Found 3 talks width keyword Coma cluster

Galaxy clusters are the perfect places to study both the always controversial nature vs nurture problem and the still not well understood evolution that galaxies follow. By studying the properties of the galaxies at different locations of the cluster we can assess the first problem, while studying the same properties over cosmic time, helps constraining the different proposed evolutionary theories. In this work we have focused in an intermediately-redshift rich cluster, RX J0152.7-1357 (z=0.83), by fully characterizing its stellar population properties with new state-of-the-art tools . By this means, we have derived for the first time in such a high-z cluster the ages, metallicities, abundance patterns and Star Formation Histories of the cluster ETGs on an individual galaxy-basis . The relations that these properties follow with galaxy velocity dispersion allow us to discuss a passive evolution scenario with respect to a cluster at z~0. Our results favor a downsizing picture where the relation between the position within the cluster, the velocity dispersion and the type of star formation history of the galaxies allow us to better understand the cluster evolution. We find that the most massive galaxies evolve passively while the lower-mass ones, generally located at the outskirts of the cluster, experience a more extended star formation history related to their later incorporation in the cluster.

The effects that environment produce on galaxy disks and how they modify the subsequent formation of bars need to be distinguished to fully understand the relationship between bars and environment. To shed light on this issue, we derive the bar fraction in three different environments ranging from the field to Virgo and Coma Clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of galaxy luminosity (and mass) in the field and Coma Cluster is statistically significant, with Virgo being an intermediate case. We interpret this result as a variation of the effect of environment on bar formation depending on galaxy luminosity. We speculate that brighter disk galaxies are stable enough against interactions to keep their cold structure, thus, the interactions are able to trigger bar formation. For fainter galaxies, the interactions become strong enough to heat up the disks inhibiting bar formation and even destroying the disks. Finally, we point out that the controversy regarding whether the bar fraction depends on environment could be resolved by taking into account the different luminosity ranges probed by the galaxy samples studied so far.

(1) In this talk I will present a recent study of the bar fraction in the Coma Cluster galaxies based on a sample of 190 galaxies selected from the Sloan Digital Sky Survey Data Release 6 and observed with the Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The unprecedented resolution of the HST-ACS images allows us to explore the presence of bars, detected by visual classification, throughout a luminosity range of 9 mag (-23 < Mr < -14), permitting us to study the poor known region of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of both luminosities (-22 < Mr < -17) and masses (10⁹ < M/M? < 10¹¹). This result holds when compared with a sample of bright/massive field galaxies. In addition, we find that the bar fraction does not vary significantly when going from the center to the cluster outskirts, implying that cluster environment plays a second-order role in bar formation/evolution. The shape of the bar fraction distribution with respect to both luminosity and mass is well matched by the luminosity distribution of disk galaxies in Coma, indicating that bars are good tracers of cold stellar disks. We discuss the implications of our results for the formation and evolution scenarios of bars and disks.

(2) The Herschel Space Observatory was launched on 14 May 2009. After a short commissioning and performance verification period, the science demonstration observations started in September 2009. Herschel is carrying out now routine science observations. The three instruments (SPIRE, PACS and HIFI) are working extremely well. The first results of the many Herschel Key Projects were presented at the ESLAB 2010 conference in ESTEC on May 4-7 2010 and will be published in a special issue of Astronomy and Astrophysics. In this talk I will introduce the observing capabilities of Herschel and will review some of the first results in extragalactic astronomy and in particular those of the Herschel Multi-tiered Extragalactic Survey (HerMES).