streams have been found. This is an argument for the hypothesis that these streams owe their origin to a common mechanism.Comment: 23 pages, 9 figure