Search

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.

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

Classification and parametrization of unresolved galaxies to be detected by Gaia is the goal of our contribution to DPAC/CU8. Gaia will observe more than several times 10 6 unresolved galaxies seen almost as point sources. For the classification and parametrization of these sources we have undertaken the following tasks: a) providing libraries of synthetic galaxy spectra (produced under the PEGASE.2 code of galaxy evolution) and a semi-empirical library using observed galaxy spectra from SDSS data archive. b) Developping an appropriate algorithm called Unresolved Galaxy Classifier (UGC). The algorithm is being developed implementing the Support Vector Machines (SVM), a supervised training technique. This algorithm utilizes Gaia simulated BP/RP galaxy spectra of our synthetic galaxy library.

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

We present a detailed reduction of a mid-infrared 12 µ m( LW10 filter) ISOCAM open time observation performed on the ESOSculptor Survey field (Arnouts et al. 1997, AA these methods yield consistent results. We also apply an empirical flux density calibration using stars in the field. For each star, the 12 µm flux density is derived by fitting optical colours from a multi-band χ 2 to stellar templates (BaSel-2.0) and using empirical optical-IR colour-colour relations. This article is a companion analysis to our 2007 paper (Rocca-Volmerange et al. 2007, A&A, 475, 801) where the 12 µm faint galaxy counts are presented and analysed per galaxy type with the evolutionary code PEGASE.3.

We hereafter aim to present mass estimates and main parameters of distant powerful radio sources, respectively for evolved stars, ionized gas, and dust. Observations and models are consistent with a scenario where large masses are accumulated whithin extremely short time scales 2: a strong constraint for large-scale structure models. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The spectra of the powerful 3CR radio galaxies present a typical distribution in the far-infrared. From the observed radio to X-ray spectral energy distribution (SED) templates, we propose to subtract the typical energy distributions of, respectively, the elliptical galaxy host and the synchrotron radiation. The resulting SED reveals that the main dust emission is well fitted by the sum of two blackbody components at the respective temperatures 340K+-50K and 40K+-16K. When the AGN is active, the energy rate released by hot dust is much more dissipative than cold dust and stellar emission, even when the elliptical galaxy emission is maximum at age of ~ 90 Myr. Hot dust appears as a huge cooling source which implies an extremely short time-scale t(cool). In balance, with the short gravitational time-scale t(grav) of massive galaxies, the dissipative self-gravitational models (Rees & Ostriker, 1977) are favoured for radio sources. They justify the existence of massive radio galaxies at z=4 (Rocca-Volmerange et al., 2004). The synchrotron emission is emitting up to the X-ray wavelength range, so that strong "EXOs" sources could be assimilated to 3CR radio sources. This analysis applied to ISO and SPITZER data on a larger sample will statistically confirm these results.

The narrow K-z relation of powerful radio galaxies in the Hubble K diagram is often attributed to the stellar populations of massive elliptical galaxies. Extended over a large range of redshifts (0 4 implies that massive clouds were already formed at early epochs. We also find that the M_(bar,max) limit is similar to the critical mass M_crit of a self-gravitating cloud regulated by cooling (Rees & Ostriker, 1977; Silk, 1977). Moreover, the critical size r_crit = 75 Kpc is remarkably close to the typical diameter of Ly_alpha haloes surrounding distant radio galaxies. This confirms the validity of the method of baryonic mass determination based on the K-band luminosity. A puzzling question that remains to be answered is the short time-scale of mass-accumulation required to form such massive galaxies at z=4. We discuss the dispersion of the K-z relation and the link between the active nucleus and a large stellar mass.

Distant radio galaxies, observed up to the highest redshifts ( z ≃6), are characterized by intense emission lines. Measuring emission line ratios bring clues on ionizing processes. When massive stars are ionizing sources, they give the information on the primeval star formation activity. However analyses are difficult for several reasons. Surface brightness and spatial resolution are rapidly decreasing with redshift. Moreover various emission processes (photoionization by the central AGN, shocks due to jet-cloud interactions or the coupling of ionized gas with radio emitting plasmas) may partly obliterate the photoionization by massive stars. The contribution of star formation at high redshift can only be derived after substraction of other contributing processes. The solution is to locally disentangle the various contributions to emission lines with the help of integral field spectroscopy. We firstly select, with the help of models, the emission line ratio diagnostics able to separate ionizing processes by reproducing at best the observations. Then we observe distant radio galaxies by using integral field units (IFUs) to build maps of emission line ratios. Models are applied by zones, allowing a comparative interpretation between zones. Results give the main sources of ionization in each zone. We present results of 3D spectroscopy on the FR-II radio galaxy 3C171 ( z =0.238) observed with OASIS/CFHT. The H α emission line map represents a typical ionized cocoon, as predicted by theory. The [OIII] λ 5007/H β map shows some striking features. Preliminary results from the zone by zone analysis of the [OIII] λ 5007/H β map with our recent modelling ( Moy and Rocca-Volmerange, 2002 ) is also highlighted.

We have analyzed the ultraviolet and optical emission line ratios of a large sample of extragalactic radio sources (QSOs and radio galaxies), with the help of models combining AGN photoionization and shocks. The results strongly suggest that the two ionizing mechanisms frequently coexist. The model sequences obtained by varying the balance between shocks and AGN photoionization account for most emission line data in the 12 line ratio diagrams we have considered. In the frequently used diagrams involving [OIII]5007/Hbeta, [OI]6300/Halpha, [NII]6584/Halpha and [SII]6716,6731, the effect of varying the shock-photoionization balance mimics a variation of the ionization parameter (U) in traditional photoionization sequences. In most of the remaining diagrams, such as [OI]6300/[OIII]5007 vs.[OIII]4363/[OIII]5007, [OIII]5007/H vs. [OIII]4363/[OIII]5007 and CIII]1909/[CII]2326 vs. CIV1549/[CII]2326, the data can only be accounted for if both photoionization and shocks contribute to the line fluxes. The coexistence of shocks and AGN photoionization also provides an explanation for the most extreme objects in the NV1240/HeII1640 vs. NV1240/CIV1549 diagram without requiring largely super-solar metallicities. In addition, we show that there is a relationship between the [OII]3727/[OIII]5007 ratio and the radio size in radio galaxies. This strongly supports the hypothesis that the most compact (< 2kpc) and the largest (> 150 kpc) sources are dominated by photoionization, while intermediate-sized radio galaxies are dominated by shocks. We briefly discuss the possible origin of the relation between the shock-ionization balance and the radio size., 11 pages, 6 figures, accepted for publication in Astronomy & Astrophysics

Star formation rates in distant radio galaxies are crucial for understanding the evolution of galaxies. Most processes at works in these targets observed at the most remote epochs are directly or not related to primeval sources of star formation: interplays of starbursts and AGNs, interactions of radio jets with environmental clouds. cooling flows, metal enrichment and dust distributions. Signatures of typical star formation (emission line ratios, equivalent widths, stellar continua) are observed in distant galaxies. However in most cases, they are superimposed to signatures of other processes (shocks, AGN light scattering). in particular at high z with the decrease of angular resolution and surface brightness. A larger variety of environmental components (lobes, jets, clouds and nucleus) simultaneously contribute to the global emission. So that to separate the varions emission processes becomes rapidly essential with higher distances. The 3D spectroscopy is unique to disentangle the various physical processes triggering star formation at high redshifts. Shocks and regions photoionized by the central AGN are identified from their typical features and may be localized in the various zones of the radio galaxy extended to its environment. We present results of a long term observationnal prograin with the successive Integral Field Units (IFU) TIGER and OASIS at CFHT. The present sample consists of three galaxies of increasing z: 3C 171 {z = 0.238), 3C 435A (z = 0.470) and 4C 41.17 (z = 3.8). Line ratios, continua and velocity fields are locallv measured. Interpretations of emission line ratios, velocity fields, equivalent widths, are possible with a coupled code based on CLOUDY and MAPPINGSIII results, as proposed by Moy et al. (2000, 2001). Stellar and nebular continua are interpretcd with the help of our evolutionary synthesis model PEGASE2. Ail models take into account metallicity effects.

We analyze coherently the stellar and nebular energy distributions of starbursts and Hii galaxies, using our evolutionary synthesis model, PEGASE (Fioc & Rocca-Volmerange 1997, 2000), coupled to the photoionization code CLOUDY (Ferland [CITE]). The originality of this study is to relate the evolution and the metallicity of the starburst to the past star formation history of the host galaxy. Extinction and geometrical effects on emission lines and continua are computed in coherency with metallicity. We compare our model predictions to an observed sample of ≈ 750 Hii regions and starbursts. When fitting [Oiii]$_{\lambda 4363}$/[Oiii]$_{\lambda 5007}$, [Oi]$_{\lambda 6300}$/H α , [Sii]$_{\lambda\lambda 6716, 6731}$/H α , [Nii]$_{\lambda 6584}$/H α and [Oiii]$_{\lambda 5007}$/H β , the most striking feature is the decreasing spread in U with increasing metallicity Z . High- U objects systematically have a low metallicity while low levels of excitation happen at any Z . The best fits of emission line ratios are obtained with a combination of a high- and a low-ionization components. No additional source of ionizing photons - shocks or hidden AGN -is needed. The high level of excitation observed in metal-poor Hii galaxies requires a very young population ($\le 3$ Myr), while starburst nuclear galaxies (SBNGs) are consistent with a wider range of age ($\le 5$ Myr). Colors ($B-V$, $V-R$) and equivalent widths are fitted in coherency with emission line ratios. An underlying population is needed, even for small-aperture observations. This underlying population not only reddens the continuum and dilutes the equivalent width of the emission lines, but also participates in the ionization process. Its main effect on line ratios is to maintain a high level of excitation when the burst stops. Models combining underlying populations typical of Hubble sequence galaxies and instantaneous starbursts with ages between 0 and 8 Myr agree satisfactorily with all the data.

We present the analysis of emission line spectra of AGNs and starbursts with the help of models coupling shocks and photoionization by AGNs and by massive stars. We show how shocks and photoionization by the central source have to coexist in AGNs in order to reproduce the observed emission line ratios. We also show how stellar photoionization models can be reconciled with the values of the [OI]/Hα and [SII]/Hα ratios observed in starbursts, without requiring an additional ionizing source such as shocks.

The Gaia satellite will survey the entire celestial sphere down to 20th magnitude, obtaining astrometry, photometry, and low resolution spectrophotometry on one billion astronomical sources, plus radial velocities for over one hundred million stars. Its main objective is to take a census of the stellar content of our Galaxy, with the goal of revealing its formation and evolution. Gaia's unique feature is the measurement of parallaxes and proper motions with hitherto unparalleled accuracy for many objects. As a survey, the physical properties of most of these objects are unknown. Here we describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellite's data. This system covers single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space. Multiple methods are used for many types of stars, producing multiple results for the end user according to different models and assumptions. Prior to its application to real Gaia data the accuracy of these methods cannot be assessed definitively. But as an example of the current performance, we can attain internal accuracies (RMS residuals) on F,G,K,M dwarfs and giants at G=15 (V=15-17) for a wide range of metallicites and interstellar extinctions of around 100K in effective temperature (Teff), 0.1mag in extinction (A0), 0.2dex in metallicity ([Fe/H]), and 0.25dex in surface gravity (logg). The accuracy is a strong function of the parameters themselves, varying by a factor of more than two up or down over this parameter range. After its launch in November 2013, Gaia will nominally observe for five years, during which the system we describe will continue to evolve in light of experience with the real data., Comment: 21 pages, accepted to A&A

The distant radiogalaxies recently discovered at the most remote distances (z≥3.5) are among the best cosmological targets. However so various features caracterize these galaxies (red stellar energy distribution, huge emission lines, high density of galaxy companions, alignment of ultraviolet and radio axes, large degree of polarisation) that their structures are not simple to understand. Stellar populations will only become the best indicators of evolution of galaxies if these structures are clearly understood from a two-dimension spectroscopy on each image point. The integral field spectrograph TIGER is a unique instrument at the CFHT to give details on the nature and velocities of the various components of distant radiogalaxies.We present the observations with TIGER of an intermediate-redshift galaxy 3C435A (z=0.471) (Rocca-Volmerange et al, 1994). The two nebular lines [OII], [OIII] and the largely extended stellar continua are observable, allowing to date galaxy with the help of our evolution model. The present and past star formation activities and the origin of alignment will be thus analysed in terms of galaxy evolution.

The DENIS project is the first attempt to carry out a complete digitized survey of the southern sky in the range 1–2.5 μm. The main objectives of the programme and the main specifications of the camera and of the data processing stream are briefly outlined

With objectives to model star formation in radio galaxies, we present results of a starburst model, built by coupling the two codes PEGASE and CLOUDY. Continuum and emission line data are used to derive the properties of a sample of local starbursts. Data are well reproduced with a new relation between the ionization parameter and the metallicity. Colors and Hα equivalent widths indicate that: (i) an underlying stellar population is needed, and (ii) burst ages span the range [0, 6] Myr.

Aims:This paper is the third in a series implementing a classification system for Gaia observations of unresolved galaxies. The system makes use of template galaxy spectra in order to determine spectral classes and estimate intrinsic astrophysical parameters. In previous work we used synthetic galaxy spectra produced by PEGASE.2 code to simulate Gaia observations and to test the performance of Support Vector Machine (SVM) classifiers and parametrizers. Here we produce a semi-empirical library of galaxy spectra by fitting SDSS spectra with the previously produced synthetic libraries. We present (1) the semi-empirical library of galaxy spectra, (2) a comparison between the observed and synthetic spectra, and (3) first results of claassification and parametrization experiments with simulated Gaia spectrophotometry of this library. Methods: We use chi2-fitting to fit SDSS galaxy spectra with the synthetic library in order to construct a semi-empirical library of galaxy spectra in which (1) the real spectra are extended by the synthetic ones in order to cover the full wavelength range of Gaia, and (2) astrophysical parameters are assigned to the SDSS spectra by the best fitting synthetic spectrum. The SVM models were trained with and applied to semi-empirical spectra. Tests were performed for the classification of spectral types and the estimation of the most significant galaxy parameters (in particular redshift, mass to light ratio and star formation history). Results: We produce a semi-empirical library of 33670 galaxy spectra covering the wavelength range 250 to 1050 nm at a sampling of 1 nm or less. Using the results of the fitting of the SDSS spectra with our synthetic library, we investigate the range of the input model parameters that produces spectra which are in good agreement with observations. (abridged), (14 pages, accepted for publication in A&A)

The galaxy populations discovered in the deepest UV-optical and infrared surveys appear so different that the basic physics of galaxy evolution is still debated. In Rocca-Volmerange et al., 2007 (hereafter RVLS2007), we proposed an interpretation of the deepest mid-IR faint galaxy counts in accordance with the already-published UV-optical NIR count analysis (Fioc & Rocca-Volmerange, 1999). The main constraint is to reproduce the galaxy number excess observed at 12 μm in the ISO-ESO-Sculptor Survey (Seymour et al., 2007) as at 15 μm and 24 μm in other ISO and SPITZER surveys. The originality of the analysis is to follow continuously the evolution of stellar and dust emissions from UV to infrared as a function of galaxy type. We use the new version of our evolutionary code PEGASE.3, extended to dust emission. Evolving UV to IR SEDs allow to compute robust k- and e- (evolution) corrections for all z and types to predict high z luminosities. We find that the fractions by galaxy types from the optical counts are all detected in the mid-IR counts, with the exception of a minor fraction of ellipticals (< 10% of all galaxies) which appear ultra-bright and dusty. The differential brigthness excess (-2.5 mag at 12 μm, -5 at 24 μm) confirms the presence of dust, while the bump is explained by strong redshifted stellar emission of ellipticals (k+e corrections). The model is valid at 12 μm, 15 μm and 24 μm. It does not need any redshift-dependent starbursts. No number density evolution is included in our models. These ULIRGs are massive evolved galaxies formed at early epochs and likely hosts of AGNs. They will be essential targets for the future telescopes SPICA, HERSCHEL and ALMA.

The ESA satellite mission Gaia will acquire spectrophotometric observations of several million unresolved galaxies during its five years of operation. In order to implement a classification scheme for these observations we need to build a new library of galaxy spectra which covers the necessary parameter space. Using the evolutionary code PEGASE.2 we have produced a library of 28885 synthetic galaxy spectra at zero redshift covering four general spectral types of galaxies over the wavelength range from 250 to 1050 nm, at a sampling of 1 nm or less. The library was also reproduced for four random values of redshift in the range of 0–0.2 and it is computed on a random grid of four key astrophysical parameters (3 for SFR and 1 for timescale of the infall of gas). The synthetic library was compared with various photometric and spectroscopic observations (e.g. from SDSS) and found in good agreement with them.

This paper is the second in a series, implementing a classification system for Gaia observations of unresolved galaxies. Our goals are to determine spectral classes and estimate intrinsic astrophysical parameters via synthetic templates. Here we describe (1) a new extended library of synthetic galaxy spectra, (2) its comparison with various observations, and (3) first results of classification and parametrization experiments using simulated Gaia spectrophotometry of this library. Using the PEGASE.2 code, based on galaxy evolution models that take account of metallicity evolution, extinction correction, and emission lines (with stellar spectra based on the BaSeL library), we improved our first library and extended it to cover the domain of most of the SDSS catalogue. We produce an extended library of 28885 synthetic galaxy spectra at zero redshift covering four general Hubble types of galaxies, over the wavelength range between 250 and 1050 nm at a sampling of 1 nm or less. The library is also produced for 4 random values of redshift in the range of 0-0.2. It is computed on a random grid of four key astrophysical parameters (infall timescale and 3 parameters defining the SFR) and, depending on the galaxy type, on two values of the age of the galaxy. The synthetic library was compared and found to be in good agreement with various observations. The first results from the SVM classifiers and parametrizers are promising, indicating that Hubble types can be reliably predicted and several parameters estimated with low bias and variance., Comment: 14 pages, accepted for publication in A&A

The ESA satellite mission Gaia will acquire spectrophotometric observations of several million unresolved galaxies during its five years of operation. Our objective is to design and implement a classification system for these data. For this purpose we need to build a new library of galaxy spectra which covers the necessary parameter space. Using the evolutionary code PEGASE.2 we have produced a library of 28885 synthetic galaxy spectra at zero redshift covering four general spectral types of galaxies over the wavelength range from 250 to 1050 nm, at a sampling of 1 nm or less. The library was also reproduced for 4 random values of redshift in the range of 0–0.2 and it is computed on a random grid of four key astrophysical parameters (3 for SFR and 1 for timescale of the infall of gas). The synthetic library was compared with various photometric and spectroscopic observations (e.g. from SDSS) and found in good agreement with them. Using simulated Gaia photometry of this library we train and test the performance of Support Vector Machine (SVM) classifiers and parametrizers. The first results are promising, indicating that galaxy types can be reliably predicted and several parameters (e.g. redshift, mass to light ratio, present SFR) can be estimated with low bias and variance from Gaia observations.

The purpose of this study is to explore the relationship between galaxy stellar masses, based on multiwavelength photometry spectral template fitting and dynamical masses based on published velocity dispersion measurements, for a sample of 48 early-type galaxies at z ~ 1 with HST/ACS morphological information. We determine photometric-stellar masses and perform a quantitative morphological analysis of cluster and field galaxies at redshift 0.6 < z < 1.2, using ground- and space-based multiwavelegth data available on the GOODS-S field and on the field around the X-ray luminous cluster RDCS1252.9-2927 at z = 1.24. We use multi-band photometry over 0.4-8um from HST/ACS, VLT/ISAAC and Spitzer/IRAC to estimate photometric-stellar masses using Composite Stellar Population (CSP) templates computed with PEGASE.2 models. We compare stellar masses with those obtained using CSPs built with Bruzual & Charlot and Maraston models. We then compare photometric-stellar mass and dynamical mass estimates as a function of morphological parameters obtained from HST/ACS imaging. Based on our sample, which spans the mass range log(Mphot)=[10, 11.5], we find that 1) PEGASE.2, BC03, M05 yield consistent photometric-stellar masses for early-type galaxies at z ~ 1 with a small scatter (0.15 dex rms); 2) adopting a Kroupa IMF, photometric-stellar masses match dynamical mass estimates for early-type galaxies with an average offset of 0.27 dex; 3) assuming a costant IMF, increasing dark matter fraction with the increasing galaxy mass can explain the observed trend., 12 pages, 10 figures, 1 table, accepted for publication in Astronomy and Astrophysics

One way to extract more information from the integrated light of galaxies is to improve the spectral resolution at which observations and analysis are carried out. The population synthesis code currently providing the highest spectral resolution is Pegase-HR, which was made available by D. Le Borgne et al. in 2004. Based on an empirical stellar library, it provides synthetic spectra between 4000 and 6800 A at lambda/d(lambda)=10000 for any star formation history, with or without chemical evolution. Such a resolution is particularly useful for the study of low mass galaxies, massive star clusters, or other galaxy regions with low internal velocity dispersions. After a summary of the main features of Pegase-HR and comparisons with other population synthesis codes, this paper focuses on the inversion of optical galaxy spectra. We explore the limits of what information can or can not be recovered, based on theoretical principles and extensive simulations. First applications to extragalactic objects are shown., Comment: Inv. talk in "The Spectral Energy Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg, 4-8 Oct. 2004, eds. C.C. Popescu and R.J. Tuffs, AIP Conf. Ser., in press

We present the final band-merged ELAIS catalogue at 6.7, 15, 90, and 175 $��$m, and the associated data at u,g,r,i,z,J,H,K, and 20cm. The origin of the survey, infrared and radio observations, data-reduction and optical identifications are briefly reviewed, and a summary of the area covered, and completeness limit for each infrared band is given. A detailed discussion of the band-merging and optical association strategy is given. The total catalogues consists of 2860 sources. For extragalactic sources observed in 3 or more infrared bands, colour-colour diagrams are presented and discussed in terms of the contributing infrared populations. Spectral energy distributions are shown for selected sources and compared with cirrus, M82 and Arp220 starburst, and AGN dust torus models. Spectroscopic redshifts are tabulated, where available. For the N1 and N2 areas, the INT ugriz Wide Field Survey, permits photometric redshifts to be estimated for galaxies and quasars. These agree well with the spectroscopic redshifts, within the uncertainty of the photometric method. The redshift distribution is given for selected ELAIS bands and colour-redshift diagrams are discussed. There is a high proportion of ultraluminous infrared galaxies in the ELAIS Catalogue ($> 10 %$ of 15 $��$m sources), many with Arp220-like colours. 10 hyperluminous infrared galaxies and 10 EROs are found in the survey. The large numbers of ultraluminous galaxies imply very strong evolution in the star-formation rate between z = 0 and 1., 21 pages, 31 figures. Accepted for publication in MNRAS

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 $��z$ > 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 $��^2$-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, 10 pages, 10 postscript figures, 2 tables; accepted for publication in Astronomy & Astrophysics; to compute redshifts see http://www.iap.fr/pegase/

We present preliminary source counts at 6.7um and 15um from the Preliminary Analysis of the European Large Area ISO survey, with limiting flux densities of \~2mJy at 15um & ~1mJy at 6.7um. We separate the stellar contribution from the extragalactic using identifications with APM sources made with the likelihood ratio technique. We quantify the completeness & reliability of our source extraction using (a) repeated observations over small areas, (b) cross-IDs with stars of known spectral type, (c) detections of the PSF wings around bright sources, (d) comparison with independent algorithms. Flux calibration at 15um was performed using stellar IDs; the calibration does not agree with the pre-flight estimates, probably due to effects of detector hysteresis and photometric aperture correction. The 6.7um extragalactic counts are broadly reproduced in the Pearson & Rowan-Robinson model, but the Franceschini et al. (1997) model underpredicts the observed source density by ~0.5-1 dex, though the photometry at 6.7um is still preliminary. At 15um the extragalactic counts are in excellent agreement with the predictions of the Pearson & Rowan-Robinson (1996), Franceschini et al. (1994), Guiderdoni et al. (1997) and the evolving models of Xu et al. (1998), over 7 orders of magnitude in 15um flux density. The counts agree with other estimates from the ISOCAM instrument at overlapping flux densities (Elbaz et al. 1999), provided a consistent flux calibration is used. Luminosity evolution at a rate of (1+z)^3, incorporating mid-IR spectral features, provides a better fit to the 15um differential counts than (1+z)^4 density evolution. No-evolution models are excluded, and implying that below around 10mJy at 15um the source counts become dominated by an evolving cosmological population of dust-shrouded starbursts and/or active galaxies., MNRAS in press. 14 pages, uses BoxedEPS (included). For more information on the ELAIS project see http://athena.ph.ic.ac.uk/

We present results and source counts at 90micron extracted from the Preliminary Analysis of the European Large Area ISO Survey (ELAIS). The survey covered about 11.6 square degrees of the sky in four main areas and was carried out with the PHOT instrument onboard the Infrared Space Observatory (ISO). The survey is at least an order of magnitude deeper than the IRAS 100micron survey and is expected to provide constraints on the formation and evolution of galaxies. The majority of the detected sources are associated with galaxies on optical images. In some cases the optical associations are interacting pairs or small groups of galaxies suggesting the sample may include a significant fraction of luminous infrared galaxies. The source counts extracted from a reliable subset of the detected sources are in agreement with strongly evolving models of the starburst galaxy population., 13 pages, accepted by MNRAS. For more details on the ELAIS project see http://athena.ph.ic.ac.uk/

ABSTRA C T A deep survey of the European Large-Area ISO Survey (ELAIS) field in the southern celestial hemisphere (hereinafter S1) has been carried out with the Australia Telescope Compact Array (ATCA) at 1.4 GHz. The S1 region, covering about 4 deg 2 , has also been surveyed in the midand far-infrared (5‐200 mm) with the Infrared Space Observatory (ISO). The radio survey provides uniform coverage of the entire S1 region, with a sensitivity (5j) of 0.4 mJy over the whole area and 0.2 mJy in the centre. To this sensitivity, virtually all the radio counterparts of the far-infrared extragalactic ISO sources should be detected. This paper presents a radio sample ‐ complete at the 5j level ‐ consisting of 581 sources detected at 1.4 GHz. Of these radio sources, 349 have peak flux density in the range 0.2‐1 mJy, forming a new homogeneous sample of sub-mJy radio sources. Due to its size, depth and multiwaveband coverage, the sample will allow us to study in greater detail the sub-mJy radio source population. The full catalogue will be available from http://athena.ph.ic.ac.uk/pubs.html

The velocity field of the ionised hydrogen in the radiogalaxy 4C 41.17 at z = 3.8 is mapped in the Lyα 1215A emission line. The three-dimensional spectroscopy was carried out with the integral field spectrograph TIGER at the 3.60m CFHT in a short exposure time (≤ 2.0h). The narrow intense peak emission is confirmed. As new results, the values of the radial velocity relative to systemic and projected along the line of sight (0km s-1 ≥ v r ≥ - 115km s-1) are mostly negative. The detection of low surface brightness ionised clouds surrounding the main body of the galaxy confirm the anisotropy of the ambient medium. Individual spectra show signatures of star formation. A comparison with previous observations of velocities in 4C 41.17 (Chambers et al., 1990, Hippelein and Meisenheimer, 1993) is presented. The radiogalaxy 3C435A, observed with TIGER at z = 0.471 (Rocca-Volmerange et al., 1994) and the present observations of 4C 41.17 are favoring an expansion model. The performance of TIGER for such faint objects is confirmed, with a sensivity comparable to long slit spectrographs with spectra better identified.

We show that the combined study of the near-IR Stellar Energy Distribution (SED) and emission lines in IR luminous starburst galaxies, using evolutionary population synthesis, gives constraints both on the star formation (SF) parameters and on the relative spatial distribution of the components (burst stars, evolved stars, H II regions, dust). We also note that the He I λ 2.06/Brγ ratio, used to constrain the stellar upper mass limit, is sensitive to a variety of other factors that should be accounted for.

On the diagram (Fe5270, Mg5175) ellipticals and bulges of disk galaxies (from SO to Sc) maintain a very different position: E’s seem to be overabundant in Mg, bulges seem to have a solar ratio Mg/Fe, except several. ones who are overabundant in Fe.

High redshift galaxies are at present time detected along distance (up to z ≥3) and time scales so extended that the look-back times reach until 90% of the age of the Universe. Among the striking facts, evidences of an intense stellar activity appear in most galaxies whatever their types or their environments. Signs of activity are essentially strong far-UV /optical /infrared stellar emissions and nebular emission lines. These spectral signatures of star formation processes are observed in extremely distant radiogalaxies as well as in clusters or in quasar environments: one of the firstly analysed effect (Butcher and Oemler, 1984) consists of an increasing number of blue galaxies with the redshift in distant cluster cores. The high density of blue galaxies in the cluster Abell 370 is interpreted as an excess of star formation activity stimulated by a ram-pressure effect (Mellier et al, 1987). Dressier and Gunn, 1983 observed strong absorption Balmer lines in spectra of elliptical galaxies. These so-called E+A galaxies are witnesses of a recent star formation activity. More recently, from a large sample of distant clusters (Gunn, Hoessel and Oke, 1986), Gunn, 1988 confirms a strong evolution of star formation for cluster galaxies until z~ 1.

The cosmological evolution of stellar populations can be studied by observing, e.g,, high-z radio galaxies, and comparing their SEDs to those of local objects. But in such objects, the nuclear activity strongly influences the optical properties; to disentangle the superposition of spatial and spectral effects, complete 3-D data cubes are needed, such as those that can be obtained with the pioneering 3-D instrument TIGER.

On the diagram (Fe5270, Mg5175) ellipticals and bulges of disk galaxies (from S0 to Sc) maintain a very different position: E's seem to be overabundant in Mg, bulges seem to have a solar ratio Mg/Fe, except several ones who are overabundant in Fe.

A model is presented for the evolution of the galaxy luminosity function in which the distribution of the galaxy masses, star formation time scales, and star formation turn-on redshifts is derived from the initial power spectrum of density fluctuations. The mass function of galaxy halos is very steep at low masses. Star formation occurs quite late, especially for massive galaxies, because it is assumed to begin only when the group surrounding a galaxy has collapsed and tidal encounters commenced. A good fit of the model to the present luminosity function of bright galaxies and to the relation between half-light radius and luminosity for galaxies fainter than M(B) about -21. The predicted relation between halo circular velocity and blue luminosity for bluer galaxies is consistent with the observed Tully-Fisher relation for spiral galaxies. A reasonable fit to the B- and R-band number counts up to B less than 24 is found. The model's main problems are discussed.

Un modele unifie de formation des galaxies est propose afin de resoudre les 2 problemes suggeres par les donnees recentes sur les galaxies a redshift eleve : le premier probleme concerne l'âge et l'histoire de la formation stellaire des radiogalaxies distantes, et le second concerne la nature du grand nombre de galaxies du champ revele par les denombrements des galaxies faibles.

On montre qu’une analyse des observations photometriques de galaxies (couleurs et luminosites integrees) a l’aide d’un modele d’evolution galactique necessite egalement la connaissance de parametres tels que Mgaz , MTOT , metallicite, sous-populations,... l’ensemble des donnees photo-metriques devant etre corrigees (extinction, effet de surfaces emettrices, fond de ciel, lumiere zodiacale) de maniere coherente.En effet, un des resultats des modeles d’evolution photometrique est que : les couleurs sont un bon indicateur du rapport : taux de formation d’etoiles actuel/taux integre, quelque soit la forme du taux de formation d’etoiles. On montre ainsi que les couleurs ne pourront donner qu’un ensemble de solutions (taux τ*(t), âge t1 ) et que des donnees complementaires sont necessaires pour trouver la solution unique.Un autre point important est l’influence de la metallicite sur les resultats. A titre d’exemple, une interpretation de l’exces de luminosite infrarouge observe a 5 kpc du centre de notre galaxie est donnee. Des conclusions plus generales seront publiees ulterieurement.Des resultats obtenus avec ces modeles sur les differents types de galaxies sont egalement presentes : galaxies bleues a sursaut de formation d’etoiles, galaxies irregulieres de type magellanique dont l’analyse est en cours et galaxies elliptiques dont l’emission UV peut etre interpretee par une formation d’etoiles due a un gaz residuel).