Starburst99: Synthesis Models for Galaxies with Active Star Formation (original) (raw)
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A Panchromatic Spectral Population Synthesis Model for Young Star-Burst Galaxies
2017
The study of the properties of galaxies to possibly map their formation and evolutionary paths is an active research field both from observational and theoretical point of view. Great observational efforts are continuously devoted to map the spectral energy distribution (SED) of galaxies in the local universe and at high-redshifts over all wavelength range, by surveying the sky with both ground and space-borne instruments. Surveys in different spectral bands have revealed galaxies with drastically different activity levels and energy budgets, symptoms of underlying disparate basic physical properties. It is these basic properties that one aims to uncover in order to get insights on the complex behaviour of mass assembly and recycling in galaxies. The fundamental tools necessary for this task are spectral synthesis models. These models are based on the availability of a complete library of stellar evolution models, that homogeneously cover the range of stellar masses, metallicities, and evolutionary phases that contribute to the integrated SED of a galaxy. From these and a library with a complete coverage of the stellar parameters, the integrated SED of simple stellar populations (SSP) can then be computed. To compare the theoretical SED with the observed one, it is important to account for, at very least, the main processes producing radiation and affecting the radiation path, i.e. stars, ionized gas nebulae for the main recombination lines and continuum emission, core-collapsed supernovae (CCSN) for the non-thermal radio emission, and the interaction between stellar radiation and dust grains in the interstellar medium (ISM). In this thesis, I focus on a major revision and extension of the SSP models based on the PAdova TRieste Stellar Evolution Code (PARSEC) stellar models. By means of PARSEC, I compute, at five different metallicities (0.0001-0.02) and four different IMF upper mass limits (40-350M) the integrated stellar light, the line and continuum emission (effects of ionized nebulae on this light) and of the nonthermal emission predicted by young SSPs. I then use the new SSP models in combination with the radiative transfer code GRASIL (GRAphites and SILicates) to include the stellar extinction by dust and the ensuing IR emission, therefore providing a panchromatic UV-to radio SED modelling. I calibrate and apply this new model to observations. Thereafter, I carry out a critical investigation of the effect of metallicity, IMF upper mass limit and star formation regime (star bursting versus normal star forming) on star formation rate (SFR) and dust attenuation properties of star forming galaxies. This allowed for the provision of a consistent set of SFR calibrations, that are explicitly dependent on metallicity and IMF upper mass limit and also on the age of the starburst, at wavelengths ranging from UV to radio. Finally, I considered the possible use of the radio slope to identify the the IMF upper mass limit where i showed that the method is well suited for high-redshift objects with a prolonged star formation.
A Database for Galaxy Evolution Modeling
Publications of The Astronomical Society of The Pacific, 1996
ABSTRACT. This paper represents a collective effort to provide an extensive electronic data base useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data is discussed here, and the data are made fully available in the AAS CD-ROM Series, Vol. 7. Several empirical stellar libraries are part of this data base. They cover the ultraviolet spectral range observed with WE, optical data from different ground-based telescopes, and ground-based infrared data. Spectral type coverage depends on the wavelength, but is mostly complete for types O to M and luminosity classes V to I. A large metallicity range is covered as well. Theoretical libraries of selected spectral indices of cool stars and of stellar continuum fluxes in the temperature range 2000-50,000 Κ as well as Wolf-Rayet energy distributions are presented. Several libraries of star clusters and early-type galaxies have been selected for this data base. We discuss an extensive set of empirical spectral templates covering the wavelength region from 1200 to 9800 Â, as well as narrow-band line indices in a large number of passbands. Bench-mark spectra of nearby galaxies for model tests are included as well. We compiled numerous evolutionary models and isochrones for stars of all mass ranges of interest, wide metallicity range, and for all evolutionary phases, including the pre-main-sequence phase. The majority of the models have been computed by the Geneva and Padova groups. Evolutionary synthesis models computed by several independent groups are made available. They can be applied to old and young systems, and are optimized with respect to different aspects of input physics. The model predictions include stellar (colors, magnitudes, absorption features) and nebular (emission-line fluxes) properties. Finally, we present models of ionized gas to be used for the interpretation of active galactic nuclei and young star-forming galaxies. The community is encouraged to make use of this electronic data base and to perform a critical comparison between the individual datasets.
The evolution of stars and gas in starburst galaxies
Monthly Notices of The Royal Astronomical Society, 2003
In systems undergoing starbursts the evolution of the young stellar population is expected to drive changes in the emission-line properties. This evolution is usually studied theoretically, with a combination of evolutionary synthesis models for the spectral energy distribution of starbursts and photoionization calculations. In this paper we present a more empirical approach to this issue. We apply empirical population synthesis techniques to samples of starburst and HII galaxies in order to measure their evolutionary state and correlate the results with their emission-line properties. A couple of useful tools are introduced that greatly facilitate the interpretation of the synthesis: (1) an evolutionary diagram, the axes of which are the strengths of the young, intermediate age and old components of the stellar population mix; and (2) the mean age of stars associated with the starburst, . These tools are tested with grids of theoretical galaxy spectra and found to work very well even when only a small number of observed properties (absorption-line equivalent widths and continuum colours) is used in the synthesis. Starburst nuclei and HII galaxies are found to lie on a well-defined sequence in the evolutionary diagram. Using the empirically defined mean starburst age in conjunction with emission-line data, we have verified that the equivalent widths of Hβ and [OIII] decrease for increasing . The same evolutionary trend was identified for line ratios indicative of the gas excitation, although no clear trend was identified for metal-rich systems. All these results are in excellent agreement with long-known, but little tested, theoretical expectations.
From theoretical stellar spectra to realistic models of the Milky Way : a never ending Odyssey
2007
The main goal of this work is to find the best-fitting galaxy model for the Milky Way by comparing 10 different models with observed star counts and colour distributions. The observational data are taken from the Basel High-Latitude (Basel)and the Sloan Digital Sky (SDSS) photometric field star Surveys, respectively. We develop a code to derive synthetic spectra, absolute and apparent magnitudes and colours for stars given by a galactic evolutionary model (3D chemodynamical code for the Milky Way by Samland & Gerhard (2003)). The model galaxies provide stellar masses, ages, chemical abundances, velocities and positions at an evolutionary time of 13.5 Gyr. By means of the spectrophotometric data (given in the libraries of stellar evolutionary tracks (Padova 1994) and synthetic stellar spectra (BaSeL 3.2)), we build synthetic colour-magnitude diagrams, star counts, and ageand metallicity distributions for a number of viewing directions and field sizes. Our intention is to first compar...
Stellar populations in local star-forming galaxies -- I. Data and modelling procedure
Monthly Notices of the Royal Astronomical Society, 2003
We present an analysis of the integrated properties of the stellar populations in the Universidad Complutense de Madrid (UCM) Survey of Hα-selected galaxies. In this paper, the first of a series, we describe in detail the techniques developed to model star-forming galaxies using a mixture of stellar populations, and taking into account the observational uncertainties. We assume a recent burst of star formation superimposed on a more evolved population. The effects of the nebular continuum, line emission and dust attenuation are taken into account. We also test different model assumptions including the choice of specific evolutionary synthesis model, initial mass function, star formation scenario and the treatment of dust extinction. Quantitative tests are applied to determine how well these models fit our multi-wavelength observations for the UCM sample. Our observations span the optical and near infrared, including both photometric and spectroscopic data. Our results indicate that extinction plays a key role in this kind of studies, revealing that low-and high-obscured objects may require very different extinction laws and must be treated differently. We also demonstrate that the UCM Survey galaxies are best described by a short burst of star formation occurring within a quiescent galaxy, rather than by continuous star formation. A detailed discussion on the inferred parameters, such as the age, burst strength, metallicity, star formation rate, extinction and total stellar mass for individual objects, is presented in paper II of this series.
Monthly Notices of the Royal Astronomical Society, 2005
We present here a new set of evolutionary population synthesis models for template galaxies along the Hubble morphological sequence. The models, which account for the individual evolution of the bulge, disc, and halo components, provide basic morphological features, along with bolometric luminosity and colour evolution (including Johnson/Cousins, Gunn g, r , i, and Washington C, M, T 1 , T 2 photometric systems) between 1 and 15 Gyr. The luminosity contribution from residual gas is also evaluated, both in terms of nebular continuum and Balmer-line enhancement. Our theoretical framework relies on the observed colours of present-day galaxies, coupled with a minimal set of physical assumptions related to simple stellar population (SSP) evolution theory, to constrain the overall distinctive properties of galaxies at earlier epochs. A comparison with more elaborate photometric models, and with empirical sets of reference spectral energy distributions (SEDs) for early-and late-type galaxies is accomplished, in order to test output reliability and investigate the internal uncertainty of the models. The match with observed colours of present-day galaxies tightly constrain the stellar birth rate, b, which smoothly increases from E to Im types. The comparison with the observed supernova (SN) rate in low-redshift galaxies shows, as well, a pretty good agreement, and allows us to tune up the inferred star formation activity and the SN and hypernova rates among the different galaxy morphological types. Among others, these results could find useful application also in cosmological studies, given for instance the claimed relationship between hypernova events and gamma-ray bursts. One outstanding feature of the back-in-time evolution model is the prevailing luminosity contribution of the bulge at early epochs. As a consequence, the current morphological look of galaxies might drastically change when moving to larger distances, and we discuss here how sensibly this bias could affect the observation (and the interpretation) of high-redshift surveys. In addition to broad-band colours, the modelling of Balmer line emission in disc-dominated systems shows that striking emission lines, like Hα, can very effectively track stellar birth rate in a galaxy. For these features to be useful age tracers as well, however, one should first assess the real change of b versus time on the basis of supplementary (and physically independent) arguments.
The Star Formation History and Chemical Evolution of Star-Forming Galaxies in the Nearby Universe
The Astrophysical Journal, 2012
We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122751 Star Forming Galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey (SDSS). For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their Star Formation History (SFH) using the spectral synthesis code STARLIGHT. The comparison
2009
We use the newest generation of the Starburst99/Mappings code to generate an extensive suite of models to facilitate detailed studies of star-forming galaxies and their ISM properties, particularly at low metallicities. The new models used include a rigorous treatment of metal opacities in the population synthesis modeling and more detailed dust physics in the photoionization code. These models span a wide range of physical parameters including metallicity, ionization parameter, and the adoption of both a instantaneous burst and continuous star formation history. We examine the agreement between our models and local (z < 0.1) star-forming galaxy populations from several large datasets, including the Sloan Digital Sky Survey, the Nearby Field Galaxy Survey, and samples of blue compact galaxies and metal-poor galaxies. We find that models adopting a continuous star formation history reproduce the metallicity-sensitive line ratios observed in the local population of star-forming galaxies, including the low-metallicity sample. However, we find that the current codes generate an insufficiently hard ionizing radiation field, leading to deficiencies in the [SII] fluxes produced by the models. We consider the advantages and short-comings of this suite of models, and discuss future work and improvements that can be applied to the modeling of star-forming galaxies.
Astrophysics and Space Science Proceedings, 2010
We have computed a series of realistic and self-consistent models that reproduce the properties of HII galaxies. The emitted spectrum of HII galaxies is reproduced by means of the photoionization code CLOUDY, using as ionizing spectrum the spectral energy distribution of the modelled HII galaxy, calculated using new and updated stellar population synthesis model (PopStar) This, in turn, is calculated according to a star formation history and a metallicity evolution given by a chemical evolution code. Our technique reproduces observed abundances, diagnostic diagrams, colours and equivalent width-colour relations for local HII galaxies.