DOCSLIB.ORG

The Cloudy HI Halo of the Milky

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Cloudy HI Halo of the Milky THE CLOUDY HI HALO OF THE MILKY WAY Dissertation zur Erlangung des Doktorgrades (Dr. rer. nat.) der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vorgelegt von Leonidas Dedes aus Veroia (Griechenland) Bonn, Juni 2008 Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn 1. Referent: PD Dr. Jürgen Kerp 2. Referent: Prof. Dr. Ulrich Klein Tag der Promotion: 02.09.2008 Erscheinungsjahr 2008 Diese Dissertation ist auf dem Hochschulschriftenserver der ULB Bonn unter: http://hss.ulb.uni-bonn.de/diss_online elektronisch publiziert. Contents 1 Introduction 1 2 Method 9 2.1 Aim .................................. 9 2.2 Properties of the HI clumps..................... 9 2.3 Detection of HI clumps........................ 10 2.4 Distancedetermination . 11 2.5 MilkyWaymassmodel. 14 2.6 Measuring the observational properties of the clumps . 15 3 The spiral structure in the Milky Way 21 3.1 Introduction .............................. 21 3.2 The model of the Galactic spiral structure . 22 3.3 Results ................................ 24 3.4 Dependenceonb .......................... 29 3.5 Discussion .............................. 32 4 A search for the structure of the gaseous HI halo using the Effels- berg 100-m telescope 43 4.1 Introduction .............................. 43 4.2 Technical details and selection criteria . 43 4.3 Theclump116.20+23.55 . 45 4.4 Theclump115.00+24.00 . 49 4.5 Effelsberg sample of HI haloclumps.. 51 5 Synthesis Observations of HI clumps 61 5.1 Introduction .............................. 61 5.2 W.S.R.Tobservations . 61 5.2.1 TechnicalDetails . 61 5.2.2 Results ............................ 62 5.3 V.L.Aobservations . 66 5.3.1 TechnicalAnalysis . 66 5.3.2 Results ............................ 67 5.4 SummaryofInterferometryResults. 68 6 Arecibo Observations 71 6.1 Introduction .............................. 71 6.2 Technicaldetails .. .. .. .. .. .. .. .. .. .. .. .. .. 71 6.3 Extended emission in Arecibo and Stray Radiation correction . 72 6.4 Results ................................ 75 6.5 Clump at α=07h049m46.60′′, δ=04d32m32.006′′ .......... 81 7 Thermal equilibrium of the neutral component of the gaseous Galac- tic halo as inferred from the study of the physical properties of HI clumps 89 7.1 Introduction .............................. 89 7.2 Summary of the Observational and Physical Properties of the HI clumps. .............................. 89 7.3 Thermal equilibrium in the neutral gas . 91 7.4 HI clumps and thermal equilibrium . 93 7.5 Stability and evaporation of the HI clumps ............. 97 8 Power spectrum analysis of the Arecibo data 99 8.1 Introduction .............................. 99 8.2 Analysis................................ 99 8.3 Results ................................101 9 Discussion 107 9.1 Introduction ..............................107 9.2 Measurements and errors . 107 9.3 Distancedetermination . .109 9.4 Galacticfountain . .111 9.5 Comparison with the CNM phase:Clumps or sheets . 114 10 Conclusions 121 11 Appendix I 125 12 Appendix II:Brightness temperature ratio K of a mix of warm/cold neutral gas. 129 13 Acknowledgments 135 14 Summary 137 References 141 List of Figures 145 List of Tables 149 1 1 Introduction Neutral hydrogen is one of the most important components of the visible matter in the universe. From the time of the theoretical predictions of the 21-cm line, by the Dutch astronomer van der Hulst (1945) up to today, observations of the neutral hydrogen emission help to expand the knowledge in the field of Radio Astronomy. Almost five decades ago, Oort et al. (1958) for the first time brought to light the large scale mor- phology of our Galaxy, the Milky Way, using the HI line. Today the HI line is utilized in various fields, as a tracer to study the dark matter content of the galaxies, and as a probe of the physical conditions pervading through the interstellar medium (ISM). In the future, with the arrival of the Square Kilometer Array (SKA), studies of neutral hydrogen will give us the opportunity to understand Galaxy evolution and enable us to probe the epoch of re-ionization giving new insights in the cosmological evolution of the Universe (Carilli & Rawlings, 2004). In Galactic astronomy, the 21-cm line plays a vital role in studying a variety of astro- physical phenomena from AU scales, up to scales of hundreds of kpc. This is due to the widespread distribution of the neutral hydrogen in the Galaxy, and its transparency which allows a detection even in areas where optical observations are very difficult (e.g., regions obscured by dust). Especially the neutral hydrogen in the Milky Way disk has been studied in great detail. I.e, large scale HI observations probed thor- oughly the vertical structure of the disk, revealing an asymmetric warp reaching in height more than 4kpc above the plane at distances of 17kpc and measuring the flar- ing of the HI disk (Nakanishi & Sofue, 2004; Levine et al., 2006a; Kalberla et al., 2007). More recent studies detected a distant spiral arm in the outer part of the galaxy (McClure-Griffiths et al., 2004) and found evidence for disruption in the HI disk in the form of giant bubbles and super-shells (McClure-Griffiths et al., 2006). On smaller scales, regarding the structure of the ISM in Milky Way disk, it is known for some time that the diffuse neutral hydrogen resides in two phases: the warm neutral medium phase with a temperature T < 8000K and a cold dense neutral phase with T ∼ 80K as- sociated with discrete small HI structures, detected in absorption line studies (Heiles, 1997). Furthermore, high above the Milky Way disk, another class of astronomical objects has been detected in the 21-cm line in 1963, the high-velocity-clouds (HVC), a pop- ulation of HI clouds incompatible with Galactic rotation having a deviation velocity υ > 90kms−1(Wakker & van Woerden, 1991). An estimate regarding their distance gives a lower limit of 5kpc (z>3.5kpc) for Complex C (Wakker et al., 1999) and for Complex A a distance d=4kpc, implying a height above the plane between 2.5kpc and 7kpc (van Woerden et al., 1998). Above the Milky Way disk, moving with high velocities, lays a population of old, low metalicity stars, Globular Clusters and remnants of the accretion from Dwarf compan- ions of the Milky Way. This layer of stars surrounding the Milky Way disk forms what 2 1 Introduction is known as the Halo. Similarly in the case of dark matter it is proposed that it forms a dark matter halo surrounding the disk and dominating the gravitational potential of the Galaxy. The question then arises, if there exists a stellar and dark matter Halo of the Milky Way Galaxy, is it possible that there exists also a similar gaseous layer surrounding the Galactic disk? If this is true, what is the origin of such a layer? Is it the result of an interaction between the Galaxy and the intergalactic medium? Is it the result from an accretion? Is it the product of other physical processes in the Galaxy like supernova explosion? The answer to the first question is positive. Even from the early fifties, it was Spitzer (1956) who proposed that there exists a semi-static hot gaseous layer which surrounds the Milky Way disk. The vertical extent of the Galactic corona would be approxi- 6 8 mately 8 kpc with a temperature reaching 10 K and a total mass of 10 M⊙. The existence of such a layer was proposed mainly to explain the stability of high latitude clouds but also to facilitate the equilibrium of spiral arms in the presence of strong magnetic fields. Interestingly the idea of a Galactic corona was partially inspired from the claim of Pickelner (1953) for the existence of a homogeneous substratum of rel- atively cool gas, with a density of 0.1 cm−3 supported from turbulent motion with velocity 70 kms−1. The first observational confirmation of the hot galactic corona hypothesis was given by Münch & Zirin (1961). Using absorption lines of distant stars outside the Milky Way disk, evidence was found for gas clouds at heights z ∼ 1 kpc above the Galactic disk. From these clouds they found that the acceptible temperature for the Galactic corona is the one postulated by Spitzer of 106 K. Shapiro & Field (1976) proposed the mechanism of the “Galactic fountain” in or- der to explain the presence of coronal gas and to introduce a process to cool the gas through convection and radiation. According to the mechanism, hot gas, produced by supernovae explosions in the disk, is buoyant. It streams upwards with a veloc- ity perpendicular to the disk smaller or equal than the speed of sound. The outcome of this motion may have the following results: a) if the cooling is inefficient, the hot gas bubble reaches great heights above the disk, forming and becoming part of the Galactic corona of the disk, in hydrostatic equilibrium b) or if the cooling mechanism is efficient, at height zc the hot bubble cools rapidly and undergoes a phase transition forming cool dense HI clouds. These clouds are not buoyant and so beyond this point they follow a ballistic motion under the influence of gravity which will bring them again at height zc. It was the latter result of this mechanism that prompted Bregman (1980) to associate the galactic fountain mechanism with the formation of the HVC. A few years later there was observational evidence that beyond the hot coronal gas surrounding the disk, there possible exists neutral gas extending high above the Milky Way disk. Lockman (1984) detected the 21-cm emission from these patches of neutral 3 gas located in the inner Galaxy at heights greater than |z|>1000 pc. He proposed that the neutral gas in this region is following Galactic rotation and that this gas may form a layer that can not be solely thermally supported nor can it be considered as a single component isothermal layer.
Load more

Recommended publications
  • Two Stellar Components in the Halo of the Milky Way
    1 Two stellar components in the halo of the Milky Way Daniela Carollo1,2,3,5, Timothy C. Beers2,3, Young Sun Lee2,3, Masashi Chiba4, John E. Norris5 , Ronald Wilhelm6, Thirupathi Sivarani2,3, Brian Marsteller2,3, Jeffrey A. Munn7, Coryn A. L. Bailer-Jones8, Paola Re Fiorentin8,9, & Donald G. York10,11 1INAF - Osservatorio Astronomico di Torino, 10025 Pino Torinese, Italy, 2Department of Physics & Astronomy, Center for the Study of Cosmic Evolution, 3Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI 48824, USA, 4Astronomical Institute, Tohoku University, Sendai 980-8578, Japan, 5Research School of Astronomy & Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Australian Capital Territory 2611, Australia, 6Department of Physics, Texas Tech University, Lubbock, TX 79409, USA, 7US Naval Observatory, P.O. Box 1149, Flagstaff, AZ 86002, USA, 8Max-Planck-Institute für Astronomy, Königstuhl 17, D-69117, Heidelberg, Germany, 9Department of Physics, University of Ljubljana, Jadronska 19, 1000, Ljubljana, Slovenia, 10Department of Astronomy and Astrophysics, Center, 11The Enrico Fermi Institute, University of Chicago, Chicago, IL, 60637, USA The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, which can be used to tightly constrain models of galaxy formation and evolution. Although the halo was once considered a single component, evidence for is dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components -- an inner and an outer halo – that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium).
    [Show full text]
  • An Outline of Stellar Astrophysics with Problems and Solutions
    An Outline of Stellar Astrophysics with Problems and Solutions Using Maple R and Mathematica R Robert Roseberry 2016 1 Contents 1 Introduction 5 2 Electromagnetic Radiation 7 2.1 Specific intensity, luminosity and flux density ............7 Problem 1: luminous flux (**) . .8 Problem 2: galaxy fluxes (*) . .8 Problem 3: radiative pressure (**) . .9 2.2 Magnitude ...................................9 Problem 4: magnitude (**) . 10 2.3 Colour ..................................... 11 Problem 5: Planck{Stefan-Boltzmann{Wien{colour (***) . 13 Problem 6: Planck graph (**) . 13 Problem 7: radio and visual luminosity and brightness (***) . 14 Problem 8: Sirius (*) . 15 2.4 Emission Mechanisms: Continuum Emission ............. 15 Problem 9: Orion (***) . 17 Problem 10: synchrotron (***) . 18 Problem 11: Crab (**) . 18 2.5 Emission Mechanisms: Line Emission ................. 19 Problem 12: line spectrum (*) . 20 2.6 Interference: Line Broadening, Scattering, and Zeeman splitting 21 Problem 13: natural broadening (**) . 21 Problem 14: Doppler broadening (*) . 22 Problem 15: Thomson Cross Section (**) . 23 Problem 16: Inverse Compton scattering (***) . 24 Problem 17: normal Zeeman splitting (**) . 25 3 Measuring Distance 26 3.1 Parallax .................................... 27 Problem 18: parallax (*) . 27 3.2 Doppler shifting ............................... 27 Problem 19: supernova distance (***) . 28 3.3 Spectroscopic parallax and Main Sequence fitting .......... 28 Problem 20: Main Sequence fitting (**) . 29 3.4 Standard candles ............................... 30 Video: supernova light curve . 30 Problem 21: Cepheid distance (*) . 30 3.5 Tully-Fisher relation ............................ 31 3.6 Lyman-break galaxies and the Hubble flow .............. 33 4 Transparent Gas: Interstellar Gas Clouds and the Atmospheres and Photospheres of Stars 35 2 4.1 Transfer equation and optical depth .................. 36 Problem 22: optical depth (**) . 37 4.2 Plane-parallel atmosphere, Eddington's approximation, and limb darkening ..................................
    [Show full text]
  • And Ecclesiastical Cosmology
    GSJ: VOLUME 6, ISSUE 3, MARCH 2018 101 GSJ: Volume 6, Issue 3, March 2018, Online: ISSN 2320-9186 www.globalscientificjournal.com DEMOLITION HUBBLE'S LAW, BIG BANG THE BASIS OF "MODERN" AND ECCLESIASTICAL COSMOLOGY Author: Weitter Duckss (Slavko Sedic) Zadar Croatia Pусскй Croatian „If two objects are represented by ball bearings and space-time by the stretching of a rubber sheet, the Doppler effect is caused by the rolling of ball bearings over the rubber sheet in order to achieve a particular motion. A cosmological red shift occurs when ball bearings get stuck on the sheet, which is stretched.“ Wikipedia OK, let's check that on our local group of galaxies (the table from my article „Where did the blue spectral shift inside the universe come from?“) galaxies, local groups Redshift km/s Blueshift km/s Sextans B (4.44 ± 0.23 Mly) 300 ± 0 Sextans A 324 ± 2 NGC 3109 403 ± 1 Tucana Dwarf 130 ± ? Leo I 285 ± 2 NGC 6822 -57 ± 2 Andromeda Galaxy -301 ± 1 Leo II (about 690,000 ly) 79 ± 1 Phoenix Dwarf 60 ± 30 SagDIG -79 ± 1 Aquarius Dwarf -141 ± 2 Wolf–Lundmark–Melotte -122 ± 2 Pisces Dwarf -287 ± 0 Antlia Dwarf 362 ± 0 Leo A 0.000067 (z) Pegasus Dwarf Spheroidal -354 ± 3 IC 10 -348 ± 1 NGC 185 -202 ± 3 Canes Venatici I ~ 31 GSJ© 2018 www.globalscientificjournal.com GSJ: VOLUME 6, ISSUE 3, MARCH 2018 102 Andromeda III -351 ± 9 Andromeda II -188 ± 3 Triangulum Galaxy -179 ± 3 Messier 110 -241 ± 3 NGC 147 (2.53 ± 0.11 Mly) -193 ± 3 Small Magellanic Cloud 0.000527 Large Magellanic Cloud - - M32 -200 ± 6 NGC 205 -241 ± 3 IC 1613 -234 ± 1 Carina Dwarf 230 ± 60 Sextans Dwarf 224 ± 2 Ursa Minor Dwarf (200 ± 30 kly) -247 ± 1 Draco Dwarf -292 ± 21 Cassiopeia Dwarf -307 ± 2 Ursa Major II Dwarf - 116 Leo IV 130 Leo V ( 585 kly) 173 Leo T -60 Bootes II -120 Pegasus Dwarf -183 ± 0 Sculptor Dwarf 110 ± 1 Etc.
    [Show full text]
  • Galactic Metal-Poor Halo E NCYCLOPEDIA of a STRONOMY and a STROPHYSICS
    Galactic Metal-Poor Halo E NCYCLOPEDIA OF A STRONOMY AND A STROPHYSICS Galactic Metal-Poor Halo Most of the gas, stars and clusters in our Milky Way Galaxy are distributed in its rotating, metal-rich, gas-rich and flattened disk and in the more slowly rotating, metal- rich and gas-poor bulge. The Galaxy’s halo is roughly spheroidal in shape, and extends, with decreasing density, out to distances comparable with those of the Magellanic Clouds and the dwarf spheroidal galaxies that have been collected around the Galaxy. Aside from its roughly spheroidal distribution, the most salient general properties of the halo are its low metallicity relative to the bulk of the Galaxy’s stars, its lack of a gaseous counterpart, unlike the Galactic disk, and its great age. The kinematics of the stellar halo is closely coupled to the spheroidal distribution. Solar neighborhood disk stars move at a speed of about 220 km s−1 toward a point in the plane ◦ and 90 from the Galactic center. Stars belonging to the spheroidal halo do not share such ordered motion, and thus appear to have ‘high velocities’ relative to the Sun. Their orbital energies are often comparable with those of the disk stars but they are directed differently, often on orbits that have a smaller component of rotation or angular Figure 1. The distribution of [Fe/H] values for globular clusters. momentum. Following the original description by Baade in 1944, the disk stars are often called POPULATION I while still used to measure R . The recognizability of globular the metal-poor halo stars belong to POPULATION II.
    [Show full text]
  • Compact Stars
    Compact Stars Lecture 12 Summary of the previous lecture I talked about neutron stars, their internel structure, the types of equation of state, and resulting maximum mass (Tolman-Openheimer-Volkoff limit) The neutron star EoS can be constrained if we know mass and/or radius of a star from observations Neutron stars exist in isolation, or are in binaries with MS stars, compact stars, including other NS. These binaries are final product of common evolution of the binary system, or may be a result of capture. Binary NS-NS merger leads to emission of gravitational waves, and also to the short gamma ray burst. The follow up may be observed as a ’kilonova’ due to radioactive decay of high-mass neutron-rich isotopes ejected from merger GRBs and cosmology In 1995, the 'Diamond Jubilee' debate was organized to present the issue of distance scale to GRBs It was a remainder of the famous debate in 1920 between Curtis and Shapley. Curtis argued that the Universe is composed of many galaxies like our own, identified as ``spiral nebulae". Shapley argued that these ``spiral nebulae" were just nearby gas clouds, and that the Universe was composed of only one big Galaxy. Now, Donald Lamb argued that the GRB sources were in the galactic halo while Bodhan Paczyński argued that they were at cosmological distances. B. Paczyński, M. Rees and D. Lamb GRBs and cosmology The GRBs should be easily detectable out to z=20 (Lamb & Reichart 2000). GRB 090429: z=9.4 The IR afterglows of long GRBs can be used as probes of very high z Universe, due to combined effects of cosmological dilation and decrease of intensity with time.
    [Show full text]
  • Dwarf Galaxies 1 Planck “Merger Tree” Hierarchical Structure Formation
    04.04.2019 Grebel: Dwarf Galaxies 1 Planck “Merger Tree” Hierarchical Structure Formation q Larger structures form q through successive Illustris q mergers of smaller simulation q structures. q If baryons are Time q involved: Observable q signatures of past merger q events may be retained. ➙ Dwarf galaxies as building blocks of massive galaxies. Potentially traceable; esp. in galactic halos. Fundamental scenario: q Surviving dwarfs: Fossils of galaxy formation q and evolution. Large structures form through numerous mergers of smaller ones. 04.04.2019 Grebel: Dwarf Galaxies 2 Satellite Disruption and Accretion Satellite disruption: q may lead to tidal q stripping (up to 90% q of the satellite’s original q stellar mass may be lost, q but remnant may survive), or q to complete disruption and q ultimately satellite accretion. Harding q More massive satellites experience Stellar tidal streams r r q higher dynamical friction dV M ρ V from different dwarf ∝ − r 3 galaxy accretion q and sink more rapidly. dt V events lead to ➙ Due to the mass-metallicity relation, expect a highly sub- q more metal-rich stars to end up at smaller radii. structured halo. 04.04.2019 € Grebel: Dwarf Galaxies Johnston 3 De Lucia & Helmi 2008; Cooper et al. 2010 accreted stars (ex situ) in-situ stars Stellar Halo Origins q Stellar halos composed in part of q accreted stars and in part of stars q formed in situ. Rodriguez- q Halos grow from “from inside out”. Gomez et al. 2016 q Wide variety of satellite accretion histories from smooth growth to discrete events.
    [Show full text]
  • Dark Matter in the Galactic Halo Rotation Curve (I.E
    Dark matter in the Galactic Halo Rotation curve (i.e. the orbital velocity V of stars and gas as a function of distance to the Galactic Center r) of the disk of the Milky Way is measured: • for the inner Galaxy by looking at the Doppler shift of 21 cm emission from hydrogen • for the outer Galaxy by looking at the velocity of star clusters relative to the Sun. (details of these methods are given in Section 2.3 of Sparke & Gallagher…) Fact that V(r) ~ constant at large radius implies that the Galaxy contains more mass than just the visible stars and gas. Extra mass - the dark matter - normally assumed to reside in an extended, roughly spherical halo around the Galaxy. ASTR 3830: Spring 2004 Possibilities for dark matter include: • molecular hydrogen gas clouds baryonic dark • very low mass stars / brown dwarfs matter - made • stellar remnants: white dwarfs, (originally) from neutron stars, black holes ordinary gas • primordial black holes • elementary particles, probably - non-baryonic dark matter currently unknown The Milky Way halo probably contains some baryonic dark matter - brown dwarfs + stellar remnants accompanying the known population of low mass stars. This uncontroversial component of dark matter is not enough - is the remainder baryonic or non-baryonic? ASTR 3830: Spring 2004 On the largest scales (galaxy clusters and larger), strong evidence that the dark matter has to be non-baryonic: • Abundances of light elements (hydrogen, helium and lithium) formed in the Big Bang depend on how many baryons (protons + neutrons) there were. light element abundances + theory allow a measurement of the number of baryons • observations of dark matter in galaxy clusters suggest there is too much dark matter for it all to be baryons, must be largely non-baryonic.
    [Show full text]
  • The Galaxy in Context: Structural, Kinematic & Integrated Properties
    The Galaxy in Context: Structural, Kinematic & Integrated Properties Joss Bland-Hawthorn1, Ortwin Gerhard2 1Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006, Australia; email: [email protected] 2Max Planck Institute for extraterrestrial Physics, PO Box 1312, Giessenbachstr., 85741 Garching, Germany; email: [email protected] Annu. Rev. Astron. Astrophys. 2016. Keywords 54:529{596 Galaxy: Structural Components, Stellar Kinematics, Stellar This article's doi: 10.1146/annurev-astro-081915-023441 Populations, Dynamics, Evolution; Local Group; Cosmology Copyright c 2016 by Annual Reviews. Abstract All rights reserved Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It is the only galaxy whose formation history can be stud- ied using the full distribution of stars from faint dwarfs to supergiants. The oldest components provide us with unique insight into how galaxies form and evolve over billions of years. The Galaxy is a luminous (L?) barred spiral with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo. Based on global properties, it falls in the sparsely populated \green valley" region of the galaxy colour-magnitude dia- arXiv:1602.07702v2 [astro-ph.GA] 5 Jan 2017 gram. Here we review the key integrated, structural and kinematic pa- rameters of the Galaxy, and point to uncertainties as well as directions for future progress. Galactic studies will continue to play a fundamen- tal role far into the future because there are measurements that can only be made in the near field and much of contemporary astrophysics depends on such observations. 529 Redshift (z) 20 10 5 2 1 0 1012 1011 ) ¯ 1010 M ( 9 r i 10 v 8 M 10 107 100 101 102 ) c p 1 k 10 ( r i v r 100 10-1 0.3 1 3 10 Time (Gyr) Figure 1 Left: The estimated growth of the Galaxy's virial mass (Mvir) and radius (rvir) from z = 20 to the present day, z = 0.
    [Show full text]
  • ROTATING GALACTIC ARMS and LEADING-EDGE SHOCK WAVES in H 111 by Robert E
    NASA TECHNICAL NOTE NASA TN D-2810 I -- c'- / 0 bo N d z c 4 VI 4 z ROTATING GALACTIC ARMS AND LEADING-EDGE SHOCK WAVES IN H 111 by Robert E. Duuidson Langley ReseurcrS Center Lungley Stution, Hampton, Vu, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 0 WASHINGTON, D. C. 0 MAY 1965 ROTATING GALACTIC ARMS AND LEADING-EDGE SHOCK WAVES IN H 111 By Robert E. Davidson Langley Research Center Langley Station, Hampton, Va. NATIONAL AERONAUT ICs AND SPACE ADMINISTRATION For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - Price $1.00 ROTATING GALACTIC ARMS AND LEADING-EDGE SHOCK WAVES IN H I11 By Robert E. Davidson Langley Research Center SUMMARY A steady-state galactic-structure theory based on magnetohydrodynamic prin- ciples has been developed. Quasi-steady states, however, are not excluded. The theory provides an energy source for the coronal heating called for in the the- ories of Pickelner and Spitzer. The magnitude of the energy source can be cal- culated and appears adequate for Spitzer's theory and possibly is adequate for Pickelner's theory. In order to agree with other aspects of our knowledge of spiral galaxies, barred spirals in particular, it is necessary to assume that spiral arms are shaped by supersonic drag with attendant shocks. The angular motion of the galactic arms through the gas in the disk produces a flow over the arms which is subsonic within a certain distance of the galactic center and is supersonic outside it. From resulting aerodynamic effects an explanation of important galactic phenomena can be made.
    [Show full text]
  • On Wave Dark Matter, Shells in Elliptical Galaxies, and the Axioms of General Relativity
    On Wave Dark Matter, Shells in Elliptical Galaxies, and the Axioms of General Relativity Hubert L. Bray ∗ December 22, 2012 Abstract This paper is a sequel to the author’s paper entitled “On Dark Matter, Spiral Galaxies, and the Axioms of General Relativity” which explored a geometrically natural axiomatic definition for dark matter modeled by a scalar field satisfying the Einstein-Klein-Gordon wave equations which, after much calculation, was shown to be consistent with the observed spiral and barred spiral patterns in disk galaxies, as seen in Figures 3, 4, 5, 6. We give an update on where things stand on this “wave dark matter” model of dark matter (aka scalar field dark matter and boson stars), an interesting alternative to the WIMP model of dark matter, and discuss how it has the potential to help explain the long-observed interleaved shell patterns, also known as ripples, in the images of elliptical galaxies. In section 1, we begin with a discussion of dark matter and how the wave dark matter model com- pares with observations related to dark matter, particularly on the galactic scale. In section 2, we show explicitly how wave dark matter shells may occur in the wave dark matter model via approximate solu- tions to the Einstein-Klein-Gordon equations. How much these wave dark matter shells (as in Figure 2) might contribute to visible shells in elliptical galaxies (as in Figure 1) is an important open question. 1 Introduction What is dark matter? No one really knows exactly, in part because dark matter does not interact signif- icantly with light, making it invisible.
    [Show full text]
  • Subaru Telescope —History, Active/Adaptive Optics, Instruments, and Scientific Achievements—
    No. 7] Proc. Jpn. Acad., Ser. B 97 (2021) 337 Review Subaru Telescope —History, active/adaptive optics, instruments, and scientific achievements— † By Masanori IYE*1, (Contributed by Masanori IYE, M.J.A.; Edited by Katsuhiko SATO, M.J.A.) Abstract: The Subaru Telescopea) is an 8.2 m optical/infrared telescope constructed during 1991–1999 and has been operational since 2000 on the summit area of Maunakea, Hawaii, by the National Astronomical Observatory of Japan (NAOJ). This paper reviews the history, key engineering issues, and selected scientific achievements of the Subaru Telescope. The active optics for a thin primary mirror was the design backbone of the telescope to deliver a high-imaging performance. Adaptive optics with a laser-facility to generate an artificial guide-star improved the telescope vision to its diffraction limit by cancelling any atmospheric turbulence effect in real time. Various observational instruments, especially the wide-field camera, have enabled unique observational studies. Selected scientific topics include studies on cosmic reionization, weak/strong gravitational lensing, cosmological parameters, primordial black holes, the dynamical/chemical evolution/interactions of galaxies, neutron star mergers, supernovae, exoplanets, proto-planetary disks, and outliers of the solar system. The last described are operational statistics, plans and a note concerning the culture-and-science issues in Hawaii. Keywords: active optics, adaptive optics, telescope, instruments, cosmology, exoplanets largest telescope in Asia and the sixth largest in the 1. Prehistory world. Jun Jugaku first identified a star with excess 1.1. Okayama 188 cm telescope. In 1953, UV as an optical counterpart of the X-ray source Yusuke Hagiwara,1 director of the Tokyo Astronom- Sco X-1.1) Sco X-1 was an unknown X-ray source ical Observatory, the University of Tokyo, empha- found at that time by observations using an X-ray sized in a lecture the importance of building a modern collimator instrument invented by Minoru Oda.2, 2) large telescope.
    [Show full text]
  • Dark Matter in Galaxies E NCYCLOPEDIA of a STRONOMY and a STROPHYSICS
    Dark Matter in Galaxies E NCYCLOPEDIA OF A STRONOMY AND A STROPHYSICS Dark Matter in Galaxies Dark matter in spiral galaxies SPIRAL GALAXIES are flat rotating systems. The stars and gas in the disk are moving in nearly circular orbits, with the gravitational field of the galaxy providing the inward acceleration required for the circular motion. The rotation of these galaxies is usually not like a solid body: the angular velocity of the rotation typically decreases with radius. To a fair approximation, assuming Newtonian gravity, the rotational velocity V(r) at radius r is related to the total mass M(r) within radius r by the equation V 2(r) = GM(r)/r, where G is the gravitational constant. The radial variation of the rotational velocity (the rotation curve) is most readily measured from the gas in the disks. The emission lines of ionized gas in the inner regions are measured with optical spectrographs. With radio synthesis telescopes, rotation curves can be measured from the neutral hydrogen (H I) which emits a narrow spectral line at 1420 MHz (21 cm wavelength). The interest in measuring rotation curves of spiral galaxies is that they give a direct measure of the radial distribution of the total gravitating mass. Until the early 1970s, most of the rotation data for spirals came from optical observations which did not Figure 1. The upper panel shows the R-band radial surface extend beyond the luminous inner regions. At that time, brightness distribution of the spiral galaxy NGC 3198. The the optical rotation curves seemed consistent with the lower panel shows itsHIrotation curve (points).
    [Show full text]