5,784 research outputs found
Spatial genetic structure in the saddled sea bream (Oblada melanura [Linnaeus, 1758]) suggests multi-scaled patterns of connectivity between protected and unprotected areas in the Western Mediterranean Sea
Marine protected areas (MPAs) and networks of MPAs are advocated worldwide for the achievement of marine conservation objectives. Although the knowledge about population connectivity is considered fundamental for the optimal design of MPAs and networks, the amount of information available for the Mediterranean Sea is currently scarce. We investigated the genetic structure of the saddled sea bream ( Oblada melanura) and the level of genetic connectivity between protected and unprotected locations, using a set of 11 microsatellite loci. Spatial patterns of population differentiation were assessed locally (50-100 km) and regionally (500-1000 km), considering three MPAs of the Western Mediterranean Sea. All values of genetic differentiation between locations (Fst and Jost's D) were non-significant after Bonferroni correction, indicating that, at a relatively small spatial scale, protected locations were in general well connected with non-protected ones. On the other hand, at the regional scale, discriminant analysis of principal components revealed the presence of a subtle pattern of genetic heterogeneity that reflects the geography and the main oceanographic features (currents and barriers) of the study area. This genetic pattern could be a consequence of different processes acting at different spatial and temporal scales among which the presence of admixed populations, large population sizes and species dispersal capacity, could play a major role. These outcomes can have important implications for the conservation biology and fishery management of the saddled sea bream and provide useful information for genetic population studies of other coastal fishes in the Western Mediterranean Sea
A radio and infrared exploration of the Cygnus X-3 environments
To confirm, or rule out, the possible hot spot nature of two previously
detected radio sources in the vicinity of the Cygnus X-3 microquasar.
We present the results of a radio and near infrared exploration of the
several arc-minute field around the well known galactic relativistic jet source
Cygnus X-3 using the Very Large Array and the Calar Alto 3.5~m telescope.
The data this paper is based on do not presently support the hot spot
hypothesis. Instead, our new observations suggest that these sources are most
likely background or foreground objects. Actually, none of them appears to be
even barely extended as would be expected if they were part of a bow shock
structure. Our near infrared observations also include a search for extended
emission in the Bracket (2.166 m) and (2.122 m)
lines as possible tracers of shocked gas in the Cygnus X-3 surroundings. The
results were similarly negative and the corresponding upper limits are
reported.Comment: Accepted for publication in A&A; 5 pages, 4 figure
Chandra X-ray counterpart of KS 1741-293
We aim to investigate the nature of the high energy source KS 1741-293 by
revisiting the radio and infrared associations proposed in the early 1990s. Our
work is mostly based on the analysis of modern survey and archive data,
including the NRAO, MSX, 2MASS and Chandra archives, and catalogues. We also
have obtained deep CCD optical observations by ourselves. The coincidence of KS
1741-293 with an extended radio and far-infrared source, tentatively suggested
in 1994, is no longer supported by modern observational data. Instead, a
Chandra source is the only peculiar object found to be consistent with all
high-energy error circles of KS 1741-293 and we propose it to be its most
likely X-ray counterpart. We also report the existence of a non-thermal radio
nebula in the vicinity of the KS 1741-293 position with the appearance of a
supernova remnant. The possibility of being associated to this X-ray binary is
discussed.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in Astronomy &
Astrophysic
On the ongoing multiple blowout in NGC 604
Several facts regarding the structure of NGC 604 are examined here. The three
main cavities, produced by the mechanical energy from massive stars which in
NGC 604 are spread over a volume of 10 pc, are shown here to be
undergoing blowout into the halo of M33. High resolution long slit spectroscopy
is used to track the impact from massive stars while HST archive data is used
to display the asymmetry of the nebula.
NGC 604 is found to be a collection of photoionized filaments and sections of
shells in direct contact with the thermalized matter ejected by massive stars.
The multiple blowout events presently drain the energy injected by massive
stars and thus the densest photoionized gas is found almost at rest and is
expected to suffer a slow evolution.Comment: 15 pages (11 text), 4 figures. To be published in Ap
Euclid : Estimation of the Impact of Correlated Readout Noise for Flux Measurements with the Euclid NISP Instrument
The Euclid satellite, to be launched by ESA in 2022, will be a major instrument for cosmology for the next decades. Euclid is composed of two instruments: the Visible instrument and the Near Infrared Spectrometer and Photometer (NISP). In this work, we estimate the implications of correlated readout noise in the NISP detectors for the final in-flight flux measurements. Considering the multiple accumulated readout mode, for which the UTR (Up The Ramp) exposure frames are averaged in groups, we derive an analytical expression for the noise covariance matrix between groups in the presence of correlated noise. We also characterize the correlated readout noise properties in the NISP engineering-grade detectors using long dark integrations. For this purpose, we assume a (1/f) (alpha)-like noise model and fit the model parameters to the data, obtaining typical values of sigma = 19.7(-0.8)(+1.1)e(-)Hz(-0.5), f(knee) = (5.2(-1.3)(+1.8) x 10(-3) Hz and alpha = 1.24(-0.21)(+0.26). Furthermore, via realistic simulations and using a maximum likelihood flux estimator we derive the bias between the input flux and the recovered one. We find that using our analytical expression for the covariance matrix of the correlated readout noise we diminish this bias by up to a factor of four with respect to the white noise approximation for the covariance matrix. Finally, we conclude that the final bias on the in-flight NISP flux measurements should still be negligible even in the white readout noise approximation, which is taken as a baseline for the Euclid on-board processing to estimate the on-sky flux.Peer reviewe
Localized starbursts in dwarf galaxies produced by impact of low metallicity cosmic gas clouds
Models of galaxy formation predict that gas accretion from the cosmic web is
a primary driver of star formation over cosmic history. Except in very dense
environments where galaxy mergers are also important, model galaxies feed from
cold streams of gas from the web that penetrate their dark matter haloes.
Although these predictions are unambiguous, the observational support has been
indirect so far. Here we report spectroscopic evidence for this process in
extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of
localized starbursts associated with gas having low metallicity. Detailed
abundance analyses based on Gran Telescopio Canarias (GTC) optical spectra of
ten XMPs show that the galaxy hosts have metallicities around 60 % solar on
average, while the large star-forming regions that dominate their integrated
light have low metallicities of some 6 % solar. Because gas mixes azimuthally
in a rotation timescale (a few hundred Myr), the observed metallicity
inhomogeneities are only possible if the metal-poor gas fell onto the disk
recently. We analyze several possibilities for the origin of the metal-poor
gas, favoring the metal-poor gas infall predicted by numerical models. If this
interpretation is correct, XMPs trace the cosmic web gas in their surroundings,
making them probes to examine its properties.Comment: Accepted for publication in ApJ
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