We will review some recent advances in understanding the evolution of stellar populations in galaxies at relatively higher redshifts (z ≳ 0.5). We will focus on “mass assembly”, “down-sizing” and “high-z zoo” which have been among the most major topics and have seen great observational achievements in the past few years. In particular, wide-field near-infrared surveys, large spectroscopic surveys, and the Spitzer observations at infrared wavelengths, have unveiled underlying stellar masses and dusty star formation in high-z galaxies, which have been crucial in making such recent progresses.

The mid infrared emission of early type galaxies traces the presence of intermediate age stellar populations as well as even tiny amounts of ongoing star formation. Here we discuss high S/N Spitzer IRS spectra of a sample of Virgo early type galaxies, with particular reference to NGC 4435. We show that, by combining mid infrared spectroscopic observations with existing broad band fluxes, it is possible to obtain a very clean picture of the nuclear activity in this galaxy.

We present the deepest, widest color-magnitude diagrams at mid infrared wavelengths ever produced for the Large Magellanic Cloud (LMC). The SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the LMC comprises a seven by seven degree mapping of the entire LMC in each of the Spitzer IRAC and MIPS bands. The present work includes mid and near infrared photometry between 1.25 and 24 microns. These data are used to identify 100's of thousands of red giants and 10's of thousands of asymptotic giant branch stars and supergiants which are classified as oxygen rich, carbon rich, or “extreme” mass losing stars, among others. SAGE will revolutionize the study of evolved stars and mass input into the ISM in the LMC because its deep photometry is sensitive to all significant mass losing sources in the galaxy and provides the context of the overall stellar populations which give rise to the mass losing AGB stars. The SAGE data can be used to help synthesize and assess models of star forming galaxies at high redshift for a range of ages and chemical compositions.

We present a detailed stellar population analysis of 27 massive elliptical galaxies within 4 very rich clusters at redshift z∼0.2. We obtained accurate estimates of the mean luminosity-weighted ages and relative abundances of CN, Mg and Fe as functions of the galaxy velocity dispersion, σ. Our results are compatible with a scenario in which the stellar populations of massive elliptical galaxies, independently of their environment and mass, had formation timescales shorter than ∼1 Gyr. This result implies that massive elliptical galaxies have evolved passively since, at least, as long ago as z∼2. For a given galaxy mass the duration of star formation is shorter in those galaxies belonging to more dense environments. Finally, we show that the abundance ratios [CN/Fe] and [Mg/Fe] are the key “chemical clocks” to infer the star formation history timescales in ellipticals. In particular, [Mg/Fe] provides an upper limit for those formation timescales, while [CN/Fe] apperars to be the most suitable parameter to resolve them in elliptical galaxies with σ<300 km s−1.

We present an emission-line diagnostic analysis of integral-field spectroscopic observations that cover the circumnuclear ring-like regions in a small number of spiral galaxies. We concentrate on the specific case of the Sa galaxy NGC 7742, which hosts a spectacular circumnuclear starburst ring and nuclear regions characterised by low-ionisation emission. The gas in the ring rotates in the opposite sense to the stars in the galaxy, suggesting a recent merging or acquisition event. The combination of integral-field measurements for the Hα+N[ii] emission lines from DensePak and the Hβ and [Oiii] emission from SAURON allows the construction of diagnostic diagrams that highlight the transition from star formation in the ring to excitation by high-velocity shocks or by an AGN near the centre. DensePak measurements for the [Sii] line ratio reveal very low gas densities in the ring, Ne<100 cm−3, characteristic of massive Hii regions. Comparison with MAPPINGS III models for starbursts with low gas densities shows that the ring is of roughly solar metallicity. We suggest that NGC 7742 cannibalised a smaller galaxy rich in metal-poor gas, and that star formation episodes in the ring have since increased the metallicity to its present value.

In this work we review the details, with emphasis on the near UV (3000-4500 Å), of the molecular database and the continuous opacity sources as implemented in the spectrum synthesis code used to calculate the spectral library presented in Coelho et al. (2005). We discuss our recent and future efforts towards the improvement of the calculation in this spectral range.

We report on recent progress in the modelling of the near-IR spectra of young stellar populations, i.e. populations in which red supergiants (RSGs) are dominant. First, we discuss the determination of fundamental parameters of RSGs from Phoenix model fits to their near-IR spectra; RSG-specific surface abundances are accounted for and effects of the microturbulence parameter are explored. New population synthesis predictions are then described and, as an example, it is shown that the spectra of young star clusters in M 82 can be reproduced very well from 0.5 to 2.4 μm. We warn of remaining uncertainties in cluster ages.

We present deep ground-based B and R observations of 12 fields in the Small Magellanic Cloud (SMC). The resulting color-magnitude diagrams (CMDs) reach the oldest main-sequence (MS) turnoff at MR∼3.5 and reveal the stellar population differences between the part of the galaxy facing the Large Magellanic Cloud (LMC) and an area on the opposite side. In the Southern part of the galaxy, we found that there are still intermediate-age stars as far as 4 kpc from the SMC center. The Chemical Enrichment History (CEH) in one of our SMC fields is also presented.

The chronology of bulge and disk formation is a major unsolved issue in galaxy formation, which impacts on our global understanding of the Hubble sequence. We present colors of the nuclear regions of intermediate-redshift disk galaxies, with the aim of obtaining empirical information of ages of bulges at 0.1 < z < 1.3. We work with a sample of 248 galaxies (123 inclined + 125 face-on) from the HST Groth Strip Survey (Groth et al. 1994) and another one with 404 objects (214 inclined + 190 face-on) from the HST GOODS-N field (Giavalisco et al. 2004), covering redshifts 0.1 z < 1.3. Those samples are apparent-diameter limited at RF814W < 1.4”, and have inclination 50° < i < 70° for the inclined samples and i < 50° for the face-on ones. We find that, as in the Local Universe, the minor axis color profiles are negative (bluer outward), and fairly gentle, indicating that bulge colors are not distinctly different from disk colors. We apply a conservative criterion to identify bulges and potential precursors of present-day bulges, based on nuclear excess surface brightness above the exponential profile of the outer parts. For galaxies with central brightness excesses, rest-frame color distributions show a red sequence. In contrast, galaxies without central brightness excesses show typical colors of star-forming populations. Clearly, something had truncated star formation in many high-density cores, already at z = 1. The truncation epoch is uncertain, 1.5 < z < 10. The color-magnitude distribution of intermediate-z bulges shows more color dispersion than that of bulges in the Local Universe. Most of bulges are as red as local bulges, while the remainder are significantly bluer, a possible sign of late bulge formation.

Massive star formation in the central regions of spiral galaxies plays an important role in the dynamical and secular evolution of their hosts. Here, we summarise a number of recent investigations of the star formation history and the physical conditions of the gas in circumnuclear regions, to illustrate not only the detailed results one can achieve, but also the potential of using state-of-the-art spectroscopic and analysis techniques in researching the central regions of galaxies in general. We review how the star formation history of nuclear rings confirms that they are long-lived and stable configurations. Gas flows in from the disk, through the bar, and into the ring, where successive episodes of massive star formation occur. A detailed analysis of the ring in NGC 7742, where we use similar data to determine the physical conditions of the line emitting gas using a combination of ionisation and stellar population modelling, is described in a second poster paper (these proceedings, p. 000; Mazzuca et al. 2006).

A great effort is being made by the international Virtual Observatory community to build tools ready to be used by scientists. Presently, providing access to theoretical spectra in general, and synthetic spectra of galaxies in particular, is a matter of current interest in the Virtual Observatory. Several ways of accessing such spectra are available. We present two of them for accessing PEGASE.HR evolutionary synthesis models: HTTP-access to a limited number of parameters using Simple Spectral Access Protocol (SSAP), and full-featured WEB-service based access using Common Execution Architecture (CEA).

In the last years we started a long-term project devoted to obtain a complete photometric and spectroscopic screening of the stellar populations of the LMC globular cluster system and surrounding fields. The ultimate goals of this project are as follows:

• • The definition of reliable and homogeneous cluster metallicity and age scales from high quality, high resolution spectra and color-magnitude diagrams.

• • The detailed study of the chemical abundance patterns of iron-peak, alpha-, s- and r-process elements, in order to constrain the star formation and chemical enrichment timescales of both the cluster and field populations and check for possible self-enrichment in the clusters.

The discovery of an excess of light in the far-ultraviolet (UV) in 1969 in elliptical galaxies was a major surprise. While it is now clear that this UV excess (UV-upturn) is probably caused by an old population of helium-burning stars. Han et al. (2002, 2003) proposed a binary model for the formation of hot subdwarfs (helium burning stars) and the model can reproduce the observations in our Galaxy. By applying the binary model to the study of evolutionary population synthesis, we have obtained an a priori model for the UV-upturn of elliptical galaxies. The model shows that the UV-upturn is most likely resulted from binary interactions and it is universal (not very much metallicity-dependant) in ellipticals. This has major implications for understanding the evolution of the UV-upturn and elliptical galaxies in general; contrary to previous postulates, it implies that the UV-upturn is not a sign of age, but could be a potentially powerful indicator for a recent minor burst of star-forming activity.

We present first results from an HST/ACS imaging survey of stars and star clusters in five nearby spiral galaxies. This contribution concentrates on NGC 1313, a highly distorted late-type barred spiral. We compare the field star and cluster formation histories in our three ACS pointings for this galaxy. In one pointing, both the cluster and field star age distributions show clear evidence for a ramp-up in the star formation rate about 108 years ago.

Based on FORS2-VLT long-slit spectroscopy, the analysis of the central absorption line indices of 9 S0 galaxies in the Fornax Cluster is presented. Central indices correlate with central velocity dispersions (σ0) as observed in ellipticals (E). However, the stellar population properties of these S0s indicates that the observed trends are produced by relative differences in age and α-element abundances and not in metallicity ([Fe/H]) as previous studies have found in E galaxies. The observed scatter in the line indices versus σ0 relations can be partially explained by the rotationally-supported nature of many of these systems. The presence of tighter line indices vs. maximum (circular) rotational velocity (VMAX) relations confirms this statement. It was also confirmed that the dynamical mass is the driving physical property of all these correlations and in our Fornax S0s it has to be estimated assuming rotational support.

The publicly available stellar database from SDSS contains many hundreds of metal-poor stars with large enhancements of carbon. The Galactic extension of SDSS, SEGUE, will identify several thousand more. Many of these Carbon-Enhanced Metal-Poor (CEMP) stars are likely to be enhanced in s-process elements created by AGB companions and dumped to the surviving member of a binary pair through either Roche-Lobe mass transfer or the operation of a stellar wind (CEMP-s stars). Based on previous high-resolution investigation of CEMP stars, an interesting subset of this sample is expected to show little or no s-process enhancement (CEMP-no stars).

Utilizing a novel technique of automatically fitting [Fe/H] and [C/Fe] for a large number of stars from SDSS through spectral synthesis methods, we are able to derive a new estimate of the frequency of CEMP stars as a function of metallicity for the largest sample of stars to date. Using this approach, we can also measure abundances (or limits) for species such as Sr and Ba, which can be used to roughly separate CEMP stars into the CEMP-s and CEMP-no classes.

We have recently obtained optical spectra for a large sample of young and intermediate-age star clusters in several nearby galaxies. The main aim of this programme is to carry out a detailed test of photometric and spectroscopic age- and metallicity indicators, but a first inspection of the data has also revealed emission lines in 3 clusters with ages of 30 Myrs or older. We identify these three objects as likely Planetary Nebula (PN) candidates and discuss their properties. Based on the cluster ages, the progenitor stars had initial masses in the range 3 to 7 M⊙, while the PN central stal luminosities and temperatures (estimated from emission line fluxes) are consistent with current masses close to 0.60 M⊙. These objects represent a rare opportunity to study PNe whose progenitor stars are known to be of intermediate masses, although detailed analysis is challenging because of the strong underlying stellar continuum from the cluster stars. Detection of 3 PNe in our sample appears consistent with expectations from stellar evolutionary theory.

The presence of blue straggler stars (BSs) as secure members of Galactic open clusters (OCs) poses a major challenge to the conventional picture of evolutionary population synthesis (EPS) based on the stellar evolution theory of single stars, since the major formation ways of BSs are all correlated with stellar interactions. With a working sample including 100 Galactic OCs with age ranging from 0.1 to 10 Gyr, the contributions of BSs to the integrated light of their host clusters are calculated on an individual cluster base. We also show in this work that the intrinsic evolutionary stages of OCs can be enormously misunderstood by the conventional simple stellar population (SSP) models, if the real/observed integrated spectral energy distributions (ISEDs) of OCs are the only thing that we can depend on and are fitted with ISEDs of conventional SSPs, and consequently the huge uncertainties in age and/or metallicity can be conservatively estimated at 50%. Thus, we strongly confirm that when the conventional EPS technique is used to study the properties of stellar populations in complicated systems such as galaxies, the contributions of BSs should be definitely taken into account in order to avoid big fitting mistake.

We are using Subaru/Suprime-Cam to survey the luminous resolved stellar populations in the outskirts of galaxies lying beyond the Local Group. We report here on first results from our analysis of the low mass edge-on galaxy, NGC 4244, lying at 4.4 Mpc. Red giant branch stars are clearly resolved in the outer disk and extraplanar regions and our preliminary stellar density maps suggest the presence of an extended and asymmetric stellar component reaching significant distances above the disk plane.

Long-slit spectra have been obtained with the Keck telescope for a sample of 11 early-type galaxies covering a range in luminosity. Rotation velocity and velocity dispersions, together with 20 Lick line-strength gradients have been measured to two effective radius. We transform line-strength gradients into age, metallicity and α/Fe. Galaxies show very shallow age gradients, strong metallicity gradients, and both positive and negative α/Fe gradients, which cannot be explained with simple outside-in scenarios of galaxy formation. We explore the correlation of the gradients with other global parameters of the galaxies, finding different behaviour for the two families of galaxies, luminous (boxy, core inner profile) and less luminous (disky, cuspy inner profile) galaxies.