A. Lançon

STELIB: A library of stellar spectra at R 2000 ?;??

We present STELIB ? , a new spectroscopic stellar library, available at http://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500 A), with an intermediate spectral resolution (<3 A) and sampling (1 A). This library includes stars of various spectral types and luminosity classes, spanning a relatively wide range in metallicity. The spectral resolution, wavelength and spectral type coverage of this library represents a substantial improvement over previous libraries used in population synthesis models. The overall absolute photo- metric uncertainty is 3%.

Evolutionary synthesis of galaxies at high spectral resolution with the code PEGASE-HR. Metallicity and age tracers

We present PEGASE-HR, a new stellar population synthesis program generating high resolution spectra (R = 10 000) over the optical range λλ = 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) = − 2t o+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 single stellar populations (SSPs) from 10 7 to 2 × 10 10 yr. 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 Hγ line. They should prove useful in the analysis of spectra from the new generation of telescopes and spectrographs.

The X-shooter Spectral Library (XSL) - I. DR1: Near-ultraviolet through optical spectra from the first year of the survey

We present the first release of the X-shooter Spectral Library (XSL). This release contains 237 stars. The spectra in this release span a wavelength range of 3000-10 200 A and have been observed at a resolving power of R ≡ λ/ Δλ ~ 10 000. The spectra were obtained at ESOs 8-m Very Large Telescope (VLT). The sample contains O-M, long-period variable, C and S stars. The spectra are flux-calibrated and telluric-corrected. We describe a new technique for the telluric correction. The wavelength coverage, spectral resolution, and spectral type of this library make it well suited to stellar population synthesis of galaxies and clusters, kinematical investigation of stellar systems, and the study of the physics of cool stars. Full Table 3 and Table A.1 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/565/A117

Near-IR spectral evolution of dusty starburst galaxies

Abstract We propose a multicomponent analysis of starburst galaxies, based on a model that takes into account the young and evolved stellar components and the gas emission, with their respective extinction, in the frame of a coherent dust distribution pattern. Near-IR signatures are preferentially investigated, in order to penetrate as deep as possible into the dusty starburst cores. We computed the 1.4-2.5 μm spectra of synthetic stellar populations evolving through strong, short timescale bursts of star formation (continuum and lines, R ≃ 500). The evolution model is specifically sensitive to cool stellar populations (AGB and red supergiant stars). It takes advantage of the stellar library of Lancon & Rocca-Volmerange (1992) [A&ASS, 96, 593], observed with the same instrument (FTS/CFHT) as the analysed galaxy sample, so that the instrumental effects are minimised. The main near-IR observable constraints are the molecular signatures of CO and H 2 O and the slope of the continuum, observed over a range exceptionally broad for spectroscopic data. The H - K colour determined from the spectra measures the intrinsic stellar energy distribution but also differential extinction, which is further constrained by optical emission line ratios. Other observational constraints are the near-IR emission lines (Brγ, He I 2.06 μm, [Fe II] 1.64 μm, H 2 2.12 μm) and the far-IR luminosity. The coherence of the results relies on the interpretation in terms of stellar populations from which all observable properties are derived, so that the link between the various wavelength ranges is secured. The luminosity L K is used for the absolute calibration. We apply this approach to the typical spectrum of the core of NGC 1614. Consistent solutions for the starburst characteristics (star-formation rate, IMF, burst age, morphology) are found and the role of each observational constraint in deriving satisfactory models is extensively discussed. The acceptable contamination of the K band light by the underlying population amounts ≥ 15% even through a 5 arcsec aperture. The model leads to a limit on the direct absorption of Lyman continuum photons by dust situated inside the ionised areas, which in turn, with standard gas-to-dust ratios, translates into small characteristic sizes for the individual coexisting H II regions of the massive starburst area (clusters containing ∼ 10 2 ionising stars). We show that room is left for IMFs extending to 120 M ⊙ , rather than truncated at ∼ 60 M ⊙ as most conservative studies conclude. High internal velocity dispersions (≥ 20 km s −1 ) are then needed for the H II regions. An original feature of this work is to base the analysis of near-infrared spectral galaxy observations on a large wavelength range, using models constructed with spectral stellar data observed with the same instrument. However a broader use of this spectral evolution model on other spectral or photometric data samples is possible if the spectral resolution of the model is adapted to observations or if colours are derived from the energy distributions. Catherine J. Cesarsky

Modelling and interpreting optical spectra of galaxies at R=10 000

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 λ/δλ = 10 000 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.

Star formation history of galaxies from optical integrated light spectra

We discuss the difficulties of recovering the star formation history (SFH) of galaxies from their integrated light spectra. In a simplified mono‐metallic unobscured linear case the conditioning number of the kernel (a time sequence of SSPs) indicates the feasibility of the inversion. We highlight two important pitfalls: (i) The quality of the SFH reconstructions artificially improves when increasing the noise in the SSP models, thus making it difficult to assess the reliability of the results in real life, (ii) Averaging the results of a large number of noisy SFH reconstructions does not constrain the underlying “real” SFH. We regularize the problem by imposing the smoothness and the positivity of the solutions. We perform a systematic study of the separation of superimposed double bursts, with free metallicity and extinction, in several pseudo‐observational regimes. When the time elapsed between the two bursts is larger than .8 dex, their properties can be constrained with a precision of .04 dex in age a...