442 research outputs found
Hard X-ray Luminosities of Multinuclei Infrared Luminous Galaxies Showing a Radio/Far-Infrared Excess
We report the results of hard X-ray observations of four multinuclei merging
infrared luminous galaxies (IRLGs). We selected these four sources for their
excess of radio to far-infrared luminosity ratio compared with starburst
galaxies. This excess suggests that activity associated with a supermassive
black hole (SMBH) contributes strongly to the IRLGs' bolometric luminosities.
Although we expect strong hard X-ray emission from the SMBH-driven activity,
the radio-excess multinuclei merging IRLGs show considerably smaller hard X-ray
luminosities relative to far-infrared (40500 m) and infrared (81000
m) luminosities than active galactic nuclei (AGNs) showing a similar
radio-excess. This result may demonstrate that emission in the hard X-ray
region from SMBH-driven activity in the multinuclei merging IRLGs is severely
suppressed compared to a typical spectral energy distribution of SMBH-driven
activity in AGNs. If this is a common property of merging IRLGs, without its
correction, hard X-ray observations underestimate the contribution of
SMBH-driven activity to the bolometric luminosities of merging IRLGs.Comment: 25 pages of text, 4 figures, aaspp4.sty, Astrophysical Journal, in
press (1999, Volume 527
Resolving vibrational from electronic coherences in two-dimensional electronic spectroscopy: The role of the laser spectrum
The observation of coherent quantum effects in photosynthetic light-harvesting complexes prompted the question whether quantum coherence could be exploited to improve the efficiency in new energy materials. The detailed characterization of coherent effects relies on sensitive methods such as two-dimensional electronic spectroscopy (2D-ES). However, the interpretation of the results produced by 2D-ES is challenging due to the many possible couplings present in complex molecular structures. In this work, we demonstrate how the laser spectral profile can induce electronic coherence-like signals in monomeric chromophores, potentially leading to data misinterpretation. We argue that the laser spectrum acts as a filter for certain coherence pathways and thus propose a general method to differentiate vibrational from electronic coherences
Two-Dimensional Electronic Spectroscopy of Chlorophyll a: Solvent Dependent Spectral Evolution
The interaction of the monomeric chlorophyll Q-band electronic transition with solvents of differing physical-chemical properties is investigated through two-dimensional electronic spectroscopy (2DES). Chlorophyll constitutes the key chromophore molecule in light harvesting complexes. It is well-known that the surrounding protein in the light harvesting complex fine-tunes chlorophyll electronic transitions to optimize energy transfer. Therefore, an understanding of the influence of the environment on the monomeric chlorophyll electronic transitions is important. The Q-band 2DES is inhomogeneous at early times, particularly in hydrogen bonding polar solvents, but also in nonpolar solvents like cyclohexane. Interestingly this inhomogeneity persists for long times, even up to the nanosecond time scale in some solvents. The reshaping of the 2DES occurs over multiple time scales and was assigned mainly to spectral diffusion. At early times the reshaping is Gaussian-like, hinting at a strong solvent reorganization effect. The temporal evolution of the 2DES response was analyzed in terms of a Brownian oscillator model. The spectral densities underpinning the Brownian oscillator fitting were recovered for the different solvents. The absorption spectra and Stokes shift were also properly described by this model. The extent and nature of inhomogeneous broadening was a strong function of solvent, being larger in H-bonding and viscous media and smaller in nonpolar solvents. The fastest spectral reshaping components were assigned to solvent dynamics, modified by interactions with the solute
Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study
The behavior of water molecules surrounding a protein can have an important bearing on its structure and function. Consequently, a great deal of attention has been focused on changes in the relaxation dynamics of water when it is located at the protein surface. Here we use the ultrafast optical Kerr effect to study the H-bond structure and dynamics of aqueous solutions of proteins. Measurements are made for three proteins as a function of concentration. We find that the water dynamics in the first solvation layer of the proteins are slowed by up to a factor of 8 in comparison to those in bulk water. The most marked slowdown was observed for the most hydrophilic protein studied, bovine serum albumin, whereas the most hydrophobic protein, trypsin, had a slightly smaller effect. The terahertz Raman spectra of these protein solutions resemble those of pure water up to 5 wt % of protein, above which a new feature appears at 80 cm–1, which is assigned to a bending of the protein amide chain
Full characterization of vibrational coherence in a porphyrin chromophore by two-dimensional electronic spectroscopy
In this work we present experimental and calculated two-dimensional electronic spectra for a 5,15-bisalkynyl porphyrin chromophore. The lowest energy electronic Qy transition couples mainly to a single 380 cm–1 vibrational mode. The two-dimensional electronic spectra reveal diagonal and cross peaks which oscillate as a function of population time. We analyze both the amplitude and phase distribution of this main vibronic transition as a function of excitation and detection frequencies. Even though Feynman diagrams provide a good indication of where the amplitude of the oscillating components are located in the excitation-detection plane, other factors also affect this distribution. Specifically, the oscillation corresponding to each Feynman diagram is expected to have a phase that is a function of excitation and detection frequencies. Therefore, the overall phase of the experimentally observed oscillation will reflect this phase dependence. Another consequence is that the overall oscillation amplitude can show interference patterns resulting from overlapping contributions from neighboring Feynman diagrams. These observations are consistently reproduced through simulations based on third order perturbation theory coupled to a spectral density described by a Brownian oscillator model
Binary Galaxies in the Local Supercluster and Its Neighborhood
We report a catalog of 509 pairs identified among 10403 nearby galaxies with
line-of-sight velocities V_LG < 3500 km/s.We selected binary systems in
accordance with two criteria (bounding and temporal), which require the
physical pair of galaxies to have negative total energy and its components to
be located inside the zero-velocity surface. We assume that individual galaxy
masses are proportional to their total K-band luminosities, M = L_K x 6M/L. The
catalog gives the magnitudes and morphological types of galaxies and also the
projected (orbital) masses and pair isolation indices. The component
line-of-sight velocity differences and projected distances of the binary
systems considered have power-law distributions with the median values of 35
km/s and 123 kpc, respectively. The median mass-to-K-band luminosity ratio is
equal to 11 M/L, and its uncertainty is mostly due to the errors of measured
velocities. Our sample of binary systems has a typical density contrast of d
ro/ro_c ~ 500 and a median crossing time of about 3.5 Gyr. We point out the
substantial fraction of binary systems consisting of late-type dwarf galaxies,
where the luminosities of both components are lower than that of the Small
Magellanic Cloud. The median projected distance for 41 such pairs is only 30
kpc, and the median difference of their line-of-sight velocities is equal to 14
km/s which is smaller than the typical error for radial-velocity (30 km/s).
This specific population of gas-rich dwarf binary galaxies such as I Zw 18 may
be at the stage immediately before merging of its components. Such objects,
which are usually lost in flux-limited (and not distance-limited) samples
deserve a thorough study in the HI radio line with high spatial and velocity
resolution.Comment: published in Astrophysical Bulletin, 2008, Vol. 63, No. 4, pp.
299-34
Merging of globular clusters within inner galactic regions. I. Do they survive the tidal interaction?
The main topic of this paper is the investigation of the modes of interaction
of globular clusters (GCs) moving in the inner part of a galaxy. This is
tackled by means of high-resolution N-body simulations, whose first results are
presented in this article. Our simulations dealt with primordial very massive
(order of 10^7 solar masses) GCs that were able to decay, because of dynamical
friction, into the inner regions of triaxial galaxies on a time much shorter
than their internal relaxation time. To check the disruptive role of both tidal
forces and GC-GC collisions, we maximised the tidal interaction considering GCs
on quasi-radial orbits.
The available CPU resources allowed us to follow 8 oscillations of the GCs
along their orbits and the main findings are: i) clusters with an initial high
enough King concentration parameter (c>=1.2), preserve up to 50% of their
initial mass; ii) the inner density distribution of the survived clusters keep
a King model profile; iii) GC-GC collisions have a negligible effect with
respect to that caused by the passage through the galactic center; iv) the
orbital energy dissipation due to the tidal interaction is of the same order of
that caused by dynamical friction; v) complex sub-structures like "ripples" and
"clumps" formed, as observed around real clusters.
These findings support the validity of the hypothesis of merging of GCs in
the galactic central region, with modes that deserve further careful
investigations.Comment: LaTeX 2e, AASTeX v5.x, 23 pages with 14 figures. Accepted for
publication on the Astrophysical Journal. Final version with major change
Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3--4 Micron Spectra
The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed
based on their ground-based 3--4 m spectra. Both the equivalent width of
the 3.3 m polycyclic aromatic hydrocarbon (PAH) emission feature and the
3.3 m PAH to far-infrared luminosity ratio () are
analyzed. Assuming nuclear compact starburst activity in these sources produces
the 3.3 m PAH emission as strongly as that in starburst galaxies with
lower far-infrared luminosities, the followings results are found: For six
IRLGs, both the observed equivalent widths and the ratios
are too small to explain the bulk of their far-infrared luminosities by compact
starburst activity, indicating that active galactic nucleus (AGN) activity is a
dominant energy source. For the other three IRLGs, while the 3.3 m PAH
equivalent widths are within the range of starburst galaxies, the
ratios after correction for screen dust extinction are a
factor of 3 smaller. The uncertainty in the dust extinction correction
factor and in the scatter of the intrinsic ratios for
starburst galaxies do not allow a determination of the ultimate energy sources
for these three IRLGs.Comment: 29 pages, 2 figures, Accepted for publication in Ap
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