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Register a new userEvolutionary synthesis of galaxies at high spectral resolution with the code PEGASE-HR
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Damien Le Borgne
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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.
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We present the HR-pyPopStar model, which provides a complete set (in ages) of high resolution (HR) Spectral Energy Distributions of Single Stellar Populations. The model uses the most recent high wavelength-resolution theoretical atmosphere libraries for main sequence, post-AGB/planetary nebulae and Wolf-Rayet stars. The Spectral Energy Distributions are given for more than a hundred ages ranging from 0.1 Myr to 13.8 Gyr, at four different values of the metallicity (Z = 0.004, 0.008, 0.019 and 0.05), considering four different IMFs. The wavelength range goes from 91 to 24 000 {AA} in linear steps {delta}{lambda} = 0.1 {AA}, giving a theoretical resolving power R_{th,5000} ~ 50 000 at 5000 {AA}. This is the main novelty of these spectra, unique for their age and wavelength ranges. The models include the ionising stellar populations that are relevant both at young (massive hot stars) as well as old (planetary nebulae) ages. We have tested the results with some examples of HR spectra recently observed with MEGARA at GTC. We highlight the importance of wavelength-resolution in reproducing and interpreting the observational data from the last and forthcoming generations of astronomical instruments operating at 8-10m class telescopes, with higher spectral resolution than their predecessors.
Photometric redshifts are estimated on the basis of template scenarios with the help of the code ZPEG, an extension of the galaxy evolution model PEGASE.2 and available on the PEGASE web site. The spectral energy distribution (SED) templates are computed for nine spectral types including starburst, irregular, spiral and elliptical. Dust, extinction and metal effects are coherently taken into account, depending on evolution scenarios. The sensitivity of results to adding near-infrared colors and IGM absorption is analyzed. A comparison with results of other models without evolution measures the evolution factor which systematically increases the estimated photometric redshift values by $Delta z$ > 0.2 for z > 1.5. Moreover we systematically check that the evolution scenarios match observational standard templates of nearby galaxies, implying an age constraint of the stellar population at z=0 for each type. The respect of this constraint makes it possible to significantly improve the accuracy of photometric redshifts by decreasing the well-known degeneracy problem. The method is applied to the HDF-N sample. From fits on SED templates by a $chi^2$-minimization procedure, not only is the photometric redshift derived but also the corresponding spectral type and the formation redshift $z_for$ when stars first formed. Early epochs of galaxy formation z > 5 are found from this new method and results are compared to faint galaxy count interpretations. The new tool is available at: http://www.iap.fr/pegase
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
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.
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.
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