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Register a new userPEGASE.2, a metallicity-consistent spectral evolution model of galaxies: the documentation and the code
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We provide here the documentation of the new version of the spectral evolution model PEGASE. PEGASE computes synthetic spectra of galaxies in the UV to near-IR range from 0 to 20 Gyr, for a given stellar IMF and evolutionary scenario (star formation law, infall, galactic winds). The radiation emitted by stars from the main sequence to the pre-supernova or white dwarf stage is calculated, as well as the extinction by dust. A simple modeling of the nebular emission (continuum and lines) is also proposed. PEGASE may be used to model starbursts as well as old galaxies. The main improvements of PEGASE.2 relative to PEGASE.1 (Fioc & Rocca-Volmerange 1997) are the following: (1)The stellar evolutionary tracks of the Padova group for metallicities between 0.0001 and 0.1 have been included; (2)The evolution of the metallicity of the interstellar medium (ISM) due to SNII, SNIa and AGB stars is followed. Stars are formed with the same metallicity as the ISM (instead of a solar metallicity in PEGASE.1), providing thus a metallicity-consistent model; (3)Lejeune et al.s library of stellar spectra is used; (4)The extinction by dust is computed for geometries corresponding to disk and spheroidal galaxies using a radiative transfer code taking into account the scattering. The main outputs (as a function of time) are spectra, colors and magnitudes in various photometric systems, luminosities, type II and Ia supernovae rates, line intensities and equivalent widths, amount and metallicity of stars and gas, mass locked in stellar remnants, optical depth and total dust emission. The corresponding article (Fioc & Rocca-Volmerange 2000) will be submitted soon. A detailed modeling of the spectrum of the dust emission and of HII regions (Moy, Rocca-Volmerange & Fioc 2000) will be included in futu
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Pegase.3 is a Fortran 95 code modeling the spectral evolution of galaxies from the far-ultraviolet to submillimeter wavelengths. It also follows the chemical evolution of their stars, gas and dust. For a given scenario (a set of parameters defining the history of mass assembly, the star formation law, the initial mass function...), Pegase.3 consistently computes the following: * the star formation, infall, outflow and supernova rates from 0 to 20 Gyr; * the stellar metallicity, the abundances of main elements in the gas and the composition of dust; * the unattenuated stellar spectral energy distribution (SED); * the nebular SED, using nebular continua and emission lines precomputed with code Cloudy (Ferland et al. 2017); * the attenuation in star-forming clouds and the diffuse interstellar medium, by absorption and scattering on dust grains, of the stellar and nebular SEDs. For this, the code uses grids of the transmittance for spiral and spheroidal galaxies. We precomputed these grids through Monte Carlo simulations of radiative transfer based on the method of virtual interactions; * the re-emission by grains of the light they absorbed, taking into account stochastic heating. The main innovation compared to Pegase.2 is the modeling of dust emission and its evolution. The computation of nebular emission has also been entirely upgraded to take into account metallicity effects and infrared lines. Other major differences are that complex scenarios of evolution (derived for instance from cosmological simulations), with several episodes of star formation, infall or outflow, may now be implemented, and that the detailed evolution of the most important elements -- not only the overall metallicity -- is followed.
We present PEGASE-HR, a new stellar population synthesis program generating high resolution spectra (R=10 000) over the optical range lambda=400--680 nm. It links the spectro-photometric model of galaxy evolution PEGASE.2 (Fioc & Rocca-Volmerange 1997) to an updated version of the ELODIE library of stellar spectra observed with the 193 cm telescope at the Observatoire de Haute-Provence (Prugniel & Soubiran 2001a). The ELODIE star set gives a fairly complete coverage of the Hertzprung-Russell (HR) diagram and makes it possible to synthesize populations in the range [Fe/H]=-2 to +0.4. This code is an exceptional tool for exploring signatures of metallicity, age, and kinematics. We focus on a detailed study of the sensitivity to age and metallicity of the high-resolution stellar absorption lines and of the classical metallic indices proposed until now to solve the age-metallicity degeneracy. Validity tests on several stellar lines are performed by comparing our predictions for Lick indices to the models of other groups. The comparison with the lower resolution library BaSeL (Lejeune et al. 1997) confirms the quality of the ELODIE library when used for simple stellar populations (SSPs) from 10 Myr to 20 Gyr. Predictions for the evolved populations of globular clusters and elliptical galaxies are given and compared to observational data. Two new high-resolution indices are proposed around the Hgamma line. They should prove useful in the analysis of spectra from the new generation of telescopes and spectrographs.
PEGASE is a new spectrophotometric evolution model for starbursts and evolved galaxies of the Hubble sequence. Its main originality is the extension to the near-infrared (NIR) of the atlas of synthetic spectra of Rocca-Volmerange & Guiderdoni (1988) with a revised stellar library including cold star parameters and stellar tracks extended to the TP-AGB and the post-AGB phase. The NIR is coherently linked to the visible and the ultraviolet, so that the model is continuous on an exceptionally large wavelength range from 220 A up to 5 microns. Moreover, a precise algorithm allows to follow very rapid evolutionary phases such as red supergiants or AGB crucial in the NIR. The nebular component is also computed in the NIR. The extinction correction is gas-dependent for spirals and ellipticals. A set of reference synthetic spectra at z=0, to which apply cosmological k- and evolution e- corrections for high-redshift galaxies, is built from fits of observational templates. Because of the lack of visible to NIR spectral templates for each Hubble type, we adopt statistical samples of colors, not fitted by previous models. A first application of this continuous model is to solve the problem of the slope of the bright galaxy counts from B=15 to 19 and of the normalization parameter of the Schechter luminosity function. Code sources, input and output data are available by anonymous ftp or at the WEB address of the authors.
We give a comprehensive description of the functions and variables defined in the authors GAP code file OrbOrd.txt, which serve mainly to compute (bounds on) the number of $operatorname{Aut}(S)$-orbits on $S$, or the set or number of element orders in $S$ for nonabelian finite simple groups of Lie type $S$.
Nuclear inflows of metal-poor interstellar gas triggered by galaxy interactions can account for the systematically lower central oxygen abundances observed in local interacting galaxies. Here, we investigate the metallicity evolution of a large set of simulations of colliding galaxies. Our models include cooling, star formation, feedback, and a new stochastic method for tracking the mass recycled back to the interstellar medium from stellar winds and supernovae. We study the influence of merger-induced inflows, enrichment, gas consumption, and galactic winds in determining the nuclear metallicity. The central metallicity is primarily a competition between the inflow of low-metallicity gas and enrichment from star formation. An average depression in the nuclear metallicity of ~0.07 is found for gas-poor disk-disk interactions. Gas-rich disk-disk interactions, on the other hand, typically have an enhancement in the central metallicity that is positively correlated with the gas content. The simulations fare reasonably well when compared to the observed mass-metallicity and separation-metallicity relationships, but further study is warranted.
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