Francesca Annibali NGC1705: a post-starburst galaxy already back to activity.
Abstract: The star formation history in different regions of the blue compact dwarf galaxy NGC1705 has been inferred by comparing synthetic color-magnitude diagrams with HST optical and near infrared photometry. We find that NGC1705 is not a young galaxy, since it has started forming stars at least 5 Gyr ago. On the other hand, we confirm the existence of a recent burst of star formation between 15 and 10 Myr ago and find evidence for a new strong activity started 3 Myr ago and still ongoing. The rate of this young burst (0.3 M_sun/yr) is higher than derived in other dwarfs and only comparable to that of NGC1569.
Emanuele Bertone High-resolution spectral synthesis: a 2 \AA mapping of the UV emission of stellar populations
Abstract: We explore, from the theoretical point of view, the spectral properties of SSPs in the ultraviolet wavelength range. Our models rely on a new stellar library of high-resolution synthetic spectra (based upon ATLAS9 and SYNTHE codes developed by R. L. Kurucz), coupled with Buzzoni's population synthesis code to track evolution of the main UV features below 4000 \AA in the integrated SED of SSPs. Our special aim is to single out those absorption features that better track Turn Off stars (and therefrom age) in a stellar aggregate.
Angela Bragaglia Old Open Clusters
Abstract: Open Clusters are very good tracers of the Galactic disk properties, and their study can offer information on the present-day and initial condition of the disk, on its formation mechanism, on its chemical enrichment history, etc. We are studying a sample of old Open clusters, both with photometry and spectroscopy, in order to derive in a homogeneous way their distance, age, reddening and detailed chemical composition. I will present recent results of this programme.
Enzo Brocato A new theoretical approach to evaluate Surface Brightness Fluctuations in stellar population systems.
Abstract: N/A
David Butler Star formation history of the late-type spiral galaxy NGC 300
Abstract: People: Butler D., Martinez-Delgado D., Brandner W.,
We present the first WFPC2 V, I photometry for the Sculptor Group galaxy NGC 300 for four fields ranging from the central region to the outer disk/halo. A dearth of bright stars exists in the central region relative to two disk fields that cannot be explained by observational effects. This supports the Davidge (1998) report of suppressed star formation there during the past 10$^9$\,yr. A comparison of the star formation history of these two disk fields indicates that stars were born at similar epochs and formation continued at significantly different mean rates until 100-200\,Myr ago. The main stellar population is predominantly old, consisting of RGB and AGB stars, based on a synthetic colour magnitude diagram (CMD) analysis. We report that a marked burst of star formation occured in both fields lasting up to 80\,Myr and ended 50-60\,Myr ago. The most likely cause is tidal shocking of molecular gas in or between spiral arms. Z is found to have been more metal poor than 0.006 in both disk fields. We compare our findings to those of M31 and consider them in the framework of galaxy formation.
Nicolas Cardiel Disentangling Stellar Population Properties from Spectroscopic Data
Abstract: The derivation of physical properties (age, metallicity, IMF, element abundance ratios) from the integrated light of stellar populations is handicapped by the fact that variations in those properties led typically to degeneracies in the observational space. Trying to solve this problem, many authors are seeking for individual and narrow absorption features which are sensitive to one physical parameter and not to the others. But this typically led to the analysis of individual and narrow spectral features which demand high signal-to-noise ratios. Here we will discuss how the functional dependence of colors and line-strength indices on signal-to-noise ratio allows the definition of a suitability parameter that can help to identify the best spectral features to face the disentangling of the observed degeneracies.
Leticia Carigi Carbon and Oxygen in metal-poor halo stars: signatures of an early enrichment by Population III stars?
Abstract: Authors: Leticia Carigi, Max Pettini, Chris J. Akerman, Poul Nissen, Martin Asplund
We have recently conducted a survey of carbon and oxygen abundances in 34 F and G dwarf and subgiant stars belonging to the halo population and spanning a range of metallicity from [Fe/H] = -0.7 to -3.2 . The new data provide tentative evidence to suggest that, as the oxygen abundance decreases below [O/H] = -1, [C/O] may not remain constant at [C/O] = -0.5, as previously thought, but increase again, possibly approaching near-solar values at the lowest metallicities (when [O/H] is approximately equal to -3). With the current dataset this is no more than a 3 sigma effect; its reality and origin need to be confirmed by further observational and theoretical work. Here we show how such high [C/O] ratios may be a signature of the first generation of stars to have enriched the Galactic halo
Eugenio Carretta Proton capture elements in NGC 2808: probing a second generation of stars in globular clusters?
Abstract: I will present results of the abundance analysis on about 80 stars along the Red Giant Branch of the galactic globular cluster NGC 2808, using spectra acquired during the Science Verification program of FLAMES at VLT. Sodium abundances are derived for stars spanning a range of about 2 mag from the RGB tip. The resulting distribution is exploited to probe if a second generation of stars born from the ejecta of intermediate mass stars does exist in globular clusters. The case of NGC 2808 is also used as a pilot to present an ongoing program with FLAMES at VLT aimed to analyze several clusters to determine if any correlation exists between the cluster properties (in particular the extension of the HB) and the distribution of stars along the Na-O anticorrelation.
A. Javier Cenarro Near-IR Spectroscopy of Early-Type Galaxies in the Coma Cluster
Abstract: We present new, near-IR spectroscopic data for a sample of 28 early-type galaxies in the Coma cluster covering a wide range of velocity dispersions (40 - 400 km/s). The indices CaT$^*$, CaT, PaT, sTiO and MgI measured for this sample are compared with the ones obtained for a similar sample of field ellipticals (Cenarro et al., 2003, MNRAS, 339, L12) and interpreted on the basis of recent models predictions (Vazdekis et al., 2003, MNRAS, 340, 1317).
Miguel Cerviņo Physical limits to the validity of synthesis models: The Lowest Luminosity Limit.
Abstract: Miguel Cerviņo & Valentina Luridiana
Abstract: In this work we establish a necessary condition for the application of stellar population synthesis models to observed star clusters. Such condition is expressed by the requirement that the total luminosity of the cluster modeled be larger than the contribution of the most luminous star included in the assumed isochrones, which is referred to as the Lowest Luminosity Limit (LLL).
We have obtained the LLL for a wide range of ages (5 Myr to 20 Gyr) and metallicities (Z=0 to Z=0.019), and, using the results of evolutionary synthesis models, we have also obtained the minimal cluster mass associated to the LLL, which is the mass value below which the observed colors are severely biased with respect to the predictions of synthesis models. we find that, the minimal mass is larger in near infrared bands (Mmin around 10$^4$ and 10$^5$ Mo for the K band), implying that severe sampling effects may affect the infrared emission of many observed stellar clusters.
Finally, we extensively discuss the advantages and the drawbacks of our method: it is, on one hand, a very simple criterion for the detection of severe sampling problems, that bypasses the need for sophisticated statistical tools; on the other hand, it is not very sensitive, and it does not identify all the objects in which sampling effects are important and a statistical analysis (like Monte Carlo simulations) is required. As such, it defines a condition necessary but not sufficient for the application of synthesis models to observed clusters.
Cesare Chiosi Burst of Star Formation in the index-index planes
Abstract: The bottom line of this study is (i) to check whether normal (quiescent) and interacting EGs have a different behavior in the popular diagnostic planes such as Hb vs. [MgFe] (and others); (ii) to seek whether the signature of mergers and/or interactions may mirror in some specific changes of the indices that could un-equivocally hint for burts of stellar activity; (iii) to evaluate the intensity of those bursts or secondary episodes of star formation; (iv) to explore whether other alternatives can exist, i.e. distinct from obvious ones resting on large age range The data show that both normal, field and interacting galaxies have the same scattered but smooth distribution in the Hb vs. [MgFe] diagnostic plane. There are two strightforward interpretations for this: (1) EGs span larges ranges of ages and metallicities. The age youth is the signature of the aggregation mechanism, each event accompanied by metal enrichment. This simple scheme cannot, however, explain other spectro-photometric properties of EGs and has to be discarded. (2) The bulk population of stars is old but subsequent episodes of star formation scatter the object in the diagnostic planes. However, even this scheme is not able to reproduce the observed distribution. The occurrence of later bursts of activity help to scatter EGs over a large range of Hb. The intensity of the bursts has to be small otherwise too many high Hb objects would be observed. In this context, the peculiar distribution of galaxies in the Hb vs. [MgFe] plane is interpreted as the trace of the increase of the average metallicity accompanying all star forming events. The above schemes are too demanding because of the many ad hoc ingredients that have to be introduced. Furthermore they neglect the observationally grounded hint that the stellar content of EGs is likely enhanced in alfa-elements. We propose here a new scheme, in which the bulk dispersion of galaxies in the index-index plane is caused by a different mean degree of enhancement. The possibility that EGs span large ranges of [alpha/Fe] and metallicities but narrow ranges of ages for the bulk population favors the monolithic scheme.
Andrew Cole Tracking the Metallicity Gradient of the Large Magellanic Cloud
Abstract: Andrew Cole, Tammy Smecker-Hane, Eline Tolstoy, & John S. Gallagher
We have measured stellar abundances for more than 600 red giants in four fields of the Large Magellanic Cloud, using the near-infrared calcium II triplet. Corrected for inclination, the fields lie at projected distances of 0.3, 2.1, 2.3, and 4.7 kiloparsecs from the LMC center of light. These data, combined with existing deep photometry, allows us to measure the evolution of the mean metallicity and age-metallicity relation with radius in the LMC. The zero-metallicity-gradient case is ruled out at the 2 sigma level. The most likely explanation for the radial metallicity variation is a strong excess of stars younger than 3 Gyr in the bar with respect to the disk.
Gabriella De Lucia Evolution of galaxy population in clusters - Model predictions and comparison with observations
Abstract: We use semi-analytic techniques to follow the formation, the evolution and chemical enrichment of cluster galaxies in a hierarchical dark matter model. The use of simple physical prescriptions for the transport of metals in the different phases considered, and the choice of few physically motivated parameters, allow us to reproduce the latest observational results both in terms of luminosity and in terms of metallicity in the stellar population and in the intra-cluster medium (ICM). Model predictions for galaxy populations at higher redshift are presented and preliminary results are shown between such predictions and observational results obtained from the EDisCS survey.
EDisCS aims at studying the evolution of cluster population over more that 50% of cosmic time by combining photometric and spectroscopic informations on a large sample of clusters at redshift ~0.5 and 0.8 with existing informations on well studied nearby clusters. The homogeneity of quality data and the large sample at disposition allow to analyse galaxy population properties, together with their cluster-to-cluster variations. The comparison with semi-analytic models allows to address the questions of which are the physical mechanisms at work during galaxy evolution on such environments.
Jesus Falcon-Barroso The near-IR Ca II triplet - sigma relation for bulges of spiral galaxies
Abstract: We present measurements of the near-infrared Calcium II triplet (CaT, CaT*), Paschen (PaT) and Magnesium (MgI) indices for a well-studied sample of 19 bulges of early to intermediate spiral galaxies. We find that both the CaT* and CaT indices decrease with central velocity dispersion (sigma) with small scatter. This dependence is similar to that recently found by Cenarro (2002) for elliptical galaxies, implying an uniform CaT* -- sigma relation that applies to galaxies from ellipticals to intermediate-type spirals. The decrease of CaT and CaT* with sigma contrasts with the well-known increase of another alpha-element index, Mg$_2$, with sigma. We discuss the role of Ca underabundance ([Ca/Fe]<0) and IMF variations in the onset of the observed relations.
Uta Fritze - V. Alvensleben Recovering Star Formation Histories of Galaxies from Resolved Stellar Populations: Possibilities and Limitations of the CMD Approach
Abstract: We present preliminary results of a detailed theoretical study of the specific possibilities and limitations of the colour magnitude diagram (CMD) approach to derive star formation histories (SFHs) of galaxies. Our evolutionary synthesis code has recently been extended to compute synthetic CMDs in various filter bands at any timestep. We have performed a set of simulations of galaxies with different SFHs and metallicities. By analysing relative differences between CMDs, we investigate to which extent different SFHs and metallicities can be discriminated as a function of lookback time.
Anna Gallazzi Constraints on metallicities and ages from moderately high resolution spectra
Abstract: We use a new, medium-high resolution population synthesis model to estimate stellar metallicities, r-band light weighted ages and stellar masses for a sample of $\sim10^5$ galaxies of the SDSS DR1. We derive median-likelihood estimates of these parameters, based on the fit of 9 spectral absorption features that are well reproduced by our model and depend only weakly on element abundance ratios. Our sample includes galaxies containing stars in the full range of ages, from passive, early-type galaxies to actively star-forming, late-type galaxies. After assessing the accuracy to which we can constrain the physical parameters of galaxies in this way, we investigate the relations between stellar metallicity and various quantities such as age, stellar mass, colors and magnitudes.
Andrea Gilbert Ages, Masses and IMFs of Super Star Clusters in NGC 1569
Abstract: Keck/NIRSPEC spectroscopy and spectral population synthesis models permit new determinations of the properties of several super star clusters (SSCs) in the dwarf irregular starburst NGC 1569. We constrain the age of a cluster using low-resolution spectra and two techniques: the effective spectral type of a cluster determined from model atmospheres, and spectral population synthesis models based on empirical stellar libraries. The near-IR light is dominated by populations with ages of 4 Myr for SSC A, 15 Myr for SSC B, and 4 to 40 Myr for several other clusters. For the brightest clusters we use high-resolution spectra to measure the intrinsic stellar velocity dispersions and thus derive virial masses. The components of double cluster SSC A have masses of 0.30 and 0.34 million M_sun, and SSC B has a mass of 0.18 million M_sun. Comparison of these measurements with population synthesis predictions implies that these three SSCs are consistent with having normal IMFs, and thus they have the potential to evolve into globular clusters.
Rosa A. Gonzalez IR Surface Brightness Fluctuations of Magellanic Globular Clusters
Abstract: Rosa A. Gonzalez Centro de Radioastronomia y Astrofisica, UNAM, Campus Morelia, Michoacan, Mexico, CP 58190
Michael C. Liu Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822
Gustavo Bruzual A. Centro de Investigaciones de Astronomia, Apartado Postal 264, Merida 5101-A, Venezuela
We present SBFs in the near--IR for 191 Magellanic globular clusters available in the Second Incremental and All Sky Data releases of the Two Micron All Sky Survey (2MASS), and compare them with fluctuations of Fornax Cluster galaxies and with model predictions as well. Our goals are twofold: first, to provide an empirical calibration of near-IR SBFs, given that existing stellar population synthesis models are particularly discrepant in the near-IR; second, since stellar population synthesis models predict a larger sensitivity to metallicity and age in the near--IR than in the optical SBFs, a near--IR study of the MC globular clusters, with their wide range of ages (~10^6 to ~ 10^{10} yr, ie., 4 orders of magnitude) and narrow range of metallicities (Z ~ 0.0006 -- 0.01, ie., 1 order of magnitude only), offers a unique way of disentangling the effects of age and metallicity.
We find that near-IR fluctuation and fluctuation colors are mostly driven by age in the Magellanic cluster populations, and that in this respect they constitute a sequence in which the Fornax Cluster galaxies fit adequately. Fluctuations are powered by red supergiants with high--mass precursors in young populations, and by intermediate--mass stars populating the AGB in intermediate--age populations. For old populations, the trend with age of both fluctuation and fluctuation colors can be explained quite straightforwardly by evolution in the structure and morphology of the red giant branch. Moreover, fluctuation colors display a tendency to redden with age that can be fit by a straight line. For the globular clusters only, (barH - barKs) = (0.18 +- 0.02)Log(age/yr) - (1.11 +- 0.20), with chi^2 per degree of freedom = 1.1; once galaxies are included, (barH - barKs) = (0.23 +- 0.02)Log(age/yr) - (1.44+-0.18), with reduced chi^2 = 1.9. Finally, we use for the first time a Poissonian approach to establish the error bars of fluctuation measurements, instead of the usual Monte Carlo simulations.
Leslie Hebb Eclipsing Binary Stars and the Low-Mass Stellar Mass-Luminosity Relation
Abstract: The stellar mass-luminosity-radius relation for low mass Mdwarf stars is currently calibrated by only three detatched eclipsing binary stars and a handful objects observed with interferometric and adaptive optics techniques. We have surveyed 5 open clusters in the Galaxy in search of low mass eclipsing binary stars with known age, distance and metallicity through deviations in their relative light curves. We present results from this survey.
Enrico V. Held Evolved stellar populations in Local Group dwarf galaxies: near-IR imaging of Fornax and Carina
Abstract: We present wide-area (20'x20') and deep JHK observations for the dwarf spheroidal galaxies Fornax and Carina, as part of a near-infrared imaging survey of dwarf galaxies in the Local Group. The extended star-formation histories of Local Group dwarf galaxies offer the opportunity to study AGB stars in a variety of stellar populations with different ages and metallicities. In combination with optical (BVI) data from the Padova Local Group wide-field survey, these new near-infrared observations provide a unique baseline to study the properties of red giant and AGB stars in nearby stellar populations.
Maren Hempel Intermediate Age Populations of Globular Clusters in Early-type Galaxies
Abstract: Combined optical and near- infrared photometry is a very powerful tool to detect globular cluster populations which differ in age by several Gyr. We use observed and simulated color- color diagrams for globular cluster systems in early-type galaxies to reveal major star formation episodes which go hand in hand with cluster formation. The relative age of the sub-populations will give evidence for the formation and evolution of the host galaxies. Hereby a possible effect of the environment will be investigated.
Ulrich Hopp No stars in Local Group High Velocity Clouds?
Abstract: To solve the dwarf galaxy crisis of hierarchical clustering, Blitz et al. proposed that compact high velocity clouds might be small dark matter halos belong to the local group. To test this hypothesis, we did VLT deep imaging to search for a stellar population of this small halos by photometry of a resolved stellar component. The test is sensitive for distances to >2 Mpc but did not reveal any population. We also used 2MASS data with a similar result and started to search for Planetary Nebulae. Our results are in excellent agreement with indepent similar results from surveying for LSB features towards CHVC and analysing the SDSS data base (Simon \& Blitz, 2002, Lewis et al. 2002, Willman et al 2002). We will put the results into a common observationl context.
Valentin Ivanov Evolutionary Population Synthesis in the Near Infrared - Abundances of Seyfert and Starburst Galaxies
Abstract: We present a near-infrared population synthesis model, based on an empirical H and K band spectral library. The library has recently been improved by adding low metallicity red supergiants from the SMC. The model is based on Starburst-99, and it is aimed at studies of most obscured central regions of Seyfert and Starburst galaxies.
The comparison between the model output and the observed spectra of Seyfert 2 galaxies from the CfA Seyfert sample indicates that their central regions have near-solar metallicities. We also present new estimates for abundances of a sample of X-ray selected starburst galaxies.
Rachel Johnson ACS observations of the outer disk and halo of M31
Abstract: Recent ground based imaging has shown that the outer disk and halo of M31 contain significant stellar density and metallicity variations.
Constraints on the ages and metallicities of the stellar populations in these substructures will be provided by our current imaging project using the HST ACS. Here I will present some initial results.
Monique Joly Stellar populations of galaxies in the near IR
Abstract: The importance of the IR domain in determining stellar populations from the integrated light of galaxies will be shown. A new code dedicated to these investigations and based on flux measurement, including emission by dust, will be presented.
Andrea Kayser Medium resolution spectroscopy in omega Centauri
Abstract: The abundances of ~600 turn-off region stars in omega Centauri will be presented. Together with their photometric values a star formation history is derived. (More to come)
David Koch Potential Additional Science From The Kepler Data Base
Abstract: The Kepler Mission will launch in 2007 and monitor the brightnesses of 100,000+ stars for four to six years. The mission will have a photometric precision of 20 ppm on a $V=12$ star integrating for 6.5 hours. The time resolution is 15 min for all stars and 1 min for up to 225 at any given time. In addition, the community may propose to monitor up to 3000 additional objects of any nature that are in the Kepler field of view located in the Cygnus region, such, as variable stars or active galactic nuclei. The list of additional objects may be modified as often as every three months. The contact person for the Participating Scientist and Data Analysis Programs is Yoji Kondo kondo@stars.gsfc.nasa.gov
Tadayuki Kodama History of Mass Assembly of Galaxies in z~1 Clusters.
Abstract: Authors: Tadayuki Kodama (National Astronomical Observatory in Japan), Richard Bower (Univ of Durham)
We present the near-infrared (Ks-band) luminosity function of galaxies in two z~1 cluster candidates, 3C336 and Q1335+28. A third cluster, 3C289, was observed but found to be contaminated by a foreground system. Our wide field imaging data reach to Ks=20.5 (5sigma), corresponding to ~M*+2.7 with respect to the passive evolution. The near-infrared luminosity traces the stellar mass of a galaxy due to its small sensitivity to the recent star formation history. Thus the luminosity function can be transformed to the stellar mass function of galaxies using the J-K colours with only a small correction (factor < 2) for the effects of on-going star formation. The derived stellar mass function spans a wide range in mass from ~3 x 10^{11} Msun down to ~6 x 10^{9} Msun (set by the magnitude limit). The form of the mass function is very similar to lower redshift counterparts such as that from 2MASS/LCRS clusters (Balogh et al. 2001) and the z=0.31 clusters (Barger et al. 1998). This indicates little evolution of galaxy masses from z=1 to the present-day. Combined with colour data that suggest star formation is completed early (z>>1) in the cluster core, it seems that the galaxy formation processes (both star formation and mass assembly) are strongly accerelated in dense environments and has been largely completed by z=1. We investigate whether the epoch of mass assembly of massive cluster galaxies is earlier than that predicted by the semi-analytic hierarchical galaxy formation models. These models predict the increase of characteristic mass by more than factor 3 between z=1 and the present day. This seems incompatible with our data.
Xu Kong Stellar population in Blue Compact Galaxies
Abstract: TBD
Damien Le Borgne Linking X-ray and optical emission of star-forming galaxies: models and observations
Abstract: The spectral modeling of stellar populations in the optical has come to a high level of detail thanks to the most recent stellar evolution theories and to improved stellar libraries. In addition to the metallicity, age and star formation history tracers available in the UV-optical-NIR spectra, complementary powerful tracers exist in X-rays. First, I will present a coupling between the UV-optical-NIR emission predicted with PEGASE and X-ray properties of star-forming galaxies. This multi-wavelength approach is made possible by modeling the simultaneous evolutions of the X-ray emitting population (mainly X-ray binaries and supernovae remnants) and of the optical emitters. I will then describe the dependence of the integrated X-ray light on the metallicity of the interstellar gas, as well as the use of X-rays as a star-formation history tracer, comparing models and observations. Finally, I will present the complementarity of X-ray and optical wavelengths for the estimation of metallicity and age: narrow spectral indices around absorption stellar lines in the optical are modeled with the high-spectral resolution code of galaxy evolution PEGASE-HR (R=10000), improving previous estimates of age and metallicity in stellar populations.
Hyun-Chul Lee Stellar Populations of the LSB galaxies
Abstract: We present the stellar populations of the LSB galaxies.
Thibault Lejeune An interactive photometry simulator for stellar population studies
Abstract: I will present an updated version of the BaSeL Interactive Server already implemented at the Coimbra Observatory (http://www.astro.mat.uc.pt/BaSeL). This new version now allows a more direct interface between the model atmosphere spectra and the stellar tracks and isochrones. Using a databse of different stellar evolution model and spectral libaries compiled from the literature, this photometry simulator provides multi-colour photometry and synthetic colour-magnitude diagrams in several photometric systems. An user-friendly web interface allows an easy way to select the models and the preferred ranges of stellar parameters (Z, Y, Fe/H, age, Teff, logg...). This web interface should provide a valuable tool to study the observed stellar populations, by comparing model predictions with observations.
Yanchun Liang Misleading results from low-resolution spectroscopy: from galaxy interstellar medium chemistry to cosmic star formation density
Abstract: Low resolution spectroscopy (R=150) from the Canada-France-Redshift Survey (CFRS) had revealed intriguing properties for low redshift galaxies (z<=0.3): nearly half of their spectra show prominent H_alpha emission line, but no H_beta emission line, and barely detected [O II] 3727 and [O III] 5007 lines. We call these objects "CFRS H_alpha-single" galaxies and have re-observed a subsample of them at higher spectral resolution, associated with a subsample of more normal emission line galaxies. Good S/N spectroscopy at the VLT and the CFHT, with moderate spectral resolution (R>600), have allowed us to perform a full diagnostic of their interstellar medium chemistry. "CFRS H_alpha-single" galaxies and most of the star forming spirals are with high extinctions (A_V>2), high stellar masses and over-solar oxygen abundances. >From the present study, we believe that it is necessary to use the spectra with resolutions higher than 600 to derive the detailed properties of galaxies (gas chemical abundances, interstellar extinction, stellar population, star formation rates and history). One major drawback is indeed the estimated extinction which requires a proper analysis of the underlying Balmer absorption lines. We discover that, with low resolution spectroscopy, star formation rates (SFRs) can be either underestimated or overestimated by factors reaching 10 (average 3.1), even if one accounts for ad hoc extinction corrections. These effects are prominent for a large fraction of evolved massive galaxies especially those experiencing successive bursts (A and F stars dominating their absorption spectra). Further estimates of the cosmic star formation density at all redshifts mandatorily requires moderate resolution spectroscopy.
Thomas Lilly Using integrated light in deriving a galaxy's SFH: Broad-band colours vs. spectra
Abstract: We present results of a detailed study aiming to understand to what precision star formation histories (SFHs) can in principle be determined for distant galaxies observable in integrated light only. Using our evolutionary synthesis code, we have performed a set of simulations of galaxies with a wide range of different SFHs. By analysing the resulting colours and spectra, we investigate to which extent different SF scenarios can be discriminated on the basis of their photometric and spectral properties, respectively. We show that it is not possible to distinguish different scenarios of star formation which have evolved for more than 1, at the utmost 3-4 Gyrs since the last star forming event. For how long different SF scenarios can be disentangled highly depends on the range of colours available and absorption lines considered as well as on the details of the SFHs to be compared. Here, we observe a complementary behaviour between the spectral and the photometric evolution of a galaxy's integrated light. We will present details on this study.
Lauren Macarthur Stellar Populations in Bulges and Disks of Spiral Galaxies
Abstract: We present first results of a long-term study of the large-scale stellar population and evolutionary properties of nearby galaxies. We have acquired deep Gemini/GMOS spectra for 7 nearby spiral galaxies and measured line indices in the bulge and inner disk. These represent the deepest spectra of their kind to date. The line indices are compared with stellar population models to characterize the luminosity-weighted ages and metal abundances in star-forming galaxies and place constraints on basic formation scenarios of spiral bulges. Careful attention is paid to disk and nebular contamination into the bulge. These results are part of a long-term project to supplement the SIRTF Nearby Galaxy Survey (SINGS) Legacy project data base with radial absorption line measurements to provide a fundamental data base for the study of star formation histories and stellar populations of present-epoch star-forming galaxies.
Walter Maciel Planetary nebulae and stellar populations: kinematics, ages and chemical composition
Abstract: W. J. Maciel, R. D. D. Costa, L. G. Lago IAG/USP
Planetary nebulae are interesting objects for the study of stellar populations, as they are the offspring of stars with a wide range of masses, and thus include objects of different populations. Also, in view of their high intrinsic brightness they can be observed in different galactic subsystems, such as the disk, bulge and halo, and in many nearby galaxies, so that the differences of the stellar populations in these systems can be highlighted. In this work, we have taken into account a large sample of galactic nebulae for which we have determined the distances and chemical composition. Since radial velocities are available for many objects, we can associate their spatial distribution and kinematical properties to the chemical composition, so that different stellar populations can be attributed with a stronger confidence. Of particular importance in this respect are the abundance gradients as derived from planetary nebulae and other objects, such as HII regions and hot stars, and the galactic rotation curve. Our results are compared with the predictions of previous classification systems of planetary nebulae. We conclude that the observed chemical composition, the estimated ages and the kinematical properties of these objects all form a consistent scheme that can be explained by the expected variations of these quantities in the different stellar populations of the Galaxy.
Lidia Makarova Star formation history of dwarf galaxies in the M81 group.
Abstract: We derive quantitative star formation histories of 16 dwarf irregular galaxies in the M~81 group. The galaxies were observed with the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope as a part of the Snapshot Survey of Probable Nearby Galaxies. We use synthetic color-magnitude diagrams to derive the ages of the major star formation episodes, star formation rates, and approximate metallicity ranges.
Eva Manthey Colours of moderate luminosity mergers
Abstract: Here we present optical and NIR colours of mergers with moderate FIR luminosity (5*109 - 1010 L_sun). These objects may not be the results of major mergers between two spirals, but rather originate in mergers between galaxies of unequal mass or a spiral and an elliptical (S + E merger). The main questions in our project are: What are the age and the intensity of a starburst triggered by the merging process? Is the extension comparable to ULIRGs where the starburst is concentrated to the center or is an extended starburst as in the prototypical S+E merger NGC 4194 characteristic for these mergers?
David Martinez Delgado STELLAR POPULATION OF THE SAGITTARIUS TIDAL STREAM
Abstract: N/A
Hugues Mathis Retrieving the star formation history of the SDSS-EDR galaxies
Abstract: We fit the stellar continuum of the SDSS EDR galaxies on high resolution population synthesis models to constrain in a non-parametric way the star formation history of the galaxies selected by mass and morphology. For this purpose we use MOPED, an optimal, linear compression algorithm, to single out the most valuable features in the high frequency part of the spectra. We find that almost all massive ellipticals have completed the bulk of their star formation by z=1.4 while the majority of spirals shows fairly constant star formation.
Claudia Mendes De Oliveira A nursery of young objects: HII regions in the intragroup medium of Stephan's Quintet.
Abstract: Four knots with spectra of vigorous star-forming regions are found in the intra-group medium of the Stephan's Quintet, not attached to any optical tails, more than 50 kpc away from the center of the most probable parent galaxy (NGC 7319). They have M$_B$ ranging from --11.5 to --12.2 mag, colours from B-R = 0.7 to 1.0 mag, radial velocities from 6580--6670 km/s and three of them are supperposed onto the HI tail east of NGC 7319, with a mean radial velocity of 6600 km/s. In addition, they have metallicities of the order of 12+log(O/H) = 8.6 $\pm$ 0.1, which suggests that they were formed from pre-enriched material. We derive a mean age of $4.6 \pm 0.6$ Myr and a mean stellar mass of $(2.0 \pm 0.3) \times 10^5~M_\odot$ for the four objects. The masses, ages, colours, velocities, metallicities and location of the objects suggest that they are HII regions that were formed away from the galaxies. This is possible given that the intragroup medium of the Stephan's quintet contains a significant amount of HI which could be compressed by collisions, increasing its density, and enhancing the star formation efficiency.
Steffen Mieske Distance to the Centaurus cluster and its subcomponents from surface brightness fluctuations
Abstract: We present $I$-band Surface Brightness Fluctuations (SBF) measurements for 15 early type galaxies (3 giants, 12 dwarfs) in the central region of the Centaurus cluster, based on deep photometric data in 7 fields obtained with VLT FORS1 and with very good seeing. From the SBF-distances to our sample galaxies we determine the distance of the Centaurus cluster to be 41.3 $\pm$ 2.1 Mpc (33.08 $\pm$ 0.11 mag). This places the Centaurus cluster at about the same distance as the ``Great Attractor''. We find a distance difference of 0.28 $\pm$ 0.37 mag between the two subcomponents Cen30 and Cen45, ruling out that both components are separated by their Hubble flow distance. A distance difference of 0.48 $\pm$ 0.21 mag is found between the central galaxies NGC 4696 (Cen30) and NGC 4709 (Cen45) of both components, supported by the different turn-over magnitudes of their respective globular cluster systems. This suggests that Cen45 is falling into but has not yet reached Cen30, supporting the idea of a large scale filament along the line of sight towards Centaurus (Churazov et al. 1999). $H_{\rm 0}$=83.0 $\pm$ 8.3 km/s/Mpc is obtained for our Cen30 sample taking into account the peculiar motion of the Local Group into the direction of the Centaurus cluster. This value of $H_{\rm 0}$ corresponds to a much smaller Hubble flow distortion in the direction of Centaurus than determined by Tonry et al. (2000), implying that the GA mass estimate by Tonry et al. may be too high and/or that the Centaurus cluster falls into the GA almost perpendicularly to the line of sight. As our mean single measurement error is very close to the measured distance scatter of the investigated galaxies, we can only derive an upper limit of $\pm$ 10 Mpc radial extension for the Centaurus cluster, corresponding to a five times larger radial than tangential extension. No evidence for an infall pattern into the Great Attractor is found within the uncertainties for the 11 galaxies with measured redshifts.
Sabine Moehler Spectroscopy of White Dwarfs in Globular Cluster
Abstract: As final stages in the evolution of low mass stars white dwarfs are rather abundant in globular clusters. Despite their intrinsic faintness they offer new possibilities to determine distances and ages of globular clusters, provided masses and spectral types are known. We therefore started a programme to obtain spectra of white dwarfs in globular clusters and I will present results from this project.
Bhasker Moorthy Stellar Populations in Bulges of Spiral Galaxies
Abstract: Bhasker K. Moorthy and Jon A. Holtzman New Mexico State University
We have obtained line strengths and gradients in the central regions of approximately 30 galaxies ranging in Hubble type from S0 to Sc. Our indices have been fully tranformed to the Lick system and corrected for velocity dispersion, rotation, and emission. Disk contamination is addressed through two dimensional bulge-to-disk decomposition. We find that bulges of most S0 and Sa galaxies are similar to ellipticals in their stellar populations. We do find some early type bulges with considerably smaller luminosity-weighted SSP ages but these either have disk-like kinematics or evidence of recent mergers. Late-type bulges occupy a wider range of luminosity-weighted ages and metallicities than early types. Most bulges have strong metallicity gradients and no age gradient. The gradients are not correlated with Hubble type. Bulges have no gradient in Mg/Fe and few bulges have larger Mg/Fe values than their disks.
Lorenzo Morelli Chemical evolution of bulges of spiral galaxies: environmental and morphological influence.
Abstract: This project is aimed at studying the chemical evolution of bulges of spiral galaxies, with the goals to understand how much the properties of bulges differ from those of elliptical galaxies and to assess if the environment plays a significative role in the chemical evolution. To achieve these goals, up to now we observed 11 spiral galaxies in field and 9 in the Fornax and Pegasus cluster. Another run has planned for September 2003. We measured the main metallicity indexes Mg2, Mgb, Fe, MgFe, Hb and the velocity dispersion as function of the galactocentric radius, in order to determine the age and chemical abundances for bulges of galaxies with morphological type ranging from S0 to Sc. In this work we present preliminary results from the first 7 cluster galaxies, which will be compared in future with those obtained for spiral galaxies in the field and with the ellipticals both in cluster and field from published works.
Alessia Moretti The globular cluster population in the outer halo of the Sombrero galaxy: VIMOS spectroscopy
Abstract: We present the first results from deep spectroscopy of the globular cluster system of the Sombrero galaxy, recently obtained with VIMOS at the VLT. Observations covering a large field-of-view around the galaxy provide deep spectra of globular cluster candidates out to a distance of ~15' (40 Kpc) from the center of M104. Typical VIMOS spectra of globular clusters are shown, together with measurements of radial velocities and absorption line indices for a sample of bona-fide candidates containing objects as faint as V=22. On the basis of these preliminary results we conclude that VIMOS spectroscopy can give an important contribution to the study of globular cluster systems in galaxies.
Mustapha Mouhcine Spectrophotometric properties of intermediate age populations from Z/Zo=1/50 to Z/Zo=2.5
Abstract: N/A
Jihane Moultaka An inverse method for stellar population synthesis
Abstract: I will talk about an inverse stellar population synthesis method developped by Didier Pelat and myself. This method provides a full knowledge of all possible exact solutions and deals with the minimisation problem when an approached solution is required. In addition, it allows to compute the uncertainties around the solutions and provides a criterium to sort the various solutions by order of merit. After introducing astrophysical constraints while searching for a solution, we found that these have little effect on the results. The method and the analysis have been applied to the central regions of a sample of 10 active and 2 normal galaxies in order to gain new insight into the starburst-AGN connection.
John Moustakas An Integrated Spectrophotometric Atlas of Actively Star-Forming Galaxies
Abstract: We present a new spectrophotometric atlas of nearby star-forming galaxies. Our observations consist of spatially integrated, high signal-to-noise spectrophotometry for $\sim350$ galaxies between $3600$ and $7000$~\AA\ at a resolution of $\sim7.5$~\AA\ (FWHM). Our sample includes a substantial fraction of starburst and infrared-luminous galaxies and spans a broad range of morphological type, star-formation properties, optical-to-infrared ratio, nuclear activity, and dust content. Here we present the data and an analysis of the nebular emission lines and continuum properties of the whole sample. Our integrated spectral atlas is suitable for a variety of applications in galaxy formation and evolution, both as a reference sample for more distant galaxies and for improving our understanding of nearby star-forming galactic systems.
Mark Northeast Testing Galactic Chemical Evolution Modeling of Spheroidal Galaxies
Abstract: Using Galactic Chemical Evolution (GCE) models it may be possible to infer the SFH of galaxies, to produce ultimately a more precise and believable method of reproducing observable galaxies than by a single burst for star formation. We have a code to model GCE in a single zone. This software models chemical abundances and the resulting stellar spectral indices, to be compared to spectral indices observed in the light from galaxies. Several variables are examined, such as those relating to star formation rate (i.e. Salpeter, with a variable efficiency as a coefficient) and the time where two major changes may have occurred. This code allows for gas inflow during the evolution of the galaxy. The code currently predicts line strengths and colours. The latest model fits are shown for several galaxies. The advantages and limitations of these models are discussed.
Pierre Ocvirk Stellar populations and their kinematics: mixed inversions of galaxy spectra
Abstract: I will present inversion techniques which aim at recovering the stellar content (age, metallicity, extinction) and kinematics of a stellar population from its observed absorption line spectrum. The originality of the mixed inversion technique is its potential to recover both stellar content and kinematics at the same time. These techniques use new synthetic high resolution spectra produced by PEGASE and minimization algorithms. The mixed inversions are safe enourgh to be applied to large ensembles of data, which could not be interpreted without such automated methods. I apply them to a subset of SDSS data and to mock data representing the bulge and disc population of the inner region of spiral galaxies
Sergio Ortolani To be decided
Abstract: Enter the abstract here
Lucimara P. Martins High-Resolution Synthetical Stellar Population Spectra
Abstract: We present an updated version of the stellar population synthesis code, Starburst99 (Leitherer et al. 1999), used to predict the spectrum of a single-metallicity stellar population, with a spectral resolution of 0.3 angstrons, in the spectral region between 3500 and 7000 angstrons. The input stellar library includes non-LTE absorption profiles for stars hotter than 25000K, generated with the code TLUSTY (Hubeny) and LTE profiles for lower temperatures, where Kurucz models were used. The temperature and gravity coverage is 5000 < Teff < 50000K and 0.0 < log g < 5.0, respectively. The metallicity is solar. We present a direct application of these models, showing how their high-resolution spectra can be very useful tools for subtraction of the stellar population of a galaxy, when one is interested in the emission line features.
Elena Pancino The metal rich stellar populations in Omega Centauri
Abstract: Authors: E. Pancino, F.R.Ferraro, M.Bellazzini, L.Origlia, V.Hill, L. Pasquini
After the recent discovery of a metal-rich, presumably younger, stellar component (the RGB-a) in the globular cluster omega Centauri, we have started a coordinated spectro-photometric project devoted to the complete characterization of this anomaous sub-population. Some of the most recent results concerning the RGB-a are presented, along with some additional side-projects connected with the study of the other sub-populations in omega Centauri.
Ben Panter Unlocking the Fossil Record
Abstract: Using a novel data compression algorithm (MOPED) we have recovered stellar populations for all galaxies in the SDSS EDR and DR1.
Isabel Perez Martin Mass-to-light determination through population synthesis models
Abstract: Population synthesis models provide an interesting tool to calculate stellar M/L ratios from broad band photometry. They can give us a way of comparing the stellar M/L ratio to the dynamical or 'total' M/L ratio. The overall goal of this work is to constrain the stellar M/L ratio values making use of population synthesis models and test whether the mass distribution obtained in this way, together with hydrodynamical simulations of the gas dynamics, can reproduce the observed position-velocity diagrams of a sample of 5 barred galaxies. The final results of this project will be presented in this poster.
Lorenzo Piovan Shells of dust around AGB stars: effects on the integrated spectrum of Single Stellar Populations
Abstract: We present models for Single Stellar Populations (SSPs) of intermediate and old ages where dust enshrouded Asymptotic Giant Branch (AGB) stars are introduced. As long known AGB stars are surrounded by dust-rich shells of matter caused by their own stellar wind, which absorb the radiation coming from the central object and re-emit it in the far infrared (IR). To this aim, particular care is devoted to follow the evolution of the AGB stars throughout the quiet and thermally pulsing regimes, to evaluate the effect of self contamination in the outermost layers by the third dredge-up mechanism, to follow the transition from oxygen-rich to carbon-rich objects (as appropriate to their initial mass and chemical composition), and finally to estimate the efficiency of mass-loss by stellar winds, all aspects that concur to the formation and properties of the dusty shells around. In addition to this, accurate physical models of the dusty shells are presented in which the re-processing of radiation from the central stars is calculated by solving the radiative transfer equations in presence of dust particles of different chemical composition. The resulting spectral energy distribution (SED) is examined to show how important features, like the 10 micron Si-O stretching mode feature and the 11 micron SiC feature, evolve with time. The SEDs are then convolved with the IRAS filters to obtain the flux in various pass-bands, i.e. 12, 25 and 60 micron, for individual AGB stars of different, mass, chemical composition, and age. The comparison is made by means of SSPs along which AGB stars of the same age but different initial masses are located. This allows us to explore the whole range of masses and ages spanned by AGB stars. The theoretical results are compared to the observational data for selected groups of stars. The same is made for the J,H,K, L pass-bands of the Johnson system. Finally, from the integrated SEDs of the SSPs, we derive the integrated Johnson J,H,K, L magnitudes and colors to be compared to infrared data for star clusters of the Magellanic Clouds. In general good agreement with the data is possible if the effects of the circumstellar shells of dust are taken into account
Robert Proctor Ages and Metallicities of Galaxies in a Range of Environments.
Abstract: Model predictions of galaxy ages and metallicities generally include a dependence on environment. To test such predictions a large number (approx 20) Lick indices are used to derive estimates of both central and spatially resolved age, Fe and alpha-element abundances of galaxies in a variety of environments (field, Virgo cluster and Hickson compact groups). The sample includes early-type (E/S0) galaxies as well as late-type (spiral bulges). We show that while correlations between central parameters are consistent across the range of environments, the data can not be described by a single set of relations. Rather, elliptical galaxies, S0s and spiral bulges each show a characteristic set of behaviours with age and mass. The spatially resolved analysis detects the presence of both age and metallicity gradients. Correlations between these gradients and central parameters are then investigated.
Alejandra Recio Hot Horizontal Branch Stellar Population in Galactic Globular Clusters
Abstract: I will present high resolution UVES spectroscopy of 61 hot horizontal branch stars in 4 different Galactic globular clusters to investigate their rotational properties and chemical abundances. In addition, using the colour-magnitude diagrams of 63 globulars, based on WFPC2+HST photometry, we have examined the HB temperature extension and its dependence on cluster parameters.
Marina Rejkuba Is there an intermediate-age population in giant elliptical NGC 5128?
Abstract: Several HST WFPC2 and NICMOS as well as VLT studies of resolved stellar halo of NGC 5128 have given contradictory answers to the question of the presence of an intermediate-age component in this nearest giant elliptical galaxy. I will present the newest results obtained from the analysis of the Long Period Variable stars and new very deep color-magntiude diagram constructed with HST ACS data which help resolving this issue.
Donatella Romano Chemical evolution of dwarf galaxies with resolved stellar populations
Abstract: Donatella Romano (INAF-Osservatorio Astronomico di Bologna, Bologna, Italy), Monica Tosi (INAF-Osservatorio Astronomico di Bologna, Bologna, Italy) Francesca Matteucci (Dipartimento di Astronomia, Universita` di Trieste, Italy).
Interpreting the color-magnitude diagrams (CMDs) of dwarf galaxies with resolved stellar populations is a tool to study their star formation histories over the last Gyrs. We present preliminary results of chemical evolution models for dwarf irregulars and BCDs with star formation histories inferred by comparing synthetic CMDs with HST optical and near infrared photometry. Particular attention is paid to the interpretation of the CNO abundance patterns.
Alfred Rosenberg Globular Clusters Relative Ages (II): The Outer Halo.
Abstract:
Patricia Sanchez-Blazquez Differences in carbon and nitrogen abundances between field and cluster early-type galaxies
Abstract: Central line-strength indices were measured in the blue spectral region for a sample of 98 early-type galaxies in different environments. For most indices (Mgb and <Fe> in particular) elliptical in rich clusters and in low density regions follow the same index-sigma relations. However, striking spectral differences between field ellipticals and their counterparts in the central region of the Coma cluster are found for the first time, with galaxies in the denser environment showing significantly lower C4668 and CN2 absorption strengths. The most convincent interpretation of these results is a difference in abundance ratios, arising from a distinct star formation and chemical enrichment histories of galaxies in different environments. An scenario in which elliptical galaxies in clusters are fully assembled at earlier stages than their low-density counterparts is discussed.
Cecilia Scannapieco Chemical Evolution in Smooth Particle Hydrodynamical Simulations
Abstract: The chemical properties of the ISM and the stellar populations are closely linked to stellar evolution and galaxy formation and evolution. Different physical processes acting at different scales play an important role in the production and distribution of chemical elements. The complexity of this problem requires sophisticated models, capable of integrating these processes together. The implementation of chemodynamical models in numerical codes, and particularly in hydrodynamical ones, opens a new and powerful tool to study the enrichment of the Universe within a cosmological framework. This implementation allows us to follow the hierarchical formation of the structure together with its chemical enrichment. Although several numerical milestones should be taken into consideration, hydrodynamical simulations including chemical enrichment allow the description of the non-linear evolution of the structure and its chemical enrichment, providing estimations that can be directly confronted with observations at different redshifts.
Mathias Schultheis Near-IR spectroscopy in the Inner Galactic Bulge
Abstract: We present near-IR spectra (HK-band) of a sample of 107 sources with mid-IR excesses at 7 and 15\,$\rm \mu$m detected during the ISOGAL survey. Making use of the DENIS interstellar extinction map from Schultheis et al. (1999) we derive luminosities and find that the $\rm M_{bol}$ vs.~$\rm ^{12}CO$ and $\rm M_{bol} \, vs.~H_{2}O$ diagrams are powerful tools for identifying supergiants, AGB stars, giants and young stellar objects. The majority of our sample are AGB stars ($\sim$ 80\%) while we find four good supergiant candidates, nine young stellar objects and 12 RGB candidates. We have used the most recent $\rm K_{0}-[15]$ relation by Jeong et al. (2002) based on recent theoretical modeling of dust formation of AGB stars to determine mass-loss rates.
We used the equivalent width of the CO bandhead at 2.3\,$\rm \mu m$, the NaI doublet and the CaI triplet to estimate metallicities using the relation by Ram\'{\i}rez et al. (2000). The metallicity distribution of the ISOGAL objects shows a mean [Fe/H] $\sim$ -0.25\,dex with a dispersion of $\rm \pm 0.40\,dex$ which is in agreement with the values of Ram\'{i}rez et al. (2000) for Galactic Bulge fields between $\rm b = -4^{o}$ and $\rm b = -1.3^{o}$.
We present a comparison between observed spectra to a grid of synthetic spectra based on hydrostatic MARCS models. We discuss the influence of $\rm T_{eff}$, log\,g, mass and metallicity on the different observed spectral features and do a first quantitative comparison between observed and synthetic spectra for different metallicities.
Marco Sirianni High Resolution observation of the SSCs in NGC1569
Abstract: AUTHORS: M.Sirianni (ESA/STScI and JHU), G.Meurer (JHU), J.Blakeslee (JHU) M. Clampin (GSFC), H. Ford (JHU), G. Illingworth (UC/Lick), R. Kimble (GSFC) and the ACS Science Team.
ABSTRACT We present high-resolution observations of the super--star clusters in the nearby irregular galaxy NGC 1569, obtained with the High Resolution Channel of the Adcanced Camera for Surveys on board the Hubble Space Telescope. We show images with a scale of 0.018"/pixel resolution which allow to solve for the first time the morfological structure of the double central cluster NGC1569A and of the other SSC NGC1569B. The size, mass, and luminosity of these superclusters confirm that these objects could be young globulars, reinforcing previous conclusion. Lucy deconvolution of the image allow to resolve the stellar components of these cluster and to measure the Upper end of the Luminosity Function.
Jonathan Smoker A search for early-type stars in the halo of NGC 2683
Abstract: Previously, we have used the INT to obtain CCD UBV images of a small fraction of the halo of M31, and identified several possible early-type stars in the halo of this galaxy. However, these objects could alternatively be disc stars in M31 at large galactocentric distances, or evolved, low luminosity stars in the Galaxy. To exclude these sources of contamination, we here describe INT wide-field-camera observations of the halo of the distant ((m-M)-28.8i edge-on spiral galaxy NGC 2683 in UBV.
Naoyuki Tamura Colour Gradients in Elliptical Galaxies : Environmental Dependence of Formation History ?
Abstract: We investigated B-R colour gradients in 29 E/S0 galaxies in a nearby rich cluster ABELL 2199. Our aims are to study statistical properties of the color gradients and, by comparing them with those in less dense environments, to examine environmental dependence of colour gradients in elliptical galaxies.
We found that the mean value of the colour gradients is -0.09 +- 0.04 mag/dex in d(B-R)/dlogr, which can be converted to a metallicity gradient of ~ -0.3 in dlogZ/dlogr assuming an old stellar population. Our data also suggest that for the galaxies brighter than $L_*$, more luminous and larger galaxies tend to have steeper colour gradients. The typical value of the colour gradients seems to be consistent with a recent monolithic collapse model and the correlation could also appear if elliptical galaxies formed through the monolithic collapse.
On the contrary, it is found based on data from the literature that any such trend between galaxy luminosity or size and colour gradient is clearly weaker for elliptical galaxies in less dense environments, though the distribution of the values of colour gradient is quite similar to that found in the rich cluster. Based on the results from our data and the published data, formation process of elliptical galaxy and its environmental dependence will be discussed.
Juan Pablo Torres Papaqui Determination of nuclear SB ages in Seyfert galaxies
Abstract: We present optical/near UV spectra of nuclear regions of Seyfert galaxies over the wavelength region 3600-5300 \AA. Many Seyferts, both type 2 and type 1 show the direct spectroscopic signature of high-order Balmer absorption lines in the near-UV. This signature is a strong evidence of the presence of recent star formation in the nuclear region of these galaxies. We applied a new method to determine ages of the stellar population of Seyfert galaxies. This method consists of the direct comparison of the profiles of the high-order Balmer and Ca K absorption lines with starburst spectral models at high resolution. We obtain strong evidence of starbursts in Seyfert nuclei supporting some kind of connection between starburst and AGN activity, but it is not yet demonstrated that starburts are present in all AGNs. If a strong connection exists, this would bear important implications for theories of AGN formation and their role in galaxy formation.
Takuji Tsujimoto The origin of low-alpha stars
Abstract: The origin of low-alpha stars in the Galactic halo and dwarf spheroidal (dSph) galaxies is discussed. It is found that low-alpha stars in the Galaxy are essentially on the main-sequence. This strongly suggests that these stars suffered from external pollution. It is also found that the Zn/Fe ratios of low-alpha stars both in the Galaxy and in dSph galaxies are lower than the average value of Galactic halo stars whereas damped Ly alpha systems have higher values. This implies that low-alpha stars accreted matter depleted from gas onto dust grains. To explain these features in low-alpha stars, we have proposed that metal-poor stars harboring planetary systems are the origin of low-alpha stars.
Gerardo A. Vazquez STARBURST99: Differences between Padova and Geneva Tracks in Star Forming Galaxies.
Abstract: We have incorporated the set of Padova tracks to S99. In this work we analyze the differences predicted for the same kind of populations using a deferent stellar evolution models as input. The Padova tracks has been updated with the TP-AGB phase taking into account the mass loss. We apply the first models with solar metallicity to M82-F, which resemble a lack of mass probably lost by stellar winds.
Carl Jakob Walcher Mixed stellar populations in integrated spectra of Nuclear star clusters
Abstract: Despite their shallow central gravitational potential, late-type bulge-less spiral galaxies frequently harbor a luminous compact stellar cluster in their dynamical center. Masses for these nuclear clusters of around 10^7 Msun are one order of magnitude higher than those of massive normal globular clusters, while their sizes of around 5 pc are comparable. We here use high-resolution (0.05A) spectra from UVES at the VLT to analyze the stellar content of this new class of massive stellar clusters. We explore ways to constrain the star formation history in the clusters from the integrated spectra with the help of the new stellar population synthesis models of Bruzual & Charlot 2003. The spectra show the presence of mixed stellar populations from multiple epochs of star formation. We conclude that repetitive events of star formation occur in the clusters and give an estimate of the duty cycle.
George Wallerstein The Nucleosynthesis History of the Sculptor Galaxy
Abstract: High resolution spectra are now available for 9 stars in Sculptor; 5 by Shetrone et al. (2003) and 4 by Geisler et al. (2003). They show a range of [Fe/H] values from -2.1 to -1.0. I will describe the trends of the abundances of a wide variety of species from sodium to europium with the Fe/H ratio. The observed ratios, [X/Fe] show a very di- fferent behavior as compared to the same ratios in the halo of our Galaxy. This indicates a difference in the supernova populations as a funtion of metallicity.
Erich Wenger BLoIS 1.0: The Basel Library of Integrated Spectra
Abstract: BLoIS 1.0: The Basel Library of Integrated Spectra
We compiled an extensive library of integrated stellar population properties based on the BaSeL stellar libraries by Westera, the evolutionary synthesis code GISSEL by Bruzual & Charlot, and the latest chemodynamical galaxy models by Samland. It has been designed for theoretical studies (such as the age-metallicity-degeneracy) as well as for comparison to observations.
The first version contains 504 Single Stellar Populations (SSPs), each consisting of integrated spectra for 221 ages between 0 and 20 Ga. We chose 14 different IMFs, varied in slope and shape, as well as 7 different metallicities between Z = 0.0001 and 0.1 (corresponding to the Padova 1994 evolutionary tracks). All SSPs for BLoIS 1.0 were created using the latest theoretical BaSeL 3.1 stellar library.
Furthermore, 5'544 Composite Stellar Populations (CSPs) were calculated with 3 different types of SFRs and the same 7 metallicities as for the SSPs. The IMF however was not varied.
Finally, we generated 1'080 CSPs incorporating not only the SFR but also the chemical evolution as derived from chemodynamical galaxy models by Samland. Apart from the integrated spectra, the library also provides 18 integrated colours, 31 indices, and 23 other properties for each stellar population and for each of the 221 timesteps. BLoIS 1.0 contains 7'128 stellar populations and roughly 1.6 Mio. integrated spectra.
Pieter Westera Stellar Populations in HII Galaxies
Abstract: We analyse the stellar content of a large number of HII galaxies from the continua and absorption features of their spectra using population synthesis methods, in order to gain information about the star formation histories of these objects. We find that all galaxies of our sample contain an old stellar population that dominates the stellar mass, and in a majority of these, we also found evidence for an intermediate-aged population on top of the presently bursting, ionizing young generation. We thus advocate that starbursts in HII galaxies are not isolated, but are generally embedded in episodes that should have durations of the order of 50 millions of years. We furthermore favour evolution models that forecast the presence of an older population than the present young generation, either by a slow continuous star formation process, or by the presence of former bursts.
Yoshihiko Yamada Spectroscopic Age and Metallicity of Elliptical Galaxies
Abstract: We obtained extremely high quality optical spectra of 13 elliptical galaxies in Virgo cluster. With those spectra we derived ages and metallicities by using $H\gamma-\sigma$ index which can break age-metallicity degeneracy. The power of this index and high quality data allow us to derive not only age and mean metallicity but also metallicities of each element. There are considerably age dispersion in low sigma galaxies, and correlations which suggest complex star formation history such as [Mg/Fe]-sigma relation etc.
Sukyoung Yi GLOBULAR CLUSTERS AS PROBES OF GALAXY EVOLUTION
Abstract: If globular clusters form during major mergers between galaxies their age distribution should provide a strong test to galaxy formation theories. We present the results of our analysis on the UBV photometric data of globular clusters in the elliptical galaxy NGC 5128 (Cen A). We used U-B as metallicity indicator. We show that, unlike other popular broadband colours (e.g., V-I), U-B is free from the age-metallicity degeneracy and thus uniquely determines metallicity using Milky Way cluster data. Then, we apply the technique to the clusters of NGC 5128 and found the following. There is a large spread in U-B, which corresponds to [Fe/H] of -2.3 through possibly over +0.3 and a large spread in B-V, which corresponds to ages of 2 through 13 Gyr. Yet, for a given metallicity, the scatter in age is very small. The derived mean age estimate gradually decreases with increasing metallicity, indicating a strikingly well-defined age-metallicity relation, unseen anywhere ever before. The result, if interpreted naively, supports the scenario in which globular clusters form episodically throughout redshifts since early universe, a prediction of hierarchical galaxy formation scenarios. We show that an even stronger test can be made if far-UV data, which can be obtained using HST and GALEX, are additionally provided.
Suk-Jin Yoon An Aligned Stream of the Most Metal-Poor Clusters in the Halo of the Milky Way
Abstract: Authors: Suk-Jin Yoon (1,2), Young-Wook Lee (2), & Sukyoung Ken Yi (1) (1) Astrophysics, Oxford University, Keble Road, Oxford, UK (2) Center for Space Astrophysics, Yonsei University, Seoul, Korea
Abstract: One of the long-standing problems in modern astronomy is the curious division of Galactic globular clusters, the ``Oosterhoff dichotomy", according to the properties of their RR Lyrae stars. Here, we report that most of the lowest-metallicity ([Fe/H] $<$ -2.0) clusters, which are essential to an understanding of the phenomenon, display a planar alignment in the outer halo. This alignment, combined with evidence from kinematics and stellar population, indicates a captured origin from a satellite galaxy, most probably from the Large Magellanic Cloud. We show that, together with the horizontal-branch evolutionary effect, the factor producing the dichotomy could be a small time-gap between the cluster-formation epochs in the Milky Way and the satellite. The results oppose the traditional view that the metal-poorest clusters represent the indigenous and oldest population of the Galaxy.
Manuela Zoccali Chemical Abundances in the Galactic Bulge
Abstract: We present a programme aimed to obtain high resolution spectra for ~800 bulge stars with GIRAFFE and 56 bulge stars with UVES, using the FLAMES facility on UT2. The data for the first half of the target stars have been collected during last August. This database will allow us to reach the following scientific results: 1) Determine the metallicity distribution of the Galactic bulge for a sample of unprecedented size, 2) Set the bulge field and globular cluster metallicities on the same scale, 3) Determine the detailed distribution of elemental ratios as a function of metallicity, hence getting insight into the timescale of bulge formation, 4) Check whether individual families can be recognized in the bulge, characterized by special values of the elemental ratios, suggestive of a bulge formation by assembly of sub-units, 5) Detect (or set limits to the number of) disk stars with solar abundance ratios that might have been diverted into the bulge by the bar, and 6) Establish whether radial gradients exist in any of the measured quantities.