19,421 research outputs found
The properties of the stellar populations in ULIRGs I: sample, data and spectral synthesis modelling
We present deep long-slit optical spectra for a sample of 36 Ultraluminous
Infrared Galaxies (ULIRGs), taken with the William Herschel Telescope (WHT) on
La Palma with the aim of investigating the star formation histories and testing
evolutionary scenarios for such objects. Here we present the sample, the
analysis techniques and a general overview of the properties of the stellar
populations. Spectral synthesis modelling has been used in order to estimate
the ages of the stellar populations found in the diffuse light sampled by the
spectra in both the nuclear and extended regions of the target galaxies. We
find that adequate fits can be obtained using combinations of young stellar
populations (YSPs,t_YSP<=2 Gyr), with ages divided into two groups: very young
stellar populations (VYSPs, t_VYSP <=100 Myr) and intermediate-young stellar
populations (IYSPs, 0.1 < t_IYSP <= 2 Gyr). Our results show that YSPs are
present at all locations of the galaxies covered by our slit positions, with
the exception of the northern nuclear region of the ULIRG IRAS 23327+2913.
Furthermore, VYSPs are presents in at least 85% of the 133 extraction apertures
used for this study. Old stellar populations (OSPs, t_{OSP} > 2 Gyr) do not
make a major contribution to the optical light in the majority of the apertures
extracted. In fact they are essential for fitting the spectra in only 5% (7) of
the extracted apertures. The estimated total masses for the YSPs (VYSPs+IYSPs)
are in the range 0.18 x 10^{10} <= M_YSP <= 50 x 10^{10} Msun. We have also
estimated the bolometric luminosities associated with the stellar populations
detected at optical wavelengths, finding that they fall in the range 0.07 x
10^{12} < L_bol < 2.2 x 10^{12} Lsun. In addition, we find that reddening is
significant at all locations in the galaxies.Comment: accepted for publication in MNRA
Probability distribution of arrival times in quantum mechanics
In a previous paper [V. Delgado and J. G. Muga, Phys. Rev. A 56, 3425 (1997)]
we introduced a self-adjoint operator whose eigenstates
can be used to define consistently a probability distribution of the time of
arrival at a given spatial point. In the present work we show that the
probability distribution previously proposed can be well understood on
classical grounds in the sense that it is given by the expectation value of a
certain positive definite operator which is nothing but a
straightforward quantum version of the modulus of the classical current. For
quantum states highly localized in momentum space about a certain momentum , the expectation value of becomes indistinguishable
from the quantum probability current. This fact may provide a justification for
the common practice of using the latter quantity as a probability distribution
of arrival times.Comment: 21 pages, LaTeX, no figures; A Note added; To be published in Phys.
Rev.
Quantum control on entangled bipartite qubits
Ising interaction between qubits could produce distortion in entangled pairs
generated for engineering purposes (as in quantum computation) in presence of
parasite magnetic fields, destroying or altering the expected behavior of
process in which is projected to be used. Quantum control could be used to
correct that situation in several ways. Sometimes the user should be make some
measurement upon the system to decide which is the best control scheme; other
posibility is try to reconstruct the system using similar procedures without
perturbate it. In the complete pictures both schemes are present. We will work
first with pure systems studying advantages of different procedures. After, we
will extend these operations when time of distortion is uncertain, generating a
mixed state, which needs to be corrected by suposing the most probably time of
distortion.Comment: 10 pages, 5 figure
Stellar population gradients in Seyfert 2 galaxies. Northern sample
We use high signal-to-noise ratio long-slit spectra in the 3600-4700A range
of the twenty brightest northern Seyfert 2 galaxies to study the variation of
the stellar population properties as a function of distance from the nucleus.
In order to characterize the stellar population and other continuum sources
(e.g. featureless continuum FC) we have measured equivalent widths Ws of six
absorption features, four continuum colours and their radial variations, and
performed spectral population synthesis as a function of distance from the
nucleus. About half the sample has CaIIK and G-band W values smaller at the
nucleus than at 1 kpc from it, due to a younger population and/or FC. The
stellar population synthesis shows that, while at the nucleus, 75% of the
galaxies present contribution > 20% of ages younger or equal than 100Myr and/or
of a FC, this proportion decreases to 45% at 3 kpc. In particular, 55% of the
galaxies have contribution > 10% of the 3 Myr/FC component (a degenerate
component in which one cannot separate what is due to a FC or to a 3 Myr
stellar population) at the nucleus, but only 25% of them have this contribution
at 3 kpc. As reference, the stellar population of 10 non-Seyfert galaxies,
spanning the Hubble types of the Seyfert (from S0 to Sc) was also studied. A
comparison between the stellar population of the Seyferts and that of the
non-Seyferts shows systematic differences: the contribution of ages younger
than 1 Gyr is in most cases larger in the Seyfert galaxies than in
non-Seyferts, not only at the nucleus but up to 1 kpc from it.Comment: 23 pages, 18 figures, MNRAS in pres
VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data
obtained with the Very Large Telescope and the Gran Telescopio Canarias of the
type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich
environment. It appears to be physically connected by a tidal bridge to another
galaxy at a projected distance of ~100 kpc, which suggests this is an
interacting system. Ionized gas is detected to a distance of at least ~133 kpc
from the nucleus. The nebula has a total extension of ~180 kpc. This is one of
the largest ionized nebulae ever detected associated with an active galaxy.
Based on the environmental properties, we propose that the origin of the nebula
is tidal debris from a galactic encounter, which could as well be the
triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that
giant, luminous ionized nebulae can exist associated with type 2 quasars of low
radio luminosities, contrary to expectations based on type 1 quasar studies.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letter
Semiquantitative theory of electronic Raman scattering from medium-size quantum dots
A consistent semiquantitative theoretical analysis of electronic Raman
scattering from many-electron quantum dots under resonance excitation
conditions has been performed. The theory is based on
random-phase-approximation-like wave functions, with the Coulomb interactions
treated exactly, and hole valence-band mixing accounted for within the
Kohn-Luttinger Hamiltonian framework. The widths of intermediate and final
states in the scattering process, although treated phenomenologically, play a
significant role in the calculations, particularly for well above band gap
excitation. The calculated polarized and unpolarized Raman spectra reveal a
great complexity of features and details when the incident light energy is
swept from below, through, and above the quantum dot band gap. Incoming and
outgoing resonances dramatically modify the Raman intensities of the single
particle, charge density, and spin density excitations. The theoretical results
are presented in detail and discussed with regard to experimental observations.Comment: Submitted to Phys. Rev.
Quantum probability distribution of arrival times and probability current density
This paper compares the proposal made in previous papers for a quantum
probability distribution of the time of arrival at a certain point with the
corresponding proposal based on the probability current density. Quantitative
differences between the two formulations are examined analytically and
numerically with the aim of establishing conditions under which the proposals
might be tested by experiment. It is found that quantum regime conditions
produce the biggest differences between the formulations which are otherwise
near indistinguishable. These results indicate that in order to discriminate
conclusively among the different alternatives, the corresponding experimental
test should be performed in the quantum regime and with sufficiently high
resolution so as to resolve small quantum efects.Comment: 21 pages, 7 figures, LaTeX; Revised version to appear in Phys. Rev. A
(many small changes
Starburst radio galaxies: general properties, evolutionary histories and triggering
In this paper we discuss the results of a programme of spectral synthesis
modelling of a sample of starburst radio galaxies in the context of scenarios
for the triggering of the activity and the evolution of the host galaxies. The
starburst radio galaxies -- comprising ~15 - 25% of all powerful extragalactic
radio sources -- frequently show disturbed morphologies at optical wavelengths,
and unusual radio structures, although their stellar masses are typical of
radio galaxies as a class. In terms of the characteristic ages of their young
stellar populations (YSP), the objects can be divided into two groups: those
with YSP ages t_ysp < 0.1 Gyr, in which the radio source has been triggered
quasi-simultaneously with the main starburst episode, and those with older YSP
in which the radio source has been triggered or re-triggered a significant
period after the starburst episode. Combining the information on the YSP with
that on the optical morphologies of the host galaxies, we deduce that the
majority of the starburst radio galaxies have been triggered in galaxy mergers
in which at least one of the galaxies is gas rich. However, the triggering (or
re-triggering) of the radio jets can occur immediately before, around, or a
significant period after the final coalescence of the merging nuclei,
reflecting the complex gas infall histories of the merger events. Overall, our
results provide further evidence that powerful radio jet activity can be
triggered via a variety of mechanisms, including different evolutionary stages
of major galaxy mergers; clearly radio-loud AGN activity is not solely
associated with a particular stage of a unique type of gas accretion event.Comment: 16 pages, 3 Figures, accepted for publication in MNRA
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