811 research outputs found
A Spitzer Study of Interacting Luminous and Ultra-Luminous Infrared Galaxies
We conducted a Spitzer Space Telescope survey of 28 Luminous (11 <
log(LIR/L_odot) < 12, LIRGs) and Ultra-Luminous Infrared Galaxies
(log(LIR/L_odot) > 12, ULIRGs). Many of these galaxies are found in pairs or
associations and are powered by either nuclear activity or starformation
(Sanders & Mirabel 1996). Our main goal is to understand the relative
importance of starbursts and AGNs in interacting systems. Is the frequency of
AGN and starbursts in these interacting galaxies related to their luminosities?
What is the importance of the merger stage and the frequency of AGNs? We
present our conclusions and diagnostic diagrams based in the observed near
infrared lines and compare to studies based solely in optical data.Comment: 3 pages, 2 figures, to appear in the Spectral Energy Distribution of
Galaxies (SED2011) conference proceedings, Preston, UK, 201
Transformations between the theoretical and observational planes in the HST-NICMOS and WFPC2 photometric systems
Color-temperature relations and bolometric corrections in the HST-NICMOS
F1110W, F160W and F222M and in the WFPC2 F439W, F555W and F814W photometric
systems, using two different sets of model atmospheres, have been derived. This
database of homogeneous, self-consistent transformations between the
theoretical and observational planes also allows combinations of visual and
infrared quantities, without any further transformation between the two
different photometric systems. The behavior of the inferred quantities with
varying the stellar parameters, the adopted model atmospheres and the
instrumental configurations are investigated. Suitable relations to transform
colors and bolometric corrections from HST to ground-based photometric systems
are also provided.Comment: 22 pages, 14 figure
Modeling charge transport in C60-based self-assembled monolayers for applications in field-effect transistors
We have investigated the conductance properties of C60-containing
self-assembled monolayers (SAMs), which are used in organic field-effect
transistors, employing a combination of molecular-dynamics simulations,
semiempirical electronic structure calculations and Landauer transport theory.
The results reveal the close relation between the transport characteristics and
the structural and electronic properties of the SAM. Furthermore, both local
pathways of charge transport in the SAMs and the influence of structural
fluctuations are analyzed.Comment: 10 figure
Modelling the Pan-Spectral Energy Distributions of Starburst & Active Galaxies
We present results of a self-consistent model of the spectral energy
distribution (SED) of starburst galaxies. Two parameters control the IR SED,
the mean pressure in the ISM and the destruction timescale of molecular clouds.
Adding a simplified AGN spectrum provides mixing lines on IRAS color : color
diagrams. This reproduces the observed colors of both AGNs and starbursts.Comment: Poster Paper for IAU 222: The Interplay among Black Holes, Stars and
ISM in Galactic Nucle
Comparison of Theoretical Starburst Photoionisation Models for Optical Diagnostics
We study and compare different examples of stellar evolutionary synthesis
input parameters used to produce photoionisation model grids using the MAPPINGS
V modelling code. The aim of this study is to (a) explore the systematic
effects of various stellar evolutionary synthesis model parameters on the
interpretation of emission lines in optical strong-line diagnostic diagrams,
(b) characterise the combination of parameters able to reproduce the spread of
local galaxies located in the star-forming region in the Sloan Digital Sky
Survey, and (c) investigate the emission from extremely metal-poor galaxies
using photoionisation models. We explore and compare the stellar input ionising
spectrum (stellar population synthesis code [Starburst99, SLUG, BPASS], stellar
evolutionary tracks, stellar atmospheres, star-formation history, sampling of
the initial mass function) as well as parameters intrinsic to the H II region
(metallicity, ionisation parameter, pressure, H II region boundedness). We also
perform a comparison of the photoionisation codes MAPPINGS and CLOUDY. On the
variations in the ionising spectrum model parameters, we find that the
differences in strong emission-line ratios between varying models for a given
input model parameter are small, on average ~0.1 dex. An average difference of
~0.1 dex in emission-line ratio is also found between models produced with
MAPPINGS and CLOUDY. Large differences between the emission-line ratios are
found when comparing intrinsic H II region parameters. We find that
low-metallicity galaxies are better explained by a density-bounded H II region
and higher pressures better encompass the spread of galaxies at high redshift.Comment: 33 pages, 26 figures, accepted for publication in Ap
The Luminosity Function of Young Star Clusters In "The Antennae" Galaxies (NGC 4038/4039)
The WFPC2 of the HST has been used to obtain high-resolution images of NGC
4038/4039 that go roughly 3 magnitudes deeper in V than previous observations
made during Cycle 2 (-14 < M_V < -6). To first order the luminosity function
(LF) is a power law, with exponent \alpha = -2.12 +/- 0.04. However, after
decoupling the cluster and stellar LFs, which overlap in the range -9 < M_V <
-6, we find an apparent bend in the young cluster LF at approximately M_V =
-10.4. The LF has a power law exponent -2.6 +/- 0.2 in the brightward and -1.7
+/- 0.2 in the faintward. The bend corresponds to a mass ~ 10^5 M_{\odot}, only
slightly lower than the characteristic mass of globular clusters in the Milky
Way (~2x10^5 M_{\odot}). The star clusters of the Antennae appear slightly
resolved, with median effective radii of 4 +/- 1 pc, similar to or perhaps
slightly larger than those of globular clusters in our Galaxy. However, the
radial extents of some of the very young clusters (ages < 10 Myr) are much
larger than those of old globular clusters. A combination of the UBVI colors,
\Halpha morphology, and GHRS spectra enables us to age-date the clusters in
different regions of The Antennae. We find two groups of young star clusters
with ages <~ 20Myr and ~100Myr, as well as an intermediate-age group (~500 Myr)
and a handful of old globular clusters from the progenitor galaxies. Age
estimates derived from GHRS spectroscopy yield 3 +/- 1 Myr for Knot K (just
south of the nucleus of NGC 4038) and 7 +/- 1 Myr for Knot S in the Western
Loop, in good agreement with ages derived from the UBVI colors. Effective
gas-outflow velocities from Knots S and K are estimated to be about 25-30 km/s.
However, the measured widths of the interstellar absorption lines suggest
dispersion velocities of ~400 km/s along the lines of sight to Knots S and K.Comment: 56 pages, 4 tables and 23 figures, texts in AAS style, to be
published in A
Electric-field control of a single-atom polar bond
The polar covalent bond between a single Au atom terminating the apex of an
atomic force microscope tip and a C atom of graphene on SiC(0001) is exposed to
an external electric field. For one field orientation the Au-C bond is strong
enough to sustain the mechanical load of partially detached graphene, whilst
for the opposite orientation the bond breaks easily. Calculations based on
density functional theory and nonequilibrium Green's function methods support
the experimental observations by unveiling bond forces that reflect the polar
character of the bond. Field-induced charge transfer between the atomic
orbitals modifies the polarity of the different electronegative reaction
partners and the Au-C bond strength
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