Download or read book Mid Infrared Fine Structure Line Ratios in Active Galactic Nuclei Observed with the Spitzer IRS Evidence for Extinction by the Torus written by and published by . This book was released on 2007 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present the first systematic investigation of the [Ne v] (14 micron/24 micron) and [S III] (18 micron/33 micron) infrared line flux ratios, traditionally used to estimate the density of the ionized gas, in a sample of 41 type 1 and type 2 active galactic nuclei (AGNs) observed with the Infrared Spectrograph on board Spitzer. The majority of galaxies with both [Ne v] lines detected have observed [Ne v] line flux ratios consistent with or below the theoretical low-density limit, based on calculations using currently available collision strengths and ignoring absorption and stimulated emission. We find that type 2 AGNs have lower line flux ratios than type 1 AGNs and that all of the galaxies with line flux ratios below the low-density limit are type 2 AGNs. We argue that differential infrared extinction to the [Ne v] emitting region due to dust in the obscuring torus is responsible for the ratios below the low-density limit and we suggest that the ratio may be a tracer of the inclination angle of the torus to our line of sight. Because the temperature of the gas, the amount of extinction, and the effect of absorption and stimulated emission on the line ratios are all unknown, we are not able to determine the electron densities associated with the [Ne v] line flux ratios for the objects in our sample. We also find that the [S III] emission from the galaxies in our sample is extended and originates primarily in star-forming regions. Since the emission from low-ionization species is extended, any analysis using line flux ratios from such species obtained from slits of different sizes is invalid for most nearby galaxies.
Download or read book Constraining the Size of the Dusty Torus in Active Galactic Nuclei written by Billy Vazquez and published by . This book was released on 2015 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The dusty torus is the key component in the Active Galactic Nuclei (AGN) Unification Scheme that explains the spectroscopic differences between Seyfert galaxies of types 1 and 2. The torus dust is heated by the nuclear source and emits the absorbed energy in the infrared (IR); but because of light travel times, the torus IR emission responds to variations of the nuclear ultraviolet/optical continuum with a delay that corresponds to the size of the emitting region. The results from a mid-infrared (MIR) monitoring campaign using the Spitzer Space Telescope and optical ground-based telescopes (B and V band imaging), which spanned over 2 years and covered a sample of 12 Seyfert galaxies, are presented. The aim was to constrain the distances from the nucleus to the regions in the torus emitting at wavelengths of 3.6 [micron] and 4.5 [micron]. MIR light curves showing the variability characteristics of these AGN are presented and the effects of photometric uncertainties on the time-series analysis of the light curves are discussed. Significant variability was observed in the IR light curves of 10 of 12 objects, with relative amplitudes ranging from ~10% to ~100% from their mean flux. The 'reverberation lags' between the 3.6 [micron] and 4.5 [micron] IR bands were determined for the entire sample and between the optical and MIR bands for NGC6418. In NGC6418, the 3.6 [micron] and 4.5 [micron] fluxes lagged behind those of the optical continuum by 47.5 (+2.0,-1.9) days and 62.5 (+2.5,-2.9) days, respectively. This is consistent with the inferred lower limit to the sublimation radius for pure graphite grains at T=1800 K but smaller by a factor of 2 than the lower limit for dust grains with a 'standard' interstellar medium (ISM) composition. There is evidence that the lags increased following approximately by a factor of 2 increase in luminosity, consistent with an increase in the sublimation radius."--Abstract.
Download or read book A Study of the X ray and Optical Variability of the Active Galactic Nucleus ESO 362 G18 written by Beatriz Agís González and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The standard UnifiedModel (UM) of Active Galactic Nuclei, established 30 years ago, has been key to shed light in the taxonomy of such a heterogenous class of objects. Its basic premise is the ubiquitous presence of an obscuring torus around the central engine, so that the observed diversity simply reflects different viewing angles of an axisymmetric geometry. Consequently, type 1 AGNs are observed with a direct view of fast moving material close to the super massive black hole (SMBH), resulting in broad emission lines in their optical/UV spectra, while type-2 AGNs are observed from a more edge-on view, intercepting the obscuring torus that blocks the broad emission line region (BLR) component from our line of sight (LOS). This scheme was consolidated with the discovery of polarized broad emission lines (PBLs), also known as hidden broad-line regions (HBLRs), in the type 2 AGN, hence presenting the same properties as type 1 nuclei in polarized light. Nowadays, additional ingredients are likely needed to account for some observational facts that are apparently in conflict with the predictions. For instance, the UM predicts the absorbing torus as an homogeneous and uniform structure. There is broad evidence, especially at infrared wavelengths, that the dusty torus is indeed clumpy instead uniform. The general goal of this thesis is to endorse the current evidence for the clumplyness of the key element of the standard UM from other wavelengths: X-rays, UV and optical. To this end, we will focus on the study of the absorption variability performed by an interesting Seyfert galaxy: ESO 362-G18. This source gets our whole attention because it is usually classified as a type 1 AGN, however a spectrum retrieved from the 6 degree Galaxy Survey (6dFGS) shows the optical spectrum of ESO 362-G18 to lack its broad emission lines. This type 2 spectrum suggests ESO 362-G18 to be a changing look Seyfert galaxy. This rare type of sources represents a violation of the UMand probes that its corresponding classification is not only angle-dependent. Thus, we decided to start a deep multi-wavelength analysis of ESO 362-G18 to get as many complementary views as possible and approach the intriguing nature of this source...
Download or read book The Interstellar Medium written by James Lequeux and published by Springer Science & Business Media. This book was released on 2005-08-29 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describing interstellar matter in our galaxy in all of its various forms, this book also considers the physical and chemical processes that are occurring within this matter. The first seven chapters present the various components making up the interstellar matter and detail the ways that we are able to study them. The following seven chapters are devoted to the physical, chemical and dynamical processes that control the behaviour of interstellar matter. These include the instabilities and cloud collapse processes that lead to the formation of stars. The last chapter summarizes the transformations that can occur between the different phases of the interstellar medium. Emphasizing methods over results, The Interstellar Medium is written for graduate students, for young astronomers, and also for any researchers who have developed an interest in the interstellar medium.
Download or read book Astrophysics Of Gas Nebulae and Active Galactic Nuclei written by Donald E. Osterbrock and published by University Science Books. This book was released on 2006 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thoroughly revised and expanded throughout, the new edition is a graduate-level text and reference book on gaseous nebulae, nova and supernova remnants. Much of the new data and new images are from the Hubble Space Telescope with two wholly new chapters being added along with other new features. The previous edition which was tried and tested for thirty years has now been succeeded by a revised, updated, larger edition, which will be valuable to anyone seriously interested in astrophysics.
Download or read book Astrophysical and Laboratory Plasmas written by A.J. Willis and published by Springer Science & Business Media. This book was released on 1996-08-31 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: Throughout his career Sir Robert Wilson has demonstrated that advances in a wide variety of fields in astrophysics and laboratory physics are achievable through the application of fundamental plasma spectroscopy. His work has included: optical studies that probed the nature of interstellar dust and first revealed the existence of O star winds; vacuum ultraviolet and X-ray diagnosis of fusion plasmas; rocket ultraviolet and X-ray observations of the Sun; and the conception, development and use of the International Ultraviolet Explorer (IUE) satellite which has contributed greatly to stellar, interstellar and extragalactic astrophysics. This volume contains reviews honouring Sir Robert and reflecting his interests.
Download or read book Active Galactic Nuclei written by Professor R. D. Blandford and published by Springer. This book was released on 2013-12-14 with total page 289 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fifty Years of Quasars written by Mauro D'Onofrio and published by Springer. This book was released on 2014-10-15 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The 50th anniversary of the discovery of quasars in 1963 presents an interesting opportunity to ask questions about the current state of quasar research. Formatted as a series of interviews with noted researchers in the field, each of them asked to address a specific set of questions covering topics selected by the editors, this book deals with the historical development of quasar research and discusses how advances in instrumentation and computational capabilities have benefitted quasar astronomy and have changed our basic understanding of quasars. In the last part of the book the interviews address the current topic of the role of quasars in galaxy evolution. They summarise open issues in understanding active galactic nuclei and quasars and present an outlook regarding what future observational facilities both on the ground and in space might reveal. Its interview format, the fascinating topic of quasars and black holes, and the lively recollections and at times controversial views of the contributors make this book both rewarding and a pleasure to read!
Download or read book The Physics and Chemistry of the Interstellar Medium written by A. G. G. M. Tielens and published by Cambridge University Press. This book was released on 2005-08-25 with total page 520 pages. Available in PDF, EPUB and Kindle. Book excerpt: Publisher Description
Download or read book Jets From Young Stars V written by José Gracia and published by Springer Science & Business Media. This book was released on 2009-11-11 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: Studying the complex physical systems of stellar jets necessitates the incorporation of nonlinear effects which occur on a wide variety of length and timescales. One of the primary methods used to study the physics of jets is numerical simulations that apply high performance computing techniques. Such techniques are also required for analysing the huge modern astrophysical datasets. This book examines those computing techniques. It is a collection of the lectures from the fifth and final school of the JETSET network, "Jets From Young Stars V: High Performance Computing in Astrophysics." It begins with an introduction to parallel programming techniques, with an emphasis on Message Passing Interface (MPI), before it goes on to review grid technology techniques and offer a practical introduction to Virtual Observatory. The second half of the book, then, is devoted to applications of high performance computing techniques, including 3D radiation transfer, to jet and star formation processes. Aimed at graduate students in astrophysics, this book presents state-of-the-art methods, thereby offering interesting new insights to researchers in the field.
Download or read book Astronomy with Radioactivities written by Roland Diehl and published by Springer Science & Business Media. This book was released on 2010-10-02 with total page 577 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book introduces the reader to the field of nuclear astrophysics, i.e. the acquisition and reading of measurements on unstable isotopes in different parts of the universe. The authors explain the role of radioactivities in astrophysics, discuss specific sources of cosmic isotopes and in which special regions they can be observed. More specifically, the authors address stars of different types, stellar explosions which terminate stellar evolutions, and other explosions triggered by mass transfers and instabilities in binary stars. They also address nuclear reactions and transport processes in interstellar space, in the contexts of cosmic rays and of chemical evolution. A special chapter is dedicated to the solar system which even provides material samples. The book also contains a description of key tools which astrophysicists employ in those particular studies and a glossary of key terms in astronomy with radioactivities.
Download or read book A Revised Shapley Ames Catalog of Bright Galaxies written by Allan Sandage and published by . This book was released on 1987 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Pluto System After New Horizons written by S. Alan Stern and published by University of Arizona Press. This book was released on 2021-08-10 with total page 684 pages. Available in PDF, EPUB and Kindle. Book excerpt: Once perceived as distant, cold, dark, and seemingly unknowable, Pluto had long been marked as the farthest and most unreachable frontier for solar system exploration. The Pluto System After New Horizons is the benchmark research compendium for synthesizing our understanding of the Pluto system. This volume reviews the work of researchers who have spent the last five years assimilating the data returned from New Horizons and the first full scientific synthesis of this fascinating system.
Download or read book Galaxies written by Francoise Combes and published by John Wiley & Sons. This book was released on 2021-03-05 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galaxies are vast ensembles of stars, gas and dust, embedded in dark matter halos. They are the basic building blocks of the Universe, gathered in groups, clusters and super-clusters. They exist in many forms, either as spheroids or disks. Classifications, such as the Hubble sequence (based on mass concentration and gas fraction) and the colormagnitude diagram (which separates a blue cloud from a red sequence) help to understand their formation and evolution. Galaxies spend a large part of their lives in the blue cloud, forming stars as spiral or dwarf galaxies. Then, via a mechanism that is still unclear, they stop forming stars and quietly end in the red sequence, as spheroids. This transformation may be due to galaxy interactions, or because of the feedback of active nuclei, through the energy released by their central super-massive black holes. These mechanisms could explain the history of cosmic star formation, the rate of which was far greater in the first half of the UniverseÂs life. Galaxies delves into all of these surrounding subjects in six chapters written by dedicated, specialist astronomers and researchers in the field, from their numerical simulations to their evolutions.
Download or read book Planet Formation written by Wolfgang Brandner and published by Cambridge University Press. This book was released on 2011-02-17 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: When this book was published in 2006, it had been just over ten years since the first planet outside our solar system was detected. Since then, much work has focused on understanding how extrasolar planets may form, and discovering the frequency of potentially habitable Earth-like planets. This volume addresses fundamental questions concerning the formation of planetary systems in general, and of our solar system in particular. Drawing from advances in observational, experimental and theoretical research, it summarises our understanding of the planet formation processes, and addresses major open questions and research issues. Chapters are written by leading experts in the field of planet formation and extrasolar planet studies. The book is based on a meeting held at Ringberg Castle in Bavaria, where experts gathered together to present and exchange their ideas and findings. It is a comprehensive resource for graduate students and researchers, and is written to be accessible to newcomers to the field.
Download or read book Astrophysics Update 2 written by John Mason and published by Springer. This book was released on 2010-11-20 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Astrophysics Updates" is intended to serve the information needs of professional astronomers and postgraduate students about areas of astronomy, astrophysics and cosmology that are rich and active research spheres. Observational methods and the latest results of astronomical research are presented as well as their theoretical foundations and interrelations. The contributed commissioned articles are written by leading exponents in a format that will appeal to professional astronomers and astrophysicists who are interested in topics outside their own specific areas of research. This collection of timely reviews may also attract the interest of advanced amateur astronomers seeking scientifically rigorous coverage.
Download or read book Einstein s Jury written by Jeffrey Crelinsten and published by Princeton University Press. This book was released on 2016-05-31 with total page 429 pages. Available in PDF, EPUB and Kindle. Book excerpt: Einstein's Jury is the dramatic story of how astronomers in Germany, England, and America competed to test Einstein's developing theory of relativity. Weaving a rich narrative based on extensive archival research, Jeffrey Crelinsten shows how these early scientific debates shaped cultural attitudes we hold today. The book examines Einstein's theory of general relativity through the eyes of astronomers, many of whom were not convinced of the legitimacy of Einstein's startling breakthrough. These were individuals with international reputations to uphold and benefactors and shareholders to please, yet few of them understood the new theory coming from the pen of Germany's up-and-coming theoretical physicist, Albert Einstein. Some tried to test his theory early in its development but got no results. Others--through toil and hardship, great expense, and perseverance--concluded that it was wrong. A tale of international competition and intrigue, Einstein's Jury brims with detail gleaned from Crelinsten's far-reaching inquiry into the history and development of relativity. Crelinsten concludes that the well-known British eclipse expedition of 1919 that made Einstein famous had less to do with the scientific acceptance of his theory than with his burgeoning public fame. It was not until the 1920s, when the center of gravity of astronomy and physics shifted from Europe to America, that the work of prestigious American observatories legitimized Einstein's work. As Crelinsten so expertly shows, the glow that now surrounds the famous scientist had its beginnings in these early debates among professional scientists working in the glare of the public spotlight.
