227 research outputs found
The electron temperatures of SDSS high-metallicity giant extragalactic HII regions
Spectra of high-metallicity (12+log(O/H) > 8.2) HII regions where oxygen
auroral lines are measurable in both the O+ and O++ zones, have been extracted
from the Data Release 6 of the Sloan Digital Sky Survey (SDSS). Our final
sample consists of 181 SDSS spectra of HII regions in galaxies in the redshift
range from ~0.025 to ~0.17. The t_2,O-t_3,O diagram is examined. In the SDSS
HII regions, the electron temperature t_2,O is found to have a large scatter at
a given value of the electron temperature t_3,O. The majority of the SDSS HII
regions lie below the t_2,O-t_3,O relation derived for HII regions in nearby
galaxies, i.e. the positions of the SDSS HII regions show a systematic shift
towards lower t_2,O temperatures or/and towards higher t_3,O temperatures. The
scatter and shift of the SDSS HII regions in the t_2,O-t_3,O diagram can be
understood if they are composite nebulae excited by two or more ionizing
sources of different temperatures.Comment: 14 pages, 11 figures accepted for publication in the MNRA
Manipulating mesoscopic multipartite entanglement with atom-light interfaces
Entanglement between two macroscopic atomic ensembles induced by measurement
on an ancillary light system has proven to be a powerful method for engineering
quantum memories and quantum state transfer. Here we investigate the
feasibility of such methods for generation, manipulation and detection of
genuine multipartite entanglement between mesoscopic atomic ensembles. Our
results extend in a non trivial way the EPR entanglement between two
macroscopic gas samples reported experimentally in [B. Julsgaard, A. Kozhekin,
and E. Polzik, Nature {\bf 413}, 400 (2001)]. We find that under realistic
conditions, a second orthogonal light pulse interacting with the atomic
samples, can modify and even reverse the entangling action of the first one
leaving the samples in a separable state.Comment: 8 pages, 6 figure
Planetary nebulae in M33: probes of AGB nucleosynthesis and ISM abundances
We have obtained deep optical spectrophotometry of 16 planetary nebulae in
M33, mostly located in the central two kpc of the galaxy, with the Subaru and
Keck telescopes. We have derived electron temperatures and chemical abundances
from the detection of the [OIII]4363 line for the whole sample. We have found
one object with an extreme nitrogen abundance, 12+log(N/H)=9.20, accompanied by
a large helium content. After combining our data with those available in the
literature for PNe and HII regions, we have examined the behavior of nitrogen,
neon, oxygen and argon in relation to each other, and as a function of
galactocentric distance. We confirm the good correlation between Ne/H and O/H
for PNe in M33. Ar/H is also found to correlate with O/H. This strengthens the
idea that at the metallicity of the bright PNe analyzed in M33, which is
similar to that found in the LMC, these elements have not been significantly
modified during the dredge-up processes that take place during the AGB phase of
their progenitor stars. We find no significant oxygen abundance offset between
PNe and HII regions at any given galactocentric distance, despite the fact that
these objects represent different age groups in the evolution of the galaxy.
Combining the results from PNe and HII regions, we obtain a representative
slope of the ISM alpha-element (O, Ar, Ne) abundance gradient in M33 of -0.025
+/- 0.006 dex/kpc. Both PNe and HII regions display a large abundance
dispersion at any given distance from the galactic center. We find that the N/O
ratio in PNe is enhanced, relative to the HII regions, by approximately 0.8
dex.Comment: 21 pages, 20 figures. Accepted for publication in MNRA
Spectral classification of emission-line galaxies from the Sloan Digital Sky Survey. II. A supplementary diagnostic for AGNs using the Dn(4000) index
In this paper we present a classification of emission-line galaxies at
intermediate and high redshifts (0.52.5 for near-infrared spectra), using the
Dn(4000) index as a supplementary diagnostic. Our goal is to complement the
diagnostic based only on emission-line ratios from the blue part of the
spectra, which suffer from some limitations for the classification of Seyfert 2
and composite galaxies. We used a sample of 89 379 galaxies with a good
signal-to-noise ratio from the Sloan Digital Sky Survey (data release 7). Using
the classification scheme presented in Paper I, we classified these galaxies
with a diagnostic diagram involving the [Oiii]5007 /Hbeta and [Oii]3726+3729
/Hbeta emission-line ratios. Then we derived a supplementary diagnostic
involving Dn(4000) to improve this classification, in the regions where objects
of different types are mixed. To show the validity of our spectral
classification we established success-rate and contamination charts, then we
compared our results to those obtained with the reference classification that
was scheme obtained also using Halpha, [Nii]6584, and [Sii]6717+6731 emission
lines. We show that our supplementary classification based on the Dn(4000)
index allows to separate unambiguously star-forming galaxies from Seyfert 2 in
the region where they were mixed in Paper I. It also significantly reduces the
region where star-forming galaxies are mixed with composites.Comment: accepted for publication in A\&A, 10 pages corrected bug in LateX
file for equations 7 and
The evolution of the mass-metallicity relation in SDSS galaxies uncovered by astropaleontology
We have obtained the mass-metallicity (M-Z) relation at different lookback
times for the same set of galaxies from the Sloan Digital Sky Survey, using the
stellar metallicities estimated with our spectral synthesis code STARLIGHT. We
have found that this relation steepens and spans a wider range in both mass and
metallicity at higher redshifts. We have modeled the time evolution of stellar
metallicity with a closed-box chemical evolution model, for galaxies of
different types and masses. Our results suggest that the M-Z relation for
galaxies with present-day stellar masses down to 10^10 M_sun is mainly driven
by the history of star formation history and not by inflows or outflows.Comment: Accepted for publication in MNRA
Analysis of Spatial Structure of the SPica H II Region
Far ultraviolet (FUV) spectral images of the Spica H II region are first
presented here for the Si II* 1533.4A and Al II 1670.8A lines and then compared
with the optical Halpha image. The H alpha and Si II* images show enhanced
emissions in the southern part of the H II region where H I density increases
outwards. This high density region, which we identify as part of the
"interaction ring" of the Loop I superbubble and the Local Bubble, seems to
bound the southern H II region. On the other hand, the observed profile of Al
II shows a broad central peak, without much difference between the northern and
southern parts, which we suspect results from multiple resonant scattering. The
extended tails seen in the radial profiles of the FUV intensities suggest that
the nebula may be embedded in a warm ionized gas. Simulation with a spectral
synthesis code yields the values of the Lyman continuum luminosity and the
effective temperature of the central star similar to previous estimates with
10^46.2 photons s^-1 and 26,000 K, respectively, but the density of the
northern H II region, 0.22 cm^-3, is much smaller than previous estimates for
the H alpha brightest region.Comment: 15 pages, 5 figures, accepted for Ap
Can solid body destruction explain abundance discrepancies in planetary nebulae?
In planetary nebulae, abundances of oxygen and other heavy elements derived
from optical recombination lines are systematically higher than those derived
from collisionally excited lines. We investigate the hypothesis that the
destruction of solid bodies may produce pockets of cool, high-metallicity gas
that could explain these abundance discrepancies. Under the assumption of
maximally efficient radiative ablation, we derive two fundamental constraints
that the solid bodies must satisfy in order that their evaporation during the
planetary nebula phase should generate a high enough gas phase metallicity. A
local constraint implies that the bodies must be larger than tens of meters,
while a global constraint implies that the total mass of the solid body
reservoir must exceed a few hundredths of a solar mass. This mass greatly
exceeds the mass of any population of comets or large debris particles expected
to be found orbiting evolved low- to intermediate-mass stars. We therefore
conclude that contemporaneous solid body destruction cannot explain the
observed abundance discrepancies in planetary nebulae. However, similar
arguments applied to the sublimation of solid bodies during the preceding
asymptotic giant branch (AGB) phase do not lead to such a clear-cut conclusion.
In this case, the required reservoir of volatile solids is only one
ten-thousandth of a solar mass, which is comparable to the most massive debris
disks observed around solar-type stars, implying that this mechanism may
contribute to abundance discrepancies in at least some planetary nebulae, so
long as mixing of the high metallicity gas is inefficient.Comment: 8 pages, no figures, ApJ in pres
Search for blue compact dwarf galaxies during quiescence II: metallicities of gas and stars, ages, and star-formation rates
We examine the metallicity and age of a large set of SDSS/DR6 galaxies that
may be Blue Compact Dwarf (BCD) galaxies during quiescence (QBCDs).The
individual spectra are first classified and then averaged to reduce noise. The
metallicity inferred from emission lines (tracing ionized gas) exceeds by ~0.35
dex the metallicity inferred from absorption lines (tracing stars). Such a
small difference is significant according to our error budget estimate. The
same procedure was applied to a reference sample of BCDs, and in this case the
two metallicities agree, being also consistent with the stellar metallicity in
QBCDs. Chemical evolution models indicate that the gas metallicity of QBCDs is
too high to be representative of the galaxy as a whole, but it can represent a
small fraction of the galactic gas, self enriched by previous starbursts. The
luminosity weighted stellar age of QBCDs spans the whole range between 1 and 10
Gyr, whereas it is always smaller than 1 Gyr for BCDs. Our stellar ages and
metallicities rely on a single stellar population spectrum fitting procedure,
which we have specifically developed for this work using the stellar library
MILES.Comment: Accepted for publication in ApJ. 20 pages. 16 figures (corrected
typos
Positive maps, majorization, entropic inequalities, and detection of entanglement
In this paper, we discuss some general connections between the notions of
positive map, weak majorization and entropic inequalities in the context of
detection of entanglement among bipartite quantum systems. First, basing on the
fact that any positive map can
be written as the difference between two completely positive maps
, we propose a possible way to generalize the
Nielsen--Kempe majorization criterion. Then we present two methods of
derivation of some general classes of entropic inequalities useful for the
detection of entanglement. While the first one follows from the aforementioned
generalized majorization relation and the concept of the Schur--concave
decreasing functions, the second is based on some functional inequalities. What
is important is that, contrary to the Nielsen--Kempe majorization criterion and
entropic inequalities, our criteria allow for the detection of entangled states
with positive partial transposition when using indecomposable positive maps. We
also point out that if a state with at least one maximally mixed subsystem is
detected by some necessary criterion based on the positive map , then
there exist entropic inequalities derived from (by both procedures)
that also detect this state. In this sense, they are equivalent to the
necessary criterion [I\ot\Lambda](\varrho_{AB})\geq 0. Moreover, our
inequalities provide a way of constructing multi--copy entanglement witnesses
and therefore are promising from the experimental point of view. Finally, we
discuss some of the derived inequalities in the context of recently introduced
protocol of state merging and possibility of approximating the mean value of a
linear entanglement witness.Comment: the published version, 25 pages in NJP format, 6 figure
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