Download or read book High resolution Ultraviolet Spectroscopy of Gas in Galaxy Halos and Large scale Structures written by Limin Song and published by . This book was released on 2011 with total page 191 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents spectroscopic studies of gas in galaxy halos and large-scale structures through high-resolution quasar absorption lines. The broad goal of this effort is to learn how galaxies acquire their gas and how they return it to the intergalactic medium, or more generally, how galaxies interact with their environment. The study of the absorption lines due to the extraplanar 21cm "Outer Arm'' (OA) of the Milky Way toward two quasars, H1821+643 and HS0624+6907, provides valuable insight into the gas accretion processes. It yields the following results. (1) The OA is a multiphase cloud and high ions show small but significant offsets in velocity and are unlikely to be cospatial with the low ions. (2) The overall metallicity of the OA is Z=0.3-0.5 of the solar abundance, but nitrogen is underabundant. (3) The abundance of N, O, and S derived are roughly consistent with outer-galaxy emission-line abundances and the metallicity gradient derived from H II regions. The similarity of the OA kinematics to several nearby high velocity clouds (HVCs, e.g. Complexes C, G, and H) suggests that these clouds could be detritus from a merging satellite galaxy. To test this hypothesis, we build up a simple model including tidal tripping, ram-pressure stripping, and dynamical friction to consider whether the OA could be debris affiliated with the Monoceros Ring. Our model can roughly reproduce the spatial and velocity characteristics of the OA. Moreover, the metallicity of the OA is similar to the higher metallcities measured in the younger stellar components of the Monoceros Ring and the progenitor candidate, the CMa overdensity. However, both our model and the Galactic warp scenario can not explain other HVCs that are likely to be related to the OA. Instead of acquiring gas, some galaxies have their gas removed through various physical processes. Ram-pressure stripping and tidal interaction are important mechanisms for galaxies to loose their gas. The high-resolution spectrum of Mrk205 combined with H I 21 cm, CO emission, and infrared observations is utilized to study a unique transforming galaxy NGC4319. We find: (1) the object has lost most of its diffuse interstellar H I. (2) molecular hydrogen remains in the disk of the galaxy. The molecular hydrogen column density is low, but the molecular gas fraction is extraordinarily high. CO emission is also clearly detected, but only from the barred central region. (3) There is very little evidence of recent star formation in the galaxy. The results appears to match many of the predictions of Quilis et al. (2000), suggesting NGC4319 is undergoing a transformation from a spiral into an S0 due to ram-pressure stripping, possibly in tandem with tidal stripping. To understand the characteristics of gas (especially warm-hot intergalactic medium) in large scale structures, similar high resolution spectra of 31 quasars were selected based on the galaxy density showing in the 2MASS map. They provide a unbiased sample for the study of the correlation between O VI/H I absorbers and galaxies and 2MASS galaxy groups at low redshift (z

Download or read book Working Papers written by National Research Council and published by National Academies Press. This book was released on 1991-02-01 with total page 347 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains working papers on astronomy and astrophysics prepared by 15 non-National Research Council panels in areas ranging from radio astronomy to the status of the profession.

Download or read book A New Science Strategy for Space Astronomy and Astrophysics written by National Research Council and published by National Academies Press. This book was released on 1997-07-06 with total page 89 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Role of Gas in Galaxy Evolution written by John Caleb Barentine and published by . This book was released on 2013 with total page 868 pages. Available in PDF, EPUB and Kindle. Book excerpt: The story of a typical spiral galaxy like the Milky Way is a tale of the transformation of metal-poor hydrogen gas to heavier elements through nuclear burning in stars. This gas is thought to arrive in early times during the assembly phase of a galaxy and at late times through a combination of hot and cold "flows" representing external evolutionary processes that continue to the present. Through a somewhat still unclear mechanism, the atomic hydrogen is converted to molecules that collect into clouds, cool, condense, and form stars. At the end of these stars' lives, much of their constituent gas is returned to the galaxy to participate in subsequent generations of star formation. In earlier times in the history of the universe, frequent and large galaxy mergers brought additional gas to further fuel this process. However, major merger activity began an ongoing decline several Gyr ago and star formation is now diminishing; the universe is in transitioning to an era in which the structural evolution of disk galaxies is dominated by slow, internal ("secular") processes. In this evolutionary regime, stars and the gas from which they are formed participate in resonant gravitational interactions within disks to build ephemeral structures such as bars, rings, and small scale-height central bulges. This regime is expected to last far into the future in a galaxy like the Milky Way, punctuated by the periodic accretion of dwarf satellite galaxies but lacking in the "major" mergers that kinematically scramble disks into ellipticals. This thesis examines details of the story of gas from infall to structure-building in three major parts. The High- and Intermediate-Velocity Clouds (HVCs/IVCs) are clouds of H [Iota] gas at velocities incompatible with simple models of differential Galactic rotation. Proposed ideas explaining their observed properties and origins include (1) the infall of low-metallicity material from the Halo, possibly as cold flows along filaments of a putative "Cosmic Web"; (2) gas removed from dwarf satellite galaxies orbiting the Milky Way via some combination of ram pressure stripping and tidal disruption; and (3) the supply and return feeds of a "Galactic Fountain" cycling gas between the Disk and Halo. Numerical values of their observed properties depend strongly on the Clouds' distances. In Chapter 2, we summarize results of an ongoing effort to obtain meaningful distances to a selection of HVCs and IVCs using the absorption-line bracketing method. We find the Clouds are not at cosmological distances, and with the exception of the Magellanic Stream, they are generally situated within a few kiloparsecs of the Disk. The strongest discriminator of the above origin scenarios are the heavy element abundances of the Clouds, but to date few reliable Cloud metal- licities have been published. We used archival UV spectroscopy, supplemented by new observations with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope and H [Iota] 21 cm emission spectroscopy from a variety of sources to compute elemental abundances relative to hydrogen for 39 HVC/IVC components along 15 lines of sight. Many of these are previously unpublished. We find support for all three origin scenarios enumerated above while more than doubling the number of robust measurements of HVCs/IVCs in existence. The results of this work are detailed in Chapter 3. In Chapter 4 we present the results of a spectroscopic study of the high-mass protostellar object NGC 7538 IRS 9 made with the Texas Echelon Cross Echelle Spectrograph (TEXES), a sensitive, high spectral resolution, mid-infrared grating spectrometer and compare our observations to published data on the nearby object NGC 7538 IRS 1. Forty-six individual lines in vibrational modes of the molecules C2H2, CH4, HCN, NH3 and CO were detected, including two isotopologues (13CO, 12C18O) and one combination mode ([nu]4+[nu]5 C2H2). Fitting synthetic spectra to the data yielded the Doppler shift, excitation temperature, Doppler b parameter, column density and covering factor for each molecule observed; we also computed column density upper limits for lines and species not detected, such as HNCO and OCS. We find differences among spectra of the two objects likely attributable to their differing radiation and thermal environments. Temperatures and column densities for the two objects are generally consistent, while the larger line widths toward IRS 9 result in less saturated lines than those toward IRS 1. Finally, we compute an upper limit on the size of the continuum-emitting region (~2000 AU) and use this constraint and our spectroscopy results to construct a schematic model of IRS 9. In Chapters 5 and 6, we describe studies of the bright, nearby, edge-on spiral galaxies NGC 4565 and NGC 5746, both previously classified as type Sb spirals with measured bulge-to-total luminosity ratios B/T [approximately equal to] 0.4. These ratios indicate merger-built, "classical" bulges but in reality represent the photometric signatures of bars seen end-on. We performed 1-D photometric decompositions of archival Hubble Space Telescope, Spitzer Space Telescope, and Sloan Digital Sky Survey images spanning a range of wavelengths from the optical to near-infrared that penetrate the thick midplane dust in each galaxy. In both, we find high surface brightness, central stellar components that are clearly distinct from the boxy bar and from the disk; we interpret these structures as small scale height "pseudobulges" built from disk material via internal, resonant gravitational interactions among disk material -- not classical bulges. The brightness profiles of the innermost component of each galaxy is well fitted by a Sersic function with major/minor axis Sersic indices of n = 1.55±0.07 and 1.33±0.12 for NGC 4565 and n = 0.99±0.08 and 1.17 ± 0.24 for NGC 5746. The true "bulge-to-total" ratios of these galaxies are considerably smaller than once believed: 0.061+0.009 and 0.136 ± 0.019, -0.008, respectively. Therefore, more galaxies than we thought contain little or no evidence of a merger-built classical bulge. We argue further that a classical bulge cannot hide behind the dust lane of either galaxy and that other structures built exclusively through secular evolution processes such as inner rings, both revealed through the infrared imagery, argue strongly against any merger violence in the recent past history of these objects. From a formation point of view, NGC 4565 and NGC 5746 are giant, pure-disk galaxies, and we do not understand how such galaxies form in a [Lamda]CDM universe. This presents a challenge to our picture of galaxy formation by hierarchical clustering because it is difficult to grow galaxies as large as these without making big, classical bulges. We summarize the work presented in this thesis in Chapter 7 and conclude with speculations about the future direction of research in this field.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Early Universe with the VLT written by Jacqueline Bergeron and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the second ESO workshop in aseries dedicated to science oppor tunities with the VLT. At the first workshop all areas of astronomical research were discussed. This second workshop is dedicated to research projects on the early Universe and has provided a forum for discussing strategies for studying faint distant objects in the optical and infrared spectral regions. This field is evolving very rapidly. There are several new surveys of galax ies and clusters of galaxies at intermediate redshift and quasars at very high redshift. Major advances in the morphological studies of distant galaxies, surveys of galaxies at high redshift and searches for primeval galaxies have been rendered possible by the new facilities provided by the Rubble Space Telescope and the Keck Telescope. Observational constraints on the evolution and formation of galaxies and large-scale structures as well as the cosmic chemical evolution were criti cally discussed with regard to theory and numerical simulations. In this context, the VLT first generation instrument capabilities were presented comprehensively and their use as cosmological tools discussed . The concluding remarks of the workshop focussed on the analysis of var ious possibilities for the VLT second generation instrumentation. Many of these topics were covered by invited reviews and talks, as well as some contributed talks. They are included in this volume together with the poster papers.

Download or read book Newsletter written by and published by . This book was released on 1984 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book NASA Newsletter for International Ultraviolet Explorer IUE written by and published by . This book was released on 1980 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The GTO Observing Program written by and published by . This book was released on 1985 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy Research Abstracts written by and published by . This book was released on 1985 with total page 868 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Origins 2003 written by and published by . This book was released on 2003 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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:

Download or read book Reports on Astronomy written by Derek McNally and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 616 pages. Available in PDF, EPUB and Kindle. Book excerpt: IAU Transactions are published as a volume corresponding to each General Assembly. Volume A is produced prior to the Assembly and contains Reports on Astronomy, prepared by each Commission President. The intention is to summarize the astronomical results that have affected the work of the Commission since the production of the previous Reports up to a time which is about one year prior to the General Assembly. Volume B is produced after the Assembly and contains accounts of Commission Meetings which were held, together with other material. The reports included in the present volume range from outline summaries to lengthy compilations and references.

Download or read book Literature 1984 Part 2 written by S. Böhme and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 928 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Literature 1987 Part 1 written by S. Böhme and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 1300 pages. Available in PDF, EPUB and Kindle. Book excerpt: Astronomy and Astrophysics Abstracts aims to present a comprehensive documen tation of the literature concerning all aspects of astronomy, astrophysics, and their border fields. It is devoted to the recording, summarizing, and indexing of the relevant publications throughout the world. Astronomy and Astrophysics Abstracts is prepared by a special department of the Astronomisches Rechen-Institut under the auspices of the International Astronomical Union. Volume 43 records literature published in 1987 and received before August 15, 1987. Some older documents which we received late and which are not surveyed in earlier volumes are included too. We acknowledge with thanks contributions of our colleagues all over the world. We also express our gratitude to all organiza tions, observatories, and publishers which provide us with complimentary copies of their publications. Starting with Volume 33, all the recording, correction, and data processing work was done by means of computers. The recording was done by our technical staff members Ms. Helga Ballmann, Ms. Beate Gobel, Ms. Monika Kohl, Ms. Sylvia Matyssek, Ms. Doris Schmitz-Braunstein, Ms. Utta-Barbara Stegemann. Mr. Jochen Heidt and Mr. Kristopher Polzine supported our task by careful proof reading. It is a pleasure to thank them all for their encouragement. Heidelberg, October 1987 The Editors Contents Introduction . . . . . . . . . . . 1 Concordance Relation: PHYS-AAA 3 Abbreviations 5 Periodicals, Proceedings, Books, Activities 001 Periodicals . . . . . . . . . . . 10 002 Bibliographical Publications, Documentation, Catalogues, Data Bases 50 003 Books ...... .

Download or read book NASA Newsletter for International Ultraviolet Explorer IUE written by United States. National Aeronautics and Space Administration and published by . This book was released on 1980 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Literature 1983 Part 1 written by S. Böhme and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 825 pages. Available in PDF, EPUB and Kindle. Book excerpt: Astronomy and Astrophysics Abstracts aims to present a comprehensive documen tation of the literature concerning all aspects of astronomy, astrophysics, and their border fields. It is devoted to the recording, summarizing, and indexing of the relevant publications throughout the world. Astronomy and Astrophysics Abstracts is prepared by a special department of the Astronomisches Rechen-Institut under the auspices of the International Astronomical Union. Volume 33 records literature published in 1983 and received before August 1, 1983. Some older documents which we received late and which are not surveyed in earlier volumes are included too. We acknowledge with thanks contributions of our colleagues all over the world. We also express our gratitude to all organizations, observatories, and publishers which provide us with complimentary copies of their publications. Starting with Volume 33, all the recording, correction, and data processing work was done by means of computers. The recording was done by our technical staff members Ms. Helga Ballmann, Ms. Mona El-Choura, Ms. Monika Kohl, and Ms. Sylvia Matyssek. Mr. Martin Schlotelburg and Mr. Ulrich Uberall supported our task by careful proofreading. It is a pleasure to thank them all for their encouragement. Heidelberg, September 1983 The Editors Contents Introduction . . . . . . . . . . . . 1 Concordance Relation: ICSU-AB-AAA 3 Abbreviations 10 Periodicals, Proceedings, Books, Activities 001 Periodicals . . . . . . . . . . . 15 002 Bibliographical Publications, Documentation, Catalogues, Atlases 47 003 Books ...... . 51 004 History of Astronomy 58 005 Biography . . 64 006 Personal Notes 65 007 Obituaries . . .