Found 188 talks archived in Galaxies

Tuesday May 3, 2011
Miss Josefa Becerra
Instituto de Astrofísica de Canarias, Spain


The MAGIC telescopes discovered very high energy (VHE, E>100 GeV) gamma-ray emission coming from the distant Flat Spectrum Radio Quasar (FSRQ) PKS 1222+21 (4C +21.35, z=0.432). It is the second most distant VHE gamma-ray source, with well measured redshift, detected until now. The detection coincides with high energy MeV/GeV gamma-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light, can be described by a single power law with photon index 2.72 ± 0.34 between 3 GeV and 400 GeV, consistent with gamma-ray emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the gamma-ray emission region to lie outside the Broad Line Region, which would otherwise absorb the VHE gamma-rays. On the other hand, the MAGIC measurement of a doubling time of about 9 minutes indicates an extremely compact emission region, in conflict with the "far dissipation" scenario. This result challenges jet emission models in FSRQs and indicates the importance of jet sub-structures.

Thursday April 28, 2011
Dr. Alberto Dominguez Diaz
Instituto de Astrofísica de Andalucia, Spain


The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for gamma-ray astronomy, but the overall spectrum of the EBL between 0.1 and 1000 microns has never been determined directly from galaxy spectral energy distribution (SED) observations over a wide redshift range. Galaxy SED-type fractions from z=0.2-1 are estimated from a multi-wavelength sample from the AEGIS collaboration that allows a new determination of the evolving EBL. Then, the transparency of the Universe to very high energy (VHE) gamma-ray photons is derived. We find the maximum transparency of the Universe allowed by the standard framework. This result challenges current VHE observations of high redshift blazars. A solution to this problem is discussed utilizing VHE spectra of the highest redshift blazars assuming the existence of a plausible dark matter candidate known as axion-like particle.

Tuesday April 26, 2011
Dr. Cristina Ramos Almeida
University of Sheffield, UK


I will present new mid-infrared imaging data for a sample of ~20 nearby Seyfert galaxies obtained with T-ReCS and MICHELLE on the Gemini Telescopes at subarcsecond resolution. Our aim is to compare the properties of Type-1 and Type-2 Seyfert tori using clumpy torus models and a Bayesian approach to fit the infrared nuclear spectral energy distributions (SEDs). These dusty tori have physical sizes smaller than 10 pc radius, as derived from our fits. Unification schemes of AGN account for a variety of observational differences in terms of viewing geometry. However, we find evidence that strong unification may not hold, and that the immediate dusty surroundings of Type-1 and Type-2 Seyfert nuclei are intrinsically different. The Type-2 tori studied here are broader, have more clumps, and these clumps have lower optical depths than those of Type-1 tori. The larger the covering factor of the torus, the smaller the probability of having direct view of the AGN, and vice-versa. In our sample, Seyfert 2 tori have larger covering factors and smaller escape probabilities than those of Seyfert 1. Thus, on the basis of the results presented here, the classification of a Seyfert galaxy as a Type-1 or Type-2 depends more on the intrinsic properties of the torus rather than on its mere inclination, in contradiction with the simplest unification model.

Tuesday April 12, 2011
Dr. Rafael Barrena
Instituto de Astrofísica de Canarias, Spain


Extended, diffuse radio emission (halos and relics) in galaxy clusters is a rare phenomenon. The origin of these radio sources and their connection with cluster mergers is still being debated. Here we present the results of the DARC program, aimed to the internal Dynamics Analysis of ”Radio” Clusters and mainly based on a long-term TNG-INT program (20 clusters at z=0.1-0.3). The study of kinematics of member galaxies show that DARC clusters are examples of very substructured systems and allow us to detect and weight the interveining subclusters, as well as to obtain infor- mation about their relative motions and the merger geometry. The multiwavelength observational picture (optical, radio and X-ray) of DARC clusters is well interpreted in a scenario of a recent, major cluster merger.

Friday March 25, 2011
Dr. Anne Sansom
University of Central Lancashire, UK


Spectroscopic analysis of stellar populations is widely used to understand the history of many systems including globular clusters, nuclear star clusters, dwarf galaxies through to giant galaxies over a wide range of redshifts. In this talk I first explore aspects of stellar population fitting, focussing on the effects of interacting binary stars on the yields and hence the spectra of early-type galaxies. The second part of the talk concentrates on what we know about supernovae type Ia and the importance of understanding their contributions to the chemical evolution of galaxies and stellar populations.

Thursday March 24, 2011
Prof. Pierre Cox
IRAM, France


In recent years, major changes were done at the IRAM Plateau de Bure interferometer and 30-meter telescope, in particular in the areas of receivers and back-ends. These enhancements increased in significant ways both the sensitivity and the efficiency of both IRAM facilities. I will present results obtained on high-z (2 < 6.4) sub-millimeter galaxies and quasars that illustrate the progress that has been made, emphasizing recent follow-up observations of sources that were uncovered in the Herschel surveys. The talk will end with a presentation of the future projects that are currently under discussion at IRAM, including the NOrthern Extended Millimeter Array (NOEMA), as well as the prospects offered by ALMA.

Thursday March 17, 2011
Dr. Alber Bosma
Astronomy Observatory of Marseilles Provence, OAMP, France


Dark Matter in Galaxies is an important subject of current astrophysical research. I will concentrate on spiral galaxies, and first give an overview of the subject from the standpoint of a radioastronomer with a long involvement in the subject. This includes a historical introduction and a review of some of the present-day debates. The currently popular Lambda-CDM model has problems on the scale of galaxies. In a second part I will address more specifically the problem that we still do not know how much dark matter there is in spiral galaxies, and how it is distributed. This is due to the fact that the M/L of the visible matter is poorly constrained and that there is a 'conspiracy' between the dark and the baryonic material. I will present various dynamical methods that have been proposed to constrain the dark matter mass distribution and discuss their advantages and disadvantages.

Thursday March 3, 2011
Miss Mar Mezcua
Max Planck Institute for Radio Astronomy, Germany


The detection and number estimates of supermassive binary black holes (SMBBHs) provide important constraints on the hierarchical models for galaxy formation and evolution. I will present two different approaches for the possible identification of SMBBHs. 1.Radio-optical studies of X-shaped radio sources:X-shaped radio galaxies are extragalactic radio sources that present two pairs of radio lobes passing symmetrically through the center of the host galaxy, giving the galaxy the X-shaped morphology seen on radio maps.This morphology can reflect either a recent merger of two supermassive black holes or the presence of a second active black hole in the galactic nucleus. This scenario is studied by determining the mass, luminosity, jet dynamic age and starburst of a sample of X-shaped sources and comparing the results to a sample of radio-loud active nuclei with similar redshift and luminosities. 2.Compact radio emission in ULX objects: Ultraluminous X-ray sources (ULXs) have luminosities exceeding 10E39 erg/s, suggesting either the presence of black holes larger than stellar mass black holes or sources apparently radiating above the Eddington limit. I will present milliarcsecond-scale radio observations of some ULXs located within optical bright galaxies, resolving their compact radio emission, and measuring its brightness temperature and spectral properties. This allows us to uncover the nature of these sources and investigate whether they are intermediate mass black holes or supermassive black holes stripped of their accretion disks in post-merger systems.

Tuesday March 1, 2011
Dr. Karsten Berger
Instituto de Astrofísica de Canarias, Spain


3C 279, the first quasar discovered to emit VHE gamma-rays by the MAGIC telescope in 2006, was re-observed by MAGIC in January 2007 during a major optical flare and from December 2008 to April 2009 following an alert from the Fermi space telescope on an exceptionally high gamma -ray state. The January 2007 observations resulted in a detection on January 16 with significance 5.2 sigma, corresponding to a F(> 150 GeV)(3.8±0.8) 10^-11 ph cm-2 s-1 while the overall data sample does not show significant signal. The December 2008 - April 2009 observations did not detect the source. We study the multi-wavelength behaviour of the source at the epochs of MAGIC observations, collecting quasi-simultaneous data at optical and X-ray frequencies and for 2009 also gamma-ray data from Fermi. We study the light curves and spectral energy distribution of the source. The spectral energy distributions of three observing epochs (including the February 2006, which has been previously published in Albert et al. 2008a) are modelled with one-zone inverse Compton models and the emission on January 16, 2007 also with two zone model and with a lepto-hadronic model. We find that the VHE gamma-ray emission detected in 2006 and 2007 challenges standard one-zone model, based on relativistic electrons in a jet scattering broad line region photons, while the other studied models fit the observed spectral energy distribution more satisfactorily.

Wednesday February 16, 2011
Dr. Yago Ascasibar
Universidad Autónoma de Madrid, Spain


Galaxies are arguably complex systems. However, they also display many scaling relations between their physical properties, hinting that it might be possible to summarize all this complexity within a few phenomenological parameters. In this talk, we will first address the question of how many parameters are indeed necessary in order to describe a galaxy, and then discuss some of them in detail, aiming towards a self-consistent, cartoon (yet remarkably accurate) picture of galaxy formation and evolution.

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