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A code computing consistently the evolution of stars, gas and dust, as well as the energy they radiate, is required to derive reliably the history of galaxies by fitting synthetic SEDs to multiwavelength observations. The new code P\'egase.3 described in this paper extends to the far-IR/submm the UV-to-near-IR modeling provided by previous versions of P\'egase. It first computes the properties of single stellar populations at various metallicities. It then follows the evolution of the stellar light of a galaxy and the abundances of the main metals in the ISM, assuming some scenario of mass assembly and star formation. It simultaneously calculates the masses of the various grain families, the optical depth of the galaxy and the attenuation of the SED through the diffuse ISM in spiral and spheroidal galaxies, using grids of radiative transfer precomputed with Monte Carlo simulations taking scattering into account. The code determines the mean radiation field and the temperature probability distribution of stochastically heated individual grains. It then sums up their spectra to yield the overall emission by dust in the diffuse ISM. The nebular emission of the galaxy is also computed, and a simple modeling of the effects of dust on the SED of star-forming regions is implemented. The main outputs are UV-to-submm SEDs of galaxies from their birth up to 20 Gyr, colors, masses of galactic components, ISM abundances of metallic elements and dust species, supernova rates. The temperatures and spectra of individual grains are also available. The paper discusses several of these outputs for a scenario representative of Milky Way-like spirals. P\'egase.3 is fully documented and its Fortran 95 source files are public. The code should be especially useful for cosmological simulations and to interpret future mid- and far-IR data, whether obtained by JWST, LSST, Euclid or e-ELT., Comment: 15 pages. In press in A&A. Source files of the code available at http://www.iap.fr/users/fioc/Pegase/Pegase.3/ (and http://www.iap.fr/pegase/); documentation at arXiv:1902.02198

Using the new evolutionary code PEGASE. 3, we undertook an evolutionary spectral synthesis of the optical-IR-submm spectral energy distribution of two distant (z = 3.8) radio galaxies, 4C 41.17 and TN J2007-1316. These two radio galaxies were selected from the HeRGE (Herschel Radio Galaxies Evolution) Project in particular for their faint active galactic nucleus contribution and because they show evidence of a large stellar contribution to their bolometric luminosity. PEGASE. 3 coherently models the reprocessing of the stellar luminosity to dust emission, allowing us to build UV to IR-submm spectral energy distribution libraries that can then be used to fit spectral energy distributions in the observer's frame. Our principal conclusion is that a single stellar population is insufficient to fit the spectral energy distribution of either radio galaxy. Our best fits are a sum of two evolving stellar populations - a recent starburst plus an old population - plus the thermal emission from an active galactic nucleus (which provides a good fit to the mid-IR emission). The two stellar components are: (i) a massive (similar or equal to 10(11) M-circle dot) starburst similar or equal to 30 Myr after formation, which is required simultaneously to fit the far-IR Herschel to submm data and the optical data; and (ii) an older massive (similar or equal to 10(11-12) M-circle dot) early-type galaxy population, similar or equal to 1.0 Gyr old, which is required principally to fit the mid-IR Spitzer/IRAC data. A young population alone is insufficient because an evolved giant star population produces a 1-mu m rest-frame peak that is observed in the IRAC photometry. This discovery confirms that many of the stellar populations in high-redshift radio galaxies were formed by massive starbursts in the early Universe. Gas-rich mergers and/or jet-cloud interactions are favoured for triggering the intense star formation necessary to explain the properties of the spectral energy distributions. The discovery of similar characteristics in two distant radio galaxies suggests that multiple stellar populations, one old and one young, may be a generic feature of the luminous infrared radio galaxy population.

We present a study of the complete ultraviolet to submillimetre spectral energy distributions (SEDs) of twelve 3CR radio galaxy hosts in the redshift range $1.0 < z < 2.5$, which were all detected in the far-infrared by the Herschel Space Observatory. The study employs the new spectro-chemical evolutionary code P��GASE.3, in combination with recently published clumpy AGN torus models. We uncover the properties of the massive host galaxy stellar populations, the AGN torus luminosities, and the properties of the recent starbursts, which had earlier been inferred in these objects from their infrared SEDs. The P��GASE.3 fitting yields very luminous (up to 10$^{13}$L$_{\odot}$) young stellar populations with ages of several hundred million years in hosts with masses exceeding 10$^{11}$M$_{\odot}$. Dust masses are seen to increase with redshift, and a surprising correlation -- or better upper envelope behaviour -- is found between the AGN torus luminosity and the starburst luminosity, as revealed by their associated dust components. The latter consistently exceeds the former by a constant factor, over a range of one order of magnitude in both quantities., 15 pages, 9 figures, accepted for publication in MNRAS

Multi-wavelength galaxy number counts provide clues on the nature of galaxy evolution. The interpretation per galaxy type with the new code PEGASE.3 of the 12mu (ISO) and 24mu (Spitzer) faint galaxy counts provide new constraints on the dust and stellar emission. It also reveals the nature of ULIRGs (L/Lsun > 10^12) and informs on the cosmic star formation history and the time-scales for mass build-up. We firstly present the faint galaxy counts at 12um derived from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) in a companion paper (Seymour et al. 2007) which go down to 0.24 mJy after corrections for incompleteness. We check that they are consistent with ISO number counts at 15um. Secondly we show that the ``normal'' scenarios which fit the deep UV-optical-near-IR counts with PEGASE.2 (Fioc et al. 1999), are unsuccessful in modelling the strong excess simultaneously observed in the cumulative and differential counts at 12um, 15um and 24um. Based on observed 12mu and 25mu IRAS luminosity functions and optical/mid-IR colors, we finally succeed in modelling cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty elliptical galaxies, interpreted as ULIRGs. This ULIRG population has similarities with high-z radio-galaxy hosts. No number density evolution is included. The Herschel observatory will hopefully confirm these results.

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.

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 IUE, 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 K 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 Angstrom, 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.

We describe a probabilistic method of cross-identifying astrophysical sources in two catalogs from their positions and positional uncertainties. The probability that an object is associated with a source from the other catalog, or that it has no counterpart, is derived under two exclusive assumptions: first, the classical case of several-to-one associations, and then the more realistic but more difficult problem of one-to-one associations. In either case, the likelihood of observing the objects in the two catalogs at their effective positions is computed and a maximum likelihood estimator of the fraction of sources with a counterpart -- a quantity needed to compute the probabilities of association -- is built. When the positional uncertainty in one or both catalogs is unknown, this method may be used to estimate its typical value and even to study its dependence on the size of objects. It may also be applied when the true centers of a source and of its counterpart at another wavelength do not coincide. To compute the likelihood and association probabilities under the different assumptions, we developed a Fortran 95 code called "Aspects" ([asp{\epsilon}], "ASsociation PositionnellE/ProbabilistE de CaTalogues de Sources" in French); its source files are made freely available. To test Aspects, all-sky mock catalogs containing up to 10^5 objects were created, forcing either several-to-one or one-to-one associations. The analysis of these simulations confirms that, in both cases, the assumption with the highest likelihood is the right one and that estimators of unknown parameters built for the appropriate association model are reliable., Comment: One typo corrected and links added. One-column format (A&A official version is in two-column format). 20 pages, 5 figures. Version 2 of code Aspects available at http://www2.iap.fr/users/fioc/Aspects/ . Detailed documentation and complements at arXiv:1404.4224. Numerical Recipes routines not needed anymore

We present inversion techniques which aim at recovering the composite nature and the kinematics of a stellar population from its high resolution absorption line spectrum. The originality of the combined inversion is its potential to recover both the stellar content and the kinematics simultaneously. These techniques use new synthetic high resolution spectra produced by PEGASE and minimization algorithms. We apply them to mock data representing the bulge and disk population of the inner region of spiral galaxies.

The nature of the blue galaxy excess, discovered in faint counts is tentatively analyzed in the frame of a multispectral approach including far-UV counts. The far-UV (2000A) counts observed from the balloon experiment FOCA20000 bring conclusive constraints on star-forming populations. The evolution is followed with the help of our new model of galaxy evolution PEGASE. From Fioc and Rocca-Volmerange, 1997b (FRV97b), a population of dwarfs, periodically bursting, is needed to interpret the 2000A data, in agreement with the optical and near-IR faint counts. However, this near UV-bright population is unable to solve the debated question of the high-z blue galaxy excess in a flat universe.

The development of NIR astronomy put new constraints on models of spectrophotometric evolution and cosmology. Since evolutionary effects should be lower in the NIR than in the visible, we may expect to see evidence of cosmological ones. To this purpose, we have improved on the NIR the model of galaxy evolution developed by Guiderdoni & Rocca-Volmerange (1987) in the UV and the visible, thus allowing a multispectral analysis of the evolution of galaxies, as valid for starbursts as for old galaxies, and of galaxy counts.

A new model of spectral evolution of galaxies (Fioc & Rocca-Volmerange 1996) named PEGASE (in french, Projet d’Etude des GAlaxies par Synthese Evolutive) has been developped. It uses the principle of isochrone synthesis and allows to compute synthetic spectra of galaxies on timescales as short as 1 Myr for starbursts or as long as 20 Gyrs for Hubble sequence galaxies. Its wavelength range extends from the far UV (200 A) to the NIR (3 μm). A new library of stellar spectra, mainly observational, has been built. Isochrones are computed for 2 sets of tracks with solar metallicity (Padova and Genova) up to the EAGB completed by the TPAGB phase (Groenewegen et al., 1993) and the PAGB phase from Schonberner (1983) and Blocker (1995). Nebular emission (continuum and lines), extinction in disks and in spheroids computed from the metallicity of the ISM and ejecta from stars are also considered.

We have improved in the NIR the model of galaxy evolution developed by Guiderdoni & Rocca-Volmerange (A&A 186, 1) in the UV and the visible, allowing thus a multispectral analysis of the evolution of galaxies and of faint galaxy counts. Since evolutionnary effects should be low in the near-infrared, cosmological ones might be put in evidence.

High-redshift radio galaxies present signs of both star formation and AGN activity, making them ideal candidates to investigate the connection and coevolution of AGN and star formation in the progenitors of present-day massive galaxies. We make use of a sample of 11 powerful radio galaxies spanning 1 < z < 4 which have complete coverage of their spectral energy distribution (SED) from UV to FIR wavelengths. Using Herschel data, we disentangle the relative contribution of the AGN and star formation by combining the galaxy evolution code PEGASE.3 with an AGN torus model. We find that three components are necessary to reproduce the observed SEDs: an evolved and massive stellar component, a submm bright young starburst, and an AGN torus. We find that powerful radio galaxies form at very high-redshift, but experience episodic and important growth at 1 < z < 4 as the mass of the associated starburst varies from 5 to 50% of the total mass of the system. The properties of star formation differ from source to source, indicating no general trend of the star formation properties in the most infrared luminous high-redshift radio galaxies and no correlation with the AGN bolometric luminosity. Moreover, we find that AGN scattered light have a very limited impact on broad-band SED fitting on our sample. Finally, our analysis also suggests a wide range in origins for the observed star formation, which we partially constrain for some sources.