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Register a new userA new grid of evolutionary synthesis models
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We present new evolutionary synthesis models for Single Stellar Populations covering a wide range in age and metallicity. The most important difference with existing models is the use of NLTE atmosphere models for the hot stars (O, B, WR, post-AGB stars, and planetary nebulae) that have an important impact in the stellar clusters ionizing spectra.
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A grid of 20 millions 3-1100$mu$m SED models is presented for synthetic young clusters embedded in dense clumps. The models depend on four primary parameters: the clump mass M$_{clump}$ and dust temperature T$_{dust}$, the fraction of mass f$_{core}$ locked in dense cores, and the age of the clump t$_{SF}$. We populate the YSO clusters using the IMF from Kroupa(2001) and the YSOs SED models grid of Robitaille et al. (2006). We conduct extensive testing of SED fitting using a simulated dataset and we find that M$_{clump}$ essentially depends on the submillimeter portion of the SED, while T$_{dust}$ is mostly determined from the shape of the SED in the 70-350$mu$m range. Thanks to the large number of models computed we verify that the combined analysis of L/M, [8-24] and [24-70] colours removes much of the SEDs f$_{core}$-t$_{SF}$ degeneracy. The L/M values are particularly useful to diagnose f$_{core}$. L/M$leq$1 identifies protoclusters with f$_{core}leq$0.1 and t$_{SF} leq 10^5$ years, while L/M$geq$10 excludes f$_{core}leq$0.1. We characterize lower limits of L/M where ZAMS stars are not found in models, and we also find models with L/M $geq$10 and no ZAMS stars, in which [8-24]$geq0.8pm 0.1$ independently from M$_{clump}$, temperature and luminosity. This is the first set of synthesis SED models suited to model for embedded and unresolved clusters of YSOs. A set of new evolutionary tracks in the L/M diagram is also presented.
The Extended Evolutionary Synthesis (EES) is beginning to fulfill the whole promise of Darwinian insight through its extension of evolutionary understanding from the biological domain to include cultural information evolution. Several decades of important foundation-laying work took a social Darwinist approach and exhibited and ecologically-deterministic elements. This is not the case with more recent developments to the evolutionary study of culture, which emphasize non-Darwinian processes such as self-organization, potentiality, and epigenetic change.
We compare six popularly used evolutionary population synthesis (EPS) models (BC03, CB07, Ma05, GALEV, GRASIL, Vazdekis/Miles) through fitting the full optical spectra of six representative types of galaxies (star-forming and composite galaxies, Seyfert 2s, LINERs, E+A and early-type galaxies), which are taken from the Sloan Digital Sky Survey (SDSS). Throughout our paper, we use the simple stellar populations (SSPs) from each EPS model and the software STARLIGHT to do our fits. Our main results are: Using different EPS models the resulted numerical values of contributed light fractions change obviously, even though the dominant populations are consistent. The stellar population synthesis does depend on the selection of age and metallicity, while it does not depend on the stellar evolution track much. The importance of young populations decreases from star-forming, composite, Seyfert 2, LINER to early-type galaxies, and E+A galaxies lie between composite galaxies and Seyfert 2s in most cases. We conclude that different EPS models do derive different stellar populations, so that it is not reasonable to directly compare stellar populations estimated from different EPS models. To get reliable results, we should use the same EPS model for the compared samples.
[Abridged]. We present SEDs for single-age, single-metallicity stellar populations (SSPs) covering the optical range at resolution 2.3A (FWHM). These SEDs constitute our base models, as they combine scaled-solar isochrones with MILES empirical stellar library, which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries. The unprecedented stellar parameter coverage of MILES allowed us to safely extend our optical SSP SED predictions from intermediate- to very-old age regimes, and the metallicity coverage of the SSPs from super-solar to [M/H]=-2.3. SSPs with such low metallicities are particularly useful for globular cluster studies. Observed spectra can be studied by means of full spectrum fitting or line-strengths. For the latter we propose a new Line Index System (LIS) to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. Apart from constant resolution as function of wavelength the system is also based on flux-calibrated spectra. Data can be analyzed at three different resolutions: 5A, 8.4A and 14A (FWHM), which are appropriate for studying globular cluster, low and intermediate-mass galaxies, and massive galaxies, respectively. Polynomials to transform current Lick/IDS line index measurements to the new system are provided. A web-page with a suite of on-line tools to facilitate the handling and transformation of the spectra is available at http://miles.iac.es.
We summarize the principles and fundamental ingredients of evolutionary synthesis models, which are stellar evolution, stellar atmospheres, the IMF, star-formation histories, nebular emission, and also attenuation from the ISM and IGM. The chapter focusses in particular on issues of importance for predictions of metal-poor and Population III dominated galaxies. We review recent predictions for the main physical properties and related observables of star-forming galaxies based on up-to-date inputs. The predicted metallicity dependence of these quantities and their physical causes are discussed. The predicted observables include in particular the restframe UV-to-optical domain with continuum emission from stars and the ionized ISM, as well as emission lines from H, He, and metals. Based on these predictions we summarize the main observational signatures (emission line strengths, colors etc.), which can be used to distinguish normal stellar populations from very metal-poor objects or even Pop III. Evolutionary synthesis models provide an important and fundamental tool for studies of galaxy formation and evolution, from the nearby Universe back to first galaxies. They are used in many applications to interpret existing observations, to predict and guide future missions/instruments, and to allow direct comparisons between state-of-the-art galaxy simulations and observations.
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