Download or read book Towards a Complete Census of Active Galactic Nuclei in the Nearby Universe written by Andrew Goulding and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As it is well established that almost all galaxies host a central supermassive black hole (SMBH), it is natural to ask, how many of these SMBHs are actively accreting? Studies aimed at answering this question can better define the fraction of nearby galaxies that harbour active galactic nuclei (AGNs), provide constraints on the growth of local SMBHs, and further our understanding towards the connection between AGN activity and galaxy evolution. In the first part of this thesis, we use high-quality mid-infrared (IR) spectroscopy to investigate the ubiquity of AGN activity in a complete volume-limited sample of nearby galaxies to D15 Mpc. We present analyses based on the detection of high-excitation emission lines to unambiguously identify AGNs in even the most heavily dust-obscured and gas-rich galaxies. We find that almost half of the AGN population are not identified in large-scale optical surveys, most likely due to strong circumnuclear star-formation activity and/or extinction through the host galaxy. In the second part of this thesis, we use sensitive hard X-ray (2-10 keV) and mid-IR constraints to calculate bolometric luminosities of these D15 Mpc AGNs and combine these luminosities with well-constrained SMBH masses to estimate relative mass accretion rates. We use these data to calculate the volume-average SMBH growth rate of galaxies in the local Universe and find that AGNs hosting SMBHs with M_BH ~ 10 6-10 7 M_o are dominated by optically unidentified AGNs. These relatively small SMBHs are acquiring a significant proportion of their mass in the present-day and are amongst the most rapidly growing in the local Universe. In the third part of this thesis, we using [NeV]3427A as an unambiguous indicator of AGN activity to assess the incidence of AGNs in a statistically significant galaxy sample derived from the Sloan Digital Sky Survey (SDSS). On the basis of [NeV], we find strong empirical evidence that the theoretical maximum starburst limit provides a good identification threshold for AGNs. However, we find that only ~27% of Seyfert galaxies have strong detections of [NeV]3427A in their optical spectroscopy. Using spectral stacking analyses we determine that the lack of high-ionisation emission line signatures are due to poor spectral sensitivity and/or high levels of dust extinction. In the final part of this thesis, we use a suite of mid-IR, optical and X-ray luminosity indicators to search for Compton-thick AGNs at z~0.03-0.2, a region of parameter space which is currently poorly constrained by deep narrow-field X-ray surveys. We use the XMM-Newton serendipity survey and the SDSS to select a sample of 14 candidate Compton-thick AGNs. On the basis of the optical [OIII], mid-IR [OIV] and 6um AGN continuum luminosities we conservatively find that the X-ray emission in almost half of our sample appear to be attenuated by a factor15, i.e., they are likely to be obscured by Compton-thick material with N_H 1.5 x 10 24 cm -2. Under the reasonable assumption that our 14 AGNs are representative of the overall X-ray undetected AGN population in the SDSS-XMM parent sample, we estimate that>20% of the optical Type-2 AGN population are likely to be obscured by Compton-thick material. These Compton-thick AGNs identified in our sample harbour some of the most rapidly growing SMBHs in the nearby Universe. Overall, the techniques and results presented in this thesis have arguably provided the most complete and unambiguous census of AGN activity in nearby galaxies to date.
Download or read book Active Galactic Nuclei from He Ii a More Complete Census of AGN in SDSS Galaxies Yields a New Population of Low luminosity AGN in Highly Star forming Galaxies written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Active Galactic Nuclei written by Volker Beckmann and published by John Wiley & Sons. This book was released on 2012-09-24 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active Galactic Nuclei This AGN textbook gives an overview on the current knowledge of the Active Galacitc Nuclei phenomenon. The spectral energy distribution will be discussed, pointing out what can be observed in different wavebands. The different physical models are presented together with formula important for the understanding of AGN physics. Furthermore, the authors discuss the AGN with respect to its environment, host galaxy, feedback in galaxies and in clusters of galaxies, variability, etc. and finally the cosmological evolution of the AGN phenomenon. This book includes phenomena based on new results in the X-Ray and gamma-ray domain from new telescopes such as Chandra, XMM-Newton, the Fermi Gamma-Ray Space Telescope, and the VHE regime not mentioned so far in AGN books. Those and other new developments as well as simulations of AGN merging events and formations, enabled through latest super-computing capabilities. From the contents: The observational picture of AGN Radiative processes The central engine AGN types and unification AGN through the electromagnetic spectrum AGN variability Environment Quasars and cosmology Formation, evolution and the ultimate fate of AGN What we do not know (yet)
Download or read book The Nearest Active Galaxies written by J. E. Beckman and published by Editorial CSIC - CSIC Press. This book was released on 1993 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Census of Mid Infrared Selected Active Galactic Nuclei in Massive Galaxy Clusters at 0 written by Adam R. Tomczak and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We conduct a deep mid-infrared census of nine massive galaxy clusters at (0 z 1.3) with a total of ~ 1500 spectroscopically confirmed member galaxies using Spitzer /IRAC photometry and established mid-infrared color selection techniques. Of the 949 cluster galaxies that are detected in at least three of the four IRAC channels at the = 3 sigma level, we identify 12 that host mid-infrared selected active galactic nuclei (IR-AGN). To compare the IR-AGN across our redshift range, we define two complete samples of cluster galaxies: (1) optically-selected members with rest-frame VAB magnitude -21.5 and (2) mid-IR selected members brighter than (M*_3.6 +0.5), i.e. essentially a stellar mass cut. In both samples, we measure fIR-AGN ~ 1% with a strong upper limit of ~3% at z
Download or read book Active Galactic Nuclei written by Volker Beckmann and published by John Wiley & Sons. This book was released on 2013-08-29 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active Galactic Nuclei This AGN textbook gives an overview on the current knowledge of the Active Galacitc Nuclei phenomenon. The spectral energy distribution will be discussed, pointing out what can be observed in different wavebands. The different physical models are presented together with formula important for the understanding of AGN physics. Furthermore, the authors discuss the AGN with respect to its environment, host galaxy, feedback in galaxies and in clusters of galaxies, variability, etc. and finally the cosmological evolution of the AGN phenomenon. This book includes phenomena based on new results in the X-Ray and gamma-ray domain from new telescopes such as Chandra, XMM-Newton, the Fermi Gamma-Ray Space Telescope, and the VHE regime not mentioned so far in AGN books. Those and other new developments as well as simulations of AGN merging events and formations, enabled through latest super-computing capabilities. From the contents: The observational picture of AGN Radiative processes The central engine AGN types and unification AGN through the electromagnetic spectrum AGN variability Environment Quasars and cosmology Formation, evolution and the ultimate fate of AGN What we do not know (yet)
Download or read book The Physics and Evolution of Active Galactic Nuclei written by Hagai Netzer and published by Cambridge University Press. This book was released on 2013-09-16 with total page 369 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive introduction to the theory underpinning our study of active galactic nuclei and the ways we observe them.
Download or read book Active Galactic Nuclei written by John Edward Dyson and published by Manchester University Press. This book was released on 1985 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Low Ionization Nuclear Emission Line Regions written by Rachel Dudik and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The horizon of the universe, once thought to extend only to the disk of the Milky Way, is now known to embrace a host of diverse galaxies, from active galaxies such as quasars and Seyfert galaxies to normal galaxies such as our own. The recent discovery that virtually all local galaxies harbor massive nuclear black holes, has provided convincing evidence that active galactic nuclei (AGNs) and normal galaxies are indeed connected. The nature of this connection and the evolutionary history connecting them, however, continues to be elusive. Low Ionization Nuclear Emission-line Regions (LINERs) are the dominant population of 'active' galaxies in our local universe and may indeed be the missing piece to the evolutionary puzzle. LINERs are dened by optical line ratios uncharacteristic of photoionization by normal main sequence stars. While classical AGNs represent at most a few percent of the galaxy population, LINERs constitute as much as 50% of the total local extragalactic population. However, despite several decades of intense research, the ionization mechanism responsible for the unusual LINER spectrum remains a mystery. What is the ionization mechanism responsible for the empirical line ratios characteristic of LINER galaxies? How do LINERs t into the overall evolution of galaxies as we know it? Are LINERs a subclass of AGN? What is the evolutionary connection, if any, between galaxies with heavy starburst activity and AGNs? The majority of LINERs are dust enshrouded and therefore very luminous in the far-infrared. The far-infrared (far-IR) luminosity to the luminosity in the optical Bband (center = 4400A), the so-called IR-brightness ratio, can be used as a gauge of the amount of dust in host galaxy. LINERs span a wide range of LFIR/LB ratios, tending predominantly toward the IR-bright end. However, the majority of research to-date has been based on optically selected samples which are partial toward IR-faint LINERs. This bias toward IR-faint galaxies could have important consequences on statistical analyses which examine the fraction of LINERs hosting AGNs. In order for an accurate picture of LINERs to emerge, IR-bright as well as IR-faint galaxies must be studied. What fraction of IR-bright LINERs are AGNs? In light of the open questions regarding these remarkable objects, the central goal of this dissertation is to carry out a systematic multi-wavelength X-ray imaging and Infrared spectroscopic survey of nearby LINERs spanning a wide range of IRbrightness ratios in order to 1) characterize the dominant energy source responsible for their optical line ratios, 2) compare the AGN detection rate in our infrared selected sample with the optically selected samples, 3) determine the luminosities, spectral characteristics and accretion properties of the AGN-LINERs and compare them with the standard active galaxies, and nally, 4) relate the host galaxies properties to the properties of the central source in an attempt to constrain the role of LINERs in galaxy evolution and formation models"--Abstract
Download or read book Quasars at All Cosmic Epochs written by Paola Marziani and published by Frontiers Media SA. This book was released on 2018-10-05 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: The last 50 years have seen a tremendous progress in the research on quasars. From a time when quasars were unforeseen oddities, we have come to a view that considers quasars as active galactic nuclei, with nuclear activity a coming-of-age experienced by most or all galaxies in their evolution. We have passed from a few tens of known quasars of the early 1970s to the 500,000 listed in the catalogue of the Data Release 14 of the Sloan Digital Sky Survey. Not surprisingly, accretion processes on the central black holes in the nuclei of galaxies — the key concept in our understanding of quasars and active nuclei in general — have gained an outstanding status in present-day astrophysics. Accretion produces a rich spectrum of phenomena in all bands of the electromagnetic spectrum. The power output of highly-accreting quasars has impressive effects on their host galaxies. All the improvement in telescope light gathering and in computing power notwithstanding, we still miss a clear connection between observational properties and theory for quasars, as provided, for example, by the H-R diagram for stars. We do not yet have a complete self-consistent view of nuclear activity with predictive power, as we do for main-sequence stellar sources. At the same time quasars offer many “windows open onto the unknown". On small scales, quasar properties depend on phenomena very close to the black hole event horizon. On large scales, quasars may effect evolution of host galaxies and their circum-galactic environments. Quasars’ potential to map the matter density of the Universe and help reconstruct the Universe’s spacetime geometry is still largely unexploited. The times are ripe for a critical assessment of our present knowledge of quasars as accreting black holes and of their evolution across the cosmic time. The foremost aim of this research topic is to review and contextualize the main observational scenarios following an empirical approach, to present and discuss the accretion scenario, and then to analyze how a closer connection between theory and observation can be achieved, identifying those aspects of our understanding that are still on a shaky terrain and are therefore uncertain knowledge. This research topic covers topics ranging from the nearest environment of the black hole, to the environment of the host galaxies of active nuclei, and to the quasars as markers of the large scale structure and of the geometry of spacetime of the Universe. The spatial domains encompass the accretion disk, the emission and absorption regions, circum-nuclear starbursts, the host galaxy and its interaction with other galaxies. Systematic attention is devoted to some key problems that remain outstanding and are clearly not yet solved: the existence of two quasar classes, radio quiet and radio loud, and in general, the systematic contextualization of quasar properties the properties of the central black hole, the dynamics of the accretion flow in the inner parsecs and the origin of the accretion matter, the quasars’ small and large scale environment, the feedback processes produced by the black hole into the host galaxy, quasar evolutionary patterns from seed black holes to the present-day Universe, and the use of quasars as cosmological standard candles. The timing is appropriate as we are now witnessing a growing body of results from major surveys in the optical, UV X, near and far IR, and radio spectral domains. Radio instrumentation has been upgraded to linear detector — a change that resembles the introduction of CCDs for optical astronomy — making it possible to study radio-quiet quasars at radio frequencies. Herschel and ALMA are especially suited to study the circum-nuclear star formation processes. The new generation of 3D magnetohydrodynamical models offers the prospective of a full physical modeling of the whole quasar emitting regions. At the same time, on the forefront of optical astronomy, applications of adaptive optics to long-slit spectroscopy is yielding unprecedented results on high redshift quasars. Other measurement techniques like 2D and photometric reverberation mapping are also yielding an unprecedented amount of data thanks to dedicated experiments and instruments. Thanks to the instrumental advances, ever growing computing power as well as the coming of age of statistical and analysis techniques, the smallest spatial scales are being probed at unprecedented resolution for wide samples of quasars. On large scales, feedback processes are going out of the realm of single-object studies and are entering into the domain of issues involving efficiency and prevalence over a broad range of cosmic epochs. The Research Topic "Quasars at all Cosmic Epochs" collects a large fraction of the contributions presented at a meeting held in Padova, sponsored jointly by the National Institute for Astrophysics, the Padova Astronomical Observatory, the Department of Physics and Astronomy of the University of Padova, and the Instito de Astrofísica de Andalucía (IAA) of the Consejo Superiór de Investigación Cientifica (CSIC). The meeting has been part of the events meant to celebrate the 250th anniversary of the foundation of the Padova Observatory.
Download or read book Big Bang Active Galactic Nuclei and Supernovae Paper written by S. Hayakawa and published by . This book was released on 1989 with total page 642 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Active Galactic Nuclei written by T. Courvoisier and published by . This book was released on 1992 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Active Galactic Nuclei written by Suzy Collin and published by . This book was released on 2003 with total page 774 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Not Dead Yet written by Kristina Nyland and published by . This book was released on 2015 with total page 446 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Spectroscopic Survey of Nearby Galactic Nuclei written by Luis Chi Ho and published by . This book was released on 1995 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Buried Treasure in Our Backyard written by Christopher Alan Dieck and published by . This book was released on 2008 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt:
