Found 178 talks archived in Galaxies

Video
Tuesday May 13, 2014
Dr. Remco van de Bosch
Max-Planck-Institut für Astronomie

Abstract

Most massive galaxies have supermassive black holes at their centres, and the masses of the black holes correlate with properties of the host-galaxy bulge component. These empirical scaling relations are important for distinguishing between various theoretical models of galaxy evolution, and they furthermore form the basis for all black-hole mass measurements at large distances. Observations have shown that the mass of the black hole is typically 0.1 per cent of the mass of the stellar bulge of the galaxy. Our spectroscopic survey with the Hobby-Eberly Telescope of 1000 nearby galaxies revealed several compact lenticular galaxies with extremely high velocity dispersions. The first example is NGC1277, which is a small, Re=1kpc, compact, lenticular galaxy with a mass of 1.2×10^11 solar masses. From the stellar kinematics we determined that the mass of the central black hole is 10^10 solar masses, more than 10 per cent of its bulge mass. I will present HST images and IFU spectroscopy of a dozen more compact galaxies that all appear to host extremely big black holes and have Salpeter-like IMFs. These local systems, with distances less than 100 Mpc, could be the passively evolved descendents of the quiescent compact nugget galaxies found at z~2 and the >10e9 Msun quasars that are found at z>6.


Video
Wednesday March 26, 2014
Dr. Thorsten Lisker
Astronomisches Rechen-Institut (ARI), Heidelberg

Abstract

Dwarf galaxies are a complex population. They comprise objects with young and old stellar populations, slow and fast rotation, as well as single- and multi-component structure. These characteristics show correlations with environmental density - we thus believe that dwarf galaxies hold a fossil record of how environment affected galaxy evolution. In this talk I will review and discuss recent progress on our understanding of dwarf galaxies in clusters, both from the observational and the modelling side. In particular, I will attempt to reconcile the proposed formation mechanisms of early-type dwarf galaxies - the most abundant population in clusters - with the continuous environmental influence predicted by cosmological simulations.


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 March 11, 2014
Dr. Martin López Corredoira
IAC

Abstract

1) López-Corredoira & Gutiérrez (2012, RAA, 12, 249): Extremely luminous QSOs exist at high redshift but they are absent at low redshift. Our analyses show that it is not due to any significant evolution of black hole masses or Eddington ratios for equal luminosity QSOs, so the problem can be translated into a "Why are not there QSOs with very high black hole masses at low redshift?". 2) López-Corredoira & Perucho (2012, A&A, 544, 56): The MOJAVE survey contains 101 quasars with a total of 354 observed radio components that are different from the radio cores, among which 95% move with apparent projected superluminal velocities with respect to the core, and 45% have projected velocities larger than 10c (with a maximum velocity 60c). Relativistic Doppler boosting explains these apparent anomalies, but it requires a huge average kinetic power to produce such powerful ejections: ~7×10^{47} erg/s, a significant portion of the Eddington luminosity and on the order of the bolometric luminosity. This amount is much higher than previous estimates of kinetic power on kpc-scales. 3) There are many other pending problems in QSOs in the literature (review at López-Corredoira 2011, IJAA, 1, 73): the different structure of the clouds along the QSO's line of sight and their tangential directions; the spatial correlation between QSOs and galaxies; inconsistencies in the AGN unification model; etc.


Video
Wednesday February 12, 2014
Mr. Simon Diaz Garcia
University of Oulu (Finland)

Abstract

The ΛCDM model predicts that galaxies originate in dark matter haloes, undergoing in their early age a process of continuous merges with other galaxies that determines the first part of their evolution. The frequency of these events decreases with time and their gradual change turns to be internally driven, becoming much slower. Bars, elongated stellar structures in the central regions of galaxies, are known to play an active role in this phase of their evolution, so-called secular.

Bars are fundamentally responsible for the redistribution of matter and the angular momentum of the baryonic and dark matter components of disc galaxies. Different simulations predict that bars get stronger and longer in time, slowing down their rotation speed.

Based on the Spitzer Survey of Stellar Structure in Galaxies (S4G) 3.6 μm imaging, we aim to study the secular evolution of disc galaxies by focusing on their stellar bar parameters. We take a large well-defined sample of about 650 nearby barred galaxies and we infer the gravitational potential from 3.6 μm images. We calculate gravitational torques, the ratio of the maximal tangential force to the mean axisymmetric radial force, in order to obtain a quantitative measure of the bar-induced perturbation strengths. In addition, we estimate the bar strength from the m=2 normalized Fourier density amplitudes and determine bar lengths both visually and by using an ellipse fitting method. Bar morphology and the interplay with spiral arms are studied via image-stacking methods as well.

In this talk I will present the statistical results derived from our measurements, providing observational evidence for the evolution of bars in accordance with the current theoretical predictions. We study bar parameters as a function of the Hubble type, addressing how the different measurements of the bar strength correlate with each other and with the galactic mass. The quality of our data allows us to probe the properties of bars in the Local Universe and connect them to the evolution of other galactic structures.


Video
Wednesday January 29, 2014
Dr. Divakara Mayya
INAOE

Abstract

The nearby spiral galaxy M81 contains a population of 3 kinds of stellar clusters - super star clusters, globular clusters and fuzzy clusters. Over the past few years, we have taken GTC longslit spectra of around 20 of these clusters, with the intention of obtaining their spectroscopic ages. These spectra have allowed us to understand the nature of the brightest globular cluster in this galaxy. In addition, we were able to address the problem of the origin of the fuzzy clusters. In the talk, I will summarize the results we have obtained so far.


Video
Tuesday January 21, 2014
Prof. Francisco Prada
Instituto de Física Teórica UAM/CSIC, Madrid

Abstract

DESI is a massively multiplexed fiber-fed spectrograph that will make the next
major advance in dark energy in the timeframe 2018-2022. On the Mayall
telescope, DESI will obtain spectra and redshifts for tens of millions of
galaxies and cuasars with 5,000 fiber postioner robots, constructing a
3-dimensional map spanning the nearby universe to 10 billion light years. DESI
is supported by the US Department of Energy Office of Science to perform this
Stage IV dark energy measurement using baryon acoustic oscillations and other
techniques that rely on spectroscopic measurements. Spain has a major role in
DESI with the construction of the Focal Plate and the development of the fiber
positioners. I will give an overview of the DESI science, instrument, and Spain
participation in the project.


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
Wednesday January 8, 2014
Dr. Ruben Sanchez-Janssen
NRC Herzberg Institute of Astrophysics

Abstract

Two competing effects appear to govern galaxy multiplicity (pairs orgroups) at low masses: while associations of low-mass haloes are naturally expected in a LCDM cosmology, galaxy formation within these haloes is thought to be rendered inefficient due to the action of several ionizing agents. Yet associations of dwarf galaxies are known to exist in the Local Volume, and their frequency appears to be unexpectedly high for LCDM expectations even in our own Local Group. Unfortunately, it is not yet well understood what role do interactions between low-mass galaxies play in determining their star formation histories, structural properties, and neutral gas content. Here I will present an investigation of the impact of dwarf-dwarf galaxy tidal interactions on their morphological and star formation properties. The UGC5205 close pair consists of two low-mass (M* ~ 5E7 Msun), late-type galaxies with a relative projected distance of only 10 kpc, and no nearby massive companions. I will show that these equal-mass interactions can be an important 'pre-processing' mechanism that acts before dwarfs are affected by a more massive central galaxy, profoundly impacting their star formation histories and morphologies.


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.



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