Use stellar evolution theory to interpret differences in stellar pops between galaxies consider the spectrum of a galaxy to be the sum of a set of simple stellar populations ssps ssps are singleage, singlemetallicity population. Evolutionary stellar population synthesis with miles i. Those explosions would have thoroughly dispersed their material, ejecting metals into the interstellar medium ism, to be incorporated into the later generations of. An isochrone data base and a rapid model for stellar. Modelling the properties colours, luminosities and spectra of ssp s is important for research into the stellar populations of galaxies since, in theory, we can reconstruct the complex histories of these galaxies by combining individual ssp s. We present a new set of stellar interior and synthesis models for predicting the integrated emission from stellar populations in star. The focus is on the simplest models, the so called simple stellar populations, that describe instantaneous generations of single stars with the same chemical composition and age. Our models indicate that mean population ages span an interval of 712 gyr and are correlated with metallicities, which range from approximately half up to three times solar. Galaxies are big, big collections of stars 1011 of stars. For example, galaxies do not consist only of astars of 2 solar mass. We present a new set of stellar interior and synthesis models for predicting the integrated emission from stellar populations in star clusters and galaxies of arbitrary age and metallicity. Currently there are two competing scenarios to explain the origin of the stellar population in globular clusters gcs. Using a given set of isochrones at a certain age and metallicity and an assumed initial mass func.
We step through the models one at a time, calculating the. The focus is on the simplest models, the so called simple stellar populations, that describe instantaneous generations of single stars with the same chemical composition and. Photometric properties of single stellar populations astronomy. Colors of ellipticals from galex university of oregon.
Stellar population models based on new generation stellar library. We present the single stellar population ssp synthesis results of our new synthetic stellar atmosphere models library with a spectral sampling of 0. The spectral resolution varies from 3a in the uv to 10a in the nearinfrared nir, corresponding to. Therefore, most results of stellar population studies are derived from singlestar stellar population ssssp models e. Constraining globular cluster formation through studies of. The stellar population synthesis technique berkeley cosmology. Establishing the reliability with which stellar population parameters can be measured is vital to extragalactic astronomy. These models are based on a recent library of synthetic stellar spectra and a new library of stellar evolutionary tracks, both computed for three different iron abundances. The stellar luminosity function is the distribution needed to describe the stellar population of a system. Such a model is su cient to explain twocolor diagrams and the colormagnitude relations for all colors using only metallicity as a variable on a solely 12 gyrs stellar population with no evidence of stars.
The age, metallicity and alphaelement abundance of galactic globular clusters from single stellar population models article in monthly notices of the royal astronomical society 3794. The models are based on accurate stellar parameters for the jones library stars and a new set of fitting functions describing the behavior of. Cmd came from one particular set of stellar evolution models. Stellar population models lets move on from the theory of gravitational collapse whew. In the low metallicity regime, however, our models combine scaledsolar isochrones with stellar spectra that do not show this abundance ratio pattern e. The base ingredient of stellar population models of galaxies are single stellar populations ssps, which are combined into star formation histories by linear combinations tinsley 1968. Hitherto, the hb has been studied primarily in single stellar populations, such as globular clusters, by comparing observations to theoretical stellar evolutionary models. Knowing the distribution of the number of stars as a function of mass, their chemical composition, and evolutionary stage, then one can compute the light coming from them. Generic to all sps models not due to inadequacies in stellar libraries probably not due to uncertainties in stellar evolution, such as the main sequence and subgiant branch although, there are few observed star clusters at these metallicities with which to calibrate ssps modeling the red sequence. The models are based on accurate stellar parameters for the jones library stars and a new set of fitting functions. A team led by icg researcher claudia maraston was the first to explore the effect of stellar population models on the properties of galaxy models in a cold dark matter universe 7,8. Single stellar population synthesis models stellar population synthesis is a powerful technique for studying galaxy evolution, allowing us to determine galaxy ages and chemical abundances.
Stellar population models based on new generation stellar. The stellar population synthesis models used were all at fixed solar metallicity to limit computing time, utilised the miles stellar library and had age ranges from 6. Its spectral resolution and wavelength range determine the spectral resolution and wavelength range of the models. Watch a simple stellar population ssp evolve in the hr diagram. The age, metallicity and alphaelement abundance of. Hierarchical modeling is a statistically rigorous way to make scienti. A hierarchical bayesian approach for reconstructing the. The horizontal branch as a probe of stellar population history. We have released the ssp model spectra based on the updated stellar populations synthesis code described vazdekis et al. The age, metallicity and alphaelement abundance of galactic globular clusters from single stellar population models article in monthly notices of the royal astronomical society 3794 july.
Stellar population models are also a key ingredient of galaxy formation and evolution models. Many theoretical stellar models show that most highmass population iii stars rapidly exhausted their fuel and likely exploded in extremely energetic pairinstability supernovae. Observations show that nearly all star clusters and stellar populations contain blue straggler stars bss. Evolutionary stellar population synthesis 1641 are solarscaled, our models are selfconsistent and scaledsolar for solar metallicity.
Terlevich all the data are available at the cds or on request to the authors. An important ingredient in stellar population models is the stellar library. In addition to overall metallicity, one must consider changes in individual elements when constructing stellar population models. Use stellar evolution theory to interpret differences in stellar pops between galaxies consider the spectrum of a galaxy to be the sum of a set of simple stellar populations ssps ssps are single age, single metallicity population. The underlying model was presented in recent articles, where we compared its predictions with observations of. We chose these codes as gandalf simultaneously fits stellar templates and gaussian emissionline models. Application to clusters in m31 and in the magellanic clouds are also considered. In a typical massivestar population of single age, stars with vastly di erent zeroagemain. This work differs from existing spectral synthesis codes in. The stochastic nature of stellar population modelling.
Galactic gcs provide an excellent medium in which to test the consistency of single stellar population ssp models as they should be our best analogue to a homogeneous single stellar population. The stellar population models of maraston 2005 and maraston et al. The target of eps models are those stellar systems that cannot be resolved into single stars, like galaxies and extragalactic globular clusters. Its range in stellar types determines the applicability of the models, and to a large extent their quality. We present unresolved single stellar population synthesis models in the. Using the andersen 1991 data on the mass, absolute visual magnitude, the effective surface temperature and the bolometric corrections, new calibrations f. Modern stellar population synthesis assumes that the stellar populations in galaxies consist of a sum of single stellar populations ssp, building blocks of more complex stellar populations, entities that consist of all stars born at the same time, with the same metallicity. These steps include introducing modelling variables and parameters, deciding on appropriate modelling assumptions, forming the model often a di. Their integrated light forms a single stellar population spectrum. Model predictions at moderately high resolution are provided for the following spectral ranges. All stars form with the same initial chemical composition. Comparison between the latest evolutionary models with the empirical data has been made to test the evolutionary models for the purpose of stellar population studies.
Single stellar populations in the nearinfrared astronomy. Any stellar population models from cmd to integrated luminosities or spectra, as well as their applications, have. Test of evolutionary models for stellar population studies. Therefore, most results of stellar population studies are derived from single star stellar population ssssp models e. We present a new set of model predictions for 16 lick absorption line indices from h. The connection between stellar population models and individual stellar spectra are stellar parameters such as e. We use markov chain monte carlo sampling techniques to reconstruct the best parameters for the imf prior, the age and the metallicity of a single stellar population. Star clusters as simple stellar populations pdf paperity. How does this depend on wavelength, population age starformation history and metallicity.
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