Found 17 talks width keyword galactic clusters

Video
Thursday March 19, 2015
Dr. Fernando Atrio Barandela
Universidad de Salamanca

Abstract

The ``dark flow'' dipole is a statistically significant dipole found at the position of galaxy clusters in filtered maps of Cosmic Microwave Background (CMB) temperature anisotropies. The dipole measured in WMAP 3, 5 and 7 yr data releases was roughly aligned with the all-sky CMB dipole and correlated with cluster X-ray luminosity. We analyzed the final WMAP 9 yr and the first Planck data releases using a catalog of 980 clusters outside the Kp0 mask to test our earlier findings. The dipoles measured on these new data sets are fully compatible with our earlier estimates, being similar in amplitude and direction to our previous results and in disagreement with the results of an earlier study by the Planck Collaboration. Further, in Planck data dipoles are independent of frequency, ruling out the Thermal Sunyaev-Zeldovich as the source of the effect. The signal is dominated by the most massive clusters, with a statistical significance better than 99%, slightly larger than in WMAP. Since both data sets differ in foreground contributions, instrumental noise and other systematics, the agreement between WMAP and Planck dipoles argues against them being due to systematic effects in either of the experiments.


Video
Tuesday September 16, 2014
Dr. Mireia Montes
IAC

Abstract

The ultra-deep multiwavelength HST Frontier Fields coverage of the Abell Cluster 2744 is used to derive the stellar population properties of its intra-cluster light (ICL). The restframe colors of the ICL of this intermediate redshift (z=0.3064) massive cluster are bluer (g-r=0.68 ±0.04; i-J=0.56±0.01) than those found in the stellar populations of its main galaxy members (g-r=0.83±0.01; i-J=0.75±0.01). Based on these colors, we derive the following mean metallicity Z=0.018±0.007 for the ICL. The ICL age is 6±3 Gyr younger than the average age of the most massive galaxies of the cluster. The fraction of stellar mass in the ICL component comprises at least 6% of the total stellar mass of the galaxy cluster. Our data is consistent with a scenario where the bulk of the ICL of Abell 2744 has been formed relatively recently (z<1). The stellar population properties of the ICL suggest that this diffuse component is mainly the result of the disruption of infalling galaxies with similar characteristics in mass (M*~ 3x10^10 Msolar) and metallicity than our own Milky Way. The amount of ICL mass in the central part of the cluster (<400 kpc) is equivalent to the disruption of 4-6 Milky Way-type galaxies.


Video
Thursday March 20, 2014
Dr. Habib Khosroshahi
School of Astronomy, IPM - Tehran

Abstract

Majority of galaxies reside in groups and clusters where they are understood to evolve also through galaxy-galaxy interactions. Multiple mergers at the core of galaxy groups can develop a luminosity deficiency or gap, which is quantified as the difference between the luminosity of the two brightest galaxies in groups and clusters. This observable carries important information about the evolution of galaxy groups, for instance, there are indications that collapsed groups with a large luminosity gap, known as fossil groups, are associated with the halos that are relatively old. In a series of recent studies, employing X-ray, optical and radio observations complemented by cosmological simulations, we have utilised the luminosity gap to probe the formation scenarios for galaxies and specially the most luminous galaxies in groups and clusters, introduce a powerful age-date routine for galaxy groups, and also obtain clues about the AGN activities and the IGM heating.


Video
Tuesday January 14, 2014
Dr. Anna Ferré-Mateu
National Astronomical Observatory of Japan

Abstract

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.


Video
Tuesday January 7, 2014
Dr. Aurelio Carnero Crosell
Observatorio Nacional de Rio de Janeiro

Abstract

In this talk I will show how we can study cosmolgy in a photometric redshift galaxy survey, by means of the angular clustering of galaxies. Previously to fit your data to a cosmological model, the need for a representative, clean and reliable galaxy catalog imposes many constrains in the selection of your data, from the day the data was taken, up to the final galaxy catalog used in the cosmological Analysis. I will try to introduce those issues that are most important for the analysis of galaxy clustering: data reduction and detection limit, catalog pruning, sample selection, photometric redshifts, star/galaxy separation and the need for a detailed angular and depth mask. Once a neat catalog is build upon the raw data of the survey, the cosmological analysis can start confidently. In this context, I will show as an example, the last cosmological results obtained from the DR8 SDSS-III photometric sample, conveniently corrected from systematic errors.


Video
Wednesday November 13, 2013
Miss Andra Stroe
Leiden Observatory

Abstract

Clusters grow by mergers, events which release huge quantities of energy and can produce massive outward-travelling shock waves that can have an important effect on cluster gas and galaxies. Giant radio relics form at these shock fronts, where accelerated electrons emit synchrotron radiation. Despite the great interest in relics, candidates with simple geometry, undisturbed morphology and high surface brightness are scarce. The complex interaction between the merger, the shock wave and gas is likely a fundamental driver of galaxy evolution. The effects of dense environments have been previously investigated for relaxed clusters, but never before in highly disturbed, merging clusters hosting a relic. The Sausage and the Toothbrush clusters are providing us with the chance to study this phenomenon and its effects on the relativistic particles and the cluster galaxies. In order to address many of the unanswered questions, we use a unique combination of facilities (GMRT, WSRT, INT) to obtain the first cluster-wide, multi-wavelength, multi-method analysis aimed at giving a complete picture of merging clusters hosting relics. We derive physical parameters such as the Mach number and injection spectral index for the diffuse sources in the field. We present index and curvature maps pinpointing spectral trends conclusive for shock acceleration of relativistic particles and test injection models such as the Jaffe-Perola and Kardashev-Pacholczyk. This analysis is fully complemented by an Halpha mapping of the cluster volume and outskirts. We provide the first direct test whether the shock drives or prohibits star formation to decipher the role of the merger in shaping the Halpha luminosity function.


Video
Tuesday October 8, 2013
Dr. Heidi Lietzen
IAC

Abstract

Galaxies in different environments have different properties. In dense environments galaxies are more likely to be red, passive ellipticals than in less dense environments. This difference can be detected both on small and large-scale environments. In this talk, I will present results on galaxy populations in different environments on two scales: the group scale and the supercluster scale. The goal of our project is to find out if there are differences between massive galaxies in similar groups, but different large-scale environments. The results will tell if the evolution of galaxies is fully determined by the mass of their dark matter halo, or if the large-scale environment also play a role. 


Video
Tuesday September 17, 2013
Prof. Justin Read
University of Surrey, UK

Abstract

Dark matter makes up most of the mass of the Universe but remains mysterious. I discuss recent progress in constraining its properties by measuring its distribution in the Universe from tiny dwarf galaxies to giant galaxy clusters, and comparing this with numerical simulations. The latest results favour a cold, collisionless particle that must lie beyond the standard model of particle physics. I discuss the known small scale problems with this model: the cusp-core and missing satellites problems, and I argue that these are likely due to baryonic "feedback" during galaxy formation. I conclude with a discussion of experiments underway to detect dark matter particles, and the role that astrophysics has to play in these too. There is an exciting a very real prospect of detecting a dark matter particle in the next five years.


Video
Monday June 3, 2013
Dr. Alastair Edge
University of Durham

Abstract

Over the past decade there has been a growing body of evidence for a closely regulated balance of heating and cooling of the intracluster medium in the cores of clusters. I will review this evidence with a particular emphasis on the role of cold gas and dust as the fuel for AGN feedback that dominates these systems.


Video
Tuesday January 29, 2013
Dr. Jairo Méndez Abreu
IAC

Abstract

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.


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