798 research outputs found
Evolutionary synthesis models of starbursts IV. Soft X-ray emission
In this work we investigate the evolution of the X-ray emission of a cluster
of single young massive stars with different metallicities. We have considered
the X-ray contribution originated by the diffuse gas heated by the mechanical
energy released by stellar winds and SN explosions as well as the X-ray
contribution from SN remnants. The resulting ionizing spectrum (i.e. lambda <
912 A) has been used to compute the expected intensity of the nebular He II
4686 A. The observational ratio He II/Hbeta could be reproduced by the models
assuming that a fraction of the mechanical energy produced by the
star-formation episode is reprocessed by interaction with the ISM as soft X-ray
radiation, contributing to the He ionization. However, the discreteness of the
stellar populations affects the ionizing flux and may be responsible for the
observed dispersion of the ratio. We have finally used the synthesis models to
estimate the contribution of circumnuclear star-forming regions to the
multiwavelength energy distribution in Active Galactic Nuclei, finding that the
UV to soft X-ray continuum in many Seyfert 2 galaxies seems to be dominated by
star-formation processes.Comment: 14 pages, 10 fig, A&A accepte
The Circumnuclear Star-forming Activities along the Hubble Sequence
In order to study the circumnuclear star-forming activity along the Hubble
sequence, we cross-correlate the Sloan Digital Sky Survey Data Release 2 (SDSS
DR2) with the Third Reference Catalog of Bright Galaxies (RC3) to derive a
large sample of 1015 galaxies with both morphological and spectral information.
Among these, 385 sources are classified as star-forming galaxies and the SDSS
fibre covered the circumnuclear regions (0.2 2.0 kpc). By using the
spectral synthesis method to remove the contribution from the underlying old
stellar population, we measure the emission lines fluxes accurately which are
then used to estimate the star formation rates(SFRs). Our main findings are
that: (1) Early-type spirals show much larger H luminosities and hence
higher SFRs, they also suffer more extinctions than late-type ones. The
equivalent widths (EWs) of H emission lines show the similar trend,
however, the very late types (Sdm Irr) do have large fractions of high
EWs. (2) We confirm that D has strong correlation with the strengthes
of metallic absorption lines (such as CN band, G band and Mg Ib). Both these
lines and the Balmer absorption lines show interesting variations between Sbc
to Sd type galaxies. (3) The bar structure tightly relates with the enhanced
star forming activity, this effect is even more significant in the early-type
spirals. But we should note that the bar structure is not a necessary or
sufficient condition for galaxies to harbor circumnuclear star formations.Comment: 14 pages, 15 figures, accepted for publication in A&
Effects of riparian plant diversity loss on aquatic microbial decomposers become more pronounced at longer times
We examined the potential long-term impacts of riparian plant diversity loss on diversity and activity of aquatic microbial decomposers. Microbial assemblages were obtained
in a mixed-forest stream by immersion of mesh bags contain-ing three leaf species (alder, oak and eucalyptus), commonly
found in riparian corridors of Iberian streams. Simulation of
species loss was done in microcosms by including a set of all
leaf species, retrieved from the stream, and non-colonized
leaves of three, two or one leaf species. Leaves were renewed
every month throughout six months, and microbial inoculum
was ensured by a set of colonized leaves from the previous
month. Microbial diversity, leaf mass loss and fungal biomass
were assessed at the second and sixth months after plant
species loss. Molecular diversity of fungi and bacteria, as the
total number of operational taxonomic units per leaf diversity
treatment, decreased with leaf diversity loss. Fungal biomass
tended to decrease linearly with leaf species loss on oak and
eucalyptus, suggesting more pronounced effects of leaf diver-sity on lower quality leaves. Decomposition of alder and
eucalyptus leaves was affected by leaf species identity, mainly
after longer times following diversity loss. Leaf decomposi-tion of alder decreased when mixed with eucalyptus, while
decomposition of eucalyptus decreased in mixtures with oak.
Results suggest that the effects of leaf diversity on microbial
decomposers depended on leaf species number and also on
which species were lost from the system, especially after
longer times. This may have implications for the management
of riparian forests to maintain stream ecosystem functioning.FEDER-POFC-COMPETE and the Portuguese
Foundation for Science and Technology supported this study (PEst-C/
BIA/UI4050/2011, PTDC/AAC-AMB/113746/2009 and PTDC/AAC-AMB/117068/2010), S. Duarte (SFRH/BPD/47574/2008) and I.
Fernandes (SFRH/BD/42215/2007)
Confidence limits of evolutionary synthesis models. IV Moving forward to a probabilistic formulation
Synthesis models predict the integrated properties of stellar populations.
Several problems exist in this field, mostly related to the fact that
integrated properties are distributed. To date, this aspect has been either
ignored (as in standard synthesis models, which are inherently deterministic)
or interpreted phenomenologically (as in Monte Carlo simulations, which
describe distributed properties rather than explain them). We approach
population synthesis as a problem in probability theory, in which stellar
luminosities are random variables extracted from the stellar luminosity
distribution function (sLDF). We derive the population LDF (pLDF) for clusters
of any size from the sLDF, obtaining the scale relations that link the sLDF to
the pLDF. We recover the predictions of standard synthesis models, which are
shown to compute the mean of the sLDF. We provide diagnostic diagrams and a
simplified recipe for testing the statistical richness of observed clusters,
thereby assessing whether standard synthesis models can be safely used or a
statistical treatment is mandatory. We also recover the predictions of Monte
Carlo simulations, with the additional bonus of being able to interpret them in
mathematical and physical terms. We give examples of problems that can be
addressed through our probabilistic formalism. Though still under development,
ours is a powerful approach to population synthesis. In an era of resolved
observations and pipelined analyses of large surveys, this paper is offered as
a signpost in the field of stellar populations.Comment: Accepted by A&A. Substantially modified with respect to the 1st
draft. 26 pages, 14 fig
Modeling the emission line sequence of H II galaxies
Using a sample of unprecedented size (about 400 objects) of H II galaxies in
which the oxygen abundances have been obtained using the temperature derived
from the [OIII] 4363/5007 line ratio, we confirm that the H II galaxies form a
very narrow sequence in many diagrams relating line ratios and Hbeta equivalent
width. We divide our sample in three metallicity bins, each of which is
compared with sequences of photoionization models for evolving starbursts with
corresponding metallicity. Our aim is to find under what conditions a
theoretical sequence can reproduce all the observed trends. Taking into account
the presence of an older, non-ionizing stellar population, for which
independent indications exist, we find that the simple model of an adiabatic
expanding bubble reproduces the observational diagrams very well if account is
taken of an aperture correction and the covering factor is assumed to decrease
with time exponentially with an e-folding time of 3 Myr. We find that the He II
4686 nebular line emission occurs too frequently and in too wide a range of
EW(Hbeta) to be attributable to either the hard radiation field from Wolf-Rayet
stars or the X-rays produced by the latest stellar generation. Assuming that
the He II 4686 line is due to photoionization by a hot plasma at a temperature
of 10^6 K, a total X-ray luminosity of 10^40 - 4x10^40 erg/s is required for at
least half of the sources. We find evidence for self-enrichment in nitrogen on
a time scale of several Myr, and argue for a possible self-enrichment in oxygen
as well.Comment: 15 pages, 6 Postscript figures, to appear in Astronomy & Astrophysic
Aedes albopictus diversity and relationships in south-western Europe and Brazil by rDNA/mtDNA and phenotypic analyses: ITS-2, a useful marker for spread studies
Background: Aedes albopictus is a very invasive mosquito, which has recently colonized tropical and temperate regions worldwide. Of concern is its role in the spread of emerging or re-emerging mosquito-borne diseases. Ae. albopictus from south-western Europe and Brazil were studied to infer genetic and phenetic diversity at intra-individual, intra-population and inter-population levels, and to analyse its spread. Methods: Genotyping was made by rDNA 5.8S-ITS-2 and mtDNA cox1 sequencing to assess haplotype and nucleotide diversity, genetic distances and phylogenetic networks. Male and female phenotyping included combined landmark-and outlined-based geometric morphometrics of wing size and shape. Results: Specimens from seven populations from Spain, France and Brazil provided 12 cox1 and 162 5.8S-ITS-2 haplotypes, with great genetic variability difference between both markers (0.9% vs 31.2%). Five cox1 haplotypes were shared with other countries, mainly Italy, USA and China, but none was shared between Europe and Brazil. The 5.8S-ITS-2 showed 2–7 intra-individual (mean 4.7) and 16–34 intra-/inter-population haplotypes (24.7), including haplotypes shared between Spain, France and Brazil. A 4.3% of ITS-2 haplotypes were shared, mainly with Italy, USA and Thailand, evidencing worldwide spread and introductions from areas where recent outbreaks of Ae. albopictus-transmitted pathogens occurred. Wing size showed sex differences. Wing shape distinguished between Brazilian and European specimens. Both genetic and morphometric markers showed differences between insular Spain and continental Spain, France and Brazil. Conclusions: ITS-2 proves to be a useful marker to assess Ae. albopictus spread, providing pronouncedly more information than cox1, including intra-individual, intra-population and inter-population levels, furnishing a complete overview of the evolutionary exchanges followed by this mosquito. Wing morphometry proves to be a useful phenotyping marker, allowing to distinguish different populations at the level of both male and female specimens. Results indicate the need for periodic surveillance monitorings to verify that no Ae. albopictus with high virus transmission capacity is introduced into Europe. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s)
Estimación de caudales ecológicos basada en simulación del hábitat fÃsico en un pequeño rÃo del sudeste de Brasil
El método de simulación del hábitat fÃsico, integrado en el marco de la metodologÃa IFIM (Instream Flow Incremental Methodology) y en otros marcos metodológicos hoy dÃa, utiliza variables hidráulicas e Ãndices de idoneidad del hábitat (a escala de microhábitat) para predecir los cambios potenciales del hábitat al cambiar el caudal circulante. Este enfoque se ha utilizado para simular los cambios potenciales de idoneidad del hábitat para tres especies de peces tropicales de diferentes órdenes, Bryconamericus ornaticeps, Ancistrus multispinis y Geophagus brasiliensis. El estudio se realizó en dos tramos de un rÃo en la zona de mata atlántica al sudeste de Brasil, durante el verano de 2013 e invierno de 2014. Se midieron las caracterÃsticas topográficas e hidráulicas por transectos (calado, velocidad media, tipos de sustrato) y se estudió el uso del microhábitat por los peces mediante observación directa bajo el agua (snorkelling); esto permitió elaborar curvas de idoneidad de microhábitat para las tres especies. Mediante la simulación del hábitat fÃsico se obtuvieron las curvas que relacionan dos indicadores, el HSI (indice medio de idoneidad en un tramo), y el HPU (Hábitat Potencial Útil) con el caudal del rÃo. Sobre dichas curvas se observaron los caudales importantes para el mantenimiento de los hábitats de las tres especies. Los resultados indicaron un caudal mÃnimo-minimorum de 0.25 m3 s-1 en época seca para conservar el hábitat de los peces. También se determinó un rango óptimo de 0.65-0.85 m3 s-1 para el hábitat de las tres especies. Los resultados pueden apoyar la elaboración de una primera propuesta de régimen ecológico de caudales, en el marco de un proceso de gestión adaptativa de los recursos hÃdricos, para conservar la salud del rÃo São Pedro y los diversos servicios ecosistémicos que aporta a la sociedad.Da Costa, M.; Moretti Mattos, T.; Muñoz Mas, R.; Martinez-Capel, F.; Fernandes, V.; Aráujo, F. (2015). Estimación de caudales ecológicos basada en simulación del hábitat fÃsico en un pequeño rÃo del sudeste de Brasil. Cuadernos de la Sociedad Española de Ciencias Forestales. (41):245-252. http://hdl.handle.net/10251/60209S2452524
Accurate parameter estimation for star formation history in galaxies using SDSS spectra
To further our knowledge of the complex physical process of galaxy formation,
it is essential that we characterize the formation and evolution of large
databases of galaxies. The spectral synthesis STARLIGHT code of Cid Fernandes
et al. (2004) was designed for this purpose. Results of STARLIGHT are highly
dependent on the choice of input basis of simple stellar population (SSP)
spectra. Speed of the code, which uses random walks through the parameter
space, scales as the square of the number of basis spectra, making it
computationally necessary to choose a small number of SSPs that are coarsely
sampled in age and metallicity. In this paper, we develop methods based on
diffusion map (Lafon & Lee, 2006) that, for the first time, choose appropriate
bases of prototype SSP spectra from a large set of SSP spectra designed to
approximate the continuous grid of age and metallicity of SSPs of which
galaxies are truly composed. We show that our techniques achieve better
accuracy of physical parameter estimation for simulated galaxies. Specifically,
we show that our methods significantly decrease the age-metallicity degeneracy
that is common in galaxy population synthesis methods. We analyze a sample of
3046 galaxies in SDSS DR6 and compare the parameter estimates obtained from
different basis choices.Comment: Resubmitted to MNRAS; 16 pages, 15 figure
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