A panoramic view of M81: New stellar systems in the debris field

Using the MegaCam imager on the Canada-France-Hawaii Telescope, we have resolved individual stars in the outskirts of the nearby large spiral galaxy M81 (NGC 3031) well below the tip of the red giant branch of metal-poor stellar populations over 60 kpc * 58 kpc. In this paper, we report the discovery of new young stellar systems in the outskirts of M81. The most prominent feature is a chain of clumps of young stars distributed along the extended southern HI tidal arm connecting M 81 and NGC 3077. The colour-magnitude diagrams of these stellar systems show plumes of bright main sequence stars and red supergiant stars, indicating extended events of star formation. The main sequence turn-offs of the youngest stars in the systems are consistent with ages of ~40 Myr. The newly reported stellar systems show strong similarities with other known young stellar systems in the debris field around M81, with their properties best explained by these systems being of tidal origin.Comment: 8 pages, MNRA

Post-Starburst Populations Near and Far - The Potential of Near-IR Spectroscopy

The efficient use of near-IR data in studies of external stellar populations depends on our ability to recognize the nature of the predominant sources of light, and to interprete these findings in terms of age and metallicity. Here we focus on elderly post-starburst populations, with ages of 0.1-1 Gyr. New models confirm that they are indeed expected to display specific spectral signatures in the near-IR, due to variable M stars of the asymptotic giant branch and to carbon stars. The signatures depend on age and metallicity. We summarize the status of current quantitative predictions and emphasize the importance of an empirical calibration of the spectral synthesis models.Comment: 6 pages, LaTeX (uses svmult.cls and the graphicx package). Includes 6 figures. To be published in the proceedings of the Ringberg Workshop on Starbursts Near and Far, held in Sept.2000 (Ed. L.J.Tacconi and D. Lutz

A Stellar Library for Evolutionary Synthesis Modeling Including Variable AGB Stars

A self-consistent spectrophotometric modelling of intermediate age post-starburst requires accurate stellar ingredients taking into account a principal feature of the stars dominating the near-IR emission during this phase: the variability of the AGB stars. A new library of stellar spectra based on averages of the empirical spectra of variable AGB stars is presented. This library is designed for convenient use in the population synthesis models. We discuss meaningful ways to compute these averages, and the non-trivial connection with the theoretical stellar parameters. Our library covers the near infrared wavelength range between 0.5 micron and 2.5 micron and exhibits fundamental differences when compared to the standard libraries using only static giants.Comment: 4 pages, to appear in the PASP Conference Proceedings series of the Workshop "Spectrophotometric dating of stars and galaxies", Annapolis, Maryland (U.S.A.), eds. I. Hubeny, S. Heap, and R. Cornet

Asymptotic Giant Branch Stars in Interacting Galaxy Globular Clusters

We present new modelling of the spectrophotometric properties of intermediate age stellar populations in the near-infrared (NIR). We take into account the evolutionary and spectroscopic properties of the Asymptotic Giant Branch (AGB) stars which dominate the integrated NIR emission of those populations. The predictions of spectrophotometric narrow-band molecular indices require the use of an effective temperature -- colour (or spectrum) calibration for AGB stars; synthetic indices show a strong dependence upon this calibration. Preliminary results of NIR observations of a supermassive 500 Myr old stellar cluster in the prototypical merger remnant NGC 7252 are presented. The spectra are indeed consistent with intermediate age models dominated by light from AGB stars, a significant fraction of which may be carbon rich. Implications for the stellar inputs used in the modelling of intermediate age stellar populations and their NIR emission are discussed.Comment: 7 pages, to appear in Massive Stellar Clusters, eds. A. Lancon and C. Boil

The usage of the Asymptotic Giant Branch Star Features As Age Indicators in Post-Starburst Galaxies

We investigate techniques that can be used to determine ages of recently star forming regions during the phase dominated in the near-IR by the asymptotic giant branch stars (10^8-10^9 yrs). In particular, we present selected near-IR spectroscopic features that identify the contribution of O-rich and C-rich AGB variable stars to the integrated spectra of post-starbursts. The observational strategy based on those features is presented. We discuss the robustness of our selected features in constraining the ages of the post-starburst population depending on its physical environment and on underlying evolved populations. The interplay between the integrated features of populations and the stellar parameters is discussed.Comment: 4 pages, to appear in the PASP Conference Proceedings series of the Workshop "Spectrophotometric dating of stars and galaxies", Annapolis, Maryland (U.S.A.), eds. I. Hubeny, S. Heap, and R. Cornet

Are small-scale sub-structures a universal property of galaxy halos? The case of the giant elliptical NGC~5128

We present an analysis of the spatial and chemical sub-structures in a remote halo field in the nearby giant elliptical galaxy Centaurus A (NGC~5128), situated at about 38 kpc from the centre of the galaxy. The observations were taken with the Advanced Camera for Surveys instrument on board the Hubble Space Telescope, and reach down to the horizontal branch. In this relatively small 3.8 kpc by 3.8 kpc field, after correcting for Poisson noise, we do not find any statistically strong evidence for the presence of small-scale sub-structures in the stellar spatial distribution on scales greater than 100 pc. However, we do detect the presence of significant small spatial-scale inhomogeneities in the stellar median metallicity over the surveyed field. We argue that these localized chemical substructures could be associated with not-fully mixed debris from the disruption of low mass systems. NGC 5128 joins the ranks of the late-type spiral galaxies the Milky Way, for which the stellar halo appears to be dominated by small-scale spatial sub-structures, and NGC~891, where localized metallicity variations have been detected in the inner extra-planar regions. This suggests that the presence of small-scale sub-structures may be a generic property of stellar halos of large galaxies.Comment: 10 pages, 8 figures, MNRAS in pres

An integral transform connecting spherical analysis on harmonic NA groups to that of odd dimensional real hyperbolic spaces

The main aim of the present paper is to establish an integral transform connecting spherical analysis on harmonic NA groups to that of odd dimensional real hyperbolic spaces. Moreover, certain interesting integral identities for the Gauss hypergeometric functions have also been given

The environmental dependence of the chemical properties of star-forming galaxies

We use a 0.040 < z < 0.085 sample of 37866 star-forming galaxies from the Fourth Data Release of the Sloan Digital Sky Survey to investigate the dependence of gas-phase chemical properties on stellar mass and environment. The local density, determined from the projected distances to the fourth and fifth nearest neighbours, is used as an environment indicator. Considering environments ranging from voids, i.e., log Sigma < -0.8, to the periphery of galaxy clusters, i.e., log Sigma =~ 0.8, we find no dependence of the relationship between galaxy stellar mass and gas-phase oxygen abundance, along with its associated scatter, on local galaxy density. However, the star-forming gas in galaxies shows a marginal increase in the chemical enrichment level at a fixed stellar mass in denser environments. Compared with galaxies of similar stellar mass in low density environments, they are enhanced by a few per cent for massive galaxies to about 20 per cent for galaxies with stellar masses < 10^{9.5} solar masses. These results imply that the evolution of star-forming galaxies is driven primarily by their intrinsic properties and is largely independent of their environment over a large range of local galaxy density.Comment: 9 pages, 7 figures, accepted by MNRA

Likewise theta functions of rank rr on Rd\mathbb{R}^d: analytic properties and associated Segal-Bargmann transform

We introduce and study the Hilbert space of $(L^2,\Gamma,\chi)$-likewise theta functions on $\mathbb{R}^d$ with respect to a given discrete subgroup $\Gamma$ of arbitrary rank and a character $\chi$ of $\Gamma$. A concrete description is given and an orthonormal basis is then constructed. Its range by the classical Segal-Bargmann transform is also characterized and leads to the so-called theta-Bargmann Fock space.Comment: 14 page

Chemical Properties of Starburst Galaxies Near and Far: Clues to Galaxy Evolution

The determination of chemical abundances in star-forming galaxies and the study of their evolution on cosmological timescales are powerful tools for understanding galaxy formation and evolution. This contribution presents the latest results in this domain. We show that detailed studies of chemical abundances in UV-selected, HII and starburst nucleus galaxies, together with the development of new chemical evolution models, put strong constraints on the evolutionary stage of these objects in terms of star formation history. Finally, we summarize our current knowledge on the chemical properties of intermediate- and high-redshift galaxies. Although the samples are still too small for statistical studies, these results give insight into the nature and evolution of distant star-forming objects and their link with present-day galaxies.Comment: 5 pages, 3 figures. To appear in the proceedings of Marseille 2001 conference "Where's the Matter? Tracing Dark and Bright Matter with the New Generation of Large Scale Surveys", M.-A. Treyer & L. Tresse (eds.), 2001, Frontier Grou