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We present the first results of a pilot study aimed at understanding the influence of bars on the evolution of galaxy discs through the study of their stellar content. We examine here the kinematics, star formation history, mass-weighted, luminosity-weighted and single stellar population (SSP) equivalent ages and metallicities for four galaxies ranging from lenticulars to late-type spirals. The data employed extend to 2-3 disc scalelengths, with S/N(angstrom) > 50, where S/N stands for the signal-to-noise ratio. Several techniques are explored to derive star formation histories and SSP-equivalent parameters, each of which is shown to be compatible. We demonstrate that the age-metallicity degeneracy is highly reduced by using spectral fitting techniques - instead of indices - to derive these parameters. Our results are robust to the choices of stellar population models. We found that the majority of the stellar mass in our sample is composed of old (similar to 10 Gyr) stars. This is true in the bulge and disc regions, even beyond 2 disc scalelengths. In the bulge region, we find that the young, dynamically cold, structures produced by the presence of the bar (e. g. nuclear discs or rings) are responsible for shaping the bulges' age and metallicity gradients, as suggested by Peletier et al. In the disc region, a larger fraction of young stars are present in the external parts of the disc compared with the inner parts. The disc growth is therefore compatible with a moderate inside-out formation scenario, where the luminosity-weighted age changes from similar to 10 Gyr in the centre to similar to 4 Gyr at 2 disc scalelengths, depending upon the galaxy. However, the presence of substructures, like star-forming rings, can produce stellar population trends that are not directly related to the growing of the disc but to the bar potential. For two galaxies, we compare the metallicity and age gradients of the disc major-axis with that of the bar, finding very important differences. In particular, the stellar population of the bar is more similar to that of the bulge than to that of the disc, indicating that, at least in those two galaxies, bars formed long ago and have survived to the present day.

We present stellar population parameters of 12 elliptical and S0 galaxies in the Coma cluster around and including the cD galaxy NGC 4874, based on spectra obtained using the Low Resolution Imaging Spectrograph on the Keck II Telescope. Our data are among the most precise and accurate absorption-line strengths yet obtained for cluster galaxies, allowing us to examine in detail the zero-point and scatter in the stellar population properties of Coma cluster early-type galaxies (ETGs). Recent observations of red sequence galaxies in the high-redshift Universe and generic hierarchical galaxy formation models lead to the following expectations for the stellar populations of local ETGs. (1) In all environments, bigger ETGs should have older stellar populations than smaller ETGs ('downsizing'); (2) ETGs at fixed stellar mass form stars earlier and thus should have older stellar population ages in the highest density environments than those in lower density environments and (3) the most massive ETGs in the densest environments should have a small spread in stellar population ages. We find the following surprising results using our sample. (1) Our ETGs have single-stellar-population-equivalent (SSP-equivalent) ages of on average 5-8 Gyr with the models used here, with the oldest galaxies having SSP-equivalent ages of less than or similar to 10-Gyr old. This average age is identical to the mean age of field ETGs. (2) The ETGs in our sample span a large range in velocity dispersion (mass) but are consistent with being drawn from a population with a single age. Specifically, 10 of the 12 ETGs in our sample are consistent within their formal errors of having the same SSP-equivalent age, 5.2 +/- 0.2 Gyr, over a factor of more than 750 in mass. We therefore find no evidence for downsizing of the stellar populations of ETGs in the core of the Coma cluster. We confirm the lack of a trend of SSP-equivalent age with mass in the core of the Coma cluster from all other samples of Coma cluster ETG absorption-line strengths available in the literature, but we do find from the largest samples that the dispersion in age increases with decreasing mass. These conclusions stand in stark contrast to the expectations from observations of high-redshift red sequence galaxies and model predictions. We suggest that Coma cluster ETGs may have formed the majority of their mass at high redshifts but suffered small but detectable star formation events at z approximate to 0.1-0.3. In this case, previous detections of 'downsizing' from stellar populations of local ETGs may not reflect the same downsizing seen in look-back studies of RSGs, as the young ages of the local ETGs represent only a small fraction of their total masses.

We continue the exploration of the BaLROG (Bars in Low Redshift Optical Galaxies) sample: 16 large mosaics of barred galaxies observed with the integral field unit SAURON. We quantify the influence of bars on the composition of the stellar component. We derive linestrength indices of H${\beta}$, Fe5015 and Mgb. Based on single stellar population (SSP) models, we calculate ages, metallicities and [Mg/Fe] abundances and their gradients along the bar major and minor axes. The high spatial resolution of our data allows us to identify breaks among index and SSP profiles, commonly at 0.13$\pm$0.06 bar length, consistent with kinematic features. Inner gradients are about ten times steeper than outer gradients and become larger when there is a central rotating component, implying that the gradients are not independent of dynamics and orbits. Central ages appear to be younger for stronger bars. Yet, the bar regions are usually old. We find a flattening of the iron (Fe5015) and magnesium (Mgb) outer gradients along the bar major axis, translating into a flattening of the metallicity gradient. This gradient is found to be 0.03$\pm$0.07 dex/kpc along the bar major axis while the mean value of the bar minor axis compares well with that of an unbarred control sample and is significantly steeper, namely -0.20$\pm$0.04 dex/kpc. These results confirm recent simulations and discern the important localized influence of bars. The elevated [Mg/Fe] abundances of bars and bulges compared to the lower values of discs suggest an early formation, in particular for early type galaxies., Comment: Accepted for publication in MNRAS, 47 pages, 39 figures. Comments are welcome and appreciated. Some of the figures might lack quality due to overall size restrictions, so please contact us if needed

Aims: We present a number of improvements to the MILES library and stellar population models. We correct some small errors in the radial velocities of the stars, measure the spectral resolution of the library and models more accurately, and give a better absolute flux calibration of the models. Methods: We use cross-correlation techniques to correct the radial velocities of the offset stars and the penalised pixel-fitting method, together with different sets of stellar templates, to re-assess the spectral resolution of the MILES stellar library and models. We have also re-calibrated the zero-point flux level of the models using a new calibration scheme. Results: The end result is an even more homogeneously calibrated stellar library than the originally released one, with a measured spectral resolution of ~2.5 Å, almost constant with wavelength, for both the MILES stellar library and models. Furthermore, the new absolute flux calibration for the spectra excellently agrees with predictions based on independent photometric libraries. Conclusions: This improved version of the MILES library and models (version 9.1) is available at the project's website (http://miles.iac.es).

We present a number of improvements to the MILES library and stellar population models. We correct some small errors in the radial velocities of the stars, measure the spectral resolution of the library and models more accurately, and give a better absolute flux calibration of the models. Methods. We use cross-correlation techniques to correct the radial velocities of the offset stars and the penalised pixel-fitting method, together with different sets of stellar templates, to re-assess the spectral resolution of the MILES stellar library and models. We have also re-calibrated the zero-point flux level of the models using a new calibration scheme. Results. The end result is an even more homogeneously calibrated stellar library than the originally released one, with a measured spectral resolution of similar to 2.5 angstrom, almost constant with wavelength, for both the MILES stellar library and models. Furthermore, the new absolute flux calibration for the spectra excellently agrees with predictions based on independent photometric libraries. Conclusions. This improved version of the MILES library and models (version 9.1) is available at the project's website (http://miles.iac.es).

We present the first results of a pilot study aimed at understanding the influence of bars on the evolution of galaxy discs through the study of their stellar content. We examine here the kinematics, star formation history, mass-weighted, luminosity-weighted, and single stellar population (SSP) equivalent ages and metallicities for four galaxies ranging from lenticulars to late-type spirals. The data employed extends to 2-3 disc scalelengths, with S/N(A)>50. Several techniques are explored to derive star formation histories and SSP-equivalent parameters, each of which are shown to be compatible. We demostrate that the age-metallicity degeneracy is highly reduced by using spectral fitting techniques --instead of indices-- to derive these parameters. We found that the majority of the stellar mass in our sample is composed of old (~10 Gyr) stars. This is true in the bulge and the disc region, even beyond two disc scalelengths. In the bulge region, we find that the young, dynamically cold, structures produced by the presence of the bar (e.g., nuclear discs or rings) are responsible for shaping the bulges' age and metallicity gradients. In the disc region, a larger fraction of young stars is present in the external parts of the disc compared with the inner disc. The disc growth is, therefore, compatible with a moderate inside-out formation scenario, where the luminosity weighted age changes from ~10 Gyrs in the centre, to ~4 Gyrs at two disc scalelengths, depending upon the galaxy. For two galaxies, we compare the metallicity and age gradients of the disc major axis with that of the bar, finding very important differences. In particular, the stellar population of the bar is more similar to the bulge than to the disc, indicating that, at least in those two galaxies, bars formed long ago and have survived to the present day. (abridged), 24 pages, 23 figures, accepted for publication in MNRAS

Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby Universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP-ITP (Peletier et al., 2007). In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo Cluster and in the field, using optical long-slit spectroscopy. We examine their stellar populations in combination with their light distribution and environment. We confirm and strengthen previous results that dEs are, on average, younger and more metal-poor than normal elliptical galaxies, and that their [alpha/Fe] abundance ratios scatter around solar. This is in accordance with the downsizing picture of galaxy formation where mass is the main driver for the star formation history. We also find new correlations between the luminosity-weighted mean age, the large-scale asymmetry, and the projected Virgocentric distance. We find that environment plays an important role in the termination of the star formation activity by ram pressure stripping of the gas in short timescales, and in the transformation of disky dwarfs to more spheroidal objects by harassment over longer timescales. This points towards a continuing infall scenario for the evolution of dEs., Comment: Accepted for publication in MNRAS: 22 pages, 13 figures and 9 tables

We present stellar population parameters of twelve early-type galaxies (ETGs) in the Coma Cluster based on spectra obtained using the Low Resolution Imaging Spectrograph on the Keck II Telescope. Our data allow us to examine in detail the zero-point and scatter in their stellar population properties. Our ETGs have SSP-equivalent ages of on average 5-8 Gyr with the models used here, with the oldest galaxies having ages of ~10 Gyr old. This average age is identical to the mean age of field ETGs. Our ETGs span a large range in velocity dispersion but are consistent with being drawn from a population with a single age. Specifically, ten of the twelve ETGs are consistent within their formal errors of having the same age, 5.2+/-0.2 Gyr, over a factor of more than 750 in mass. We therefore find no evidence for downsizing of the stellar populations of ETGs in the core of the Coma Cluster. We suggest that Coma Cluster ETGs may have formed the majority of their mass at high redshifts but suffered small but detectable star formation events at z~0.1-0.3. Previous detections of 'downsizing' from stellar populations of local ETGs may not reflect the same downsizing seen in lookback studies of RSGs, as the young ages of the local ETGs represent only a small fraction of their total masses. (abridged), 49 pages, 20 figures (19 EPS, 1 JPEG). MNRAS, in press. For version with full resolution of Fig. 1 see http://www.astro.rug.nl/~sctrager/coma.pdf; for Table 2, see http://www.astro.rug.nl/~sctrager/coma_table2.pdf; for Table B3, see http://www.astro.rug.nl/~sctrager/coma_tableB3.pdf