Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies: An ALMA mm-wave spectral scan of NGC 4418

We obtained an ALMA Cycle 0 spectral scan of the dusty LIRG NGC 4418, spanning a total of 70.7 GHz in bands 3, 6, and 7. We use a combined local thermal equilibrium (LTE) and non-LTE (NLTE) fit of the spectrum in order to identify the molecular species and derive column densities and excitation temperatures. We derive molecular abundances and compare them with other Galactic and extragalactic sources by means of a principal component analysis. We detect 317 emission lines from a total of 45 molecular species, including 15 isotopic substitutions and six vibrationally excited variants. Our LTE/NLTE fit find kinetic temperatures from 20 to 350 K, and densities between 10$^5$ and 10$^7$ cm$^{-3}$. The spectrum is dominated by vibrationally excited HC$_3$N, HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find high abundances of HC$_3$N, SiO, H$_2$S, and c-HCCCH and a low CH$_3$OH abundance. A principal component analysis shows that NGC 4418 and Arp 220 share very similar molecular abundances and excitation, which clearly set them apart from other Galactic and extragalactic environments. The similar molecular abundances observed towards NCG 4418 and Arp 220 are consistent with a hot gas-phase chemistry, with the relative abundances of SiO and CH$_3$OH being regulated by shocks and X-ray driven dissociation. The bright emission from vibrationally excited species confirms the presence of a compact IR source, with an effective diameter $$350 K. The molecular abundances and the vibrationally excited spectrum are consistent with a young AGN/starburst system. We suggest that NGC 4418 may be a template for a new kind of chemistry and excitation, typical of compact obscured nuclei (CON). Because of the narrow line widths and bright molecular emission, NGC 4418 is the ideal target for further studies of the chemistry in CONs.Comment: accepted by A&A on 29/06/201

Widespread HCO emission in the M82's nuclear starburst

We present a high-resolution (~ 5'') image of the nucleus of M82 showing the presence of widespread emission of the formyl radical (HCO). The HCO map, the first obtained in an external galaxy, reveals the existence of a structured disk of ~ 650 pc full diameter. The HCO distribution in the plane mimics the ring morphology displayed by other molecular/ionized gas tracers in M82. More precisely, rings traced by HCO, CO and HII regions are nested, with the HCO ring lying in the outer edge of the molecular torus. Observations of HCO in galactic clouds indicate that the abundance of HCO is strongly enhanced in the interfaces between the ionized and molecular gas. The surprisingly high overall abundance of HCO measured in M82 (X(HCO) ~ 4x10^{-10}) indicates that its nuclear disk can be viewed as a giant Photon Dominated Region (PDR) of ~ 650 pc size. The existence of various nested gas rings, with the highest HCO abundance occurring at the outer ring (X(HCO) ~ 0.8x10^{-9}), suggests that PDR chemistry is propagating in the disk. We discuss the inferred large abundances of HCO in M82 in the context of a starburst evolutionary scenario, picturing the M82 nucleus as an evolved starburst.Comment: 13 pages, 3 figures, to appear in ApJ Letters; corrected list of author

Quantitative assessment and comparison of cloud service providers' privacy practices

The economic and technical advantages of cloud computing are widely recognized by the industry. However, the lack of knowledge on the privacy features offered by cloud service providers remains as one of the barriers for the adoption of cloud services. In this paper we describe a mechanism for the quantitative assessment of the privacy practices of different cloud service providers, so that cloud service clients can compare among them and choose the one that better fits their needs. Our contributions have been validated in three different scenarios

Large scale grain mantle disruption in the Galactic Center

We present observations of C2H5OH toward molecular clouds in Sgr A, Sgr B2 and associated with thermal and non-thermal features in the Galactic center. C2H5OH emission in Sgr A and Sgr B2 is widespread, but not uniform. C2H5OH emission is much weaker or it is not detected in some molecular clouds in both complexes, in particular those with radial velocities between 70 and 120 km/s. While most of the clouds associated with the thermal features do not show C2H5OH emission, that associated with the Non-Thermal Radio Arc shows emission. The fractional abundance of C2H5OH in most of the clouds with radial velocities between 0 and 70 km/s in Sgr A and Sgr B2 is relatively high, of few 1e-8. The C2H5OH abundance decreases by more than one order of magnitude (aprox. 1e-9) in the clouds associated with the thermal features. The large abundance of C2H5OH in the gas-phase indicates that C2H5OH has formed in grains and released to gas-phase by shocks in the last aprox. 1e5 years.Comment: In press in Astrophysical Journal Letters 7 pages, 1 table, 1 figur

Classical and semi-classical energy conditions

The standard energy conditions of classical general relativity are (mostly) linear in the stress-energy tensor, and have clear physical interpretations in terms of geodesic focussing, but suffer the significant drawback that they are often violated by semi-classical quantum effects. In contrast, it is possible to develop non-standard energy conditions that are intrinsically non-linear in the stress-energy tensor, and which exhibit much better well-controlled behaviour when semi-classical quantum effects are introduced, at the cost of a less direct applicability to geodesic focussing. In this article we will first review the standard energy conditions and their various limitations. (Including the connection to the Hawking--Ellis type I, II, III, and IV classification of stress-energy tensors). We shall then turn to the averaged, nonlinear, and semi-classical energy conditions, and see how much can be done once semi-classical quantum effects are included.Comment: V1: 25 pages. Draft chapter, on which the related chapter of the book "Wormholes, Warp Drives and Energy Conditions" (to be published by Springer), will be based. V2: typos fixed. V3: small typo fixe

SiO chimneys and supershells in M82

In this Letter we present the first images of the emission of SiO and H13CO+ in the nucleus of the starburst galaxy M82. Contrary to other molecular species that mainly trace the distribution of the star-forming molecular gas within the disk, the SiO emission extends noticeably out of the galaxy plane. The bulk of the SiO emission is restricted to two major features. The first feature, referred to as the SiO supershell, is an open shell of 150 pc diameter, located 120 pc west from the galaxy center. The SiO supershell represents the inner front of a molecular shell expanding at 40 km/s, produced by mass ejection around a supercluster of young stars containing supernova remnant SNR 41.95+57.5. The second feature is a vertical filament, referred to as the SiO chimney, emanating from the disk at 200 pc east from the galaxy center. The SiO chimney reaches a 500 pc vertical height, and it is associated with the most prominent chimney identified in radio continuum maps. The kinematics, morphology, and fractional abundances of the SiO gas features in M82 can be explained in the framework of shocked chemistry driven by local episodes of gas ejection from the starburst disk.Comment: 10 pages, 2 figures, published in ApJLetters, 200

Incorporating chemical signalling factors into cell-based models of growing epithelial tissues

In this paper we present a comprehensive computational framework within which the effects of chemical signalling factors on growing epithelial tissues can be studied. The method incorporates a vertex-based cell model, in conjunction with a solver for the governing chemical equations. The vertex model provides a natural mesh for the finite element method (FEM), with node movements determined by force laws. The arbitrary Lagrangian–Eulerian formulation is adopted to account for domain movement between iterations. The effects of cell proliferation and junctional rearrangements on the mesh are also examined. By implementing refinements of the mesh we show that the finite element (FE) approximation converges towards an accurate numerical solution. The potential utility of the system is demonstrated in the context of Decapentaplegic (Dpp), a morphogen which plays a crucial role in development of the Drosophila imaginal wing disc. Despite the presence of a Dpp gradient, growth is uniform across the wing disc. We make the growth rate of cells dependent on Dpp concentration and show that the number of proliferation events increases in regions of high concentration. This allows hypotheses regarding mechanisms of growth control to be rigorously tested. The method we describe may be adapted to a range of potential application areas, and to other cell-based models with designated node movements, to accurately probe the role of morphogens in epithelial tissues

Hamiltonian embedding of the massive noncommutative U(1) theory

We show that the massive noncommutative U(1) can be embedded in a gauge theory by using the BFFT Hamiltonian formalism. By virtue of the peculiar non-Abelian algebraic structure of the noncommutative massive U(1) theory, several specific identities involving Moyal commutators had to be used in order to make the embedding possible. This leads to an infinite number of steps in the iterative process of obtaining first-class constraints. We also shown that the involutive Hamiltonian can be constructed.Comment: 8 pages, Revtex (multicol