Download or read book The Small Scale Physical Evolution of Molecular Gas in Nearby Galaxies written by Viviana Casasola and published by . This book was released on 2008 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: Le futur immédiat, grâce à la construction de nouveaux instruments - essentiellement ALMA-sera caractérisé par une révolution dans le champ de l'astronomie millimétrique. Cette thèse de doctorat est dédiée à un des principaux sujets qu'ALMA pourra approfondir, le gaz moléculaire dans les galaxies extérieures, avec l'objectif d'être bien préparé à l'arrivée de ce instrument. Cette thèse étudie la physique de l'excitation collisionnelle à petite échelle, les propriétés de fragmentation, la distribution, et la cinématique du gaz moléculaire en deux galaxies proches (Messier 81 et NGC 3147) avec des observations obtenues soit avec un instrument millimétrique à antenne unique, soit avec un interféromètre. En complément à ces deux études, cette thèse présente un travail statistique et son interprétation sur les relations existantes entre les différentes composantes du MIS, obtenu en analysant un échantillon de galaxies de tout type morphologique, activité nucléaire, et type d'interaction.
Download or read book The Evolution of Galaxies written by Marc Sauvage and published by Springer Science & Business Media. This book was released on 2002-07-31 with total page 538 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galaxies have a history. This has become clear from recent sky surveys which have shown that distant galaxies, formed early in the life of the Universe, differ from the nearby ones. New observational windows at ultraviolet, infrared and millimetric wavelengths (provided by ROSAT, IRAM, IUE, IRAS, ISO) have revealed that galaxies contain a wealth of components: very hot gas, atomic hydrogen, molecules, dust, dark matter ... A significant advance is expected due to new instruments (VLT, FIRST, XMM) which will allow one to explore the most distant Universe. Three Euroconferences have been planned to punctuate this new epoch in galactic research, bringing together specialists in various fields of Astronomy. The first one, held in Granada (Spain) in May 2000, addressed the observational clues. The second one took place in October 2001 in St Denis de la Réunion (France) and reviewed the basic building blocks and small-scale processes in galaxy evolution. The third one will take place in July 2002 in Kiel (Germany) and will be devoted to the overall modelling of galaxy evolution. This book contains the proceedings of the second conference. It is suitable for researchers and PhD students in Astrophysics.
Download or read book The Undiscovered CO written by Garrett Kent Keating and published by . This book was released on 2016 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular gas, observed through tracers such as CO rotational transitions, is a vital component of galactic evolution and star formation. Recent detections of the CO molecule in massive galaxies at high redshift have demonstrated its existence in the early Universe, and have motivated its use as a means of exploring large-scale structure and as a probe of galaxy evolution in the early Universe. But many questions about molecular gas and the evolution of galaxies in the early Universe still remain: its distribution at high redshift understood is so poorly that theoretical models of the mean abundance of CO for the first several billion years of cosmic history span orders of magnitude. Direct detection of molecular gas in galaxies at these redshifts have only found the largest and most luminous of galaxies in the early Universe, whereas the bulk of the molecular gas is expected to be in the unseen masses of smaller galaxies. While difficult to detect individually, these smaller galaxies are likely detectable as an integrated ensemble with the technique of ``intensity mapping". This technique, similar to those employed by HI epoch of reionization experiments, utilizes measurements of different 3D Fourier modes to construct a power spectrum. In this thesis, I present results from the CO Power Spectrum Survey (COPSS), an intensity mapping experiment performed with the Sunyaev Zel'dovich Array (SZA). I present power spectrum constraints from of the first and second phase of this project, utilizing an archival dataset (covering 44 fields in 1400 hours observing time) and a 5000-hour observing campaign (covering 19 fields) with the SZA. With these data, we are capable of observing CO(1-0) emission arising from $z=2.3{-}3.3$, surveying a volume of more than ten million cubic megaparsecs. With this measurement, we place the first-ever constraints on the CO autocorrelation power spectrum, and place constraints on the CO(1-0) galaxy luminosity function and the cosmic molecular gas density at $z\sim3$. I also present a series of simulations designed to probe the impact of cosmic variance, continuum foregrounds, and systematic errors on our measurement with the SZA. I will also present simulations designed to probe the challenges that will face intensity mapping experiments with the Yuan-Tseh Lee Array (YTLA). Finally, I will present some preliminary work on CO(3-2) and [CII] intensity mapping experiments.
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 Molecular Gas Dust and Star Formation in Galaxies IAU S292 written by Tony Wong and published by Cambridge University Press. This book was released on 2013-04-11 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our knowledge of the molecular gas content in galaxies has advanced rapidly in the past decade with systematic surveys from ground-based radio facilities, coupled with advances in observations and modeling of the thermal dust emission associated with the gas. This Symposium Proceedings provides a timely overview of the latest observations of molecular gas and dust in the Milky Way and in other galaxies. It also covers related topics including the initial conditions for star formation, observational tracers of star formation and interstellar conditions, and simulations of the turbulent, multiphase interstellar medium. Featuring ten review articles by leaders in the field, and including early results and prospects for the ALMA observatory, this volume will prove especially useful for graduate students or scientists who are pursuing or planning research in this area.
Download or read book Secular Evolution of Galaxies written by Jesús Falcón-Barroso and published by Cambridge University Press. This book was released on 2012 with total page 657 pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation and evolution of galaxies is one of the most important topics in modern astrophysics. Secular evolution refers to the relatively slow dynamical evolution due to internal processes induced by a galaxy's spiral arms, bars, galactic winds, black holes and dark matter haloes. It plays an important role in the evolution of spiral galaxies with major consequences for galactic bulges, the transfer of angular momentum, and the distribution of a galaxy's constituent stars, gas and dust. This internal evolution is in turn the key to understanding and testing cosmological models of galaxy formation and evolution. Based on the twenty-third Winter School of the Canary Islands Institute of Astrophysics, this volume presents reviews from nine world-renowned experts on the observational and theoretical research into secular processes, and what these processes can tell us about the structure and formation of galaxies. The volume provides a firm grounding for graduate students and early career researchers working on galactic dynamics and galaxy evolution.
Download or read book Lighting the Dark Molecular Gas and a Bok Globule written by Aditya G. Togi and published by . This book was released on 2016 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stars are the building blocks of galaxies. The gas present in galaxies is the primary fuel for star formation. Galaxy evolution depends on the amount of gas present in the interstellar medium (ISM). Stars are born mainly from molecular gas in the GMCs. Robust knowledge of the molecular hydrogen H2 gas distribution is necessary to understand star formation in galaxies. Since H2 is not readily observable in the cold interstellar medium (ISM), the molecular gas content has traditionally been inferred using indirect tracers like carbon-monoxide (CO), dust emission, gamma ray interactions, and star formation efficiency. Physical processes resulting in enhancement and reduction of these indirect tracers can result in misleading estimates of molecular gas masses. My dissertation work is based on devising a new temperature power law distribution model for H2, a direct tracer, to calculate the total molecular gas mass in galaxies. The model parameters are estimated using mid infrared (MIR) H2 rotational line fluxes obtained from IRS-Spitzer (Infrared Spectrograph- Spitzer) instrument and the model is extrapolated to a suitable lower temperature to recover the total molecular gas mass. The power law model is able to recover the dark molecular gas, undetected by CO, in galaxies at metallicity as low as one-tenth of our Milky Way value. I have applied the power law model in U/LIRGs and shocks of Stephan's Quintet to understand molecular gas properties, where shocks play an important role in exciting H2. Comparing the molecular gas content derived through our power law model can be useful in studying the application of our model in mergers. The parameters derived by our model is useful in understanding variation in molecular gas properties in shock regions of Stephan's Quintet. Low mass stars are formed in small isolated dense cores known as Bok globules. Multiple star formation events are seen in a Bok globule. In my thesis I also studied a Bok globule, B207, and determined the physical properties and future evolutionary stage of the cloud. My thesis spans studying ISM properties in galaxies from kpc to sub-pc scales. Using the power law model in the coming era of James Webb Space Telescope (JWST) with the high sensitivity MIR Instrument (MIRI) spectrograph we will be able to understand the properties of molecular gas at low and high redshifts.
Download or read book Galaxies Through Cosmic Time written by Amber Bauermeister and published by . This book was released on 2012 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past decade, molecular gas observations have begun probing the high redshift universe in a systematic way using increasingly powerful millimeter instruments. This work has significantly advanced our understanding of the history of gas consumption by star formation in galaxies, revealing the high redshift universe to be similar in many ways to what we know locally. Specifically, molecular gas studies suggest that at both high and low redshift, the molecular gas reservoir in galaxies is insufficient to support on-going star formation. This is the molecular gas depletion problem, and motivates the research presented in this dissertation. I first investigate the molecular gas depletion problem on cosmic scales. Using the observed cosmic densities of the star formation rate, atomic gas and molecular gas, combined with measurements of the molecular gas depletion time in local galaxies, I derive the history of gas consumption by star formation from z = 0 to z ~ 4. I show that models in which the molecular gas is not replenished, or is only replenished by atomic gas, are not consistent with observational constraints. I find that star formation on cosmic timescales must be fueled by intergalactic ionized gas at an average rate that roughly traces the star formation rate density of the universe. Further, I predict the volume averaged density of molecular gas to increase by a factor of 1.5 - 10 to z ~ 1.5 over the currently measured value, which implies that galaxies at high redshift must, on average, be more molecular gas-rich than they are at the present epoch, consistent with observations. Next I focus on the observational constraints on the molecular gas content of galaxies from z ~ 1 - 2 to today. Recent observations suggest z ~ 1 - 2 galaxies harbor molecular gas reservoirs an order of magnitude larger than their local counterparts, implying significant evolution of the molecular gas content of galaxies over the past 8 billion years. However, this period of time has been relatively un-observed in molecular gas. To fill in this observational gap, I carry out the Evolution of molecular Gas in Normal Galaxies (EGNoG) survey, a study of molecular gas in 31 star-forming galaxies from z = 0.05 to z = 0.5. With observations of the CO(1-0) and CO(3-2) rotational lines using the Combined Array for Research in Millimeter-wave Astronomy (CARMA), the EGNoG survey accomplishes two goals: tracing the evolution of the molecular gas content of galaxies at intermediate redshifts and constraining the excitation of the molecular gas in these galaxies. With 24 detections out of 31 observed galaxies, I calculate an average molecular gas fraction of 7 - 20% at z ~ 0.05 - 0.5, which is in line with observations at high and low redshift and agrees well with the evolution predicted by a simple empirical prescription for gas consumption by star formation in galaxies from z ~ 1 - 2 to today. The EGNoG observations of four galaxies at z = 0.3 (the gas excitation subsample) yield robust detections of both lines in three galaxies (and an upper limit on the fourth). I find an average line ratio, r31 = L'(CO(3-2)) / L'(CO(1-0)), of 0.46 ± 0.07 (with systematic errors less than 40%), which implies sub-thermal excitation of the CO(3-2) line. As the EGNoG galaxies are representative of the main sequence of star-forming galaxies, I extend this result to include main sequence galaxies at high redshift. To support the observations carried out at CARMA as part of the EGNoG survey, I give two appendices. The first details the data reduction and flux measurement for the EGNoG survey, including a description of the use of polarized calibrators to calibrate data from single, linearly polarized feeds. In the second appendix, I describe the absolute flux calibration of CARMA data and the automated monitoring system I helped put in place in order to maintain a historical record of the flux of common calibrators. Finally, I return to the gas depletion problem in the local universe. I carry out a pilot study of atomic (HI) gas in groups of galaxies in order to investigate the role of tidal interactions in transporting atomic gas from the outskirts of galaxy disks to the central regions so that it may replenish the molecular gas and fuel ongoing star formation. I image three groups of galaxies in the 21 cm line of HI with the Allen Telescope Array (ATA), detecting many galaxies not previously observed in HI as well as four previously undetected clouds of HI between galaxies that account for up to 3% of the HI reservoir of the groups. To investigate the potential role of this gas in the ongoing star formation in the group, I compare the mass of the detected HI gas in and between galaxies in the group to the estimated star formation rates of the group members.
Download or read book The Nuclei of Normal Galaxies written by R. Genzel and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 513 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our Galactic center's proximity allows astronomers to study physical pro cesses within galactic nuclei at a level of detail that will never be possible in the more distant, but usually also more spectacular, extragalactic systems. Recent advances in instrumentation from the radio, through the submillime ter and infrared wavebands, and out to the X- and "'(-ray bands now allow observations of the Galactic Center over thirteen orders of magnitude in wave length. Our knowledge about the central few hundred parsecs of our Galaxy has consequently increased vastly over the past decade. The same new instru ments provide high resolution, high quality measurements of nearby ''normal'' galactic nuclei; that is, nuclei whose modest energy output is comparable to that of our own (and most other) galaxies. Theorists, spurred in part by the new observations, have been able to refine models of the energetics, dynam ics, and evolution of the gas and stellar systems deep within galactic nuclei.
Download or read book Dense Molecular Gas in Galaxies and the Evolution of Luminous Infrared Galaxies written by Yu Gao and published by . This book was released on 1996 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Sky Eye written by Rendong Nan and published by Springer Nature. This book was released on 2021-10-28 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book introduces the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), also known as the "The Sky Eye", one of the China’s big science facilities. Using easy-to-understand language, the book covers the scientific background, construction process, achievements, and effects of FAST on the development of the national economy. With a large number of intuitive and vivid images and videos, the book presents basic information on FAST for general readers who are interested in astronomy.
Download or read book The Clustering of Young Stellar Clusters in Nearby Galaxies written by Kathryn Grasha and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Star clusters form the basic building blocks of galaxies. They span a wide range of ages, from a few million years to billions of years, making them exceptional tracers of the star formation histories of their host galaxies. Star formation is the process by which galaxies build up their stellar populations and their visible mass and occurs in a continuous, hierarchical "social" fashion across a large dynamical range, from individual stars up to kiloparsec-scale ensembles of stellar aggregates. It is the formation, evolution, and eventual destruction of these large hierarchical star-forming complexes that provide an essential role in understanding the physical mechanism and dynamical evolution of star formation on sub-galactic scales. First, using star clusters from local galaxies as part of the LEGUS (Legacy Extragalactic UV Survey) sample, we find that star formation is coherent over scales of a few hundred parsec up to a few kpc depending on the galaxy. In all cases, these hierarchies are short lived and unbound, dissolving in a few tens to a hundred Myr. The recovered correlations between the spatial separations and ages of star clusters contained within these structures are consistent with theoretical expectations of arising from a turbulence-driven ISM. We also find evidence that the maximum size of correlated star formation is driven by galactic shear. Second, we combine our star cluster catalogs with exquisite molecular gas observations to connect the detailed stellar population information to the natal gas from which it formed. We find that the timescale for star clusters to lose association with their natal clouds is of order a few Myr, with their ages rising rapidly as they become spatially separated from their molecular clouds. Third, we introduce initial work that employs the use of machine learning as a process to identify star clusters, a quicker and more homogeneous method than traditional visual classification techniques employed for most stellar cluster catalogs. The work contained in this dissertation represents the first large-scale study of its kind outside of the Local Group to characterize turbulence as the physical driver of correlated star formation and the association timescale of star clusters with their molecular reservoirs, marking a turning point in the effort to link local star forming structures to those that are common at high redshift.
Download or read book Physical Conditions of Molecular Gas in the Galaxy written by Seiichi Sakamato and published by . This book was released on 1993 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Physical Processes in the Interstellar Medium written by Lyman Spitzer, Jr. and published by John Wiley & Sons. This book was released on 2008-11-20 with total page 335 pages. Available in PDF, EPUB and Kindle. Book excerpt: Physical Processes in the Interstellar Medium discusses the nature of interstellar matter, with a strong emphasis on basic physical principles, and summarizes the present state of knowledge about the interstellar medium by providing the latest observational data. Physics and chemistry of the interstellar medium are treated, with frequent references to observational results. The overall equilibrium and dynamical state of the interstellar gas are described, with discussions of explosions produced by star birth and star death and the initial phases of cloud collapse leading to star formation.
Download or read book Molecular Gas in Dwarf Galaxies written by Adam Kirby Leroy and published by . This book was released on 2006 with total page 578 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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.
Download or read book Chemical Evolution of Galaxies with Active Star Formation written by Takakubo, K. and published by . This book was released on 1987 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:
