4,279 research outputs found
The core size of the Fornax dwarf Spheroidal
We exploit the detection of three distinct stellar subpopulations in the red
giant branch of the Fornax dwarf Spheroidal to probe its density distribution.
This allows us to resolve directly the evolution with radius of the dark matter
mass profile. We find that a cored dark matter halo provides a perfect fit to
the data, being consistent with all three stellar populations well within
1-sigma, and for the first time we are able to put constraints on the core size
of such a halo. With respect to previous work, we do not strengthen the
statistical exclusion of a dark matter cusp in Fornax, but we find that
Navarro-Frenk-White haloes would be required to have unrealistically large
scale radii in order to be compatible with the data, hence low values of the
concentration parameter. We are then forced to conclude that the Fornax dwarf
Spheroidal sits within a dark matter halo having a constant density core, with
a core size of between 0.6 and 1.8 kpc.Comment: MNRAS Letters, submitte
Filosofia e vita. Riconsiderare con gli antichi la dimensione pubblica del pensare: un confronto con Hannah Arendt.
VEXAS:VISTA EXtension to Auxiliary Surveys Data Release 1. The southern Galactic hemisphere
We present the first public data release of the VISTA EXtension to Auxiliary
Surveys (VEXAS), comprising of 9 cross-matched multi-wavelength photometric
catalogs where each object has a match in at least two surveys. We aim at a
spatial coverage as uniform as possible in the multi-wavelength sky, with the
purpose of providing the astronomical community with reference magnitudes and
colours for various scientific uses, including: object classification (e.g.
quasars, galaxies, and stars; high-z galaxies, white dwarfs, etc.); photometric
redshifts of large galaxy samples; searches of exotic objects such as, for
example, extremely red objects and lensed quasars. We have cross-matched the
wide-field VISTA catalogs (the VISTA Hemisphere Survey and the VISTA Kilo
Degree Infrared Galaxy Survey) with the AllWISE mid-infrared Survey, requiring
that a match exists within 10 arcsec. We have further matched this table with
X-Ray and radio data (ROSAT, XMM, SUMSS). We also performed a second
cross-match between VISTA and AllWISE, with a smaller matching radius (3"),
including WISE magnitudes. We have then cross-matched this resulting table
( objects) with three photometric wide-sky optical deep
surveys (DES, SkyMapper, PanSTARRS). We finally include matches to objects with
spectroscopic follow-up by the SDSS and 6dFGS. To demonstrate the power of
all-sky multi-wavelength cross-match tables, we show two examples of scientific
applications of VEXAS, in particular using the publicly released tables to
discover strong gravitational lenses (beyond the reach of previous searches),
and to build a statistically large sample of extremely red objects. The VEXAS
catalog is currently the widest and deepest, public, optical-to-IR photometric
and spectroscopic database in the Southern Hemisphere.Comment: 13 pages, 10 figures, accepted for publication on Astronomy and
Astrophysic
KiDS0239-3211: A new gravitational quadruple lens candidate
We report the discovery of a candidate to quadrupole gravitationally lensed
system KiDS0239-3211 based on the public data release 3 of the KiDS survey and
machine learning techniques
Mixture Models for Photometric Redshifts
Determining photometric redshifts to high accuracy is paramount to measure
distances in wide-field cosmological experiments. With only photometric
information at hand, photo-zs are prone to systematic uncertainties in the
intervening extinction and the unknown underlying spectral-energy distribution
of different astrophysical sources. Here, we aim to resolve these model
degeneracies and obtain a clear separation between intrinsic physical
properties of astrophysical sources and extrinsic systematics. We aim at
estimates of the full photo-z probability distributions, and their
uncertainties. We perform a probabilistic photo-z determination using Mixture
Density Networks (MDN). The training data-set is composed of optical ()
point-spread-function and model magnitudes and extinction measurements from the
SDSS-DR15, and WISE midinfrared (m and m) model magnitudes.
We use Infinite Gaussian Mixture models to classify the objects in our data-set
as stars, galaxies or quasars, and to determine the number of MDN components to
achieve optimal performance. The fraction of objects that are correctly split
into the main classes is 94%. Our method improves the bias of photometric
redshift estimation (i.e. the mean = (zp - zs)/(1 + zs)) by one
order of magnitude compared to the SDSS photo-z, and decreases the fraction of
outliers (i.e. 3rms). The relative,
root-mean-square systematic uncertainty in our resulting photo-zs is down to
1.7% for low-redshift galaxies (zs 0.5). We have demonstrated the
feasibility of machine-learning based methods that produce full probability
distributions for photo-z estimates with a performance that is competitive with
state-of-the art techniques. Our method can be applied to wide-field surveys
where extinction can vary significantly across the sky and with sparse
spectroscopic calibration samples.Comment: 14 pages, 9 figures, 7 tables, submitted to A&A 14/10/202
VEXAS: VISTA EXtension to Auxiliary Surveys -- Data Release 2: Machine-learning based classification of sources in the Southern Hemisphere
We present the second public data release (DR) of the VISTA EXtension to
Auxiliary Surveys (VEXAS), where we classify objects into stars, galaxies and
quasars based on an ensemble of machine learning algorithms. The aim of VEXAS
is to build the widest multi-wavelength catalogue, providing reference
magnitudes, colours and morphological information for a large number of
scientific uses. We apply an ensemble of 32 different machine learning models,
based on three different algorithms and on different magnitude sets, training
samples and classification problems on the three VEXAS DR1 optical+infrared
(IR) tables. The tables were created in DR1 cross-matching VISTA near-IR data
with WISE far-IR data and with optical magnitudes from the Dark Energy Survey
(VEXAS-DESW), the Sky Mapper Survey (VEXAS-SMW), and the PanSTARRS (VEXAS-PSW).
We assemble a large table of spectroscopically confirmed objects (415 628
unique objects), based on the combination of 6 different spectroscopic surveys
that we use for training. We develop feature imputation to classify also
objects for which magnitudes in one or more bands are missing. We classify in
total ~90 million objects in the Southern Hemisphere. Among these,~62.9M
(~52.6M) are classified as 'high confidence' ('secure') stars, ~920k (~750k) as
'high confidence' ('secure') quasars and ~34.8M (~34.1M) as 'high confidence'
('secure') galaxies, with probabilities (). The density of high-confidence extragalactic objects varies
strongly with the survey depth: at , there are
111/deg quasars in the VEXAS-DESW footprint and 103/deg in the
VEXAS-PSW footprint, while only 10.7/deg in the VEXAS-SM footprint.
Improved depth in the midIR and coverage in the optical and nearIR are needed
for the SM footprint that is not already covered by DESW and PSW.Comment: 25 pages, 18 figures, 8 tables. Accepted for publication on A&A. The
VEXAS tables are publicly available through the ESO Phase 3 here:
https://archive.eso.org/scienceportal/home?data_collection=VEXAS. The DR2
tables update the DR1 with the addition of imputed magnitudes and membership
probabilities to each of the three classe
Structural relaxation of E' gamma centers in amorphous silica
We report experimental evidence of the existence of two variants of the E'
gamma centers induced in silica by gamma rays at room temperature. The two
variants are distinguishable by the fine features of their line shapes in
paramagnetic resonance spectra. These features suggest that the two E' gamma
differ for their topology. We find a thermally induced interconversion between
the centers with an activation energy of about 34 meV. Hints are also found for
the existence of a structural configuration of minimum energy and of a
metastable state.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Edge Effects in the Directionally Biased Distribution of Choristoneura rosaceana (Lepidoptera: Tortricidae) in Apple Orchards
Edge effect tests have been used in a number of studies on obliquebanded leafroller, Choristoneura rosaceana (Harris), to test for evidence of mated female immigration into pheromone-treated orchards. This type of test compares obliquebanded leafroller presence or activity around the perimeter of an orchard against presence or activity in the interior. Higher numbers detected around the edges of an orchard would indicate higher levels of flight activity at the edge, a pattern that could be generated by high levels of immigration. Recent work has shown that the spatial distribution of recaptured obliquebanded leafroller adults released from a single location can be directionally biased, which could obscure the ability to detect an edge effect. To test this theory, data from an orchard study conducted in 1991 that found no significant edge effect was reanalyzed. When we accounted for the directional bias in the distribution of first-generation mated female moths, we found an edge effect with significantly more mated females captured in the edge traps than in the center or mid-interior traps. No edge effect was found when the directional bias was ignored. In addition, second-generation males and mated females both showed a significant edge effect that had not been detected in the original analysis, which had combined both first- and second-generation dat
The Role of Autophagy and Apoptosis During Embryo Development
Programmed cell death (PCD) and cell survival are two sides of the same coin. Autophagy and apoptosis are crucial processes during embryo development of Invertebrates and Vertebrates organisms, as they are necessary for the formation of a new organism, starting from a fertilized egg. Fertilization triggers cell remodeling from each gamete to a totipotent zygote. During embryogenesis, the cells undergo various processes, thus allowing the transformation of the embryo into an adult organism. In particular, cells require the appropriate tools to suddenly modify their morphology and protein content in order to respond to intrinsic and external stimuli. Autophagy and apoptosis are involved in cell proliferation, differentiation and morphogenesis. Programmed cell death is a key physiological mechanism that ensures the correct development and the maintenance of tissues and organs homeostasis in multicellular organisms. PCD has been classified into three types, according to the morphology that the dying cells acquire and the molecular machinery involved: PCD type I or apoptosis; PCD type II or autophagy and PCD type III or necrosis (not involved in physiological development). These different types of cell death have specific features that can be used to be identified and characterized. Apoptosis is a highly conserved, genetically-controlled process through which certain cells destroy themselves. Autophagy is an evolutionarily conserved pathway used by eukaryotes for degrading and recycling various cellular constituents, such as long-lived proteins and entire organelles, that was mainly detected in those tissues where abundant cell death is required. Both autophagy and apoptosis are induced under stress conditions as an adaptive response against stress. Usually, environmental stress cause severe effects on embryonic development. Embryos of different species, exposed to different types of physical or chemical stress, temporarily suspend their development and activate several protective strategies, including PCD II and PCD III. Research has yet to elucidate the interplay between these key processes. Not all types of PCD are always detected in association with a developmental process. Unlike the degeneration of tissues of some invertebrates, the tissues of vertebrates undergo PCD preferentially through an apoptotic mechanisms. In this chapter, we will briefly describe some specific features of apoptotic and autophagic processes. We will focus our attention in some useful model systems of invertebrates and vertebrates organisms, where autophagy and apoptosis occur both in physiological and stress conditions; specifically, we will analyze embryos of: the nematode Caenorhabditis elegans, the insect Drosophila melanogaster, the sea urchin Paracentrotus lividus, the fish Danio Rerio, the mouse mammalian model, and finally we will consider the differentiation of the male and female embryonic germlines in humans
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