The Star Formation History (SFH) of the Phoenix dwarf galaxy has been obtained using IAC-star and IAC-pop. The observations are based on WFPC2@HST. The results show a Star Formation Rate (SFR) decreasing with time and that star formation has happened in Phoenix up to 0.5 Gyr ago. The metallicity decrease with the stellar age: z>0.0007 for stars younger than 5 Gyr and z<0.0004 for stars older than 10 Gyr. Using the SFH as a function of galactocentric radius, the length scale αN of the star density distribution profile has been obtained as a function of the time. The results show that αN decreases smoothly with time, suggesting a sort of shrinking scenario for the evolution of Phoenix.

The stellar binary fraction in star clusters is a key factor in understanding the effects of binary stars on the properties and dynamical evolution of the host cluster. Using a very accurate stellar catalogue based on deep Hubble Space Telescope (HST) observations of the young rich Large Magellanic Cloud cluster NGC 1818, we assess its binary content. Based on artificial star tests we have established a method to very efficiently determine the probability of chance blends and superpositions. Combining the measured photometric errors and the superposition statistics, we construct synthetic colour-magnitude diagrams (CMDs) as a function of input binary fraction. The binary fraction of the cluster is then calculated by means of a Kolmogorov-Smirnoff (K–S) test between the synthetic and the observed CMDs. The likely binary fraction for this cluster is 50–70.

The outer regions of M31 contain significant substructure. Here we investigate the origins of the substructure in three fields close to the major axis of M31 using colour-magnitude diagrams produced from HST-ACS.

The Small Magellanic Cloud (SMC) is the only dwarf galaxy in the Local Group that is known to have formed and preserved populous star clusters continuously over the past 12 Gyr. Due to its proximity (≈ 60 kpc), stars can be resolved well below the oldest main sequence turnoff points. This facilitates accurate age and metallicity determinations without suffering from the age-metallicity degeneracy. Therefore, the SMC star clusters provide a unique closely spaced set of single-age, single-metallicity tracers to derive a well-sampled age-metallicity relation required for the understanding of the star formation history of this satellite galaxy. Up to date spectroscopically based metallicity estimates exist only for the small number of 7 clusters (Da Costa & Hatzidimitriou 1998). Our project now more than doubles the available data set by the observation of 10 additional clusters.

We analysed HST/WFPC2 colour-magnitude diagrams (CMDs) from 15 populous Large Magellanic Cloud (LMC) stellar clusters with ages between ∼0.3 Gyr and ∼3 Gyr. These (V, B-V) CMDs are photometrically homogeneous and reach typically V ∼22. Accurate and self-consistent physical parameters (age, metallicity, distance modulus and reddening) were extracted for each cluster by comparing the observed CMDs with synthetic ones. These determinations were made by means of simultaneous statistical comparison of MS fiducial lines and red clump position, offering objective and robust criteria to determine the best models. In general, the best models show a satisfactory fit to the data, adequately constraining the physical parameters of each cluster. The inferred spatial distribution of these clusters is roughly aligned with the LMC disk. The set of ages and metallicities homogeneously derived here can be used to calibrate integrated light studies applied to distant galaxies.

1. The data. We study detailed star formation histories (SFH) of 14 dwarf galaxies in the central parts (≤ 300 Kpc) of the two nearby galaxy groups: M 81 (D=3.6 Mpc) and Cen A (D = 3.8 Mpc). The images of 7 galaxies were selected from the sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope within our prog. 9771 & 10235, (PI I.Karachentsev). The rest of the images (ACS and WFPC2) were taken from the Hubble Archive (prog. 9884, 5898 and 6964).

How clumpy are galactic halos? Recent observations around both the Milky Way and the Andromeda galaxy (M31) have revealed numerous faint stellar streams and dwarf galaxies, leading to the belief that more of these may yet remain undetected. In this contribution, we present the map produced from the Megacam/CFHT survey that our group has undertaken in the outer halo of M31 and that, for the first time, gives a deep panoramic view of a significant region of the outer halo of a spiral galaxy. This panoramic survey, which covers ∼ 60 sq. deg. of the southern quadrant of the M31 halo, extends the WFC/INT survey of the inner halo (Ferguson et al. 2002) from a projected distance of ∼ 50 to ∼ 150 kpc. It is deep enough to cover three magnitudes below the tip of the red giant branch of stellar populations at the distance of M31. The survey reveals:

• • Three faint dwarf galaxies with absolute magnitudes in the range -7.3 < M_V < -6.4 and the most remote M31 globular cluster at a projected distance of ∼ 120 kpc from M31 (see Martin et al. 2006 for more details).

• • That the giant stream of Ibata et al. (2001) covers a much wider area than previously expected from shallower surveys, has an apocenter at 125±25 kpc from M31 and is probably due to the accretion of a small disk galaxy.

• • A new stellar stream or shell approximately perpendicular to the minor axis of M31 at a projected distance of 120 kpc and with a metallicity of [Fe/H] ∼ -1.5 (assuming it is at the distance of M31).

• • A new stellar stream along the ma jor axis of M31 that extends to at least 100 kpc from M31 with [Fe/H] ∼ -1.3 (once again assuming it is at the distance of M31).

• • Regions void of any stellar structure brighter than 34-35 mag/arcsec2 at a distance of 100 to 130 kpc from M31.

The survey shows that the outer halo of the Andromeda galaxy is very structured, in qualitative agreement with recent cosmological simulations (e.g. Bullock & Johnston, 2005).

The Canis Major overdensity (CMa) was initially proposed to be the remnant of a tidally disrupting dSph galaxy. Since its nature is still subject of debate, the goal of the present work was to conduct a large-scale RR Lyrae survey in CMa, in order to see if there is an overdensity of these stars. The survey spans a total area of ∼ 34 sq. deg. with observations in V and R filters, made with the 1.0m Jürgen Stock Schmidt telescope at the National Astronomical Observatory of Venezuela. Current results in a subregion, including spectroscopic observations, show that the small number of RR Lyrae stars found can be accounted for by the halo and thick disk components of our Galaxy.

We have undertaken a large, multi-colour, photometric, survey of distant (D > 500 kpc) Local Group dwarf galaxies with the Subaru SuprimeCam wide field camera. These data reach to below the horizontal branch level of these systems, to a depth equivalent to earlier HST WFPC2 studies but over an area ∼ 100 times larger, making them ideal for studies of the global stellar content and structural characteristics of these systems. All eight of our targets show radial gradients and spatially distinct, multiple structural components. This implies that dwarf galaxies in general possess multiple stellar components, akin to larger galaxies. Dynamical models of these systems which do not account independently and consistently for each individual density component may be limited in their applicability.

We are performing a uniform and unbiased imaging survey of the Large Magellanic Cloud (LMC), using the IRAC and MIPS instruments on board the Spitzer Space Telescope (Spitzer). Meixner et al. (2006) provides an overview of the project and initial results and their Table 1 (repeated here) outlines the survey's salient characteristics. In this project, we are surveying the agents of a galaxys evolution (SAGE), i.e. the interstellar medium (ISM) and stars, and their interaction on the galaxy wide scale of the LMC. Spitzer IRAC and MIPS images provide key insights into the life cycle of matter in a galaxy because the infrared emission from dust grains is an effective tracer of the ISM, star formation, and stellar mass-loss. Three key science goals determined the coverage and depth of the survey. The detection of diffuse ISM with column densities > 1.2×1021 H cm−2 permits detailed studies of dust processes in the ISM. SAGE's point source sensitivity enables a complete census of newly formed stars with masses >3 M⊙ that will determine the current star formation rate in the LMC. SAGE's detection of evolved stars with mass loss rates > 10−8 M⊙ yr−1 will quantify the rate at which evolved stars inject mass into the ISM of the LMC (Blum et al. 2006). The SAGE data are nonproprietary. The preliminary SAGE catalog of epoch 1 photometry, prepared by the SAGE Team and released to the public on January 3, 2006, contains over 4 million IRAC sources, band merged with 2MASS photometry and over 60,000 MIPS 24 micron sources. Preliminary estimates indicate that foreground Milky Way stars and background galaxies may comprise as much as 18% and 12%, respectively, of these catalogs. To learn more about the SAGE project: http://sage.stsci.edu/.

We present the result of a search for Cepheids in the Local Group dwarf irregular galaxy (DIG) Pegasus. We identified 20 Cepheid stars with periods 0d.6 < P < 15d.3. We have compared them with previously published Cepheids and we have carried out an accurate completeness analysis in order to obtain the fraction of them which are lost. Using their period-luminosity relation we obtain a distance for Pegasus of 950±30 Kpc.

Multi-object spectrographs available on 8-m class telescopes provide the unique opportunity to directly investigate the kinematical and chemical properties of significant samples of resolved stars in galaxies of the Local Group. We present here the first results concerning an extensive study of stellar populations of the Carina dSph galaxy, based on data collected with the multi-object spectrographs FORS2 and FLAMES, both available at VLT. Preliminary estimates concerning the radial velocity distributions of the different samples are presented.

During Cycle 14 a total of 113 HST orbits were secured to observe five isolated dwarf galaxies, namely Tucana, LGS3, LeoA, IC1613, and Cetus. The aim of the project is a full characterization of the stellar content of these galaxies, in term of their SFH, radial distributions, halo populations and variable stars. Deep (V≈29) F475W, F814W data allowed us to fully sample all the evolutionary phases from the tip of the Red Giant Branch (RGB) to well below the old Main Sequence Turnoff (MSTO). Here we describe the observational design, and the reduction and calibration strategy adopted. A comparison of the results obtained using two different packages, ALLFRAME and Dolphot, is presented.

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.

We present a progress report of a project to study the quantitative star formation history (SFH) in different parts of the Small Magellanic Cloud (SMC). We use the information in [(B-R), R] color-magnitude diagrams (CMDs), which reach down to the oldest main-sequence turnoffs and allow us to retrieve the SFH in detail. We show the first results of the SFH in a SMC field located in the Southern direction (at ∼1 kpc from the SMC center). This field is particularly interesting because in spite of being located in a place in which the HI column density is very low, it still presents a recent enhancement of star formation.

We present HST/ACS observations of five regions in the outskirts of M31. Four are centered on prominent stellar overdensities roughly aligned with the major axis. Well-populated colour magnitude diagrams (CMDs) show that these fields differ in morphology from the fifth (Minor Axis) field. Comparisons with isochrones present tantalising evidence that they contain a small contingent of very young (≤ 1Gyr) stars, at odds with what may be expected of typical halo populations, suggesting that this low-latitude substructure could feasibly have formed in the disk.

I review efforts to determine the ages and chemical compositions of early-type galaxies from their integrated spectra. After reviewing the history of integrated light analyses, we consider how reliably the light-weighted mean ages and chemical compositions of galaxies can be extracted from current state-of-the-art population synthesis modelling and observational data. Particular attention is given to assessing the best strategies for pursuing integrated spectrum analysis, both from observational and modelling standpoints. Finally, we consider efforts to move beyond light-weighted mean ages and metallicities, specifically, to constrain star formation histories with multiple episodes of star formation.

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.

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 summarize results from McDermid et al. (2006), who present a set of follow-up observations of the sauron representative survey of early-type galaxies. We used the oasis integral-field spectrograph (while at the Canada-France-Hawaii Telescope) to obtain high spatial resolution spectra of 28 elliptical and lenticular galaxies. These seeing-limited data have on average twice the spatial resolution of the sauron data, albeit over a smaller field. These new data reveal previously unresolved features in these objects' stellar kinematics, stellar populations, and ionized gas properties. In this contribution, we focus on the discovery of a population of compact kinematically decoupled cores in a number of our sample galaxies. These compact cores are related to regions of young stars, and counter-rotate around the host galaxy's minor axis. We compare these objects to previously known decoupled components, which in contrast are composed of old stars, and which rotate around axes unrelated to the host galaxy's kinematics or shape. A key difference between these two kinds of decoupled cores are their physical size and relative mass. The compact decoupled cores are smaller than a few hundred parsec, and constitute less than a few percent of the total galaxy mass. The ‘classical’ decoupled cores exist on kiloparsec scales, and comprise around a factor 10 more mass. We suggest that the small components are only found with young ages because of their low mass-to-light ratio. We show that after a few Gyrs, these components ‘fade’ into the background galaxy, making them more difficult to detect. We draw the following conclusions: 1) young stars found in early-type galaxies are very often associated with centrally-concentrated counter-rotating components; 2) the small mass fraction and kinematic decoupling of these cores suggests that the star formation is associated to minor accretion events, which effectively drive the spread in luminosity-weighted ages found in early-type galaxies; and 3) such decoupled components may be common in all early-type galaxies, but not directly observed due to their small contribution to the total galaxy light at older ages.