A comparison is carried out among the star formation histories of early-type galaxies in fossil groups, clusters and low density environments. Although they show similar evolutionary histories, a significant fraction of the fossils are younger than their counterparts, suggesting that they can be precursors of the isolated ETG galaxies.

Double bars might be the key mechanisms to transport gas to the very central regions of galaxies, so double-barred galaxies are key objects to better understand the galaxy formation and evolution scenarios. In order to disentangle the role of double bars in the galaxy build up, we are performing a whole kinematical and stellar population analysis of these objects from high S/N spectroscopic data.

During the last decade, the development of more sophisticated surveys allows the exploration of the chemical enrichment of galaxies and their environment at different cosmic times. In this context, it has been suggested that galactic winds play a fundamental role in the regulation of the star formation and the transportation of metals outside the galaxies. In this work, we study the influence of Supernovae winds in the chemical evolution of galaxies and the intergalactic medium by employing cosmological numerical simulations within a hierarchical Universe. We focus on the origin and evolution of the mass-metallicity relation (MZR).

The Tully-Fisher Relation (TFR) is of fundamental importance for galaxy formation as it provides information about the relation between the baryonic content of galaxies and the depth of their dark halos potential wells. In recent years, it has been possible to study this relation at different redshifts. However, there are still controversies about its origin and evolution. In this work, we try to address the origin of the Tully-Fisher Relation by employing cosmological hydrodynamical simulations.

Analysis of integrated spectra of star clusters in the Magellanic Clouds can bring important information for studies on the chemical evolution of the Clouds. The aim of the present work is to derive ages and metallicities from integrated spectra of 15 star clusters in the Small Magellanic Cloud (SMC), some of them not studied so far. Making use of a full spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models available in the literature. We derived ages and metallicities for the sample clusters employing the codes STARLIGHT and ULySS. Out of the 15 clusters in our sample, 9 are old/intermediate age clusters and 6 are young clusters. We point out the results for the newly identified as old/intermediate age clusters HW1, NGC 152, Lindsay 3 and 11. We also confirm old ages for NGC 361, NGC 419 and Kron 3, and the oldest well-known SMC cluster NGC 121.

At high-z the most superdense massive galaxies are supposed to be the result of gas-rich mergers resulting in compact remnant (Khochfar & Silk (2006); Naab et al. (2007)). After this, dry mergers are expected to be the mechanism that moves these very massive galaxies towards the current stellar mass size relation. Whitin these merging scenarios, a non-negligible fraction (1-10%) of these galaxies is expected to survive since that epoch retaining their compactness and presenting old stellar populations in the past universe.Using the NYU Value-Added Galaxy Catalog (DR6), we find only a tiny fraction of galaxies (~0.03%) with re ≤ 1.5 kpc and M* ≥ 8x1010M⊙ in the local Universe (z~0.2). Surprisingly, they are relatively young (~2Gyr) and metal rich ([Z/H]~0.2) These results have been published in Trujillo et al. (2009)

We observed two fields near M32 with the ACS/HRC (Program GO-10572, PI: T. Lauer) on board the Hubble Space Telescope, located at distances of about 1.8' and 5.4' (hereafter F1 and F2, respectively) from the center of M32. To obtain a very detailed and deep color-magnitude diagram (CMD) and to look for short period variability, we obtained time-series imaging of each field in 32-orbit-long exposures using the F435W (B) and F555W (V) filters, spanning a temporal range of 2 days per filter. We focus on our detection of variability on RR Lyrae variable stars, which represents the only way to obtain information about the presence of a very old population (larger than 10 Gyr) in M32 from optical data. Here we present results obtained from the detection of 31 RR Lyrae in these fields: 17 in F1 and 14 in F2. We claim we detected 7+4−3 RR Lyrae variables belonging to M32 in F1 thus indicating the presence of a metal-poor ancient population in M32.

We present the Fundamental Plane (FP) of field early-type galaxies at 0.5 < z < 1.0. Our project is a continuation of our efforts to understand the formation and evolution of early-type galaxies in different environments. The target galaxies were selected from the comprehensive and homogeneous data set of the Gemini/HST Galaxy Cluster Project. The distant field early-type galaxies follow a steeper FP relation compared to the local FP. The change in the slope of the FP can be interpreted as a mass-dependent evolution. Similar results have been found for cluster early-type galaxies in high redshift galaxy clusters at 0.8 < z <1. Therefore, the slope change of the FP appears to be independent of the environment of the galaxies.

Spectral synthesis of stellar populations has proven to be one of the most powerful methods to decompose the different mixtures of stellar contributions in galaxies, and applications of this technique routinely appear in the literature nowadays. Our group, for instance, the SEAGal (Semi Empirical Analysis of Galaxies) collaboration, has derived the star formation history of all galaxies in the SDSS with the starlight code, obtaining various results of astrophysical interest. As any other fossil method, the results rely heavily on high spectral resolution evolutionary synthesis models. To test this model dependence we run starlight on samples of star-forming and passive galaxies from the SDSS using different sets of models.

We explore models using “Padova 1994” and modified “Padova” evolutionary tracks with a different receipt for the asymptotic giant branch phase, as well as different stellar libraries (STELIB versus MILES+Granada). We then compare derived properties such as mean age, mean metallicity, extinction, star-formation and chemical histories. Despite a broad brush agreement, systematic differences emerge from this comparison. The different evolutionary tracks used lead to essentially the same results, at least insofar as optical spectra are concerned. Different stellar libraries, on the other hand, have a much bigger impact. The newer models produce quantifiably better fits and eliminate some pathologies (like suspicious combinations of base elements, systematical spectral residuals in some windows, and, sometimes, negative extinction) of fits derived with STELIB-based models, but there are still some caveats. These empirical tests provide useful feedback for model makers.

Spectral synthesis is largely used in the literature to decompose stellar populations with integrated light of galaxies as if the star formation histories (SFH) could be approximated by single bursts. In the case of our method (see http://www.starlight.ufsc.br/ for the SEAGal - Semi Empirical Analysis of Galaxies - collaboration), the starlight code combines the spectra of simple stellar populations (SSP) of different ages and metallicities, computed with high spectral resolution evolutionary synthesis models of Bruzual & Charlot (2003), to reproduce the observed spectrum of a given galaxy from which we can derived a huge amount of galaxy properties such as: the population vector, stellar mass, extinction and others. We have done that for all galaxies of the SDSS database. Despite all the results of astrophysical interest, we have decided to use continuous composite stellar models (CSP) with a single metallicity and a star formation rate ∝ τ−1e−t/τ, where t stands for the time that the star formation started (1, 5 and 13 Gyr ago) and τ is the attenuation factor chosen to be 1, 5, 10 and 99 Gyr. When the attenuation with respect to the time t is very low, this mimics a single burst, and when we choose it to be very large (99 Gyr), this is almost a constant star formation rate. We have perturbed each composite model spectrum 10 times with three distinct signal/noise ratios equal to 10, 15 and 30 in λ0 = 4020 Å. These models were inserted into our code to verify how a picture of single bursts deal with continuous composite models of galaxies. Our CSP models can be easily integrated in an analytical form. Therefore, we have derived theoretically the mean ages and metallicities and compared them to the output derived by the synthesis. We can see that the synthesized mean ages weighted by light tend to be lower than the models, due to the degeneracies involved in the problem. The same thing can be found for the mean metallicities weighted by light, which tend to be higher for the output values.

The goal of this work is to determine the properties of the stellar populations in a sample of LIRGs and ULIRGs. Using the ages as a clock we investigate: a) whether LIRGs-ULIRGs evolve into Radio Galaxies and QSOs; b) whether cool LIRGs-ULIRGs can evolve into warm LIRGs-ULIRGs; c) the merger sequence deduced from the morphological studies is reflected in the properties of the stellar populations. Using evolutionary synthesis models with high spectral resolution stellar libraries we have found that the intermediate age stellar population dominates at optical wavelengths. The stellar population in LIRGs is similar to ULIRGs and ULIRGs-QSOs transition objects.

Massive O- and B-type stars are “cosmic engines” in the Universe and can be the dominant source of luminosity in a galaxy. Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity.

We find that 90% of the observed stars show some variability with only 4% showing significant variability over the 4-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while 20% of the sample consists of known binaries, we find that another 15-30% of the sample shows indications of binarity.

This work has been supported in part by a grant from the Vanderbilt University Learning Sciences Institute, NASA grant # NNX08AV70G, and NSF Career grant AST-0349075.

As part of our near-infrared photometric survey of nearby dwarf galaxies, we present recent results for Leo I and Leo II dwarf spheroidal galaxies. We selected O- and C-rich AGB stellar populations using two-color diagrams and compared their luminosity functions and star counts with the predictions of the most recent AGB theoretical models.

In recent years, a series of papers (Kroupa & Weidner 2003, Weidner & Kroupa 2004, Weidner & Kroupa 2005 and Weidner & Kroupa 2006, WK06 from now on) have proposed that the stellar content of an entire galaxy may not be well described by the same initial mass function (IMF) that describes the distribution of stellar masses in the star clusters, where these stars form. The reason is that star clusters also form with a cluster mass function (CMF), which is a power law with a power law index of ~−2. If the lowest mass clusters are of masses smaller than the physical upper mass limit for stars they will be deficient in high mass stars. Therefore, if the stellar content of all clusters is added together, making up the Integrated Galactic Initial Mass Function (IGIMF), the distribution of stellar masses may be steeper at the high mass end, depending on the exact shape of the CMF.

We describe and analyze the color dispersion of LRG's at redshifts, z=0.4-0.5.

The mid-ultraviolet is an important diagnostic region due to its sensitivity to the hottest stars of a stellar population. Sources of mid-UV flux include main sequence turn-off stars, the basic clocks of stellar evolution, and also blue horizontal branch stars and blue stragglers. We describe some observed trends in mid-UV colors and spectral indices.

We present the first results of a comprehensive HST study of the star-formation history of Fornax dSph, based on WFPC2 imaging of 7 Fornax fields. Our observations reach the oldest main-sequence turnoffs, allowing us to address fundamental questions of dwarf galaxy evolution, such as the spatial variations in the stellar content, and whether the old stellar population is made up of stars formed in a very early burst or the result of a more continuous star formation.

The value of different forms of energy contained in TDC region as well as the structure and physical characteristics of star formation in the Taurus Dark Clouds are analyzed.

We present a measurement of the rate of high-z Type Ia supernovae (SNe Ia) using multi-epoch observations of Subaru/XMM-Newton Deep Field (SXDF) with Suprime-Cam on the Subaru Telescope. Although SNe Ia are regarded as a standard candle, progenitor systems of SNe Ia have not been resolved yet. One of the key parameters to show the progenitor systems by observations is the delay time distribution between the binary system formation and subsequent SN explosion. Recently, a wide range of delay time is studied by SN Ia rates compared with an assumed cosmic star formation history. If SNe Ia with short delay time are dominant, the cosmic SN Ia rate evolution should closely trace that of the cosmic star formation. In order to detect a lot of high-z SNe Ia and measure SN Ia rates, we repeatedly carried out wide and deep imaging observations in the í-band with Suprime-Cam in 2002 (FoV~1 deg2, mi < 25.5 mag). We obtained detailed light curves of the variable objects, and 50 objects are classified as SNe Ia using the light curve fitting method at the redshift range of 0.2 < z < 1.3. In order to check the completeness and contamination of the light curve classification method, we performed Monte Carlo simulations and generated ~100,000 light curves of SNe Ia and II from templates. The control time and detection efficiency of the SN survey are also calculated using the artificial light curves. We derived an increasing trend of rates at around z ~ 1.2. Our results are almost consistent with other SN Ia rate results from low-z to high-z. Our results are the first results of high-z SN Ia rates with large statistics using light curves obtained by ground based telescopes, and give us visions of the SN rate studies for the future.

We discuss the possible angular momentum loss mechanisms in AM Her type cataclysmic variables and their corresponding mass loss rates using the observed physical parameters of them.