262 research outputs found
Colour gradients of high-redshift Early-Type Galaxies from hydrodynamical monolithic models
We analyze the evolution of colour gradients predicted by the hydrodynamical
models of early type galaxies (ETGs) in Pipino et al. (2008), which reproduce
fairly well the chemical abundance pattern and the metallicity gradients of
local ETGs. We convert the star formation (SF) and metal content into colours
by means of stellar population synthetic model and investigate the role of
different physical ingredients, as the initial gas distribution and content,
and eps_SF, i.e. the normalization of SF rate. From the comparison with high
redshift data, a full agreement with optical rest-frame observations at z < 1
is found, for models with low eps_SF, whereas some discrepancies emerge at 1 <
z < 2, despite our models reproduce quite well the data scatter at these
redshifts. To reconcile the prediction of these high eps_SF systems with the
shallower colour gradients observed at lower z we suggest intervention of 1-2
dry mergers. We suggest that future studies should explore the impact of wet
galaxy mergings, interactions with environment, dust content and a variation of
the Initial Mass Function from the galactic centers to the peripheries.Comment: 13 pages, 7 figures, 1 table, accepted for publication on MNRA
Modeling the chemical evolution of Omega Centauri using three-dimensional hydrodynamical simulations
We present a hydrodynamical and chemical model for the globular cluster Omega
Cen, under the assumption that it is the remnant of an ancient dwarf spheroidal
galaxy (dSph), the bulk of which was disrupted and accreted by our Galaxy ~10
Gyr ago. We highlight the very different roles played by Type II and Type Ia
supernovae (SNe) in the chemical enrichment of the inner regions of the
putative parent dSph. While the SNe II pollute the interstellar medium rather
uniformly, the SNe Ia ejecta may remain confined inside dense pockets of gas as
long as succesive SNe II explosions spread them out. Stars forming in such
pockets have lower alpha-to-iron ratios than the stars forming elsewhere. Owing
to the inhomogeneous pollution by SNe Ia, the metal distribution of the stars
in the central region differs substantially from that of the main population of
the dwarf galaxy, and resembles that observed in Omega Cen. This inhomogeneous
mixing is also responsible for a radial segregation of iron-rich stars with
depleted [alpha/Fe] ratios, as observed in some dSphs. Assuming a star
formation history of ~1.5 Gyr, our model succeeds in reproducing both the iron
and calcium distributions observed in Omega Cen and the main features observed
in the empirical alpha/Fe versus Fe/H plane. Finally, our model reproduces the
overall spread of the color-magnitude diagram, but fails in reproducing the
morphology of the SGB-a and the double morphology of the main sequence.
However, the inhomogeneous pollution reduces (but does not eliminate) the need
for a significantly enhanced helium abundance to explain the anomalous position
of the blue main sequence. Further models taking into account the dynamical
interaction of the parent dwarf galaxy with the Milky Way and the effect of AGB
pollution will be required.Comment: 15 pages, 13 figures. MNRAS accepte
Les risques naturels et leur gestion en Equateur : diversité des exemples, complémentarité des approches
International audienceLes conditions naturelles et humaines sont très favorables au déclenchement de catastrophes en Équateur. Le présent ouvrage ne vise pas à l'exhaustivité en matière de risques dans ce pays, mais il en présente certaines facettes à travers quelques travaux menés dans un pays où la recherche sur les risques naturels s'est fortement développée depuis quelques années. Le caractère pluridisciplinaire de la revue concorde parfaitement avec les différentes approches impliquées par la notion de risque. Aussi, des contributions provenant de champs variés sont-elles présentées (lire la préface associée à ce dépôt)
The HI content of Early-Type Galaxies from the ALFALFA survey I. Catalogued HI sources in the Virgo cluster
Aims: We are using the Arecibo Legacy Fast ALFA survey (ALFALFA), which is
covering 17% of the sky at 21 cm, to study the HI content of Early-Type
galaxies (ETG) in an unbiased way. The aim is to get an overall picture of the
hot, warm and cold ISM of ETG, as a function of galaxy mass and environment, to
understand its origin and fate, and to relate it to the formation and evolution
history of these objects. Methods: This paper deals with the first part of our
study, which is devoted to the 8-16 deg. declination strip in the Virgo
cluster. In this sky region, using the Virgo Cluster Catalogue (VCC), we have
defined an optical sample of 939 ETG, 457 of which are brighter than the VCC
completeness limit at B_T=18.0. We have correlated this optical sample with the
catalogue of detected HI sources from ALFALFA. Results: Out of the 389 ETG from
the VCC with B_T<=18.0, outside the 1 deg. region of poor HI detection around
M87, and corrected for background contamination of VCC galaxies without a known
radial velocity, only 9 galaxies (2.3%) are detected in HI with a completeness
limit of 3.5 and 7.6 x 10^7 Mo of HI for dwarf and giant ETG, respectively. In
addition 4 VCC ETG with fainter magnitudes are also detected. Our HI detection
rate is lower than previously claimed. The majority of the detected ETG appear
to have peculiar morphology and to be located near the edges of the Virgo
cluster. Conclusions: Our preliminary conclusion is that cluster ETG contain
very little neutral gas, with the exceptions of a few peculiar dwarf galaxies
at the edge of the ETG classification and of very few larger ETG, where the
cold gas could have a recent external origin.Comment: Accepted for publication in Astronomy and Astrophysics; 6 pages, 3
figure
Diluting the material forming the second generation stars in Globular Clusters: the contribution by unevolved stars
In this short communication we consider the possibility that stars less
evolved than the polluters are the source of the dilution needed to explain the
observed composition of second-generation globular cluster (GC) stars and the
Na-O and Mg-Al anticorrelations. If these stars can lose 0.5-1% of their mass
during the relevant epochs, there is enough diluting material to produce the
observed anticorrelations. In this case, the original mass of proto-GCs was
several tens times higher than the current mass of GCs. While not strictly
impossible, this is a stringent hypothesis that needs more support. Should this
scenario be found true, then the link between the primordial (first-generation)
population in GC and the field population would be very strong.Comment: Accepted for publication on Astronomy and Astrophysic
Neck paraganglioma and follicular lymphoma: A case report
Background: Paragangliomas and pheochromocytomas are sympathetic or parasympathetic tumors derived from the paraganglia and the adrenal medulla, respectively. Paragangliomas and pheochromocytomas can be sporadic or familial, the latter frequently being multifocal and possibly due to succinate dehydrogenase complex genes mutations. In addition, 12% of sporadic paragangliomas are related to covered succinate dehydrogenase complex mutations. The importance of identifying succinate dehydrogenase complex mutations is related to the risk for these patients of developing multiple tumors, including non-endocrine ones, showing an aggressive clinical presentation. Case presentation: We report the case of a 45-year-old Caucasian man with an indolent mass in his neck. Ultrasound of his neck, magnetic resonance imaging, and 1,4,7,10-tetraazacyclododecane-N(I),N(II),N(III),N(IIII)-tetraacetic acid(D)-Phe(1)-thy(3)-octreotide (68Ga-DOTATOC) positron emission tomography-computed tomography and endocrine work-up were consistent with a carotid body paraganglioma with concomitant nodal enlargement in several body regions, which turned out to be a follicular lymphoma at histology. He was found to carry a germline Succinate dehydrogenase subunit B gene (SDHB) mutation. Conclusion: It is crucial to look for a second malignancy in the case of a paraganglioma demonstrating succinate dehydrogenase complex germline mutations
On the radial distribution of stars of different stellar generations in the globular cluster NGC 3201
We study the radial distribution of stars of different stellar generations in
the globular cluster NGC 3201. From recently published multicolour photometry,
a radial dependence of the location of stars on the giant branch was found. We
coupled the photometric information to our sample of 100 red giants with Na, O
abundances and known classification as first or second-generation stars. We
find that giants stars of the second generation in NGC 3201 show a tendency to
be more centrally concentrated than stars of the first generation, supporting
less robust results from our spectroscopic analysis.Comment: Accepted for publication on Astronomy and Astrophysic
Insulin-Like Growth Factor-I Promotes Neurogenesis and Synaptogenesis in the Hippocampal Dentate Gyrus during Postnatal Development
Th
Insulin-Like Growth Factor-I Accelerates the Cell Cycle by Decreasing G1 Phase Length and Increases Cell Cycle Reentry in the Embryonic Cerebral Cortex
Neurogenesis in the developing cerebral cortex of mice occurs in the dorsal telencephalon between embryonic day 11 (E11) and E17, during which time the majority of cortical projection neurons and some glia are produced from proliferating neuroepithelial cells in the ventricular zone. The number of cells produced by this process is governed by several factors, including cell cycle kinetics and the proportion of daughter cells exiting the cell cycle after a given round of cell division. Th
Advances in pre-treatment evaluation of pancreatic ductal adenocarcinoma: a narrative review
Background and Objective: Despite advances in the multidisciplinary management of pancreatic cancer, overall prognosis remains poor, due to early progression of the disease. There is a need to also take action in staging, to make it increasingly accurate and complete, to define the setting of the therapeutic strategy. This review was planned to update the current status of pre-treatment evaluation for pancreatic cancer. Methods: We conducted an extensive review, including relevant articles dealing with traditional imaging, functional imaging and minimally invasive surgical procedures before treatment for pancreatic cancer. We searched articles written in English only. Data in the PubMed database, published in the period between January 2000 and January 2022, were retrieved. Prospective observational studies, retrospective analyses and meta-analyses were reviewed and analysed. Key Content and Findings: Each imaging modality (endoscopic ultrasonography, endoscopic retrograde staging laparoscopy) has its own diagnostic advantages and limitations. The sensitivity, specificity and accuracy for each image set are reported. Data that support the increasing role of neoadjuvant therapy (radiotherapy and chemotherapy) and the meaning of a patient-tailored treatment selection, based on tumour staging, are also discussed. Conclusions: A multimodal pre-treatment workup should be searched as it improves staging accuracy, orienting patients with resectable tumors towards surgery, optimizing patient selection with locally advanced tumors to neoadjuvant or definite therapy and avoiding surgical resection or curative radiotherapy in those with metastatic disease
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