266 research outputs found
PopStar Evolutionary Synthesis Models II: Optical emission-line spectra from Giant H{\sc ii} regions
This is the second paper of a series reporting the results from the PopStar
evolutionary synthesis models. Here we present synthetic emission line spectra
of H{\sc ii} regions photoionized by young star clusters, for seven values of
cluster masses and for ages between 0.1 and 5.2 Myr. The ionizing Spectral
Energy Distributions (SEDs) are those obtained by the PopStar code
\citep*{mgb09} for six different metallicities, with a very low metallicity
set, Z=0.0001, not included in previous similar works. We assume that the
radius of the H{\sc ii} region is the distance at which the ionized gas is
deposited by the action of the mechanical energy of the winds and supernovae
from the central ionizing young cluster. In this way the ionization parameter
is eliminated as free argument, since now its value is obtained from the
cluster physical properties (mass, age and metallicity) and from the gaseous
medium characteristics (density and abundances). We discuss our results and
compare them with those from previous models and also with a large and data set
of giant H{\sc ii} regions for which abundances have been derived in a
homogeneous manner. The values of the [OIII] lines (at 4363,
4959, 5007\AA) in the lowest metallicity nebulae are found to be very weak and
similar to those coming from very high metallicity regions (solar or
over-solar). Thus, the sole use of the oxygen lines is not enough to
distinguish between very low and very high metallicity regions. In these cases
we emphasize the need of the additional support of alternative metallicity
tracers, like the [SIII] lines in the near-\textit{IR}.Comment: 20 pages, 26 figures, accepted for publication in MNRAS Main Journa
The many faces of LINER-like galaxies: a WISE view
We use the SDSS and WISE surveys to investigate the real nature of galaxies
defined as LINERs in the BPT diagram. After establishing a mid-infrared colour
W2-W3 = 2.5 as the optimal separator between galaxies with and without star
formation, we investigate the loci of different galaxy classes in the W_{Ha}
versus W2-W3 space. We find that: (1) A large fraction of LINER-like galaxies
are emission-line retired galaxies, i.e galaxies which have stopped forming
stars and are powered by hot low-mass evolved stars (HOLMES). Their W2-W3
colours show no sign of star formation and their Ha equivalent widths, W_{Ha},
are consistent with ionization by their old stellar populations. (2) Another
important fraction have W2-W3 indicative of star formation. This includes
objects located in the supposedly `pure AGN' zone of the BPT diagram. (3) A
smaller fraction of LINER-like galaxies have no trace of star formation from
W2-W3 and a high W_{Ha}, pointing to the presence of an AGN. (4) Finally, a few
LINERs tagged as retired by their W_{Ha} but with W2-W3 values indicative of
star formation are late-type galaxies whose SDSS spectra cover only the old
`retired' bulge. This reinforces the view that LINER-like galaxies are a mixed
bag of objects involving different physical phenomena and observational effects
thrusted into the same locus of the BPT diagram.Comment: Accepted for publication in MNRAS; 9 pages, 6 figure
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
Convergence of expansions in Schr\"odinger and Dirac eigenfunctions, with an application to the R-matrix theory
Expansion of a wave function in a basis of eigenfunctions of a differential
eigenvalue problem lies at the heart of the R-matrix methods for both the
Schr\"odinger and Dirac particles. A central issue that should be carefully
analyzed when functional series are applied is their convergence. In the
present paper, we study the properties of the eigenfunction expansions
appearing in nonrelativistic and relativistic -matrix theories. In
particular, we confirm the findings of Rosenthal [J. Phys. G: Nucl. Phys. 13,
491 (1987)] and Szmytkowski and Hinze [J. Phys. B: At. Mol. Opt. Phys. 29, 761
(1996); J. Phys. A: Math. Gen. 29, 6125 (1996)] that in the most popular
formulation of the R-matrix theory for Dirac particles, the functional series
fails to converge to a claimed limit.Comment: Revised version, accepted for publication in Journal of Mathematical
Physics, 21 pages, 1 figur
The redshift evolution of oxygen and nitrogen abundances in emission-line SDSS galaxies
The oxygen and nitrogen abundance evolutions with redshift and galaxy stellar
mass in emission-line SDSS galaxies are investigated. This is the first such
study for nitrogen abundances, and it provides an additional constraint for the
study of the chemical evolution of galaxies. We have devised a criterion to
recognize and exclude from consideration AGNs and star-forming galaxies with
large errors in the line flux measurements. To select star-forming galaxies
with accurate line fluxes measurements, we require that, for each galaxy, the
nitrogen abundances derived with various calibrations based on different
emission lines agree. Using this selection criterion, subsamples of
star-forming galaxies have been extracted from catalogs of the MPA/JHU group.
We found that the galaxies of highest masses, those with masses > 10^11.2
M_sun, have not been enriched in both oxygen and nitrogen over the last 3 Gyr:
they have formed their stars in the so distant past that these have returned
their nucleosynthesis products to the interstellar medium before z=0.25. The
galaxies in the mass range from 10^11.0 M_sun to 10^11.2 M_sun do not show an
appreciable enrichment in oxygen, but do show some enrichment in nitrogen: they
also formed their stars before z=0.25 but later in comparison to the galaxies
of highest masses; these stars have not returned nitrogen to the interstellar
medium before z=0.25 because they have not had enough time to evolve. This
suggests that stars with lifetimes of 2-3 Gyr contribute to the nitrogen
production. Finally, galaxies with masses < 10^11 M_sun show enrichment in both
oxygen and nitrogen during the last 3 Gyr: they have undergone appreciable star
formation and have converted up to 20% of their mass into stars over this
period.Comment: 43 pages, 15 figures, accepted for publication in the Astrophysical
Journa
Emission lines in early-type galaxies: active nuclei or stars?
We selected 27244 nearby, red, giant early-type galaxies (RGEs) from the
Sloan Digital Sky Survey (SDSS). In a large fraction (53%) of their spectra the
[O III] emission line is detected, with an equivalent width (EW) distribution
strongly clustered around ~0.75 A. The vast majority of those RGEs for which it
is possible to derive emission line ratios (amounting to about half of the
sample) show values characteristic of LINERs. The close connection between
emission lines and stellar continuum points to stellar processes as the most
likely source of the bulk of the ionizing photons in RGEs, rather than active
nuclei. In particular, the observed EW and optical line ratios are consistent
with the predictions of models in which the photoionization comes from to hot
evolved stars. Shocks driven by supernovae or stellar ejecta might also
contribute to the ionization budget. A minority, ~4%, of the galaxies show
emission lines with an equivalent that is width a factor of ~2 greater than the
sample median. Only among them are Seyfert-like spectra found. Furthermore, 40%
of this subgroup have a radio counterpart, compared to ~6% of the rest of the
sample. These characteristics argue in favor of an AGN origin for their
emission lines. Emission lines diagnostic diagrams do not reveal a distinction
between the AGN subset and the other members of the sample, and consequently
they are not a useful tool for establishing the dominant source of the ionizing
photons, which is better predicted by the EW of the emission lines.Comment: Accepted for publication in A&
Small-spatial scale variations of nebular properties and the abundance discrepancy in three Galactic HII regions
We present results of long-slit spectroscopy in several slit positions that
cover different morphological structures of the central parts of three bright
Galactic HII regions: M8, M17 and NGC7635. We study the spatial distributions
of a large number of nebular parameters such as the extinction coefficient,
line fluxes, physical conditions and ionic abundances at the maximum spatial
resolution attainable with our instrumentation. Particularly, our goal is to
study the behaviour of the abundance discrepancy factor of O^{2+}, ADF(O^{2+}),
defined as the logarithmic difference of the O^{2+} abundances derived from
collisionally excited and recombination lines. We find that the ADF(O^{2+})
remains fairly constant along the slit positions of M8 and M17. In the case of
NGC7635, we only detect the OII recombination lines in the integrated spectrum
along the whole slit, where the ADF(O^{2+}) reaches a remarkably high value of
about 0.59 dex. We compare our results with previous ones obtained for the
Orion Nebula. We find several evidences that suggest the presence of a
candidate to Herbig-Haro object in M8.Comment: 18 pages, 9 figures. Table A1 available only in the online version.
Accepted for publication in MNRAS
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
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