1,167 research outputs found
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 and
10 cm. The spectrum is dominated by vibrationally excited HCN,
HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find high
abundances of HCN, SiO, HS, and c-HCCCH and a low CHOH 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 CHOH 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
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 LagrangianâEulerian 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
Structural and compositional properties of brown dwarf disks: the case of 2MASS J04442713+2512164
In order to improve our understanding of substellar formation, we have
performed a compositional and structural study of a brown dwarf disk.
We present the result of photometric, spectroscopic and imaging observations
of 2MASS J04442713+2512164, a young brown dwarf (M7.25) member of the Taurus
association. Our dataset, combined with results from the literature, provides a
complete coverage of the spectral energy distribution from the optical to the
millimeter including the first photometric measurement of a brown dwarf disk at
3.7mm, and allows us to perform a detailed analysis of the disk properties.
The target was known to have a disk. High resolution optical spectroscopy
shows that it is intensely accreting, and powers a jet and an outflow. The disk
structure is similar to that observed for more massive TTauri stars. Spectral
decomposition models of Spitzer/IRS spectra suggest that the mid-infrared
emission from the optically thin disk layers is dominated by grains with
intermediate sizes (1.5micron). Crystalline silicates are significantly more
abondant in the outer part and/or deeper layers of the disk, implying very
efficient mixing and/or additional annealing processes. Sub-millimeter and
millimeter data indicate that most of the disk mass is in large grains (>1mm)Comment: 17 pages, 10 figures, 7 tables, accepted for A&
Simulation of facet heating in high-power red lasers
A two-dimensional self-consistent laser model has been used for the simulation of the facet heating of red emitting AlGaInP lasers. It solves in the steady-state the complete semiconductor optoelectronic and thermal equations in the epitaxial and longitudinal directions and takes into account the population of different conduction band valleys. The model considers the possibility of two independent mechanisms contributing to the facet heating: recombination at surface traps and optical absorption at the facet. The simulation parameters have been calibrated by comparison with measurements of the temperature dependence of the threshold current and slope efficiency of broad-area lasers. Facet temperature has been measured by micro-Raman spectrometry in devices with standard and non absorbing mirrors evidencing an effective decrease of the facet heating due to the non absorbing mirrors. A good agreement between experimental values and calculations is obtained for both devices when a certain amount of surface traps and optical absorption is assumed. A simulation analysis of the effect of non absorbing mirrors in the reduction of facet heating in terms of temperature, carrier density, material gain and Shockly-Read-Hall recombination rate profiles is provided
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