Outliers from the Mass--Metallicity Relation II: A Sample of Massive Metal-Poor Galaxies from SDSS

We present a sample of 42 high-mass low-metallicity outliers from the mass--metallicity relation of star-forming galaxies. These galaxies have stellar masses that span log(M_*/M_sun) ~9.4 to 11.1 and are offset from the mass--metallicity relation by -0.3 to -0.85 dex in 12+log(O/H). In general, they are extremely blue, have high star formation rates for their masses, and are morphologically disturbed. Tidal interactions are expected to induce large-scale gas inflow to the galaxies' central regions, and we find that these galaxies' gas-phase oxygen abundances are consistent with large quantities of low-metallicity gas from large galactocentric radii diluting the central metal-rich gas. We conclude with implications for deducing gas-phase metallicities of individual galaxies based solely on their luminosities, specifically in the case of long gamma-ray burst host galaxies.Comment: Accepted for publication in ApJ; 11 pages, 11 figure

Cardiovascular disease in a cohort exposed to the 1940-45 Channel Islands occupation

BACKGROUND To clarify the nature of the relationship between food deprivation/undernutrition during pre- and postnatal development and cardiovascular disease (CVD) in later life, this study examined the relationship between birth weight (as a marker of prenatal nutrition) and the incidence of hospital admissions for CVD from 1997–2005 amongst 873 Guernsey islanders (born in 1923–1937), 225 of whom had been exposed to food deprivation as children, adolescents or young adults (i.e. postnatal undernutrition) during the 1940–45 German occupation of the Channel Islands, and 648 of whom had left or been evacuated from the islands before the occupation began. METHODS Three sets of Cox regression models were used to investigate (A) the relationship between birth weight and CVD, (B) the relationship between postnatal exposure to the occupation and CVD and (C) any interaction between birth weight, postnatal exposure to the occupation and CVD. These models also tested for any interactions between birth weight and sex, and postnatal exposure to the occupation and parish of residence at birth (as a marker of parish residence during the occupation and related variation in the severity of food deprivation). RESULTS The first set of models (A) found no relationship between birth weight and CVD even after adjustment for potential confounders (hazard ratio (HR) per kg increase in birth weight: 1.12; 95% confidence intervals (CI): 0.70 – 1.78), and there was no significant interaction between birth weight and sex (p = 0.60). The second set of models (B) found a significant relationship between postnatal exposure to the occupation and CVD after adjustment for potential confounders (HR for exposed vs. unexposed group: 2.52; 95% CI: 1.54 – 4.13), as well as a significant interaction between postnatal exposure to the occupation and parish of residence at birth (p = 0.01), such that those born in urban parishes (where food deprivation was worst) had a greater HR for CVD than those born in rural parishes. The third model (C) found no interaction between birth weight and exposure to the occupation (p = 0.43). CONCLUSION These findings suggest that the levels of postnatal undernutrition experienced by children, adolescents and young adults exposed to food deprivation during the 1940–45 occupation of the Channel Islands were a more important determinant of CVD in later life than the levels of prenatal undernutrition experienced in utero prior to the occupatio

Probing the ISM Near Star Forming Regions with GRB Afterglow Spectroscopy: Gas, Metals, and Dust

We study the chemical abundances of the interstellar medium surrounding high z gamma-ray bursts (GRBs) through analysis of the damped Lya systems (DLAs) identified in afterglow spectra. These GRB-DLAs are characterized by large HI column densities N(HI) and metallicities [M/H] spanning 1/100 to nearly solar, with median [M/H]>-1. The majority of GRB-DLAs have [M/H] values exceeding the cosmic mean metallicity of atomic gas at z>2, i.e. if anything, the GRB-DLAs are biased to larger metallicity. We also observe (i) large [Zn/Fe] values (>+0.6) and sub-solar Ti/Fe ratios which imply substantial differential depletion, (ii) large a/Fe ratios suggesting nucleosynthetic enrichment by massive stars, and (iii) low C^0/C^+ ratios (<10^{-4}). Quantitatively, the observed depletion levels and C^0/C^+ ratios of the gas are not characteristic of cold, dense HI clouds in the Galactic ISM. We argue that the GRB-DLAs represent the ISM near the GRB but not gas directly local to the GRB (e.g. its molecular cloud or circumstellar material). We compare these observations with DLAs intervening background quasars (QSO-DLAs). The GRB-DLAs exhibit larger N(HI) values, higher a/Fe and Zn/Fe ratios, and have higher metallicity than the QSO-DLAs. We argue that the differences primarily result from galactocentric radius-dependent differences in the ISM: GRB-DLAs preferentially probe denser, more depleted, higher metallicity gaslocated in the inner few kpc whereas QSO-DLAs are more likely to intersect the less dense, less enriched, outer regions of the galaxy. Finally, we investigate whether dust obscuration may exclude GRB-DLA sightlines from QSO-DLA samples; we find that the majority of GRB-DLAs would be recovered which implies little observational bias against large N(HI) systems.Comment: 16 pages, 9 figures. Submitted to Ap

Lepton Models for TeV Emission from SNR RX J1713.7-3946

(Aims.) SNR RX J1713.7-3946 is perhaps one of the best observed shell-type supernova remnants with emissions dominated by energetic particles accelerated near the shock front. The nature of the TeV emission, however, is an issue still open to investigation. (Methods.) We carry out a systematic study of four lepton models for the TeV emission with the Markov chain Monte Carlo method. (Results.) It is shown that current data already give good constraints on the model parameters. Two commonly used parametric models do not appear to fit the observed radio, X-ray, and gamma-ray spectra. Models motivated by diffusive shock acceleration and by stochastic acceleration by compressive waves in the shock downstream give comparably good fits. The former has a sharper spectral cutoff in the hard X-ray band than the latter. Future observations with the HXMT and NuSTAR may distinguish these two models.Comment: 4 pages, 2 figures, accepted by A&A Lette

MHD numerical simulations of colliding winds in massive binary systems - I. Thermal vs non-thermal radio emission

In the past few decades detailed observations of radio and X-rays emission from massive binary systems revealed a whole new physics present in such systems. Both thermal and non-thermal components of this emission indicate that most of the radiation at these bands originates in shocks. OB and WR stars present supersonic and massive winds that, when colliding, emit largely due to the free-free radiation. The non-thermal radio and X-ray emissions are due to synchrotron and inverse compton processes, respectively. In this case, magnetic fields are expected to play an important role on the emission distribution. In the past few years the modeling of the free-free and synchrotron emissions from massive binary systems have been based on purely hydrodynamical simulations, and ad hoc assumptions regarding the distribution of magnetic energy and the field geometry. In this work we provide the first full MHD numerical simulations of wind-wind collision in massive binary systems. We study the free-free emission characterizing its dependence on the stellar and orbital parameters. We also study self-consistently the evolution of the magnetic field at the shock region, obtaining also the synchrotron energy distribution integrated along different lines of sight. We show that the magnetic field in the shocks is larger than that obtained when the proportionality between $B$ and the plasma density is assumed. Also, we show that the role of the synchrotron emission relative to the total radio emission has been underestimated.Comment: MNRAS accepte

Association of RENAL nephrometry score with outcomes of minimally invasive partial nephrectomy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98294/1/iju3222.pd

Analytic solution for nonlinear shock acceleration in the Bohm limit

The selfconsistent steady state solution for a strong shock, significantly modified by accelerated particles is obtained on the level of a kinetic description, assuming Bohm-type diffusion. The original problem that is commonly formulated in terms of the diffusion-convection equation for the distribution function of energetic particles, coupled with the thermal plasma through the momentum flux continuity equation, is reduced to a nonlinear integral equation in one variable. Its solution provides selfconsistently both the particle spectrum and the structure of the hydrodynamic flow. A critical system parameter governing the acceleration process is found to be $\Lambda = M^{-3/4}\Lambda_1$, where $\Lambda_1 =\eta p_1/mc$, with a suitably normalized injection rate $\eta$, the Mach number M >> 1, and the cut-off momentum $p_1$. We particularly focus on an efficient solution, in which almost all the energy of the flow is converted into a few energetic particles. It was found that (i) for this efficient solution (or, equivalently, for multiple solutions) to exist, the parameter $\zeta =\eta\sqrt{p_0 p_1}/mc$ must exceed a critical value $\zeta_{cr} \sim 1$ ($p_0$ is the injection momentum), (ii) the total shock compression ratio r increases with M and saturates at a level that scales as $ r \propto \Lambda_1 (iii) the downstream power-law spectrum has the universal index q=3.5 over a broad momentum range. (iv) completely smooth shock transitions do not appear in the steady state kinetic description.Comment: 39 pages, 3 PostScript figures, uses aasms4.sty, to appear in Aug. 20, 1997 issue ApJ, vol. 48

Relation Between Stellar Mass and Star Formation Activity in Galaxies

For a mass-selected sample of 66544 galaxies with photometric redshifts from the Cosmic Evolution Survey (COSMOS), we examine the evolution of star formation activity as a function of stellar mass in galaxies. We estimate the cosmic star formation rates (SFR) over the range 0.2 < z < 1.2, using the rest-frame 2800 A flux (corrected for extinction). We find the mean SFR to be a strong function of the galactic stellar mass at any given redshift, with massive systems (log (M/M(Sun)) > 10.5) contributing less (by a factor of ~ 5) to the total star formation rate density (SFRD). Combining data from the COSMOS and Gemini Deep Deep Survey (GDDS), we extend the SFRD-z relation as a function of stellar mass to z~2. For massive galaxies, we find a steep increase in the SFRD-z relation to z~2; for the less massive systems, the SFRD which also increases from z=0 to 1, levels off at z~1. This implies that the massive systems have had their major star formation activity at earlier epochs (z > 2) than the lower mass galaxies. We study changes in the SFRDs as a function of both redshift and stellar mass for galaxies of different spectral types. We find that the slope of the SFRD-z relation for different spectral type of galaxies is a strong function of their stellar mass. For low and intermediate mass systems, the main contribution to the cosmic SFRD comes from the star-forming galaxies while, for more massive systems, the evolved galaxies are the most dominant population.Comment: 34 pages; 8 figures; Accepted for publication in Ap

Probing Nearby CR Accelerators and ISM Turbulence with Milagro Hot Spots

Both the acceleration of cosmic rays (CR) in supernova remnant shocks and their subsequent propagation through the random magnetic field of the Galaxy deem to result in an almost isotropic CR spectrum. Yet the MILAGRO TeV observatory discovered a sharp ($\sim10^{\circ})$ arrival anisotropy of CR nuclei. We suggest a mechanism for producing a weak and narrow CR beam which operates en route to the observer. The key assumption is that CRs are scattered by a strongly anisotropic Alfven wave spectrum formed by the turbulent cascade across the local field direction. The strongest pitch-angle scattering occurs for particles moving almost precisely along the field line. Partly because this direction is also the direction of minimum of the large scale CR angular distribution, the enhanced scattering results in a weak but narrow particle excess. The width, the fractional excess and the maximum momentum of the beam are calculated from a systematic transport theory depending on a single scale $l$ which can be associated with the longest Alfven wave, efficiently scattering the beam. The best match to all the three characteristics of the beam is achieved at $l\sim1$pc. The distance to a possible source of the beam is estimated to be within a few 100pc. Possible approaches to determination of the scale $l$ from the characteristics of the source are discussed. Alternative scenarios of drawing the beam from the galactic CR background are considered. The beam related large scale anisotropic CR component is found to be energy independent which is also consistent with the observations.Comment: 2 figures, ApJ accepted version2 minor changes and correction

Electroweak Physics, Experimental Aspects

Collider measurements on electroweak physics are summarised. Although the precision on some observables is very high, no deviation from the Standard Model of electroweak interactions is observed. The data allow to set stringent limits on some models for new physics.Comment: Plenary Talk at the UK Phenomenology Workshop on Collider Physics, Durham, 199