ALMA detection of [CII] 158 micron emission from a strongly lensed z=2 star-forming galaxy

Our objectives are to determine the properties of the interstellar medium (ISM) and of star-formation in typical star-forming galaxies at high redshift. Following up on our previous multi-wavelength observations with HST, Spitzer, Herschel, and the Plateau de Bure Interferometer (PdBI), we have studied a strongly lensed z=2.013 galaxy, the arc behind the galaxy cluster MACS J0451+0006, with ALMA to measure the [CII] 158 micron emission line, one of the main coolants of the ISM. [CII] emission from the southern part of this galaxy is detected at 10 $\sigma$. Taking into account strong gravitational lensing, which provides a magnification of $\mu=49$, the intrinsic lensing-corrected [CII]158 micron luminosity is $L(CII)=1.2 \times 10^8 L_\odot$. The observed ratio of [CII]-to-IR emission, $L(CII)/L(FIR) \approx (1.2-2.4) \times 10^{-3}$, is found to be similar to that in nearby galaxies. The same also holds for the observed ratio $L(CII)/L(CO)=2.3 \times 10^3$, which is comparable to that of star-forming galaxies and active galaxy nuclei (AGN) at low redshift. We utilize strong gravitational lensing to extend diagnostic studies of the cold ISM to an order of magnitude lower luminosity ($L(IR) \sim (1.1-1.3) \times 10^{11} L_\odot$) and SFR than previous work at high redshift. While larger samples are needed, our results provide evidence that the cold ISM of typical high redshift galaxies has physical characteristics similar to normal star forming galaxies in the local Universe.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy & Astrophysics, Letter

Molecular gas in NUclei of GAlaxies (NUGA) XV. Molecular gas kinematics in the inner 3kpc of NGC6951

Within the NUclei of GAlaxies project we have obtained IRAM PdBI and 30m 12CO(1-0) and 12CO(2-1) observations of the spiral galaxy NGC 6951. Previous work shows that there is indirect evidence of gas inflow from 3 kpc down to small radii: a large-scale stellar bar, a prominent starburst ring (r~580 pc) and a LINER/Seyfert 2 nucleus. In this paper we study the gas kinematics as traced by the CO line emission in detail. We quantify the influence of the large-scale stellar bar by constructing an analytical model of the evolution of gas particles in a barred potential. From this model gravitational torques and mass accumulation rates are computed. We compare our model-based gravitational torque results with previous observationally-based ones. The model also shows that the large-scale stellar bar is indeed the dominant force for driving the gas inward, to the starburst ring. Inside the ring itself a nuclear stellar oval might play an important role. Detailed analysis of the CO gas kinematics there shows that emission arises from two co-spatial, but kinematically distinct components at several locations. The main emission component can always be related to the overall bar-driven gas kinematics. The second component exhibits velocities that are larger than expected for gas on stable orbits, has a molecular gas mass of 1.8x10^6Msun, is very likely connected to the nuclear stellar oval, and is consistent with inflowing motion towards the very center. This may form the last link in the chain of gas inflow towards the active galactic nucleus in NGC 6951.Comment: 17 pages, accepted by A&A (17 feb 2011

Grasses continue to trump trees at soil carbon sequestration following herbivore exclusion in a semiarid African savanna

Although studies have shown that mammalian herbivores often limit aboveground carbon storage in savannas, their effects on belowground soil carbon storage remain unclear. Using three sets of long‐term, large herbivore exclosures with paired controls, we asked how almost two decades of herbivore removal from a semiarid savanna in Laikipia, Kenya affected aboveground (woody and grass) and belowground soil carbon sequestration, and determined the major source (C3 vs. C4) of belowground carbon sequestered in soils with and without herbivores present. Large herbivore exclusion, which included a diverse community of grazers, browsers, and mixed‐feeding ungulates, resulted in significant increases in grass cover (~22%), woody basal area (~8 m2/ha), and woody canopy cover (31%), translating to a ~8.5 t/ha increase in aboveground carbon over two decades. Herbivore exclusion also led to a 54% increase (20.5 t/ha) in total soil carbon to 30‐cm depth, with ~71% of this derived from C4 grasses (vs. ~76% with herbivores present) despite substantial increases in woody cover. We attribute this continued high contribution of C4 grasses to soil C sequestration to the reduced offtake of grass biomass with herbivore exclusion together with the facilitative influence of open sparse woody canopies (e.g., Acacia spp.) on grass cover and productivity in this semiarid system

Stratospheric Lifetimes of CFC-12, CCl4, CH4, CH3CL and N20 from Measurements Made By The Atmospheric Chemistry Experiment-Fourier Transform Spectrometer

Long lived halogen-containing compounds are important atmospheric constituents since they can act both as a source of chlorine radicals, which go on to catalyse ozone loss, and as powerful greenhouse gases. The long-term impact of these species on the ozone layer is dependent on their stratospheric lifetimes. Using observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) we present calculations of the stratospheric lifetimes of CFC-12, CCl4, CH4, CH3Cl and N2O. The lifetimes were calculated using the slope of the tracer-tracer correlation of these species with CFC-11 at the tropopause. The correlation slopes were corrected for the changing atmospheric concentrations of each species based on age of air and CFC-11 measurements from samples taken aboard the Geophysica aircraft - along with the effective linear trend of the volume mixing ratio (VMR) from tropical ground based AGAGE (Advanced Global Atmospheric Gases Experiment) sites. Stratospheric lifetimes were calculated using a CFC-11 lifetime of 45 yr. These calculations produced values of 113 + (-) 26 (18) yr (CFC-12), 35 + (-) 11 (7) yr (CCl4), 69 + (-) 65 (23) yr (CH3Cl), 123 + (-) 53 (28) yr (N2O) and 195 + (-) 75 (42) yr (CH4). The errors on these values are the weighted 1 sigma non-systematic errors. Systematic errors were estimated by recalculating lifetimes using VMRs which had been modified to reflect differences between ACE-FTS retrieved VMRs and those from other instruments. The results of these calculations, including systematic errors, were as follows: 113 + (-) 32 (20) for CFC-12, 123 + (-) 83 (35) for N2O, 195 + (-) 139 (57) for CH4, 35 + (-) 14 (8) for CCl4 and 69 + (-) 2119 (34) yr for CH3Cl. For CH3Cl & CH4 this represents the first calculation of the stratospheric lifetime using data from a space based instrument

Growth Of Tungsten Selenide Films Through Pyrolytic Conversion And Anodic Electrooxidation Of Ammonium Selenotungstate ((NH4)2WSe4)

WxSey thin films have been prepared by the spray pyrolysis and anodic electrodeposition of solutions of ammonium selenotungstate, (NH4)2WSe4, with y/x usually between two and three for the sprayed films and y x\u3e\u3e1 for the electrodeposited films. The sprayed films indicated regions of crystalline WSe2 and have optical absorbance spectra consistent with a mixture of WSe2, WSe3, and selenium. The electrodeposited films are totally amorphous, highly photoconductive, and have optical absorbance spectra typical of amorphous or vitreous selenium. The sprayed films transform into WO3 at temperatures greater than 350°C in the presence of oxygen wile the electrode-posited films tend to evaporate and/or decompose upon annealing. © 1985

Rapid Domain Wall Motion in Permalloy Nanowires Excited by Spin-Polarized Current Applied Perpendicular to the Nanowire

We study domain wall (DW) dynamics in permalloy nanowires excited by alternating spin-polarized current applied perpendicular to the nanowire. Spin torque ferromagnetic resonance measurements reveal that DW oscillations at a pinning site in the nanowire can be excited with velocities as high as 800 m/s at current densities below 10$^7$ A/cm$^2$

Derivation of tropospheric methane from TCCON CH₄ and HF total column observations

The Total Carbon Column Observing Network (TCCON) is a global ground-based network of Fourier transform spectrometers that produce precise measurements of column-averaged dry-air mole fractions of atmospheric methane (CH₄). Temporal variability in the total column of CH₄ due to stratospheric dynamics obscures fluctuations and trends driven by tropospheric transport and local surface fluxes that are critical for understanding CH₄ sources and sinks. We reduce the contribution of stratospheric variability from the total column average by subtracting an estimate of the stratospheric CH₄ derived from simultaneous measurements of hydrogen fluoride (HF). HF provides a proxy for stratospheric CH₄ because it is strongly correlated to CH₄ in the stratosphere, has an accurately known tropospheric abundance (of zero), and is measured at most TCCON stations. The stratospheric partial column of CH₄ is calculated as a function of the zonal and annual trends in the relationship between CH₄ and HF in the stratosphere, which we determine from ACE-FTS satellite data. We also explicitly take into account the CH₄ column averaging kernel to estimate the contribution of stratospheric CH₄ to the total column. The resulting tropospheric CH₄ columns are consistent with in situ aircraft measurements and augment existing observations in the troposphere