On the X-ray Properties of OH Megamaser Sources: Chandra Snapshot Observations

We present Chandra snapshot observations for a sample of 7 sources selected from the Arecibo OH megamaser (OHM) survey at z~0.13-0.22 and with far-infrared luminosities in excess of 10^{11} L_sun. In contrast with the known H2O megamasers, which are mostly associated with powerful Active Galactic Nuclei (AGN), the situation is far less clear for OHMs, which have been poorly studied in the X-ray band thus far. All of the observed sources are X-ray weak, with only one OHM, IRAS FSC 03521+0028 (z=0.15), being detected by Chandra (with 5 counts). The results from this pilot program indicate that the X-ray emission, with luminosities of less than ~10^{42} erg/s, is consistent with that from star formation (as also suggested in some cases by the optical spectra) and low-luminosity AGN emission. If an AGN is present, its contribution to the broad-band emission of OHM galaxies is likely modest. Under reasonable assumptions about the intrinsic X-ray spectral shape, the observed count distribution from stacking analysis suggests absorption of ~10^{22} cm^{-2}.Comment: 8 pages, 3 figures, accepted for publication in MNRA

Draft Genome Sequence of Curtobacterium flaccumfaciens Strain UCD-AKU (Phylum Actinobacteria).

Here we present the draft genome of an actinobacterium, Curtobacterium flaccumfaciens strain UCD-AKU, isolated from a residential carpet. The genome assembly contains 3,692,614 bp in 130 contigs. This is the first member of the Curtobacterium genus to be sequenced

High-dimensional quantum dynamics of adsorption and desorption of H2_2 at Cu(111)

We performed high-dimensional quantum dynamical calculations of the dissociative adsorption and associative desorption of hydrogen on Cu(111). The potential energy surface (PES) is obtained from density functional theory calculations. Two regimes of dynamics are found, at low energies sticking is determined by the minimum energy barrier, at high energies by the distribution of barrier heights. Experimental results are well-reproduced qualitatively, but some quantitative discrepancies are identified as well.Comment: 4 two column pages, revtex, 4 figures, to appear in Phys. Rev. Let

Relaxation at late stages in an entropy barrier model for glassy systems

The ground state dynamics of an entropy barrier model proposed recently for describing relaxation of glassy systems is considered. At stages of evolution the dynamics can be described by a simple variant of the Ehrenfest urn model. Analytical expression for the relaxation times from an arbitrary state to the ground state is derived. Upper and lower bounds for the relaxation times as a function of system size are obtained.Comment: 9 pages no figures. to appear in J.Phys. A: Math. and Ge

HI and OH absorption in the lensing galaxy of MG J0414+0534

We report the detection of \HI 21-cm absorption in the $z=0.96$ early-type lensing galaxy towards MG J0414+0534 with the Green Bank Telescope. The absorption, with total $N_{\rm HI}=1.6 \times 10^{18} (T_{\rm s}/f) {\rm cm}^{-2}$, is resolved into two strong components, probably due to the two strongest lens components, which are separated by 0.4\arcsec. Unlike the other three lenses which have been detected in \HI, J0414+0534 does not exhibit strong OH absorption, giving a OH/\HI column density ratio of N_{\rm OH}/N_{\rm HI}\lapp10^{-6} (for $T_{\rm s}=100$ K, $T_{\rm x}=10$ K and $f_{\rm HI}=f_{\rm OH}=1$). This underabundance of molecular gas may indicate that the extreme optical--near-IR colour ($V-K=10.26$) along the line-of-sight is not due to the lens. We therefore suggest that despite the strong upper limits on molecular absorption at the quasar redshift, as traced by millimetre lines, the extinction occurs primarily in the quasar host galaxy.Comment: Accepted by MNRAS Letters, 5 (and a bit) pages, 5 figure

ALMA Observations of Circumnuclear Disks in Early Type Galaxies: 12CO(2-1) and Continuum Properties

We present results from an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 program to map CO(2-1) emission in nearby early-type galaxies (ETGs) that host circumnuclear gas disks. We obtained $\sim0.3''-$resolution Band 6 observations of seven ETGs selected on the basis of dust disks in Hubble Space Telescope images. We detect CO emission in five at high signal-to-noise ratio with the remaining two only faintly detected. All CO emission is coincident with the dust and is in dynamically cold rotation. Four ETGs show evidence of rapid central rotation; these are prime candidates for higher-resolution ALMA observations to measure the black hole masses. In this paper we focus on the molecular gas and continuum properties. Total gas masses and H$_2$ column densities for our five CO-bright galaxies are on average $\sim10^8$ $M_\odot$ and $\sim10^{22.5}$ cm$^{-2}$ over the $\sim$kpc-scale disks, and analysis suggests that these disks are stabilized against gravitational fragmentation. The continuum emission of all seven galaxies is dominated by a central, unresolved source, and in five we also detect a spatially extended component. The $\sim$230 GHz nuclear continua are modeled as power laws ranging from $S_\nu \sim \nu^{-0.4}$ to $\nu^{1.6}$ within the observed frequency band. The extended continuum profiles of the two radio-bright (and CO-faint) galaxies are roughly aligned with their radio jet and suggests resolved synchrotron jets. The extended continua of the CO-bright disks are coincident with optically thick dust absorption and have spectral slopes that are consistent with thermal dust emission.Comment: 20 pages, 10 figures; accepted for publication in Ap

Elastic and thermodynamic properties of the shape-memory alloy AuZn

The current work reports on the elastic shear moduli, internal friction, and the specific heat of the B2 cubic ordered alloy AuZn as a function of temperature. Measurements were made on single-crystal and polycrystalline samples using Resonant Ultrasound Spectroscopy (RUS), semi-adiabatic calorimetry and stress-strain measurements. Our results confirm that this alloy exhibits the shape-memory effect and a phase transition at 64.75 K that appears to be continuous (second-order) from the specific heat data. It is argued that the combination of equiatomic composition and a low transformation temperature constrain the chemical potential and its derivatives to exhibit behavior that lies at the borderline between that of a first-order (discontinuous) and a continuous phase transition. The acoustic dissipation does not peak at the transtion temperature as expected, but shows a maximum well into the low-temperature phase. The Debye temeprature value of 219 K, obtained from the low-temperature specific heat data is in favorable agreement with that determined from the acoustic data (207 K) above the transition.Comment: 25 pages, 6 figures, submitted to Phys. Rev.

Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: Bitartrate on Cu(110)

Local or global ordering of chiral molecules at a surface is a key step in both chiral separation and heterogeneous enantioselective catalysis. Using density functional theory and scanning probe microscopy results, we find that the accepted structural model for the well known bitartrate on Cu(110) chiral system cannot account for the chiral segregation observed. Instead, we show that this strongly bound, chiral adsorbate changes its adsorption footprint in response to the local environment. The flexible adsorption geometry allows bitartrate to form stable homochiral trimer chains in which the central molecule restructures from a rectangular to an oblique footprint, breaking its internal hydrogen bonds in order to form strong intermolecular hydrogen bonds to neighbouring adsorbates. Racemic structures containing mixed enantiomers do not form strong hydrogen bonds, providing the thermodynamic driving force for the chiral separation that is observed experimentally. This result shows the importance of considering the dynamical response of molecular adsorption footprints at the surface in directing chiral assembly and segregation. The ability of strongly-chemisorbed enantiomers to change footprint depending on the local adsorption environment indicates that supramolecular assemblies at surfaces may exhibit more complex dynamical behaviour than hitherto suspected, which, ultimately, could be tailored to lead to environment and stimuli-responsive chiral surfaces

Detection of chloronium and measurement of the 35Cl/37Cl isotopic ratio at z=0.89 toward PKS1830-211

We report the first extragalactic detection of chloronium (H2Cl+), in the z=0.89 absorber in front of the lensed blazar PKS1830-211. The ion is detected through its 1_11-0_00 line along two independent lines of sight toward the North-East and South-West images of the blazar. The relative abundance of H2Cl+ is significantly higher (by a factor ~7) in the NE line of sight, which has a lower H2/H fraction, indicating that H2Cl+ preferably traces the diffuse gas component. From the ratio of the H2^35Cl+ and H2^37Cl+ absorptions toward the SW image, we measure a 35Cl/37Cl isotopic ratio of 3.1 (-0.2; +0.3) at z=0.89, similar to that observed in the Galaxy and the solar system.Comment: Accepted for publication in A&A Lette

THE COMPARISON OF PHYSICAL PROPERTIES DERIVED FROM GAS AND DUST IN A MASSIVE STAR-FORMING REGION

We explore the relationship between gas and dust in a massive star-forming region by comparing the physical properties derived from each. We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud (G32.02+0.05), which shows a range of evolutionary states, from quiescent to active. The gas properties were derived using radiative transfer modeling of the (1,1), (2,2), and (4,4) transitions of NH3 on the Karl G. Jansky Very Large Array, while the dust temperatures and column densities were calculated using cirrus-subtracted, modified blackbody fits to Herschel data. We compare the derived column densities to calculate an NH3 abundance, χ$_{{\rm NH}_{3}}$ = 4.6 × 10–8. In the coldest star-forming region, we find that the measured dust temperatures are lower than the measured gas temperatures (mean and standard deviations T dust, avg ~ 11.6 ± 0.2 K versus T gas, avg ~ 15.2 ± 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (~0.5 Myr) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable. Finally, we calculate millimeter fluxes based on the temperatures and column densities derived from NH3, which suggest that millimeter dust continuum observations of massive star-forming regions, such as the Bolocam Galactic Plane Survey or ATLASGAL, can probe hot cores, cold cores, and the dense gas lanes from which they form, and are generally not dominated by the hottest core