553 research outputs found
Resolved CO(1-0) Nuclei in IRAS 14348-1447: Evidence for Massive Bulge Progenitors to Ultraluminous Infrared Galaxies
High-resolution, CO(1-0) interferometry of the ultraluminous infrared galaxy
IRAS 14348-1447 is presented. The merger system has a molecular gas mass of
\~3x10^10 solar masses and a projected nuclear separation of 4.8 kpc (3.5"),
making it one of the most molecular gas-rich galaxies known and an ideal
candidate for studying the intermediate stages of an ultraluminous merger
event. The CO morphology shows two molecular gas components associated with the
stellar nuclei of the progenitors, consistent with the idea that the molecular
disks are gravitationally bound by the dense bulges of the progenitor galaxies
as the interaction proceeds. In contrast, less luminous infrared galaxies
observed to date with projected nuclear separations of ~<5 kpc show a dominant
CO component between the stellar nuclei. This discrepancy may be an indication
that the progenitors of mergers with lower infrared luminosity do not possess
massive bulges, and that the gas is stripped during the initial encounter of
their progenitors. A comparison of the CO and radio luminosities of the NE and
SW component show them to have comparable radio and CO flux ratios of
f(NE)/f(SW) ~0.6, possibly indicating that the amount of star-forming molecular
gas in the progenitors is correlated with the supernovae rate. The estimate of
molecular gas masses of the nuclei and the extent of the radio emission are
used to infer that the nuclei of IR 14348-1447 have gas densities comparable to
the cores of elliptical galaxies.Comment: LaTex, 5 pages with 1 postscript and 1 jpg figure, ApJ Letters, in
pres
Nonlinear quantum model for atomic Josephson junctions with one and two bosonic species
We study atomic Josephson junctions (AJJs) with one and two bosonic species
confined by a double-well potential. Proceeding from the second quantized
Hamiltonian, we show that it is possible to describe the zero-temperature AJJs
microscopic dynamics by means of extended Bose-Hubbard (EBH) models, which
include usually-neglected nonlinear terms. Within the mean-field approximation,
the Heisenberg equations derived from such two-mode models provide a
description of AJJs macroscopic dynamics in terms of ordinary differential
equations (ODEs). We discuss the possibility to distinguish the Rabi,
Josephson, and Fock regimes, in terms of the macroscopic parameters which
appear in the EBH Hamiltonians and, then, in the ODEs. We compare the
predictions for the relative populations of the Bose gases atoms in the two
wells obtained from the numerical solutions of the two-mode ODEs, with those
deriving from the direct numerical integration of the Gross-Pitaevskii
equations (GPEs). Our investigations shows that the nonlinear terms of the ODEs
are crucial to achieve a good agreement between ODEs and GPEs approaches, and
in particular to give quantitative predictions of the self-trapping regime.Comment: Accepted for the publication in J. Phys. B: At. Mol. Opt. Phy
Evidences for a quasi 60-year North Atlantic Oscillation since 1700 and its meaning for global climate change
The North Atlantic Oscillation (NAO) obtained using instrumental and
documentary proxy predictors from Eurasia is found to be characterized by a
quasi 60-year dominant oscillation since 1650. This pattern emerges clearly
once the NAO record is time integrated to stress its comparison with the
temperature record. The integrated NAO (INAO) is found to well correlate with
the length of the day (since 1650) and the global surface sea temperature
record HadSST2 and HadSST3 (since 1850). These findings suggest that INAO can
be used as a good proxy for global climate change, and that a 60-year cycle
exists in the global climate since at least 1700. Finally, the INAO ~60-year
oscillation well correlates with the ~60- year oscillations found in the
historical European aurora record since 1700, which suggests that this 60-year
dominant climatic cycle has a solar-astronomical origin
Optimization of PECVD process for ultra thin tunnel SiOx film as passivation layer for silicon heterojunction solar cells
Ultra thin silicon oxide a SiOx H films have been grown by means of plasma enhanced chemical vapor deposition PECVD to replace the standard hydrogenated amorphous silicon a Si H passivation layer for silicon heterojunction solar cells to reduce parasitic absorption. Additionally, silicon oxide surfaces are well known as superior substrates for the nucleation enhancement for nanocrystalline silicon doped films. Symmetrical passivation samples were fabricated with variable a SiOx H layers with a thickness of 10 1.5 nm and characterized after several annealing steps 25 650 C . The best value reached so far on lt;100 gt; oriented Si wafers is implied open circuit voltage of 686 mV and minority carrier lifetime of 1.6 ms after annealing at 300 C. Such values were found to be reproducible even for ultra thin a SiOx H layers 1.5 n
Mid-Infrared Diagnostics of LINERs
We report results from the first mid-infrared spectroscopic study of a
comprehensive sample of 33 LINERs, observed with the Spitzer Space Telescope.
We compare the properties of two different LINER populations: infrared-faint
LINERs, with LINER emission arising mostly in compact nuclear regions, and
infrared-luminous LINERs, which often show spatially extended (non-AGN) LINER
emission. We show that these two populations can be easily distinguished by
their mid-infrared spectra in three different ways: (i) their mid-IR spectral
energy distributions (SEDs), (ii) the emission features of polycyclic aromatic
hydrocarbons (PAHs), and (iii) various combinations of IR fine-structure line
ratios. IR-luminous LINERs show mid-IR SEDs typical of starburst galaxies,
while the mid-IR SEDs of IR-faint LINERs are much bluer. PAH flux ratios are
significantly different in the two groups. Fine structure emission lines from
highly excited gas, such as [O IV], are detected in both populations,
suggesting the presence of an additional AGN also in a large fraction of
IR-bright LINERs, which contributes little to the combined mid-IR light. The
two LINER groups occupy different regions of mid-infrared emission-line
excitation diagrams. The positions of the various LINER types in our diagnostic
diagrams provide important clues regarding the power source of each LINER type.
Most of these mid-infrared diagnostics can be applied at low spectral
resolution, making AGN- and starburst-excited LINERs distinguishable also at
high redshifts.Comment: 11 pages, including 2 eps figures, accepted for publication in ApJ
Spitzer Quasar and ULIRG evolution study (QUEST): I. The origin of the far infrared continuum of QSOs
This paper addresses the origin of the far-infrared (FIR) continuum of QSOs,
based on the Quasar and ULIRG Evolution Study (QUEST) of nearby QSOs and ULIRGs
using observations with the Spitzer Space Telescope. For 27 Palomar-Green QSOs
at z <~ 0.3, we derive luminosities of diagnostic lines ([NeII]12.8um,
[NeV]14.3um, [OIV]25.9um) and emission features (PAH7.7um emission which is
related to star formation), as well as continuum luminosities over a range of
mid- to far-infrared wavelengths between 6 and 60um. We detect star-formation
related PAH emission in 11/26 QSOs and fine-structure line emission in all of
them, often in multiple lines. The detection of PAHs in the average spectrum of
sources which lack individual PAH detections provides further evidence for the
widespread presence of PAHs in QSOs. Similar PAH/FIR and [NeII]/FIR ratios are
found in QSOs and in starburst-dominated ULIRGs and lower luminosity
starbursts. We conclude that the typical QSO in our sample has at least 30% but
likely most of the far-infrared luminosity (~ 10^(10...12)Lsun) arising from
star formation, with a tendency for larger star formation contribution at the
largest FIR luminosities. In the QSO sample, we find correlations between most
of the quantities studied including combinations of AGN tracers and starburst
tracers. The common scaling of AGN and starburst luminosities (and fluxes) is
evidence for a starburst-AGN connection in luminous AGN. Strong correlations of
far-infrared continuum and starburst related quantities (PAH, low excitation
[NeII]) offer additional support for the starburst origin of far-infrared
emission.Comment: 39 pages, 8 figures, accepted for publication in Ap
Molecular Gas in the Powerful Radio Nucleus of the Ultraluminous Infrared Galaxy PKS 1345+12
Millimeter CO(1-0) interferometry and high resolution, Hubble Space Telescope
(HST) 1.1, 1.6, and 2.2 micron imaging of the radio compact galaxy PKS 1345+12
are presented. With an infrared luminosity of 2x10^{12} L_sun, PKS 1345+12 is a
prime candidate for studying the link between the ultraluminous infrared galaxy
phenomenon and radio galaxies. These new observations probe the molecular gas
distribution and obscured nuclear regions of PKS 1345+12 and provide
morphological support for the idea that the radio activity in powerful radio
galaxies is triggered by the merger of gas rich galaxies. Two nuclei separated
by 2" (4.0 kpc) are observed in the near-infrared; the extended southeastern
nucleus has colors consistent with reddened starlight, and the compact
northwestern nucleus has extremely red colors indicative of an optical quasar
with a warm dust component. Further, the molecular gas, 3mm continuum, and
radio emission are coincident with the redder nucleus, confirming that the
northwestern nucleus is the site of the AGN and that the molecular gas is the
likely fuel source.Comment: LaTex, 5 pages with 1 postscript and 1 jpg figure, ApJ Letters, in
press (August 20, 1999
ALMA Observations of Warm Molecular Gas and Cold Dust in NGC 34
We present ALMA Cycle-0 observations of the CO (6-5) line emission
(rest-frame frequency = 691.473 GHz) and of the 435 dust continuum
emission in the nuclear region of NGC 34, a local luminous infrared galaxy
(LIRG) at a distance of 84 Mpc (1" = 407 pc) which contains a Seyfert 2 active
galactic nucleus (AGN) and a nuclear starburst. The CO emission is well
resolved by the ALMA beam (), with an integrated flux of
. Both the morphology
and kinematics of the CO (6-5) emission are rather regular, consistent with a
compact rotating disk with a size of 200 pc. A significant emission feature is
detected on the red-shifted wing of the line profile at the frequency of the
line, with an integrated flux of . However, it cannot be ruled out
that the feature is due to an outflow of warm dense gas with a mean velocity of
. The continuum is resolved into an elongated
configuration, and the observed flux corresponds to a dust mass of . An unresolved central core () contributes of the continuum flux and of
the CO (6-5) flux, consistent with insignificant contributions of the AGN to
both emissions. Both the CO (6-5) and continuum spatial distributions suggest a
very high gas column density () in the nuclear
region at .Comment: 10 pages, 13 figures, accepted for publication in Astrophysical
Journa
ALMA Observations of Warm Dense Gas in NGC 1614 --- Breaking of Star Formation Law in the Central kpc
We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the
435um dust continuum emission in the central kpc of NGC 1614, a local luminous
infrared galaxy (LIRG) at a distance of 67.8 Mpc (1 arcsec = 329 pc). The CO
emission is well resolved by the ALMA beam (0".26 x 0".20) into a
circum-nuclear ring, with an integrated flux of f_{CO(6-5)} = 898 (+-153) Jy
km/s, which is 63(+-12)% of the total CO(6-5) flux measured by Herschel. The
molecular ring, located between 100pc < r < 350pc from the nucleus, looks
clumpy and includes seven unresolved (or marginally resolved) knots with median
velocity dispersion of 40 km/s. These knots are associated with strong star
formation regions with \Sigma_{SFR} 100 M_\sun/yr/kpc^{2} and \Sigma_{Gas}
1.0E4 M_\sun/pc^{2}. The non-detections of the nucleus in both the CO (6-5)
line emission and the 435um continuum rule out, with relatively high
confidence, a Compton-thick AGN in NGC 1614. Comparisons with radio continuum
emission show a strong deviation from an expected local correlation between
\Sigma_{Gas} and \Sigma_{SFR}, indicating a breakdown of the Kennicutt-Schmidt
law on the linear scale of 100 pc.Comment: 13 pages, 10 figures; accepted by Ap
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