We analyse the star-forming (SF) properties of the two brightest galaxies in the IC 65 group of galaxies and that of the four newly detected dwarf galaxies in the area of the group. The dIrr galaxies around the IC 65 contain a number of HII regions which show a range of stellar ages, and provide an evidence of propagating SF. The two brightest group galaxies show SF rates of ∼ 1 − 2 M⊙ yr−1, and can fuel the current SF level for about the next 3 – 7 Gyr.

The combination of stellar population synthesis models and photoionization models allows a better understanding of the spectral features of HII regions and HII galaxies. In this work we show that sampling effects in the initial mass function (IMF) are very important in the low cluster mass case. To this aim, we compute photoionization models ionized by realistic clusters made up of various combinations of individual stars and clusters made up with a synthesis model. We discuss the differences in the position on diagnostic diagrams and their implications.

We present a new method for measuring the recent star formation history (SFH) of galaxies from their 4000Å break and Balmer absorption line strength. By making use of the whole 3750-4150Å spectral region, the method achieves a higher signal-to-noise ratio than traditional indices. The new technique is ideally suited to finding evidence for weak or old starbursts in good quality spectra, or studying post-starburst galaxies at high redshift. On application to massive, bulge dominated galaxies in the SDSS, we find clear correlations between the recent star formation history of bulges and the properties of the AGN.

Chemodynamical disc galaxy simulations calibrated with stellar populations synthesis models allow to build mock multi-wavelength images from numerical simulations. The morphological evolution of the mass and colour distributions can thus be simultaneously followed. We present the evolution of the stellar disc and bar structural parameters and summarize a number of important results we got in the recent past.

The evolution of stellar disks is of great importance for understanding many aspects of galaxy formation. In this work we perform stellar population synthesis on radially resolved photometry of 564 disk galaxies from the SDSS DR5, selected to have both spectra of the central regions and photometry. To explore fully the multi-dimensional likelihood space defined by the output parameters of the spectral synthesis, we use Markov Chain Monte Carlo to quantify the expectation values, the uncertainties and the degeneracies of the parameters. We find good agreement between the parameter values obtained using the SDSS broad-band colors and the spectra respectively. In general the derived mean stellar age and the best-fit stellar metallicity decline in value from the galaxy center to the outer regions (around 1.5 half-light radii), based on sub-samples defined by concentration index. We also find that the radial dependency of the stellar population parameters exhibits a significant variation, and this diversity is likely related to morphology and the physics of star formation.

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.

We analyse a sample of 1,652 elliptical galaxies morphologically selected from the SDSS DR4 with respect to their stellar population properties such as luminosity weighted ages, metallicities and α/Fe element abundance ratios. We confirm and statistically strengthen earlier results that all three stellar population parameters correlate with velocity dispersion, hence galaxy mass. Most surprisingly and differently from previous work, however, these scaling relations turn out to be independent of environmental density for the bulk of the population. This implies that the formation epochs and timescales of the stellar populations in massive galaxies are entirely independent of the environmental density and only driven by galaxy mass. At the low-mass end some fraction of the galaxies show signs of recent star formation on top of the general downsizing trend. It is only the fractional amount of such rejuvenated galaxies that reveals strong dependence with environment. The influence of the environment apparently undergoes a phase transition at about z∼ 1. An early galaxy formation phase without environmental dependence is followed by a rejuvenation phase at redshifts below z∼ 1 affecting mostly low-mass galaxies, during which the environment plays a crucial role.

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 combine together physical parameters estimates for a large sample of galaxies drawn from the Sloan Digital Sky Survey Data Release Two (SDSS DR2), spanning wide ranges in galaxy properties, in order to provide a census of the physical parameters of galaxies in the local Universe. Stellar metallicities, masses and ages for this sample have been estimated comparing the strengths of selected absorption features in each observed spectrum to a comprehensive Monte Carlo library of star formation histories, following a Bayesian statistical approach. This allows us also to derive the total amount of metals locked up in stars today, and hence the average stellar metallicity of galaxies in the local Universe, finding a value of . We also quantify the relative contribution to the total densities of mass and metals in stars from galaxies with different properties.

We present a study of the morphologies and stellar content of the galaxies in the central ∼ 74”×64” region of the galaxy cluster Abell 2218 (see Fig. 1). The spectroscopic data were obtained with the integral field unit PMAS (Roth et al. 2005) in the PPAK mode (Verheijen et al. 2004; Kelz et al. 2006), at the 3.5 m telescope of the Calar Alto Observatory. The covered wavelength range was 4650–8000 Å, with a spectral resolution FWHM∼ 10Å. These data were combined with with deep HST/ACS F475W, F555W, F625W and F850LP imaging, and additional data from the literature.

In Fig. 2 we show the rest-frame B-V vs. MV colour-magnitude diagram for the identified cluster members. The data are segregated according to an objective morphological classification based on the Sérsic index. Contrary to previous results (e.g. Ziegler et al. 2001; Smail et al. 2001) there is a clear indication that the cluster population is not dominated by early-type galaxies, and that there exists an almost parity between early- and late-type objects. In addition, the late-type galaxies spread over a wider range of colours and luminosities with respect to the early-types. This indicates that early-type objects are more massive and have older stellar populations, while late-type galaxies are less massive and exhibit a wider range of stellar population properties.

The results agree with the two-steps scenario for the evolution of galaxies in clusters (e.g. Poggianti 2003), which explains the co-existence of a primordial population of early-type galaxies formed at early epochs, with an additional population of late-type galaxies that have been captured by the cluster, infalling, suffering a short enhancement of the star formation that is later quenched by the interaction with the environment, and that afterwards evolved passively, becoming redder and fainter. Finally, galaxy-galaxy interactions and dry merging processes were responsible for the building up of new massive spheroidal galaxies.

Full details are given in Sánchez et al. (2007).

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.

We describe our results on multi-colour observations of extremely red galaxies found in two gravitational lensing clusters (Abell 1835 and AC114). Applying a colour criteria of R-K≥ 5.6 we have selected 12(10) EROs, of which 10(4) have no R-band detection. 5 of these objects have exceptional red colours (R-K>7.5). We compare their colours with other galaxy populations, like distant red galaxies and infrared detected extremely red galaxies, in order to differentiate between them.

Properties related to dust attenuation and star formation of an UV selected sample of intermediate redshift galaxies are presented in this work. We find hints of a decrease of the LIR/LFUV ratio with increasing redshift at low values of the total luminosity. Downsizing is observed at all redshifts, and the SSFR is found to increase with increasing redshift at all stellar masses.

Spiral galaxies can be affected by interactions in clusters, that also may distort the internal velocity field. If unrecognized from single-slit spectroscopy, this could lead to a wrong determination of the maximum rotation velocity as pointed out by Ziegler et al. 2003. This parameter directly enters into the Tully--Fisher relation, an important tool to investigate the evolution of spiral galaxies. To overcome this problem, we measure the 2D-velocity fields by observing three different slit positions per galaxy using FORS2 at the VLT providing us with full coverage of each galaxy and an adequate spatial resolution. The kinematic properties are compared to structural features determined on the HST/ACS images to assess possible interaction processes. As a next step, the whole analysis will be performed for three more clusters, so that we will be able to establish a high-accuracy TFR for spirals at z∼0.5.

We summarise the current status of our project to identify and classify ~ 6-10 galaxies thanks to strong gravitational lensing. Building on the detailed work by Richard et al. (2006), we present results from new follow-up observations undertaken with the ACS/HST and the Spitzer space telescope and compare our results with findings from the Hubble Ultra-Deep Field (UDF).

We investigate how morphological information of galaxies help us to improve photometric redshift estimation. Using a catalog of morphologically classified bright galaxies derived from the Third Data Release of the Sloan Digital Sky Survey, the statistical properties of different photometrical parameters as a function of morphology are examined. Parameters that best correlates with morphology are used as an additional information to better estimate the redhift. Improvements of several percent are obtained.

The study of stellar populations is a discipline that is highly dependent on both imaging and spectroscopy. I discuss techniques in different regimes of resolving power: broadband imaging (R∼4), intermediate band imaging (R∼16, 64), narrowband spectral imaging (R∼256, 1024, 4096). In recent years, we have seen major advances in broadband all-sky surveys that are set to continue across optical and IR bands, with the added benefit of the time domain, higher sensitivity, and improved photometric accuracy. Tunable filters and integral field spectrographs are poised to make further inroads into intermediate and narrowband imaging studies of stellar populations. Further advances will come from AO-assisted imaging and imaging spectroscopy, although photometric accuracy will be challenging. Integral field spectroscopy will continue to have a major impact on future stellar population studies, extending into the near infrared once the OH suppression problem is finally resolved. A sky rendered dark will allow a host of new ideas to be explored, and old ideas to be revisited.