4,628 research outputs found
Study of stellar populations in the bulges of barred galaxies
We have obtained long-slit spectroscopy for a sample of 20 early-type barred
galaxies to study the influence of bars in the building of galaxy bulges. Line
strength indices were measured and used to derive age and metallicity gradients
in the bulge region by comparing with stellar population models. The same
analysis was also carried out with similar data of unbarred galaxies taken from
the literature. The bulges of barred galaxies seem to be more metal rich, at a
given velocity dispersion (sigma), than the bulges of unbarred galaxies, as
measured by some metallicity sensitive indices. There are indications that the
ratio of relative abundance of alpha-elements with respect to iron, [E/Fe],
derived for the bulges of barred galaxies tend to lie above the values of the
unbarred galaxies at a given sigma. The metallicity gradients for the majority
of the bulges are negative, less metal rich towards the end of the bulge. The
gradient values show a large scatter for galaxies with sigma below 150 km/s.
The age distribution is related to the presence of bulge substructure such as a
nuclear ring or an inner disk. The metallicity of both the bulge and the bar
are very well correlated indicating a close link between the enrichment
histories of both components. Bulges of barred early type galaxies might have
suffered a different chemical enrichment compared to the bulges of unbarred
galaxies of the same morphological type, same central velocity dispersion and
low inclination angles. The hinted stellar populations differences separating
the bulges of barred and unbarred galaxies and the strong link existing between
the metallicity of the bulge and the presence of a bar points to scenarios were
they both form simultaneously in processes leading to rapid and massive
episodes of star formation, possibly linked to the bar formation.Comment: Accepted for publication in Astronomy and Astrophysic
Warp evidences in precessing galactic bar models
Most galaxies have a warped shape when they are seen from an edge-on point of
view. The reason for this curious form is not completely known so far and in
this work we apply dynamical system tools to contribute to its explanation.
Starting from a simple, but realistic, model formed by a bar and a disc, we
study the effect produced by a small misalignment between the angular momentum
of the system and its angular velocity. To this end, a precession model is
developed and considered, assuming that the bar behaves like a rigid body.
After checking that the periodic orbits inside the bar keep being the skeleton
of the inner system, even after inflicting a precession to the potential, we
compute the invariant manifolds of the unstable periodic orbits departing from
the equilibrium points at the ends of the bar to get evidences of their warped
shapes. As it is well known, the invariant manifolds associated with these
periodic orbits drive the arms and rings of barred galaxies and constitute the
skeleton of these building blocks. Looking at them from a side-on viewpoint, we
find that these manifolds present warped shapes as those recognized in
observations. Lastly, test particle simulations have been performed to
determine how the stars are affected by the applied precession, confirming this
way the theoretical results obtained.Comment: 14 pages, 21 figures, Accepted for publication in A&A (15th Jan 2016
Cell migration within confined sandwich-like nanoenvironments
Aim: We introduced sandwich-like cultures to provide cell migration studies with 4 representative nano-bio-environments where both ventral and dorsal cell receptors are activated. Methods: We have investigated different nano-environmental conditions by changing the protein coating (fibronectin, vitronectin) and/or materials (using polymers that adsorb proteins in qualitatively different conformations) of this sandwich system to show their specific role in cell migration. Results: Here we show that cell migration within sandwich cultures greatly differs from 2D cultures and shares some similarities with migration within 3D environments. Beyond differences in cell morphology and migration, dorsal stimulation promotes cell remodeling of the ECM over simple ventral 12 receptor activation in traditional 2D cultures.</p
Origin of marine planktonic cyanobacteria
Marine planktonic cyanobacteria contributed to the widespread oxygenation of the oceans towards the end of the Pre-Cambrian and their evolutionary origin represents a key transition in the geochemical evolution of the Earth surface. Little is known, however, about the evolutionary events that led to the appearance of marine planktonic cyanobacteria. I present here phylogenomic (135 proteins and two ribosomal RNAs), Bayesian relaxed molecular clock (18 proteins, SSU and LSU) and Bayesian stochastic character mapping analyses from 131 cyanobacteria genomes with the aim to unravel key evolutionary steps involved in the origin of marine planktonic cyanobacteria. While filamentous cell types evolved early on at around 2,600–2,300 Mya and likely dominated microbial mats in benthic environments for most of the Proterozoic (2,500–542 Mya), marine planktonic cyanobacteria evolved towards the end of the Proterozoic and early Phanerozoic. Crown groups of modern terrestrial and/or benthic coastal cyanobacteria appeared during the late Paleoproterozoic to early Mesoproterozoic. Decrease in cell diameter and loss of filamentous forms contributed to the evolution of unicellular planktonic lineages during the middle of the Mesoproterozoic (1,600–1,000 Mya) in freshwater environments. This study shows that marine planktonic cyanobacteria evolved from benthic marine and some diverged from freshwater ancestors during the Neoproterozoic (1,000–542 Mya)
Recommended from our members
Prevalence of type 2 diabetes among minority groups
The purpose of this study was twofold. First, the study evaluated Loma Linda University Medical Center\u27s (LLUMC) Diabetes Treatment Center\u27s (DTC) effectiveness in providing diabetes education and services to high risk minority populations. Second, the results of the study helped the DTC determine the need for expanding its present efforts in the form of community health prevention services to San Bernardino County residents
Two semi-automated computational approaches for spectroscopic analysis of stellar photospheres: detailed characterization at high resolution and abundance determination at medium resolution
We report on two distinct computational approaches to self-consistently
measure photospheric properties of large samples of stars. Both procedures
consist of a set of several semi-integrated tasks based on shell and Python
scripts, which efficiently run either our own codes or open source software
commonly adopted by the astronomical community. One approach aims to derive the
main stellar photospheric parameters and abundances of a few elements by
analysing high-resolution spectra from a given public library homogeneously
constructed. The other one is applied to recover the abundance of a single
element in stars with known photospheric parameters by using mid-resolution
spectra from another open homogeneous database and calibrating derived
abundances. Both semi-automated computational approaches provide homogeneity
and objectivity to every step of the process and represent a fast way to reach
partial and final results as well as to estimate measurement errors, making
possible to systematically evaluate and improve the distinct steps.Comment: 7 pages, 4 figures, conference paper (I Workshop of Computacao
Cientifica em Astronomia, Brazil, 2011) to appear in the Journal of
Computational Interdisciplinary Sciences - JCI
- …