372 research outputs found
Evidence For An Unusual Kinetic Phenomenon In The Metallation Of Porphyrins
Reaction of copper(II) with water soluble porphyrins (H₂porph) in the presence of ethylenediamine shows an unusual and so far unreported kinetic phenomenon that can be explained in terms of supramolecular assembly formation apparently involving all solute species as confirmed via light scattering and conductivity measurements
The metallicity gradient of M 33: chemical abundances of HII regions
We present spectroscopic observations of a sample of 72 emission-line
objects, including mainly HII regions, in the spiral galaxy M 33. Spectra were
obtained with the multi-object, wide field spectrograph AF2/WYFFOS at the 4.2m
WHT telescope. Line intensities, extinction, and electron density were
determined for the whole sample of objects. The aim of the present work was to
derive chemical and physical parameters of a set of HII regions, and from them
the metallicity gradient. Electron temperatures and chemical abundances were
derived for the 14 HII regions where both [OII] and [OIII] emission line fluxes
were measured, including the electron temperature sensitive emission line
[OIII] 436.3 nm and in a few cases [NII] 575.5 nm. The ionization correction
factor (ICF) method was used to derive the total chemical abundances. The
presence of abundance gradients was inferred from the radial behaviour of
several emission-line ratios, and accurately measured from chemical abundances
directly derived in 14 HII regions. The oxygen abundances of our HII regions,
located in the radial region from ~2 to ~7.2 kpc, gave an oxygen gradient
-0.054+/-0.011 dex/kpc The overall oxygen gradient for M 33 obtained using ours
and previous oxygen determinations in a large number of HII regions with direct
electron temperature determination as well as abundance in young stars
presented a two slope shape: -0.19 dex/kpc for the central regions (R<3kpc),
and -0.038dex/kpc for the outer regions (R>=3kpc).Comment: 16 pages, 14 figures, A&A accepted 10/05/200
Dissecting the RELICS cluster SPT-CLJ0615-5746 through the intracluster light: confirmation of the multiple merging state of the cluster formation
The intracluster light (ICL) fraction, measured at certain specific
wavelengths, has been shown to provide a good marker for determining the
dynamical stage of galaxy clusters, i.e., merging versus relaxed, for small to
intermediate redshifts. Here, we apply it for the first time to a high-redshift
system, SPT-CLJ0615-5746 at z=0.97, using its RELICS (Reionization Lensing
Cluster Survey) observations in the optical and infrared. We find the ICL
fraction signature of merging, with values ranging from 16 to 37%. A careful
re-analysis of the X-ray data available for this cluster points to the presence
of at least one current merger, and plausibly a second merger. These two
results are in contradiction with previous works based on X-ray data, which
claimed the relaxed state of SPT-CLJ0615-5746, and confirmed the evidences
presented by kinematic analyses. We also found an abnormally high ICL fraction
in the rest-frame near ultraviolet wavelengths, which may be attributed to the
combination of several phenomena such as an ICL injection during recent mergers
of stars with average early-type spectra, the reversed star formation-density
relation found at this high redshift in comparison with lower-redshift
clusters, and projection effects.Comment: 15 pages, 12 figures, submitted to A&
Recent star formation in clusters of galaxies: extreme compact starbursts in A539 and A634
We report on the detection of two Halpha-emitting extreme compact objects
from deep images of the Abell 634 and Abell 539 clusters of galaxies at z ~
0.03. Follow up long slit spectroscopy of these two unresolved sources revealed
that they are members of their respective clusters showing HII type spectra.
The luminosity and the extreme equivalent width of Halpha+[NII] measured for
these sources, together with their very compact appearance, has raised the
question about the origin of these intense starbursts in the cluster
environment. We propose the compact starburst in Abell 539 resulted from the
compression of the interstellar gas of a dwarf galaxy when entering the cluster
core; while the starburst galaxy in Abell 634 is likely to be the result of a
galaxy-galaxy interaction, illustrating the preprocessing of galaxies during
their infall towards the central regions of clusters. The contribution of these
compact star-forming dwarf galaxies to the star formation history of galaxy
clusters is discussed, as well as a possible link with the recently discovered
early-type ultra-compact dwarf galaxies. We note that these extreme objects
will be rarely detected in normal magnitude-limited optical or NIR surveys,
mainly due to their low stellar masses (of the order of 10^6 solar masses),
whereas they will easily show up in dedicated Halpha surveys given the high
equivalent width of their emission lines.Comment: Accepted for publication in the Astronomical Journal. 31 pages, 10
fig
The influence of urban wastes on the interstitial water chemistry in coastal marine sediments of Cadiz Bay
The authors determined, with visual profiles, the concentration of nutrients (i.e. ammonia, nitrate, phosphate and silica), inorganic carbon and sulphate in the interstitial water of Cadiz Bay, as well as organic carbon in sediment, using samples from three stations on Sancti Petri sound. These three stations suffer from different contamination levels due to untreated urban wastewater. Our results show a degradation of the organic matter, principally in the first 30 cm of sediment. These concentration changes are important in the superficial water layer, indicating the efficiency of aerobic oxidation, the organic matter's principal mineralisation mechanism. Two stations, those nearest to the waste point, had the highest organic carbon concentrations in their sediment, as well as the highest vertical gradients of nutrient concentrations in their interstitial water. Sulphate reduction is the principal mechanism involved in the oxidation of organic matter. On the other hand, at the other station studied, with lower organic carbon levels, the gradients were smoother.Se han caracterizado los perfiles verticales en el agua intersticial de las concentraciones de nutrientes (amonio, nitrato, fosfato y silicato), carbono inorgánico y sulfato, así como de carbono orgánico en el sedimento en tres estaciones del caño de Sancti Petri, sujetas a distinto grado de contaminación por vertidos urbanos sin depurar. Analizando globalmente las variaciones con la profundidad de las concentraciones de las distintas especies estudiadas, se puede afirmar que existe una degradación continuada de la materia orgánica, al menos, en los primeros 30 cm del sedimento. Esta hipótesis se encuentra reforzada por la propia disminución de la concentración de carbono orgánico en el sedimento con la profundidad. Estos cambios de concentración son especialmente acusados en la lámina de agua más superficial, poniendo de manifiesto la eficiencia de la oxidación aeróbica como mecanismo de mineralización de la materia orgánica. Las dos estaciones más próximas al vertido, que poseen concentraciones de carbono orgánico más elevadas en el sedimento, presentan también mayores gradientes verticales de concentración de nutrientes en el agua intersticial, y la sulfatorreducción adquiere una mayor importancia relativa como vía de oxidación de la materia orgánica. Por el contrario, en la estación situada en el extremo sur del caño, menos afectada por los aportes de materia orgánica, se observan gradientes más suaves.Instituto Español de Oceanografí
Nearby supernova host galaxies from the CALIFA Survey: II. SN environmental metallicity
The metallicity of a supernova (SN) progenitor, together with its mass, is
one of the main parameters that rules their outcome. We present a metallicity
study of 115 nearby SN host galaxies (0.005<z<0.03) which hosted 142 SNe using
Integral Field Spectroscopy (IFS) from the CALIFA survey. Using O3N2 we found
no statistically significant differences between the gas-phase metallicities at
the locations of the three main SN types (Ia, Ib/c and II) all having
~8.500.02 dex. The total galaxy metallicities are also very similar and we
argue that this is because our sample consists only of SNe discovered in
massive galaxies (log(M/Msun)>10 dex) by targeted searches. We also found no
evidence that the metallicity at the SN location differs from the average
metallicity at the GCD of the SNe. By extending our SN sample with published
metallicities at the SN location, we studied the metallicity distributions for
all SN subtypes split into SN discovered in targeted and untargeted searches.
We confirm a bias toward higher host masses and metallicities in the targeted
searches. Combining data from targeted and untargeted searches we found a
sequence from higher to lower local metallicity: SN Ia, Ic, and II show the
highest metallicity, which is significantly higher than SN Ib, IIb, and Ic-BL.
Our results support the picture of SN Ib resulting from binary progenitors and,
at least part of, SN Ic being the result of single massive stars stripped of
their outer layers by metallicity driven winds. We studied several proxies of
the local metallicity frequently used in the literature and found that the
total host metallicity allows for the estimation of the metallicity at the SN
location with an accuracy better than 0.08 dex and very small bias. In
addition, weak AGNs not seen in total spectra may only weakly bias (by 0.04
dex) the metallicity estimate from integrated spectra. (abridged)Comment: 24 pages, 16 Figures, 13 Tables, Accepted in A&
Synthesis, Structure and Antitumour Properties of a New 1,2-Propylenediaminetetraacetate-Ruthenium(III) Compound
A novel complex formed by ruthenium (III) and the sequestering ligand
1,2-propylenediaminetetraacetic acid (PDTA) has been synthetized and characterized. The structure
of the monomeric compound, studied by X-ray diffraction , shows an almost symmetric octahedral
geometry around the metal ion, with two chlorine atoms in a cis conformation. The antitumour
activity against a variety of murine and human cancers is reported
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