Found 9 talks width keyword quasars

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Thursday March 26, 2015
Dr. Stefan Geier
GTC

Abstract

Our Universe is filled with a mind-blowing diversity and different types and appearances of galaxies. Finding out about how they formed and evolved is one of the most challenging tasks in astronomy. When looking about 10 billion years back, to an epoch about 3 billion years after the big bang, we can see galaxies at earlier stages of their lives. In this talk, studies of different kinds of galaxies in the early universe will be presented. Two examples of the very intriguing population of massive quiescent z~2 galaxies were analyzed in terms of their stellar populations and morphologies. As the spectroscopic sample is still small, especially for galaxies at the faint end of the luminosity function, we make use of the biggest available "telescopes" in the universe: We search for red z~2 galaxies whose apparent brightnesses have been boosted by the Gravitational Lensing effect of intermediate redshift galaxy clusters with available mass models. Our findings indicate older ages for these galaxies than expected. Also, their remarkable compactness was corroborated. Furthermore, I'm going to present a study of a special case of so-called Damped Lyman-alpha Absorbers (DLAs), with two intervening galaxies in the line of sight of a higher-redshift QSO, which is also one example of only about a dozen known galaxy counterparts of a DLA. It fits into the emerging paradigm that galaxies which are responsible for higher metallicity DLAs are more massive and luminous than typical DLA galaxies. Motivated by that particular discovery, during the past few years we have undertaken a survey targeting candidate dust-reddened quasars missing in the sample from Sloan Digital Sky Survey. Spectroscopic follow-up with the NOT and the NTT has demonstrated a very high success rate of our selection (>90%). The main motivation is to search for quasars reddened by foreground dusty galaxies and we have found several such examples. We have also serendipitously found quasars with abnormal, very UV-steep extinction curves as well as a large number of broad absorption line quasars (BALs). The latter allow us to study the dependence of the BAL QSO population on redshift, reddening and luminosity. The results show a strong evolution of the BAL QSO fraction with cosmic time, with a peak at z~2.5 where several quantities in the Universe are also found to peak or vary. In addition,the dependence of this fraction with reddening and luminosity provides new constraints on the models for broad absorption origin in quasars. We are currently carrying out a pilot study of a search for even redder quasars selected from a combination of SDSS, UKIDSS and WISE photometry with the aim of selecting very dust-obscurred quasars or high-redshift BALs at z>2. Preliminary results from the first run et the NOT in March 2015 of the brightest candidates show very promising results which will also be briefly shown in the talk.


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Tuesday September 23, 2014
Dr. José A. de Diego Onsurbe
UNAM

Abstract

Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to detect. Variance based probes such as the C and F tests, or a combination of both, are popular methods to compare the light-curves of the quasar and a comparison star. Recently, detection claims in some studies depend on the agreement of the results of the C and F tests, or of two instances of the F-test, in rejecting the non-variation null hypothesis. However, the C-test is a non-reliable statistical procedure, the F-test is not robust, and the combination of tests with concurrent results is anything but a straightforward methodology. A priori Power Analysis calculations and post hoc analysis of Monte-Carlo simulations show excellent agreement for the Analysis of Variance test to detect microvariations, as well as the limitations of the F-test. Additionally, combined tests yield correlated probabilities that make the assessment of statistical significance unworkable. However, it is possible to include data from several field stars to enhance the power in a single F - test or ANOVA nested designs, increasing the reliability of the statistical analysis. These would be the preferred methodology when several comparison stars are available. These results show the importance of using adequate methodologies, and avoid inappropriate procedures that can jeopardize microvariability detections. Power analysis and Monte-Carlo simulations are useful tools for research planning, as they can reveal the robustness and reliability of different research approaches.


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Thursday June 26, 2014
Prof. Clive Tadhunter
University of Sheffield

Abstract

There is increasing speculation that quasars are intimately linked to the evolution of their host galaxies. Not only are they triggered as galaxies build up mass through gas accretion, but they also have the potential to drive massive outflows that can directly affect galaxy evolution by heating the gas and expelling it from galaxy bulges. However, there remain considerable uncertainties about how, when and where quasars are triggered as galaxies evolve, and the true energetic significance for the quasar-induced outflows and their acceleration mechanism have yet to be established. In this talk I will present new Gemini, VLT, Spitzer and Herschel results on samples of luminous AGN in the local Universe which provide key information on the triggering mechanisms for quasars and physics of their outflows.


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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.


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Thursday December 20, 2012
Prof. Clive Tadhunter
University of Sheffield

Abstract

In the 50 years since their discovery, it has become increasingly recognised that quasars are not merely signposts to the distant Universe, but also play a key role in the overall galaxy evolution process. However, if we are to incorporate quasars into models of galaxy evolution, it's important to understand how, when and where they are triggered. In this talk I will review the latest observational results on the triggering of quasars, based on the morphologies of their host galaxies and star formation properties; I will also discuss the future prospects for understanding quasar triggering using Herschel and ALMA data.


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Thursday June 30, 2011
Prof. Scott Tremaine
Institute for Advanced Study, Univ. Princeton, USA

Abstract

The massive black holes found at the centers of most nearby galaxies including our own, are believed to be the ashes of the fuel that powered quasars early in the history of the universe. I will briefly review the astronomical evidence for these objects and then describe some of the exotic dynamical phenomena that originate in their vicinity, including hypervelocity stars, resonant relaxation, and warped and lopsided stellar disks.


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

Abstract

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.


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

Abstract

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.


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Monday March 22, 2010
Prof. Richard McMahon
Institute of Astronomy, University of Cambridge, UK

Abstract

Survey operations with the VISTA telescope with it wide field near IR camera started in Feb 2010, following a science verification phase that started in Oct, 2009. I will describe this new 4.2m wide field telescope and the ESO VISTA Public survey program. I will give details of all ESO six public surveys which will be used for a range of galactic and extragalactic science. I am the PI of the largest, by area, VISTA survey, I will focus my talk on the VISTA Hemisphere Survey and I will show how this survey will be used to find quasars in the Epoch of Reionization at redshift greater than 7. The VISTA Hemisphere Survey (VHS) has been been awarded 300 clear nights on the 4.2m ESO VISTA telescopes. VHS observations started i February, 2010 and the survey will take 5 years to complete. The VHS will cover the whole southern celestial hemisphere (dec<0) to a depth 4 magnitudes fainter than 2MASS/DENIS in at least two wavebands J and K. In the South Galactic Cap, 5000 square degrees will be imaged deeper, including H band, and will have supplemental deep multi-band grizY imaging data provided by the Dark Energy Survey (DES). The remainder of the high galactic latitude sky will be imaged in YJHK and combined with ugriz wavebands from the VST ATLAS, SDSS BOSS and Skymapper optical surveys. The medium term scientific goals include: a huge expansion in our knowledge of the lowest-mass and nearest stars; deciphering the merger history and genesis of our own Galaxy; measurement of large-scale structure out to z=1 and measuring the properties of Dark Energy; discovery of the first quasars with z > 7. In my talk, I will describe the scientific motivation and methodology of the search for quasars with z > 7.

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