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Author : Alice Eltvedt
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (134 download)
Download or read book The Quasar Proximity Effect and the Intergalactic Medium at Low Redshift written by Alice Eltvedt and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Alexander Peter Calverley
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (798 download)
Download or read book Probing the Intergalactic Medium with High-redshift Quasars written by Alexander Peter Calverley and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Clues about the timing of reionization and the nature of the ionizing sources responsible are imprinted in the ionization and thermal state of the IGM. In this thesis, I use high-resolution quasar spectra in conjunction with state-of-the-art hydrodynamical simulations to probe the IGM at high redshift, focusing on the ionization and thermal state of the gas. After reionization, the ionization state of the IGM is set by the intensity of the ultraviolet background(UVB), quantified by the hydrogen photoionization rate,?_bkg. At high redshifts this has been estimated by measuring the mean flux in the Ly? forest, and scaling?_bkg in simulations such that the simulated mean flux matches the observed value. In Chapter 3 I investigate whether the precision of these estimates can be improved by using the entire flux probability distribution function (PDF) instead of only the mean flux. Although I find it cannot improve the precision directly, the flux PDF can potentially be used to constrain other sources of error in observational estimates of?_bkg, and somay increase the precision indirectly. The ionizing output of a quasar will locally dominate over the UVB, and this leads to enhanced transmission bluewards of the quasar Ly? line, known as the proximity effect. In Chapter 4 I present the first measurements of?_bkg at z> 5 from the proximity effect. The UVB intensity declines smoothly with redshift over 4.6 z 6.4, implying a smooth evolution in the mean free path of ionizing photons. This suggests that reionization ends at z 6.4. There is a drop in?_bkg by roughly a factor of five, which corresponds to a drop in the ionizing emissivity by about a factor of two. Such a redshift evolution in the emissivity cannot continue to much higher redshift without reionization failing to complete, which suggests that reionization cannot have ended much higher than z = 6.4. Estimates of?_bkg from the proximity effect and the mean flux are generally discrepant at z? 2?4, with those from the proximity effect systematically higher. This is generally attributed to effects of the quasar environment. I investigate the significance of several environmental biases on proximityeffect measurements at z? 5?6 in Chapter 5. The biases are found to be small, and so the proximity effect is expected to give relatively unbiased estimates of?_bkg at z 5, in contrast to lower redshifts. Photoionization heats the gas in the IGM, and so the thermal history of the IGM provides important constraints on reionization. The thermal state of the IGM is reflected in the level of small-scalestructure in the Ly? forest. In Chapter 6 I quantify the small-scale structure using two independent statistics, the curvature and the peakiness, and convert these into a temperature by comparing with simulations. These are the first measurements of the temperature in the general IGM at z> 5. Bothstatistics show an increase in the temperature by a factor of roughly two from z = 4.4 to 5.6. This rise is sensitive, however, to any smoothing of the gas density distribution due to the thermal historyspanning reionization. I find that this should only be a small effect, as otherwise the corrected temperatures at z? 4?5 are implausibly low. The temperature evolution therefore suggests a late reionization. The temperatures at z? 4.8 are well fit by an adiabatic cooling curve, for which reasonablepeak temperatures at the end of reionization are reached at 6? z? 7. The temperatures atz? 4?5 are consistent with reionization being carried out by Pop II stars. In conclusion, the ionization and thermal state of the IGM at z? 5?6 suggest a late hydrogen reionization, driven by star-forming galaxies and ending around 6.5? z? 7. This is consistent with other recent lines of observational evidence, and supports theoretical models that infer a late reionization from the observed star formation rate history.
Author : Patrick Petitjean
Publisher : Atlantica Séguier Frontières
ISBN 13 : 9782863322291
Total Pages : 490 pages
Book Rating : 4.3/5 (222 download)
Download or read book Structure and Evolution of the Intergalactic Medium from QSO Absorption Line Systems written by Patrick Petitjean and published by Atlantica Séguier Frontières. This book was released on 1997 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Adam Andrew Miller
Publisher :
ISBN 13 :
Total Pages : 44 pages
Book Rating : 4.:/5 (724 download)
Download or read book Quasar Continuum Fitting and Silicon Absorption on the Low Redshift Intergalactic Medium written by Adam Andrew Miller and published by . This book was released on 2006 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present results on the evolution of Ly[alpha] absorption at low redshift, and the first systematic search for Si II absorption systems in the low redshift IGM. Our sample consists of 832 Ly[alpha] absorbers from 328 spectra of 204 QSOs taken from the Hubble Space Telescope archive. We develop a new, reproducible method of quasar continuum fitting, designed to quickly identify absorption lines and measure the relative line strength (a proxy for equivalent width). Our method, which fails to identify the weakest lines, does manage to detect the strong features in a given spectrum and provides enough information to identify metal absorption line systems. We confirm the results of previous studies of Ly[alpha] evolution at low redshift and find the number density of absorbers can be described by a power law in (l+z) that is much flatter than that found for Lya evolution at high redshift. Specifically, we measure a power law index of [gamma] = 0.57 ± 0.16 for lines with a rest relative line strength greater than 0.10 [Angstroms]. We also identify the presence of 14 Si II systems at z [approx] 1. The number of Si ii 1193 and 1260 [Angstroms] systems per unit redshift path length at a mean redshift of z = 0.9 is N(z)= 1.6 ± 0.6. This density is similar to that found for C Ii, Mg ii, and O vi absorbers.
Author : Shigeru Kubono
Publisher : World Scientific
ISBN 13 : 9814546607
Total Pages : 472 pages
Book Rating : 4.8/5 (145 download)
Download or read book Origin Of Matter And Evolution Of Galaxies written by Shigeru Kubono and published by World Scientific. This book was released on 1997-05-07 with total page 472 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on nucleosynthesis and chemical evolution of the universe. The discussion on the universe, using a common language of atomic elements and nucleosynthesis, is presented by leading figures from a wide variety of fields — astronomy, astrophysics, cosmology, nuclear physics and particle physics. One of the highlights is the paper on MACHO's by C Alcock, which was the first to be released to the world. Perspectives of the fields are also presented, such as the SUBARU project and the Radioactive Nuclear Beam Project at INS, University of Tokyo.
Author : Malcolm Longair
Publisher : Springer Science & Business Media
ISBN 13 : 3540734775
Total Pages : 1481 pages
Book Rating : 4.5/5 (47 download)
Download or read book Galaxy Formation written by Malcolm Longair and published by Springer Science & Business Media. This book was released on 2007-12-12 with total page 1481 pages. Available in PDF, EPUB and Kindle. Book excerpt: Delineating the huge strides taken in cosmology in the past ten years, this much-anticipated second edition of Malcolm Longair's highly appreciated textbook has been extensively and thoroughly updated. It tells the story of modern astrophysical cosmology from the perspective of one of its most important and fundamental problems – how did the galaxies come about? Longair uses this approach to introduce the whole of what may be called "classical cosmology". What’s more, he describes how the study of the origin of galaxies and larger-scale structures in the Universe has provided us with direct information about the physics of the very early Universe.
Author : Hayley Finley
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (896 download)
Download or read book Overdense Regions in the Intergalactic Medium and the Environments of High-redshift Quasars written by Hayley Finley and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Ragini Singh
Publisher :
ISBN 13 :
Total Pages : 240 pages
Book Rating : 4.:/5 (896 download)
Download or read book Quasars and the Transverse Proximity Effect written by Ragini Singh and published by . This book was released on 2012 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quasars, first identified in the 1960s, have been used as cosmological probes to study the Inter-Galactic Medium. This includes the process of its metal enrichment and how material is clustered at different scales in the high redshift Universe. The effect of quasars on their environment can help shed light on the variability of their luminosity and anisotropies in the geometry of the quasar radiation field. One way to probe the effects of quasars on their environment is through the Transverse Proximity Effect (TPE). The TPE should be visible as a diminution of the Lyman-alpha forest absorption in the spectrum of a background quasar, at a foreground quasar's redshift, when the two quasars are transversely separated by 5 Mpc. Alternatively, the TPE can also be detected as a local enhancement of the ionising radiation field proximate to the foreground quasar, via the strength of different atomic species in the background quasar's spectrum. This thesis aims to use the CFHTLS data to search for quasar pairs at z 2.2 having small transverse separations on the sky by using an efficient selection method, which we prove is capable of detecting numerous rare proximate quasar pairs. The best pairs can be used to detect the TPE by analysing the metal lines in the spectrum of the background quasar, a technique demonstrated in this thesis that is superior to simply using the diminution of the Lyman-alpha forest absorption as a detection tool. Such studies can reveal important information regarding quasar lifetimes and opening angles when conducted on a statistically significant scale. We utilise an effective statistical technique, Kernel Density Estimation (KDE), to select quasars from the photometric data sets using the ugriz colour space. The KDE algorithm has been successfully applied to the CFHTLS data, detecting 1,000 quasars at z > 2.2, using the AAOmega spectrograph on the Anglo-Australian Telescope. We have detected 40 TPE candidates, with one standout candidate in our sample due to its small angular separation (11.9"), with the foreground quasar at z = 2.23 and background quasar at z = 2.56. We have followed-up this best pair using MIKE (echelle spectrograph) on Magellan. The background quasar's spectrum has revealed two metal absorption systems lying close to the redshift of the foreground quasar (z = 2.23). We have identified absorption features due to HI, CIV, CII, SiIV and SiII in our data. Photoionisation modelling of these absorbers using MAPPINGS III, based on the column densities of the metal lines, has revealed that the absorbers are being ionised by the foreground quasar, i.e. we detect the TPE as an enhancement in the ionisation, above the UV background, proximate to the foreground quasar. The fact that the quasar is affecting both the metal line absorbers which lie within its ionisation region suggests that its radiation cone has a half angle that is quite wide (> 45 degrees). Since the transverse separation between our two quasars is ~100 kpc, we find that the minimum lifetime of our foreground quasar is ~ 0.3 Myr.
Author : Keri L. Dixon
Publisher :
ISBN 13 :
Total Pages : 113 pages
Book Rating : 4.:/5 (848 download)
Download or read book Inhomogeneous He II Reionization and Its Implications for the Intergalactic Medium written by Keri L. Dixon and published by . This book was released on 2012 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent observations suggest that quasars fully ionize helium around redshift z ~ 3. Most directly, the optical depth derived from the He II Lyman-[alpha] (Ly[alpha]) forest fluctuates significantly above and near z ~ 2.8 and then evolves smoothly at lower redshifts. These fluctuations may be indicative of patchy He II reionization, which is expected (primarily) due to the rarity and brightness of quasars and the inhomogeneous intergalactic medium. This dissertation presents approximate methods for interpreting observations of this epoch and quantifying the magnitude of fluctuations. From these opacity measurements, we compute, using a semi-analytic model, the evolution of the mean photoionization rate and attenuation length for helium over the redshift range 2.0 z 3.2. The average effective optical depth indicates a sharp decrease in the photoionization rate and, provided the quasar emissivity evolves smoothly, in the effective attenuation length at z ~ 2.8. A simple model with reionization ending at z ~ 2.7 is most consistent with the data, although the constraints are weak thanks to sparse, uncertain data. We further present a fast, semi-numeric procedure to approximate detailed cosmological simulations. We produce the distribution of dark matter halos, ionization state of helium, and density field at z = 3 in broad agreement with recent simulations. Given our speed and flexibility, we investigate a range of source and active quasar prescriptions. We find order-of-magnitude fluctuations in the He II ionization rate in the post-reionization Universe. During reionization, the fluctuations are even stronger and develop a bimodal distribution, in contrast with semi-analytic models and the hydrogen equivalent. We also examine large-scale fluctuations in the He II Ly[alpha]; forest transmission during and after He II reionization. Like previous studies, we show that the rarity of quasars and the inhomogeneous intergalactic medium induce order unity fluctuations in the mean optical depth after reionization, even when averaged over large segments (~10-100 Mpc in length). During reionization, we find a broader distribution with an extended high-opacity tail. These conclusions are fairly insensitive underlying model assumptions, including quasar properties and the mean free path of photons. We compare to existing data along ~10 He II Ly[alpha]; forest lines of sight spanning z ~ 2 - 3.2, demonstrating that the observed fluctuations are likely due to ongoing reionization.
Author : William C. Keel
Publisher : Springer Science & Business Media
ISBN 13 : 3540725350
Total Pages : 277 pages
Book Rating : 4.5/5 (47 download)
Download or read book The Road to Galaxy Formation written by William C. Keel and published by Springer Science & Business Media. This book was released on 2007-08-17 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation of galaxies is one of the greatest puzzles in astronomy, the solution is shrouded in the depths of space and time, but has profound implications for the universe we observe today. This book discusses the beginnings of the process from cosmological observations and calculations. It examines the different theories of galaxy formation and shows where each theory either succeeds or fails in explaining what we actually observe. In addition, the book looks ahead to what we may expect to uncover about the epoch of galaxy formation from the new and upcoming generations of telescopes and technology.
Author : Rudy C. Gilmore
Publisher :
ISBN 13 :
Total Pages : 460 pages
Book Rating : 4.:/5 (81 download)
Download or read book Extragalactic Background Light and Gamma-ray Attenuation written by Rudy C. Gilmore and published by . This book was released on 2009 with total page 460 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Menas Kafatos
Publisher : Springer Science & Business Media
ISBN 13 : 9400901453
Total Pages : 569 pages
Book Rating : 4.4/5 (9 download)
Download or read book Examining the Big Bang and Diffuse Background Radiations written by Menas Kafatos and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 569 pages. Available in PDF, EPUB and Kindle. Book excerpt: IAU Symposium No. 168, Examining the Big Bang and Diffuse Background Radiations, took place on August 23-26, 1994 at the XXIInd IAU General Assembly in the Hague, Netherlands. The meeting attracted a large number - over 250 - of astronomers, reflecting the strong interest engendered by the great advances in cosmology made in recent years. There is still a multitude of unresolved problems in modern cosmology and the symposium offered a wonderful occasion to examine them objectively, at a place where many leading workers in related fields gathered together. After the introduction by IAU President L. Woltjer and the historical background by Vice Present Virginia Trimble, the volume begins with reviews of the cosmic microwave radiation from COBE (Cosmic Background Explorer). Reviews of recent observations then extend from radio to infrared, visible light, ultraviolet, X-rays and gamma-rays. It is followed by theoretical models for the Big Bang and Inflation, and alternative views to the Big Bang. Following a discourse on Probes and Future Tests, the meeting ended with a Panel Discussion on `Major Unsolved Problems of Cosmology'. Some forty-four contributed papers - both oral and poster reports - are included after the invited talks and panel discussions.
Author : Georges Meylan
Publisher : Springer Science & Business Media
ISBN 13 : 3540494588
Total Pages : 481 pages
Book Rating : 4.5/5 (44 download)
Download or read book QSO Absorption Lines written by Georges Meylan and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 481 pages. Available in PDF, EPUB and Kindle. Book excerpt: The controversial question of whether the majority of the narrow absorption lines observed in QSO spectra represent cosmological intervening systems or ejecta from the QSO themselves is settled. QSO absorption line spectroscopy, initially a mere technique, has matured into an essential extragalactic research tool for understanding the content of the Universe at redshifts between 0 and 4, and beyond. The only previous important meeting devoted to "QSO Absorption Lines" was held in May 1987 at the Space Telescope Science Institute in Baltimore, Maryland, U.S.A. Since that time, nearly a decade ago, research has been ex tremely active in this now well-established field of astrophysics. Theoretical stud ies and simulations have taken advantage of the constant progress in computer technology, and during these last few years, the observational results have bene fited largely from the new facillities offered by the Hubble Space Telescope in the UV wavelength range and the Keck Telescope for high-resolution spectroscopy.
Author : Donald E. Osterbrock
Publisher : University Science Books
ISBN 13 : 9781891389344
Total Pages : 488 pages
Book Rating : 4.3/5 (893 download)
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.
Author : David Levy
Publisher : St. Martin's Press
ISBN 13 : 1466876131
Total Pages : 656 pages
Book Rating : 4.4/5 (668 download)
Download or read book The Scientific American Book of the Cosmos written by David Levy and published by St. Martin's Press. This book was released on 2014-07-22 with total page 656 pages. Available in PDF, EPUB and Kindle. Book excerpt: Finally, the entire body of our scientific knowledge of the universe is available in one definitive volume. Scientific American, the oldest and most popular science magazine in the world, has prepared the most comprehensive and comprehensible book on the subject ever. Under the direction of renowned astronomer David H. Levy, this spectacular book assembles the best minds in science to give clear and accessible explanations of the nature of the cosmos. Newly commissioned essays by working scientists at the top of their fields and classic writings by such luminaries as Albert Einstein, Francis Crick, and Carl Sagan take us to the frontiers of space and time-from sub-atomic particles to the edge of the universe. Both thoughtful and provocative, this book asks-and answers-the big questions, such as: o How did our solar system evolve? o What forces lie at the center of the atom? o What is the size of the universe? o What is dark matter? o What is the possibility of extraterrestrial life? o What is the importance of superstrings? o How do galaxies form? Dazzling full-color and black-and-white photographs aid in articulating the latest theories about the size, age, nature, and expansion of the universe, and make this book a delight to behold. Essays are grouped by topic, from the largest phenomena, such as the formation of the universe, down to the smallest detail, such as the makeup of an atom. In addition, each section contains an illuminating introduction by David Levy that binds the essays together and creates a whole picture. The Scientific American Book of the Cosmos is a valuable addition to the bookshelf of both professional astronomers and science enthusiasts alike.
Author : Abraham Loeb
Publisher : Princeton University Press
ISBN 13 : 1400845602
Total Pages : 560 pages
Book Rating : 4.4/5 (8 download)
Download or read book The First Galaxies in the Universe written by Abraham Loeb and published by Princeton University Press. This book was released on 2013-01-15 with total page 560 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive, self-contained introduction to one of the most exciting frontiers in astrophysics today: the quest to understand how the oldest and most distant galaxies in our universe first formed. Until now, most research on this question has been theoretical, but the next few years will bring about a new generation of large telescopes that promise to supply a flood of data about the infant universe during its first billion years after the big bang. This book bridges the gap between theory and observation. It is an invaluable reference for students and researchers on early galaxies. The First Galaxies in the Universe starts from basic physical principles before moving on to more advanced material. Topics include the gravitational growth of structure, the intergalactic medium, the formation and evolution of the first stars and black holes, feedback and galaxy evolution, reionization, 21-cm cosmology, and more. Provides a comprehensive introduction to this exciting frontier in astrophysics Begins from first principles Covers advanced topics such as the first stars and 21-cm cosmology Prepares students for research using the next generation of large telescopes Discusses many open questions to be explored in the coming decade
Author : Andrei Mesinger
Publisher : Springer
ISBN 13 : 331921957X
Total Pages : 292 pages
Book Rating : 4.3/5 (192 download)
Download or read book Understanding the Epoch of Cosmic Reionization written by Andrei Mesinger and published by Springer. This book was released on 2015-11-28 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: The dawn of the first stars, galaxies and black holes signaled a fundamental milestone in our Universe’s evolution: the Epoch of Reionization. The light from these galactic ancestors began spreading out, ionizing virtually every atom in existence. Our Universe transitioned from darkness to light, from cold to hot, from simple and boring to the wondrous cosmic zoo we see around us today. Despite its importance, observations of reionization have been few, and their interpretation has been highly controversial. Fortunately, this is rapidly changing. We will soon enter the "Big Data” era of this mysterious epoch, driven by an upcoming wave of observations with state-of-the-art telescopes as well as new sophisticated analysis tools. The aim of this volume is to summarize the current status and future outlook of the reionization field. We bring together leading experts in many sub-disciplines, highlighting the measurements that will illuminate our understanding of reionization and the cosmic dawn: (i) 21cm interferometry; (ii) high-redshift quasar spectra; (iii) high-redshift galaxy surveys; (iv) primary and secondary anisotropies of the Cosmic Microwave Background; (v) high-resolution studies of the metal content of early galaxies. We seek a roadmap to interpreting the wealth of upcoming observations. What is the best use of limited observational resources? How do we develop theoretical tools tailored for each observation? Ultimately, what will we learn about the epoch of reionization and our galactic ancestors?
