DOCSLIB.ORG

Galactic Astronomy

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Galactic Astronomy Astrophysics III: Galactic Astronomy Lecture, D-PHYS, ETH Zurich, Spring Semester 2016 Tuesday: 12.45{13.30, HIT F13, and Wednesday: 8.45{10.30, HIT J51, H¨onggerberg Exercises: Wednesday: 10:45{12:30, HIT J51 Dates: Feb. 23 to June 1, 2016 (except for Easter break, March 27 { April 3) Website: www.astro.ethz.ch/education/courses/Astrophysics 3 Lecturer: Prof. Dr. H.M. Schmid, Office, HIT J22.2, Tel: 044-63 27386; e-mail: schmid@astro.phys.ethz.ch Teaching Assistants and Co-Lecturers: Natalia Engler, HIT J 41.2, natalia.engler@phys.ethz.ch Bruderer Claudio, HIT J 41.2, claudio.bruderer@phys.ethz.ch ETH Zurich, Institut f¨urAstronomie, Wolfgang Pauli Str. 27 ETH-H¨onggerberg, 8093 Zurich Contents 1 Introduction 1 1.1 The Milky Way and the Universe . 1 1.2 Short history of the research in galactic astronomy . 3 1.3 Lecture contents and literature . 4 2 Components of the Milky Way Galaxy 7 2.1 Geometric components . 7 2.2 Stars . 9 2.2.1 Properties of main-sequence stars . 10 2.2.2 Observational Hertzsprung-Russell diagrams . 12 2.2.3 Stellar clusters and associations . 15 2.2.4 Globular clusters. 17 2.2.5 Age and metallicity of stars . 19 2.2.6 Cepheids and RR Lyr variables as distance indicators . 21 2.2.7 Star count statistics . 23 2.3 Stellar Dynamics . 29 2.3.1 Velocity parameters relative to the sun . 29 2.3.2 Solar motion relative to the local standard of rest . 30 2.3.3 Velocity dispersion in the solar neighborhood . 32 2.3.4 Moving groups . 33 2.3.5 High velocity stars . 33 2.3.6 Radial velocity dispersion in clusters . 34 2.3.7 Kinematics of the galactic rotation . 35 2.3.8 The GAIA revolution . 41 2.4 Interstellar matter (ISM) in the Milky Way . 43 2.4.1 The ISM in the solar neighborhood . 43 2.4.2 Global distribution of the ISM in the Galaxy . 45 2.4.3 Galactic rotation curve from line observations . 45 2.4.4 H i and CO observations in other galaxies . 47 3 Galactic dynamics 49 3.1 Potential theory . 49 3.1.1 Basic equations for the potential theory . 49 3.1.2 Newton's theorems . 50 3.1.3 Equations for spherical systems . 52 3.1.4 Simple spherical cases and characteristic parameters . 53 3.1.5 Spherical power law density models . 55 iii 3.1.6 Potentials for flattened systems . 56 3.1.7 The potential of the Milky Way . 57 3.2 The motion of stars in spherical potentials . 59 3.2.1 Orbits in a static spherical potential . 59 3.2.2 Radial and azimuthal velocity component. 62 3.2.3 Motion in a Kepler potential . 63 3.2.4 Motion in the potential of a homogeneous sphere . 64 3.3 Motion in axisymmetric potentials . 65 3.3.1 Motion in the meridional plane . 65 3.3.2 Nearly circular orbits: epicycle approximation . 66 3.3.3 Density waves and resonances in disks . 69 3.4 Two-body interactions and system relaxation . 71 3.4.1 Two-body interaction . 71 3.4.2 Relaxation time . 74 3.4.3 The dynamical evolution of stellar clusters . 74 4 Physics of the interstellar medium 81 4.1 Gas . 81 4.1.1 Description of a gas in thermodynamic equilibrium . 81 4.1.2 Description of the diffuse gas . 83 4.1.3 Ionization . 85 4.1.4 H ii-regions . 87 4.2 Dust . 89 4.2.1 Extinction, reddening and interstellar polarization . 89 4.2.2 Particle properties . 91 4.2.3 Temperature and emission of the dust particles . 92 4.2.4 Evolution of the interstellar dust . 93 4.3 Magnetic fields . 95 4.4 Radiation field . 96 4.5 Cosmic rays . 96 4.5.1 Properties of the cosmic rays . 96 4.5.2 Motion in the magnetic field . 97 4.5.3 The origin of the cosmic rays . 98 4.6 Radiation processes . 99 4.6.1 Radiation transport . 99 4.7 Spectral lines: bound-bound radiation processes . 101 4.7.1 Rate equations for the level population . 102 4.7.2 Collisionally excited lines . 103 4.7.3 Collisionally excited molecular lines . 108 4.7.4 Recombination lines: excitation through recombination . 109 4.7.5 Absorption lines . 110 4.8 Free-bound and free-free radiation processes . 115 4.8.1 Recombination continuum . 115 4.8.2 Photoionization or photo-electric absorption . 116 4.9 Free-free radiation processes or bremsstrahlung . 117 4.9.1 Radiation from accelerated charges . 117 4.9.2 Thermal bremsstrahlung . 118 v 4.10 Compton and Thomson scattering . 120 4.11 Temperature equilibrium . 122 4.11.1 Heating function H for neutral and photo-ionized gas . 122 4.11.2 Cooling of the gas . 123 4.11.3 The cooling function Λ(T ) . 123 4.11.4 Cooling time scale . 126 4.11.5 Equilibrium temperatures. 126 4.12 Dynamics of the interstellar gas . 128 4.12.1 Basic equations for the gas dynamics . 128 4.12.2 Shocks . 130 4.12.3 Example: supernova shells . 133 5 Star formation 135 5.1 Molecular clouds. 135 5.2 Elements of star formation . 136 5.2.1 Time scale for contraction . 140 5.3 Initial mass function . 141 5.4 Proto-stars . 142 6 Milky Way formation and evolution 145 6.1 Virial theorem and galaxy formation . 145 6.2 Timing the Milky Way evolution with high redshift observation . 147 6.3 Gas infall and minor mergers today . 148 6.3.1 Gas inflow . 148 6.3.2 Mergers with dwarf galaxies . 148 6.4 The chemical evolution of the Milky Way . 149 6.4.1 Nucleosynthesis and stellar yields . 149 6.4.2 The role of SN Ia. 151 6.4.3 Modelling the chemical evolution of the Milky Way . 152 vi Chapter 1 Introduction 1.1 The Milky Way and the Universe This lecture concentrates on the physical properties of the Milky Way galaxy and the processes which are important to understand its current structure and properties. Another strong focus is set on observational data which provide the basic empirical information for our models and theories of the Milky Way. The place of our Galaxy in the Universe is roughly illustrated in the block diagram in Fig. 1.1. { The Milky Way is a quite normal spiral galaxy among billions of galaxies in the observable Universe. { The galaxies were born by the assembly of baryonic matter in the growing potential wells of dark matter concentrations in an expanding Universe. This process started about 14 billion years ago with the big bang. The galaxies evolved with time by assembling initially gas rich matter fragments, going through phases of strong star formation, having phases of high activity of the central black hole, and many episodes of minor and perhaps also major interactions with other galaxies. Although the Milky Way belongs to one of the frequent galaxy types, it represents just one possible outcome of the very diverse galaxy evolution processes. { Initially, the big bang produced matter only in the form of hydrogen, helium and dark matter. The heavy elements which we see today were mainly produced in galaxies from H and He by nuclear processes in previous generations of intermediate and high mass stars (see Fig. 1.1). Stars form through the collapse of dense, cool interstellar clouds. Then they evolve due to nuclear reactions until they expel a lot of their mass at the end of their evolution in stellar winds or supernova (SN) explosions. This matter, enriched in heavy elements, goes back to the interstellar gas in the Milky Way and may form again a new generation of stars. The remnants of the stellar evolution, mostly white dwarfs (WD) and neutron stars (NS), contain also a lot of heavy elements which are no more available for the galactic nucleo-synthesis cycle. { Many galaxies, including the Milky Way, have a super-massive black hole (SM-BH) in their center. The black hole grows by episodic gas accretion which may be triggered by galaxy interaction. Supernovae explosions, active phases of the central black hole, 1 2 CHAPTER 1. INTRODUCTION or galaxy interactions are responsible for the loss of interstellar matter of a galaxy to the intergalactic medium. On the other side cold intergalactic matter (IGM), from either primordial origin or gas which was already in a galaxy, can fall onto the Milky Way and enhance the gas content. Big Bang p,e,α,DM (re)-combination H,He,DM ISM IGM SM-BH young stars evolved stars other galaxies low mass stars WD and NS Milky Way Figure 1.1: The Milky Way in relation to the big bang, the intergalactic matter (IGM), the internal interstellar matter (ISM), different types of stars (WD: white dwarfs; NS: neutron stars), the central, super-massive black hole (SM-BH), and other interacting galaxies. 1.2. SHORT HISTORY OF THE RESEARCH IN GALACTIC ASTRONOMY 3 1.2 Short history of the research in galactic astronomy Our knowledge on the Milky Way is constantly improving. The Milky Way research profits also a lot from new results gained in other fields in astronomy, like stellar evolution theory, interstellar matter studies, extra-galactic astronomy, or dark matter research. Most important for the progress is the steady.
Load more

Recommended publications
  • ASTR 503 – Galactic Astronomy Spring 2015 COURSE SYLLABUS
    ASTR 503 – Galactic Astronomy Spring 2015 COURSE SYLLABUS WHO I AM Instructor: Dr. Kurtis A. Williams Office Location: Science 145 Office Phone: 903-886-5516 Office Fax: 903-886-5480 Office Hours: TBA University Email Address: Kurtis.Williams@tamuc.edu Course Location and Time: Science 122, TR 11:00-12:15 WHAT THIS COURSE IS ABOUT Course Description: Observations of galaxies provide much of the key evidence supporting the current paradigms of cosmology, from the Big Bang through formation of large-scale structure and the evolution of stellar environments over cosmological history. In this course, we will explore the phenomenology of galaxies, primarily through observational support of underlying astrophysical theory. Student Learning Outcomes: 1. You will calculate properties of galaxies and stellar systems given quantitative observations, and vice-versa. 2. You will be able to categorize galactic systems and their components. 3. You will be able to interpret observations of galaxies within a framework of galactic and stellar evolution. 4. You will prepare written and oral summaries of both current and fundamental peer- reviewed articles on galactic astronomy for your peers. WHAT YOU ABSOLUTELY NEED Materials – Textbooks, Software and Additional Reading: Required: • Galactic Astronomy, Binney & Merrifield 1998 (Princeton University Press: Princeton) • Access to a desktop or laptop computer on which you can install software, read PDF files, compile code, and access the internet. Recommended: • Allen’s Astrophysical Quantities, 4th Edition, Arthur Cox, 2000 (Springer) Course Prerequisites: Advanced undergraduate classical dynamics (equivalent of Phys 411) or Phys 511. HOW THE COURSE WILL WORK Instructional Methods / Activities / Assessments Assigned Readings There is far too much material in the text for us to cover every single topic in class.
    [Show full text]
  • The Solar System and Its Place in the Galaxy in Encyclopedia of the Solar System by Paul R
    Giant Molecular Clouds http://www.astro.ncu.edu.tw/irlab/projects/project.htm Æ Galactic Open Clusters Æ Galactic Structure Æ GMCs The Solar System and its Place in the Galaxy In Encyclopedia of the Solar System By Paul R. Weissman http://www.academicpress.com/refer/solar/Contents/chap1.htm Stars in the galactic disk have different characteristic velocities as a function of their stellar classification, and hence age. Low-mass, older stars, like the Sun, have relatively high random velocities and as a result c an move farther out of the galactic plane. Younger, more massive stars have lower mean velocities and thus smaller scale heights above and below the plane. Giant molecular clouds, the birthplace of stars, also have low mean velocities and thus are confined to regions relatively close to the galactic plane. The disk rotates clockwise as viewed from "galactic north," at a relatively constant velocity of 160-220 km/sec. This motion is distinctly non-Keplerian, the result of the very nonspherical mass distribution. The rotation velocity for a circular galactic orbit in the galactic plane defines the Local Standard of Rest (LSR). The LSR is then used as the reference frame for describing local stellar dynamics. The Sun and the solar system are located approxi-mately 8.5 kpc from the galactic center, and 10-20 pc above the central plane of the galactic disk. The circular orbit velocity at the Sun's distance from the galactic center is 220 km/sec, and the Sun and the solar system are moving at approximately 17 to 22 km/sec relative to the LSR.
    [Show full text]
  • Rocket Team to Discern If Our Star Count Should Go Way up | NASA
    6/10/2021 Rocket Team to Discern if Our Star Count Should Go Way Up | NASA (https://www.nasa.gov/specials/apollo50th/index.html) (/multimedia/nasatv/index.html) (/) NASA TV Search Stars (/subject/6892/stars) (/sites/default/files/ciber_launch_0.jpg) Jun 3, 2021 S E I R O T S Rocket Team to Discern if Our Star Count Should Go Way Up E R UPDATE June 7, 2021: The Cosmic Infrared Background Experiment-2 or CIBER-2 was successfully launched on a NASA Black Brant O M IX sounding rocket at 2:25 a.m. EDT from the White Sands Missile Range in New Mexico. Preliminary indications show that the intended targets were viewed by the payload and good data was received. The payload flew to an apogee of about 193 miles before descending by parachute for recovery. The universe contains a mind-boggling number of stars – but scientists’ best estimates may be an undercount. A NASA-funded sounding rocket is launching with an improved instrument to look for evidence of extra stars that may have been missed in stellar head counts. The Cosmic Infrared Background Experiment-2, or CIBER-2, mission is the latest in a series of sounding rocket launches that began in 2009. Led by Michael Zemcov, assistant professor of physics and astronomy at the Rochester Institute of Technology in New York, CIBER-2’s launch window opens at the White Sands Missile Range in New Mexico on June 6, 2021. If you’ve had the pleasure of seeing an open sky on a clear, dark night, you’ve probably been struck by the sheer number of stars.
    [Show full text]
  • Relaxation Time
    Today in Astronomy 142: the Milky Way’s disk More on stars as a gas: stellar relaxation time, equilibrium Differential rotation of the stars in the disk The local standard of rest Rotation curves and the distribution of mass The rotation curve of the Galaxy Figure: spiral structure in the first Galactic quadrant, deduced from CO observations. (Clemens, Sanders, Scoville 1988) 21 March 2013 Astronomy 142, Spring 2013 1 Stellar encounters: relaxation time of a stellar cluster In order to behave like a gas, as we assumed last time, stars have to collide elastically enough times for their random kinetic energy to be shared in a thermal fashion. But stellar encounters, even distant ones, are rare on human time scales. How long does it take a cluster of stars to thermalize? One characteristic time: the time between stellar elastic encounters, called the relaxation time. If a gravitationally bound cluster is a lot older than its relaxation time, then the stars will be describable as a gas (the star system has temperature, pressure, etc.). 21 March 2013 Astronomy 142, Spring 2013 2 Stellar encounters: relaxation time of a stellar cluster (continued) Suppose a star has a gravitational “sphere of influence” with radius r (>>R, the radius of the star), and moves at speed v between encounters, with its sphere of influence sweeping out a cylinder as it does: v V= π r2 vt r vt If the number density of stars (stars per unit volume) is n, then there will be exactly one star in the cylinder if 2 1 nV= nπ r vtcc =⇒=1 t Relaxation time nrvπ 2 21 March 2013 Astronomy 142, Spring 2013 3 Stellar encounters: relaxation time of a stellar cluster (continued) What is the appropriate radius, r? Choose that for which the gravitational potential energy is equal in magnitude to the average stellar kinetic energy.
    [Show full text]
  • Structure of the Outer Galactic Disc with Gaia DR2 Ž
    A&A 637, A96 (2020) Astronomy https://doi.org/10.1051/0004-6361/201937289 & c ESO 2020 Astrophysics Structure of the outer Galactic disc with Gaia DR2 Ž. Chrobáková1,2, R. Nagy3, and M. López-Corredoira1,2 1 Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain e-mail: zofiachrobakova@gmail.com 2 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain 3 Faculty of Mathematics, Physics, and Informatics, Comenius University, Mlynská dolina, 842 48 Bratislava, Slovakia Received 9 December 2019 / Accepted 31 March 2020 ABSTRACT Context. The structure of outer disc of our Galaxy is still not well described, and many features need to be better understood. The second Gaia data release (DR2) provides data in unprecedented quality that can be analysed to shed some light on the outermost parts of the Milky Way. Aims. We calculate the stellar density using star counts obtained from Gaia DR2 up to a Galactocentric distance R = 20 kpc with a deconvolution technique for the parallax errors. Then we analyse the density in order to study the structure of the outer Galactic disc, mainly the warp. Methods. In order to carry out the deconvolution, we used the Lucy inversion technique for recovering the corrected star counts. We also used the Gaia luminosity function of stars with MG < 10 to extract the stellar density from the star counts. Results. The stellar density maps can be fitted by an exponential disc in the radial direction hr = 2:07 ± 0:07 kpc, with a weak dependence on the azimuth, extended up to 20 kpc without any cut-off.
    [Show full text]
  • In-Class Worksheet on the Galaxy
    Ay 20 / Fall Term 2014-2015 Hillenbrand In-Class Worksheet on The Galaxy Today is another collaborative learning day. As earlier in the term when working on blackbody radiation, divide yourselves into groups of 2-3 people. Then find a broad space at the white boards around the room. Work through the logic of the following two topics. Oort Constants. From the vantage point of the Sun within the plane of the Galaxy, we have managed to infer its structure by observing line-of-sight velocities as a function of galactic longitude. Let’s see why this works by considering basic geometry and observables. • Begin by drawing a picture. Consider the Sun at a distance Ro from the center of the Galaxy (a.k.a. the GC) on a circular orbit with velocity θ(Ro) = θo. Draw several concentric circles interior to the Sun’s orbit that represent the circular orbits of other stars or gas. Now consider some line of sight at a longitude l from the direction of the GC, that intersects one of your concentric circles at only one point. The circular velocity of an object on that (also circular) orbit at galactocentric distance R is θ(R); the direction of θ(R) forms an angle α with respect to the line of sight. You should also label the components of θ(R): they are vr along the line-of-sight, and vt tangential to the line-of-sight. If you need some assistance, Figure 18.14 of C/O shows the desired result. What we are aiming to do is derive formulae for vr and vt, which in principle are measureable, as a function of the distance d from us, the galactic longitude l, and some constants.
    [Show full text]
  • Stellar Dynamics and Stellar Phenomena Near a Massive Black Hole
    Stellar Dynamics and Stellar Phenomena Near A Massive Black Hole Tal Alexander Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 234 Herzl St, Rehovot, Israel 76100; email: tal.alexander@weizmann.ac.il | Author's original version. To appear in Annual Review of Astronomy and Astrophysics. See final published version in ARA&A website: www.annualreviews.org/doi/10.1146/annurev-astro-091916-055306 Annu. Rev. Astron. Astrophys. 2017. Keywords 55:1{41 massive black holes, stellar kinematics, stellar dynamics, Galactic This article's doi: Center 10.1146/((please add article doi)) Copyright c 2017 by Annual Reviews. Abstract All rights reserved Most galactic nuclei harbor a massive black hole (MBH), whose birth and evolution are closely linked to those of its host galaxy. The unique conditions near the MBH: high velocity and density in the steep po- tential of a massive singular relativistic object, lead to unusual modes of stellar birth, evolution, dynamics and death. A complex network of dynamical mechanisms, operating on multiple timescales, deflect stars arXiv:1701.04762v1 [astro-ph.GA] 17 Jan 2017 to orbits that intercept the MBH. Such close encounters lead to ener- getic interactions with observable signatures and consequences for the evolution of the MBH and its stellar environment. Galactic nuclei are astrophysical laboratories that test and challenge our understanding of MBH formation, strong gravity, stellar dynamics, and stellar physics. I review from a theoretical perspective the wide range of stellar phe- nomena that occur near MBHs, focusing on the role of stellar dynamics near an isolated MBH in a relaxed stellar cusp.
    [Show full text]
  • PHYS 1302 Intro to Stellar & Galactic Astronomy
    PHYS 1302: Introduction to Stellar and Galactic Astronomy University of Houston-Downtown Course Prefix, Number, and Title: PHYS 1302: Introduction to Stellar and Galactic Astronomy Credits/Lecture/Lab Hours: 3/2/2 Foundational Component Area: Life and Physical Sciences Prerequisites: Credit or enrollment in MATH 1301 or MATH 1310 Co-requisites: None Course Description: An integrated lecture/laboratory course for non-science majors. This course surveys stellar and galactic systems, the evolution and properties of stars, galaxies, clusters of galaxies, the properties of interstellar matter, cosmology and the effort to find extraterrestrial life. Competing theories that address recent discoveries are discussed. The role of technology in space sciences, the spin-offs and implications of such are presented. Visual observations and laboratory exercises illustrating various techniques in astronomy are integrated into the course. Recent results obtained by NASA and other agencies are introduced. Up to three evening observing sessions are required for this course, one of which will take place off-campus at George Observatory at Brazos Bend State Park. TCCNS Number: N/A Demonstration of Core Objectives within the Course: Assigned Core Learning Outcome Instructional strategy or content Method by which students’ Objective Students will be able to: used to achieve the outcome mastery of this outcome will be evaluated Critical Thinking Utilize scientific Star Property Correlations – They will be instructed to processes to identify students will form and test prioritize these properties in Empirical & questions pertaining to hypotheses to explain the terms of their relevance in Quantitative natural phenomena. correlation between a number of deciding between competing Reasoning properties seen in stars.
    [Show full text]
  • PDF (Pbcameron Thesis.Pdf)
    The Formation and Evolution of Neutron Stars: Astrometry, Timing, and Transients Thesis by P. Brian Cameron In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 2009 (Defended June 2, 2008) ii c 2009 P. Brian Cameron All Rights Reserved iii Acknowledgements I have been incredibly fortunate these last five years to work with and have the support of so many amazing people. Foremost, I would like to acknowledge my enormous debt to my advisor, Shri Kulkarni. His vision and tireless dedication to astronomy were inspiring, and led to the topics in this thesis being at the forefront of astrophysics. Our styles contrasted, but his energy, open advice, and support made for a very rewarding collaboration. In this same vein, I am grateful to Matthew Britton whose ideas and open door made the last 2 years incredibly enjoyable. I have also had the privilege of working with a number talented people on a wide variety of topics. I am grateful to Bryan Jacoby, David Kaplan, Bob Rutledge, and Dale Frail for their insights and patience. I would also like to thank the NGAO crowd that got me thinking hard about astrometry: Rich Dekany, Claire Max, Jessica Lu, and Andrea Ghez. No observer could ever function with out people working tirelessly at the telescope and when you return from it. I am grateful for the patience and dedication of the Keck astronomers, especially Al Conrad, Randy Campbell and Jim Lyke, as well as those at Palomar: Jean Mueller, and Karl Dunscombe. I am indebted to the excellent staff here at Caltech for putting up with my endless questions and requests: Patrick Shopbell, Anu Mahabal, and Cheryl Southard.
    [Show full text]
  • Galactic Astronomy with AO: Nearby Star Clusters and Moving Groups
    Galactic astronomy with AO: Nearby star clusters and moving groups T. J. Davidgea aDominion Astrophysical Observatory, Victoria, BC Canada ABSTRACT Observations of Galactic star clusters and objects in nearby moving groups recorded with Adaptive Optics (AO) systems on Gemini South are discussed. These include observations of open and globular clusters with the GeMS system, and high Strehl L observations of the moving group member Sirius obtained with NICI. The latter data 2 fail to reveal a brown dwarf companion with a mass ≥ 0.02M in an 18 × 18 arcsec area around Sirius A. Potential future directions for AO studies of nearby star clusters and groups with systems on large telescopes are also presented. Keywords: Adaptive optics, Open clusters: individual (Haffner 16, NGC 3105), Globular Clusters: individual (NGC 1851), stars: individual (Sirius) 1. STAR CLUSTERS AND THE GALAXY Deep surveys of star-forming regions have revealed that stars do not form in isolation, but instead form in clusters or loose groups (e.g. Ref. 25). This is a somewhat surprising result given that most stars in the Galaxy and nearby galaxies are not seen to be in obvious clusters (e.g. Ref. 31). This apparent contradiction can be reconciled if clusters tend to be short-lived. In fact, the pace of cluster destruction has been measured to be roughly an order of magnitude per decade in age (Ref. 17), indicating that the vast majority of clusters have lifespans that are only a modest fraction of the dynamical crossing-time of the Galactic disk. Clusters likely disperse in response to sudden changes in mass driven by supernovae and stellar winds (e.g.
    [Show full text]
  • Arxiv:1802.01493V7 [Astro-Ph.GA] 10 Feb 2021 Ceeainbtti Oe Eoe Rbeai Tselrsae.I Scales
    Variable Modified Newtonian Mechanics II: Baryonic Tully Fisher Relation C. C. Wong Department of Electrical and Electronic Engineering, University of Hong Kong. H.K. (Dated: February 11, 2021) Recently we find a single-metric solution for a point mass residing in an expanding universe [1], which apart from the Newtonian acceleration, gives rise to an additional MOND-like acceleration in which the MOND acceleration a0 is replaced by the cosmological acceleration. We study a Milky Way size protogalactic cloud in this acceleration, in which the growth of angular momentum can lead to an end of the overdensity growth. Within realistic redshifts, the overdensity stops growing at a value where the MOND-like acceleration dominates over Newton and the outer mass shell rotational velocity obeys the Baryonic Tully Fisher Relation (BTFR) with a smaller MOND acceleration. As the outer mass shell shrinks to a few scale length distances, the rotational velocity BTFR persists due to the conservation of angular momentum and the MOND acceleration grows to the phenomenological MOND acceleration value a0 at late time. PACS numbers: ?? INTRODUCTION A common response to the non-Newtonian rotational curve of a galaxy is that its ”Newtonian” dynamics requires cold dark matter (DM) particles. However, the small observed scatter of empirical Baryonic Tully-Fisher Relation (BTFR) of gas rich galaxies, see McGaugh [2]-Lelli [3], Milgrom [4] and Sanders [5], continues to motivate the hunt for a non-Newtonian connection between the rotational speeds and the baryon mass. On the modified DM theory front, Khoury [6] proposes a DM Bose-Einstein Condensate (BEC) phase where DM can interact more strongly with baryons.
    [Show full text]
  • V. Spatially-Resolved Stellar Angular Momentum, Velocity Dispersion, and Higher Moments of the 41 Most Massive Local Early-Type Galaxies
    MNRAS 000,1{20 (2016) Preprint 9 September 2016 Compiled using MNRAS LATEX style file v3.0 The MASSIVE Survey - V. Spatially-Resolved Stellar Angular Momentum, Velocity Dispersion, and Higher Moments of the 41 Most Massive Local Early-Type Galaxies Melanie Veale,1;2 Chung-Pei Ma,1 Jens Thomas,3 Jenny E. Greene,4 Nicholas J. McConnell,5 Jonelle Walsh,6 Jennifer Ito,1 John P. Blakeslee,5 Ryan Janish2 1Department of Astronomy, University of California, Berkeley, CA 94720, USA 2Department of Physics, University of California, Berkeley, CA 94720, USA 3Max Plank-Institute for Extraterrestrial Physics, Giessenbachstr. 1, D-85741 Garching, Germany 4Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA 5Dominion Astrophysical Observatory, NRC Herzberg Institute of Astrophysics, Victoria BC V9E2E7, Canada 6George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA Accepted XXX. Received YYY; in original form ZZZ ABSTRACT We present spatially-resolved two-dimensional stellar kinematics for the 41 most mas- ∗ 11:8 sive early-type galaxies (MK . −25:7 mag, stellar mass M & 10 M ) of the volume-limited (D < 108 Mpc) MASSIVE survey. For each galaxy, we obtain high- quality spectra in the wavelength range of 3650 to 5850 A˚ from the 246-fiber Mitchell integral-field spectrograph (IFS) at McDonald Observatory, covering a 10700 × 10700 field of view (often reaching 2 to 3 effective radii). We measure the 2-D spatial distri- bution of each galaxy's angular momentum (λ and fast or slow rotator status), velocity dispersion (σ), and higher-order non-Gaussian velocity features (Gauss-Hermite mo- ments h3 to h6).
    [Show full text]