Found 29 talks width keyword stellar populations
Crucial issues in cosmology and astrophysics are to understand the
process of galaxy formation and evolution and the nature of what
appears to be the dominant form of matter in the Universe, i.e. dark
matter. Dwarf galaxies provide important information on both of these
issues. In this talk, I will focus on the dwarf galaxies found in the
Local Group, as it is the galaxy population that can be studied in
the greatest detail than any other from the properties of their
resolved stellar populations. I will show how wide-area surveys have
led to a leap forward in our observational understanding of these
galaxies and discuss future prospects.
The general picture of galaxy formation and evolution includes bars as the main drivers of the internal secular processes affecting the lifetime of disc galaxies. Bars are present in a very high fraction of all the spiral galaxies found at different redshifts, and the processes inducing their formation or the effects they may have on their host galaxies are still under discussion. Particularly interesting is the case of double-barred galaxies: at least 20% of all spirals have turned out to host not only one but two bars embedded in them. These two bars appear randomly oriented and independently rotating. The formation of such a double-barred system has been the goal of several numerical simulations and the results obtained so far can be roughly divided in two big groups: gas-rich and gas-free formation scenarios. In the same way a single bar does, double-bar systems might also promote gas inflow and contribute to the internal secular evolution. Moreover, they have also been proposed as a very efficient mechanism for the feeding of the active galactic nuclei.
All the previous theoretical hypothesis on the formation and evolution of double-barred galaxies have not been tested due to the lack of observational works focused on these systems. With this motivation, during my PhD I observed a sample of double-barred galaxies in order to fully analyse their kinematics and stellar populations. Among the most interesting results, it is important to highlight the discovery of the sigma-hollows, which are the only known kinematical signature of the presence of inner bars, or the fact that inner bars are younger and more metal-rich than their surrounding regions. In this talk I will present the whole work and discuss the results in the framework of the different formation scenarios and the role that these inner bars may be playing in the evolution of their host galaxies.
Taking advantage of the ultra-deep near-infrared imaging obtained with the Hubble Space Telescope on the Hubble Ultra Deep Field, we detect and explore for the first time the properties of the stellar haloes of two Milky Way-like galaxies at z~1. We find that the structural properties of those haloes (size and shape) are similar to the ones found in the local universe. However, these high-z stellar haloes are approximately three magnitudes brighter and exhibit bluer colours ((g-r)<0.3 mag) than their local counterparts. The stellar populations of z~1 stellar haloes are compatible with having ages <1 Gyr. This implies that the stars in those haloes were formed basically at 1<z<2. This result matches very well the theoretical predictions that locate most of the formation of the stellar haloes at those early epochs. A pure passive evolutionary scenario, where the stellar populations of our high-z haloes simply fade to match the stellar halo properties found in the local universe, is consistent with our data.
In recent years accurate photometric and spectroscopic observations have
provided sound evidence that Galactic Globular Clusters can not be longer
considered the prototype of Simple Stellar Populations. In this talk we
present the most recent updates concerning the empirical evidence and
discuss the theoretical framework required for interpreting observations.
Current shortcomings in the interpretation of how the multiple stellar
populations formed in a given cluster are also discussed.
The classical idea that globular clusters are the prototypes of simple stellar populations has been revolutionized in the last few years. Multiple sequences of stars have been detected in the colour-magnitude diagram of a number of clusters, mostly thanks to high-precision HST photometry, and the correlation with the chemical properties of different generations of stars has been demonstrated. In this talk, we will first present a summary of the observational picture, and we will then introduce the SUMO project (a SUrvey of Multiple pOpulations). This is a long-term project, lead here at the IAC and aimed at detecting and characterizing multiple populations in a large sample of globular clusters. We will review the scope, the observing and reduction strategy, and the first results. So far, data for more than 30 clusters have been secured, using the wide field imagers available at the 2.2m ESO/MPI and INT telescope, thus covering both hemispheres. We will present a new photometric index which turned out to be very effective in detecting multiple RGBs in nearly all the clusters analyzed so far. The connection with the chemical content of the different populations will be also discussed.
The basis of stellar population modeling was established around 40 years ago somehow
optimized to the technical facilities and observational data available at that epoch. Since then,
it has been used extensively in astronomy and there has been great improvements relating
their associated ingredients in concordance with the development of more powerful computational
and observational facilities.
However, there has been no similar improvements in the understanding about what is
actually modeling neither in improve the modeling itself to include the current technical advances
to obtain more accurate result in the physical inferences obtained from them.
In this talk I present some advances in the subject of stellar
population modeling and how to take advantage of current facilities to obtain more robust
and accurate inferences from stellar systems at different scales
covering the continuum between fully resolved populations to fully unresolved ones in a unified framework.
Over the past years observations of young and populous star clusters have shown that the stellar initial mass function (IMF) can be conveniently described by a two-part power-law with an exponent alpha2 = 2.3 for stars more massive than about 0.5 Msol and an exponent of alpha1 = 1.3 for less massive stars. A consensus has also emerged that most, if not all, stars form in stellar groups and star clusters, and that the mass function of these can be described as a power-law (the embedded cluster mass function, ECMF) with an exponent beta ~2. These two results imply that the integrated galactic IMF (IGIMF) for early-type stars cannot be a Salpeter power-law, but that they must have a steeper exponent. An application to star-burst galaxies shows that the IGIMF can become top-heavy. This has important consequences for the distribution of stellar remnants and for the chemo-dynamical and photometric evolution of galaxies.
It has been thirty years since the seminal work of Alan Dressler on the density-morphology relation, which established environment as a driving mechanism for galaxy formation and evolution. In the following three decades, we have learned that both the intrinsic processes (nature) and environment (nurture) contribute towards shaping the galaxy populations, and the connection between these two still remains an open question. I will summarize recent results on the interplay between environment and galaxy evolution, obtained from the SDSS DR4 galaxy groups catalogue (Yang et al. 2007) by comparing the properties of central and satellite galaxies as a function of their stellar mass and the dark matter mass of their
We present the K band FP of the ETGs members of the clusters observed by the WINGS survey. The data confirm a different tilt of the FP with respect to the V solution and the presence of a substantial tilt in the K band. This led us to further investigate the hypothesis that ETG non-homology greatly contribute to the tilt of the FP.
The WINGS data show that there are now several evidence of both structural and dynamical non-homology for the class of ETGs. Among these we will discuss in detail the tight relation between the mass of the ETGs, their stellar mass-to-light ratio M/L, and the Sersic index n describing the shape of their light profiles. We guess through a series of mock simulations that this relation acts as a fine-tuning that keeps small the scatter around the FP. We therefore conclude that ETG non-homology is closely connected either with the problem of the tilt and with the small scatter around the FP.
The present work shows the Spectral Energy Distributions (SEDs) in the near-infrared using the IRTF stellar library obtained using the models based on the Single Stellar population Models (SSP) from Vazdekis et al. (1996 - 2010) which work in the optical, and use the CaT and MILES stellar libraries. In this near-infrared research, the isochrones of Marigo et al. (2008) were chosen and which have a range of metallicity [Fe/H] between -2.27 and 0.019, and ages up to 15.85 Gy. Also, they provide the corresponding ?uxes in the IR bands I to M (0.7 to 5.0 microns). The IRTF stellar library contains spectra of 292 stars (F, G, K and M stars) at a resolution of 2000, between 0.8 to 5.2 microns. The features of the SED (spectrum obtained by the integration of the spectra of the stars, at constant metallicity and age) are analysed by comparing to those found on Ivanov et al. (2004) for the IR range. In addition, t he comparison of the models with galaxy observations of early type galaxies by Marmol-Queralto et al. (2009) are presented.
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