DOCSLIB.ORG

Clusters of Galaxy Hierarchical Structure the Universe Shows Range of Patterns of Structures on Decidedly Different Scales

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Clusters of Galaxy Hierarchical Structure the Universe Shows Range of Patterns of Structures on Decidedly Different Scales Astronomy 218 Clusters of Galaxy Hierarchical Structure The Universe shows range of patterns of structures on decidedly different scales. Stars (typical diameter of d ~ 106 km) are found in gravitationally bound systems called star clusters (≲ 106 stars) and galaxies (106 ‒ 1012 stars). Galaxies (d ~ 10 kpc), composed of stars, star clusters, gas, dust and dark matter, are found in gravitationally bound systems called groups (< 50 galaxies) and clusters (50 ‒ 104 galaxies). Clusters (d ~ 1 Mpc), composed of galaxies, gas, and dark matter, are found in currently collapsing systems called superclusters. Superclusters (d ≲ 100 Mpc) are the largest known structures. The Local Group Three large spirals, the Milky Way Galaxy, Andromeda Galaxy(M31), and Triangulum Galaxy (M33) and their satellites make up the Local Group of galaxies. At least 45 galaxies are members of the Local Group, all within about 1 Mpc of the Milky Way. The mass of the Local Group is dominated by 11 11 10 M31 (7 × 10 M☉), MW (6 × 10 M☉), M33 (5 × 10 M☉) Virgo Cluster The nearest large cluster to the Local Group is the Virgo Cluster at a distance of 16 Mpc, has a width of ~2 Mpc though it is far from spherical. It covers 7° of the sky in the Constellations Virgo and Coma Berenices. Even these The 4 brightest very bright galaxies are giant galaxies are elliptical galaxies invisible to (M49, M60, M86 & the unaided M87). eye, mV ~ 9. Virgo Census The Virgo Cluster is loosely concentrated and irregularly shaped, making it fairly M88 M99 representative of the most M100 common class of clusters. M90 M89 M86 Because of its proximity, at M59 M84 least 3500 galaxies are known, M87 M58 mostly dwarf ellipticals and M60 spheroidals. Among the brightest 207 M49 galaxies are 128 bright spirals, 49 lenticulars and 30 ellipticals, also typical of large irregular clusters. Giant Elliptical Galaxy The giant elliptical galaxy M87 M87 is truly a monster, with a mass of 2.4 × 1012 M☉ within 32 kpc but ~2 13 × 10 M☉ within 240 kpc. M87 has an active nucleus, with a jet that was first observed in 1918 and is one of the brightest 5 kpc radio sources in the sky (Virgo A). M87’s central black hole is one of the most massive known, 9 with MBH = 6.6 × 10 M☉. It is accreting matter at a rate �̇ ~ −1 0.1 M☉ /yr . Coma Cluster Denser, richer clusters tend to be regularly shaped. An example is the Coma cluster, located just north of the Virgo Cluster in the constellation Coma Berenices on the sky. At an average redshift of z = 0.023, it lies 100 Mpc away. The center of the Coma cluster is dominated by 2 giant elliptical galaxies, NGC 4889 & NGC 4874. The galaxy population, especially near the center, is dominated by ellipticals and S0, only 15% of bright galaxies are spiral. Cluster Kinematics Galaxy clusters are gravitationally bound systems, thus all of the galaxies orbit the common center of mass. For the Local Group, the typical velocity is 150 km s−1. The Milky Way and Andromeda are approaching each other at a combined 119 km s−1. At this rate, they will cover the 770 kpc separating them in 6.3 Gyr. For the Virgo cluster, the spiral galaxies show a much larger velocity dispersion (888 km s−1) than that typical of the elliptical, lenticular and dwarf galaxies (573 km s−1). The regular shapes of regular galaxy clusters suggest they are in dynamical equilibrium, with uniform velocity dispersions of 800 ‒ 1000 km s−1. For Coma cluster, the velocity dispersion σ = 880 km s−1. Cluster Mass For a system in dynamical equilibrium, the virial theorem applies, thus the velocity dispersion of galaxies in a rich cluster can be used to estimate the cluster’s mass. Fritz Zwicky, in 1933, showed that for Coma, σ = 880 km s−1 and the half-light radius rh = 1.5 Mpc. 15 ≈ 2 × 10 M☉ ≈ 4 × 1045 kg 10 In contrast, the luminosity LB ≈ 2 × 10 LB,☉ ≈ 400 LB,MW. This gives a mass to light M/LB ≈ 250 M☉/LB,☉. Intergalactic Gas The space between galaxies in clusters is filled with hot (~10 million K), low density (100‒1000 m−3), X-ray 36‒38 emitting (Lx ~ 10 W) intracluster gas and stray stars. The gas maps the gravitational potential of the cluster. Abell 1835 Source of the Gas The intracluster gas is predominantly hydrogen and helium, however X-ray spectra reveal emission lines of heavy elements, like Fe, S, Si, Mg & O in high ionization states, for example Fe XXV, Fe XXVI. These heavy elements come from supernovae and represent a metallicity nearly ⅓ of that in the Sun. Ram stripping While supernovae are capable of ejecting gas directly from galaxies, the intracluster medium can also remove gas from galaxies directly via ram stripping. As a galaxy moves through the ICM, interactions between the ICM and the gas in the galaxy strip the gas from the galaxy. This radio galaxy’s swept- back lobes provide a direct observation of interaction with intracluster gas. Gas Mass For the Coma cluster the average gas temperature is 8 〈Tgas〉 ≈ 10 K and the total mass of X-ray emitting gas 14 is Mgas ≈ 2 × 10 M☉. This represents ~ 5 times more mass than is present in the stars of the cluster. Maintaining hydrostatic equilibrium with the hot gas requires kBTc ≈ 2 G M μmp /R This can be reorganized to 45 ~ 10 kg calculate the mass, using ~ 0.5 × 1015 M ☉ 〈Tgas〉 = Tc and rh =R/2, Lensing Clusters The dark matter present in the cluster affects not only the galaxies of the cluster and its intracluster medium. The light of more distant galaxies is also bent as it passes the foreground cluster’s mass, distorting the image of distant galaxies into arcs of light. Lens Reconstruction The distorted images of an extended object reveal much about the defects in a glass lens. In a similar fashion, the multiple distorted images of a galaxy disclose the mass of the lensing 15 cluster, typically ~ 10 M☉. Numerical reconstruction of the lens unveils a map of the dark matter in a galaxy cluster. Though smoother than the distribution of light, the dark matter is nonetheless clumpy. Beyond the Neighborhood Despite the large numbers of galaxies in rich clusters like the Virgo cluster and Coma cluster, 80% of galaxies reside in groups or poor clusters. The environment beyond the Local Group is illustrative. The next nearest galaxies are members of the Sculptor group (6 galaxies, at an average distance of 1.8 Mpc), M81 group (8 galaxies, 3.1 Mpc away) and Centaurus group (17 galaxies, 3.5 Mpc). Because these groups are nearby, they appear large on the sky. For example, the Sculptor group covers 20°. Within 10 Mpc lie 4 more groups; M101 (5 galaxies, 7.7 Mpc), M66 (3 galaxies, 9.4 Mpc), Leo I (8 galaxies, 9.4 Mpc) & NGC 1023 (6 galaxies, 9.5 Mpc). Virgo Supercluster There are about 20 groups of galaxies closer to us than the Virgo cluster. Their spatial distribution forms a plane which intersects the Virgo cluster. This establishes our membership in the Virgo (or Local) supercluster. The Virgo supercluster forms a flattened ellipsoid (r ~ 20 Mpc), centered on the Virgo cluster. Nearby superclusters include Hydra-Centaures (d ~ 70 Mpc) & Persus-Pisces (d ~ 40 Mpc). Supercluster membership Superclusters are only now collapsing under their own gravity. To estimate the density of the supercluster, one can equate the time for gravitational freefall to the age of the Universe 11 −3 ⇒ ≈ 3 × 10 M☉ Mpc −26 −3 −3 ≈ 2 × 10 kg m ≈ 14 atom m Virgocentric Infall Because the members of a supercluster are gravitationally bound to the supercluster, they “orbit” the supercluster’s barycenter. By mapping departures in the velocity field for galaxy clusters from the pure “Hubble flow”, we can measure the motion of the Local Group. Though values as large as 300 km s−1 have been suggested, the current value for the Virgocentric peculiar velocity of the Local Group is 168 ± 50 km s−1 compared to a Hubble flow −1 of H0d = 1140 km s . Looking Deeper As we look deeper into the universe, we see a repeating pattern of more and more clusters and superclusters. For example, the Abell 1689 cluster of galaxies, lies 670 Mpc on the far side of the Virgo cluster. However the distribution of clusters is not uniform. Images like this Herschel space observatory infrared observation of the Lockman hole, a 1° dust-free lane in Ursa Major, show the galaxy distribution is clumpy, with filaments rich in galaxies and voids. Mapping the Galaxies Understanding this pattern of filaments and voids requires a 3-dimensional map. Distances at this scale are impossible, but redshifts are available, thus these maps are called redshift surveys. The first example of these were the CfA redshift surveys of the 1980s. They revealed a structure to the Universe dominated by walls and voids. This map shows the redshifts of all galaxies brighter than mB = 15.5 as a function of right ascension (8h ‒ 17h) for a narrow range in declination (26.5°‒ 32.5°). Zone of Avoidance As early as 1878, it was noted that there was a gap in the distribution of galaxies (then nebulae). It was named the Zone of Avoidance by Hubble, who mapped it in 1931. The result of interstellar extinction due to gas and dust, the only means of mapping galaxies in the Zone of Avoidance is by radio or X-ray observations.
Load more

Recommended publications
  • SDSS DR7 Superclusters Morphology
    A&A 532, A5 (2011) Astronomy DOI: 10.1051/0004-6361/201116564 & c ESO 2011 Astrophysics SDSS DR7 superclusters Morphology M. Einasto1,L.J.Liivamägi1,2,E.Tago1,E.Saar1,E.Tempel1,2,J.Einasto1, V. J. Martínez3, and P. Heinämäki4 1 Tartu Observatory, 61602 Tõravere, Estonia e-mail: [email protected] 2 Institute of Physics, Tartu University, Tähe 4, 51010 Tartu, Estonia 3 Observatori Astronòmic, Universitat de València, Apartat de Correus 22085, 46071 València, Spain 4 Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, Finland Received 24 January 2011 / Accepted 2 May 2011 ABSTRACT Aims. We study the morphology of a set of superclusters drawn from the SDSS DR7. Methods. We calculate the luminosity density field to determine superclusters from a flux-limited sample of galaxies from SDSS DR7 and select superclusters with 300 and more galaxies for our study. We characterise the morphology of superclusters using the fourth Minkowski functional V3, the morphological signature (the curve in the shapefinder’s K1-K2 plane) and the shape parameter (the ratio of the shapefinders K1/K2). We investigate the supercluster sample using multidimensional normal mixture modelling. We use Abell clusters to identify our superclusters with known superclusters and to study the large-scale distribution of superclusters. Results. The superclusters in our sample form three chains of superclusters; one of them is the Sloan Great Wall. Most superclusters have filament-like overall shapes. Superclusters can be divided into two sets; more elongated superclusters are more luminous, richer, have larger diameters and a more complex fine structure than less elongated superclusters. The fine structure of superclusters can be divided into four main morphological types: spiders, multispiders, filaments, and multibranching filaments.
    [Show full text]
  • And Transition-Type Dwarf Galaxies: Clues from the Sculptor Group,,
    A&A 550, A7 (2013) Astronomy DOI: 10.1051/0004-6361/201219959 & c ESO 2013 Astrophysics Population gradients and photometric metallicities in early- and transition-type dwarf galaxies: Clues from the Sculptor group,, S. Lianou1,E.K.Grebel2,G.S.DaCosta3, M. Rejkuba4, H. Jerjen3,andA.Koch5 1 Institute for Astronomy, Astrophysics, Space Applications & Remote Sensing, National Observatory of Athens, I. Metaxa and Vas. Pavlou, 15236 Palaia Penteli, Greece e-mail: [email protected] 2 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany 3 Research School of Astronomy & Astrophysics, Australian National University, Mt Stromlo Observatory, via Cotter Rd, Weston, ACT 2611, Australia 4 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany 5 Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany Received 6 July 2012 / Accepted 8 November 2012 ABSTRACT Aims. We focus on the resolved stellar populations of one early-type and four transition-type dwarf galaxies in the Sculptor group, with the aim to examine the potential presence of population gradients and place constraints on their mean metallicities. Methods. We use deep Hubble Space Telescope images to construct color–magnitude diagrams, from which we select stellar popu- lations that trace different evolutionary phases in order to constrain their range of ages and metallicities, as well as to examine their spatial distribution. In addition, we use the resolved stars in the red giant branch in order to derive photometric metallicities. Results. All studied dwarfs contain intermediate-age stars with ages of ∼1 Gyr and older as traced by the luminous asymptotic gi- ant branch and red clump stars, while the transition-type dwarfs contain also stars younger than ∼1 Gyr as traced by a young main sequence and vertical red clump stars.
    [Show full text]
  • The Puzzle of the Strange Galaxy Made of 99.9% Dark Matter Is Solved 13 October 2020
    The puzzle of the strange galaxy made of 99.9% dark matter is solved 13 October 2020 The galaxy Dragonfly 44 was discovered in a deep survey of the Coma cluster, a cluster with several thousand galaxies. From the start, the galaxy was considered remarkable by the researchers because the quantity of dark matter they inferred was almost as much as that in the Milky Way, the equivalent of a billion solar masses. However, instead of containing around a hundred thousand million stars, as has the Milky Way, DF44 has only a hundred million stars, a thousand times Image and amplification (in color) of the ultra-diffuse fewer. This means that the amount of dark matter galaxy Dragonfly 44 taken with the Hubble space was ten thousand times greater than that of its telescope. Credit: Teymoor Saifollahi and NASA/HST. stars. If this had been true, it would have been a unique object, with almost 100 times as much dark matter as that expected from the number of its stars. At present, the formation of galaxies is difficult to understand without the presence of a ubiquitous, Nevertheless, by an exhaustive analysis of the but mysterious component, termed dark matter. system of globular cluster around Dragonfly 44, the Astronomers have measure how much dark matter researchers have detected that the total number of there is around galaxies, and have found that it globular clusters is only 20, and that the total varies between 10 and 300 times the quantity of quantity of dark matter is around 300 times that of visible matter.
    [Show full text]
  • A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra
    San Jose State University From the SelectedWorks of Aaron J. Romanowsky 2016 A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra-Diffuse Galaxy Dragonfly 44 Pieter van Dokkum, Yale University Roberto Abraham, University of Toronto Jean P. Brodie, University of California Observatories Charlie Conroy, Harvard-Smithsonian Center for Astrophysics Shany Danieli, Yale University, et al. Available at: https://works.bepress.com/aaron_romanowsky/117/ The Astrophysical Journal Letters, 828:L6 (6pp), 2016 September 1 doi:10.3847/2041-8205/828/1/L6 © 2016. The American Astronomical Society. All rights reserved. A HIGH STELLAR VELOCITY DISPERSION AND ∼100 GLOBULAR CLUSTERS FOR THE ULTRA-DIFFUSE GALAXY DRAGONFLY 44 Pieter van Dokkum1, Roberto Abraham2, Jean Brodie3, Charlie Conroy4, Shany Danieli1, Allison Merritt1, Lamiya Mowla1, Aaron Romanowsky3,5, and Jielai Zhang2 1 Astronomy Department, Yale University, New Haven, CT 06511, USA 2 Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada 3 University of California Observatories, 1156 High Street, Santa Cruz, CA 95064, USA 4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, USA 5 Department of Physics and Astronomy, San José State University, San Jose, CA 95192, USA Received 2016 June 20; revised 2016 July 14; accepted 2016 July 15; published 2016 August 25 ABSTRACT Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these ultra-diffuse galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here, we present the stellar kinematics of Dragonfly44, one of the largest Coma UDGs, using a 33.5 hr fi +8 -1 integration with DEIMOS on the Keck II telescope.
    [Show full text]
  • Introduction to Astronomy from Darkness to Blazing Glory
    Introduction to Astronomy From Darkness to Blazing Glory Published by JAS Educational Publications Copyright Pending 2010 JAS Educational Publications All rights reserved. Including the right of reproduction in whole or in part in any form. Second Edition Author: Jeffrey Wright Scott Photographs and Diagrams: Credit NASA, Jet Propulsion Laboratory, USGS, NOAA, Aames Research Center JAS Educational Publications 2601 Oakdale Road, H2 P.O. Box 197 Modesto California 95355 1-888-586-6252 Website: http://.Introastro.com Printing by Minuteman Press, Berkley, California ISBN 978-0-9827200-0-4 1 Introduction to Astronomy From Darkness to Blazing Glory The moon Titan is in the forefront with the moon Tethys behind it. These are two of many of Saturn’s moons Credit: Cassini Imaging Team, ISS, JPL, ESA, NASA 2 Introduction to Astronomy Contents in Brief Chapter 1: Astronomy Basics: Pages 1 – 6 Workbook Pages 1 - 2 Chapter 2: Time: Pages 7 - 10 Workbook Pages 3 - 4 Chapter 3: Solar System Overview: Pages 11 - 14 Workbook Pages 5 - 8 Chapter 4: Our Sun: Pages 15 - 20 Workbook Pages 9 - 16 Chapter 5: The Terrestrial Planets: Page 21 - 39 Workbook Pages 17 - 36 Mercury: Pages 22 - 23 Venus: Pages 24 - 25 Earth: Pages 25 - 34 Mars: Pages 34 - 39 Chapter 6: Outer, Dwarf and Exoplanets Pages: 41-54 Workbook Pages 37 - 48 Jupiter: Pages 41 - 42 Saturn: Pages 42 - 44 Uranus: Pages 44 - 45 Neptune: Pages 45 - 46 Dwarf Planets, Plutoids and Exoplanets: Pages 47 -54 3 Chapter 7: The Moons: Pages: 55 - 66 Workbook Pages 49 - 56 Chapter 8: Rocks and Ice:
    [Show full text]
  • Tip of the Red Giant Branch Distance for the Sculptor Group Dwarf ESO 540-032?
    A&A 371, 487–496 (2001) Astronomy DOI: 10.1051/0004-6361:20010389 & c ESO 2001 Astrophysics Tip of the red giant branch distance for the Sculptor group dwarf ESO 540-032? H. Jerjen1 and M. Rejkuba2,3 1 Research School of Astronomy and Astrophysics, The Australian National University, Mt Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia 2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei M¨unchen, Germany e-mail: [email protected] 3 Department of Astronomy, P. Universidad Cat´olica, Casilla 306, Santiago 22, Chile Received 19 January 2001 / Accepted 9 March 2001 Abstract. We present the first VI CCD photometry for the Sculptor group galaxy ESO 540-032 obtained at the Very Large Telescope UT1+FORS1. The (I, V − I) colour-magnitude diagram indicates that this intermediate- type dwarf galaxy is dominated by old, metal-poor ([Fe/H] ≈−1.7 dex) stars, with a small population of slightly more metal-rich ([Fe/H] ≈−1.3 dex), young (age 150 − 500 Myr) stars. A discontinuity in the I-band luminosity function is detected at I0 =23.44 0.09 mag. Interpreting this feature as the tip of the red giant branch and adopting MI = −4.20 0.10 mag for its absolute magnitude, we have determined a Population II distance modulus of (m − M)0 =27.64 0.14 mag (3.4 0.2 Mpc). This distance confirms ESO 540-032 as a member of the nearby Sculptor group but is significantly larger than a previously reported value based on the Surface Brightness Fluctuation (SBF) method.
    [Show full text]
  • Galaxy Clusters: Waking Perseus
    PUBLISHED: 2 JUNE 2017 | VOLUME: 1 | ARTICLE NUMBER: 164 news & views GALAXY CLUSTERS Waking Perseus The Perseus cluster contains over 1,000 a Kelvin–Helmholtz instability, which galaxies packed into a region ~3,500 kpc propagates in the wave direction and in extent. It is inevitable that such close- causes the dark area indicated in the packed galaxies will interact, and the image. This dark ‘bay-like’ feature is Chandra X-ray Observatory has observed approximately the size of the Milky Way, the beautiful result of that interaction and may be the result of a cold front in (pictured). This is no snapshot — the cluster gas: an interface where the Chandra observed the galaxy cluster temperature drops dramatically on scales for over 16 days in order to capture this much smaller than the mean free path. image. Stephen Walker and colleagues An advantage of this comparison of have retrieved the archival data and observations and simulations is that processed it to enhance the edges of (unmeasurable) physical quantities the surface brightness distribution. This can be estimated. In this case, the bay analysis, reported last year (Sanders et al., 50 kpc feature only appears in this form when Mon. Not. R. Astron. Soc. 460, 1898–1911; the ratio of the thermal pressure to the ROYAL ASTRONOMICAL SOCIETY ASTRONOMICAL ROYAL 2016), highlighted two features in the magnetic pressure is ~200, and this X-ray emission that are discussed by determination in turn allows the authors Walker et al. (Mon. Not. R. Astron. Soc. pattern seen in the image could have been to obtain an order-of-magnitude estimate 468, 2506–2516; 2017): the swirling wave generated by a passing galaxy cluster about of the magnetic field.
    [Show full text]
  • On the Nature of Filaments of the Large-Scale Structure of the Universe Irina Rozgacheva, I Kuvshinova
    On the nature of filaments of the large-scale structure of the Universe Irina Rozgacheva, I Kuvshinova To cite this version: Irina Rozgacheva, I Kuvshinova. On the nature of filaments of the large-scale structure of the Universe. 2018. hal-01962100 HAL Id: hal-01962100 https://hal.archives-ouvertes.fr/hal-01962100 Preprint submitted on 20 Dec 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. On the nature of filaments of the large-scale structure of the Universe I. K. Rozgachevaa, I. B. Kuvshinovab All-Russian Institute for Scientific and Technical Information of Russian Academy of Sciences (VINITI RAS), Moscow, Russia e-mail: [email protected], [email protected] Abstract Observed properties of filaments which dominate in large-scale structure of the Universe are considered. A part from these properties isn’t described within the standard ΛCDM cosmological model. The “toy” model of forma- tion of primary filaments owing to the primary scalar and vector gravitational perturbations in the uniform and isotropic cosmological model which is filled with matter with negligible pressure, without use of a hypothesis of tidal interaction of dark matter halos is offered.
    [Show full text]
  • Lecture 6: Galaxy Dynamics (Basic) Elliptical Galaxy Dynamics
    Lecture 6: Galaxy Dynamics (Basic) • Basic dynamics of galaxies – Ellipticals, kinematically hot random orbit systems – Spirals, kinematically cool rotating system • Key relations: – The fundamental plane of ellipticals/bulges – The Faber-Jackson relation for ellipticals/bulges – The Tully-Fisher for spirals disks • Using FJ and TF to calculate distances – The extragalactic distance ladder – Examples 1 Elliptical galaxy dynamics • Ellipticals are triaxial spheroids • No rotation, no flattened plane • Typically we can measure a velocity dispersion, σ – I.e., the integrated motions of the stars • Dynamics analogous to a gravitational bound cloud of gas (I.e., an isothermal sphere). • I.e., dp GM(r)ρ(r) HYDROSTATIC − = EQUILIBRIUM dr r2 Check Wikipedia “Hydrostatic PRESSURE FORCE GRAVITATIONAL FORCE Equilibrium” to see PER UNIT VOLUME PER UNIT VOLUME deriiation. € 2 1 Elliptical galaxy dynamics • For an isothermal sphere gas pressure is given by: 2 Reminder from p = ρ(r)σ Thermodynamics: P=nRT/V=ρT, 1 E=(3/2)kT=(1/2)mv^2 ρ(r) ∝ r2 σ 2 GM(r) 2 ⇒ 3 ∝ 4 2σ r r r M(r) = G M(r) ∝σ 2r € 3 € Elliptical galaxy dynamics • As E/S0s are centrally concentrated if σ is measured over sufficient area M(r)=>M, I.e., Total Mass ∝σ 2r • σ is measured from either: – Radial velocity distributions from individual stellar spectra – From line widths€ in integrated galaxy spectra [See Galactic Astronomy, Binney & Merrifield for details on how these are measured in practice] 4 2 Elliptical galaxy dynamices • We have three measureable quantities: – L = luminosity (or magnitude) – Re = effective or half-light radius – σ = velocity dispersion • From these we can derive Σο the central surface brightness (nb: one of these four is redundant as its calculable from the others.) • How are these related observationally and theoretically ? x y • I.e., what does: L ∝ Σ o σ ν look like ? Σο Log logL THE FUNDAMENTAL PLANE € Logσ 5 Fundamental Plane Theory 2 (I.e., stars behaving as if isothermal sphere) IF σν ∝ M Re 2 Surf.
    [Show full text]
  • Isolated Elliptical Galaxies in the Local Universe
    A&A 588, A79 (2016) Astronomy DOI: 10.1051/0004-6361/201527844 & c ESO 2016 Astrophysics Isolated elliptical galaxies in the local Universe I. Lacerna1,2,3, H. M. Hernández-Toledo4 , V. Avila-Reese4, J. Abonza-Sane4, and A. del Olmo5 1 Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. V. Mackenna 4860, Santiago, Chile e-mail: [email protected] 2 Centro de Astro-Ingeniería, Pontificia Universidad Católica de Chile, Av. V. Mackenna 4860, Santiago, Chile 3 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany 4 Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 70-264, 04510 México D. F., Mexico 5 Instituto de Astrofísica de Andalucía IAA – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain Received 26 November 2015 / Accepted 6 January 2016 ABSTRACT Context. We have studied a sample of 89 very isolated, elliptical galaxies at z < 0.08 and compared their properties with elliptical galaxies located in a high-density environment such as the Coma supercluster. Aims. Our aim is to probe the role of environment on the morphological transformation and quenching of elliptical galaxies as a function of mass. In addition, we elucidate the nature of a particular set of blue and star-forming isolated ellipticals identified here. Methods. We studied physical properties of ellipticals, such as color, specific star formation rate, galaxy size, and stellar age, as a function of stellar mass and environment based on SDSS data. We analyzed the blue and star-forming isolated ellipticals in more detail, through photometric characterization using GALFIT, and infer their star formation history using STARLIGHT.
    [Show full text]
  • Mining the Sky with Redshift Surveys 3 Semblance Whatever to the Predictions of Models of the Time
    Mining the Sky with Redshift Surveys Marc Davis1 & Jeffrey A. Newman1 University of California, Berkeley, CA 94720, USA Abstract. Since the late 1970’s, redshift surveys have been vital for progress in understanding large-scale structure in the Universe. The original CfA redshift sur- vey collected spectra of 20-30 galaxies per clear night on a 1.5 meter telescope; over a two year period the project added ≈ 2000 new redshifts to the literature. Subsequent low-z redshift surveys have been up to an order of magnitude larger, and ongoing surveys will yield a similar improvement over the generation preced- ing them. Full sky redshift surveys have a special role to play as predictors of cosmological flows, and deep pencil beam surveys have provided fundamental con- straints on the evolution of properties of galaxies. With the 2DF redshift survey and the SDSS survey, our knowledge of the statistical clustering of low-redshift galaxies will achieve unprecedented precision. Measurements of clustering in the distant Universe are more limited at present, but will become much better in this decade as the VLT/VIRMOS and Keck/DEIMOS projects produce results. As in so many other fields, progress in large scale structure studies, both observational and theoretical, has been made possible by improvements in technologies, especially computing. This review briefly highlights twenty years of progress in this evolving discipline and describes a few novel cosmological tests that will be attempted with the Keck/DEIMOS survey. 1 The Original Center for Astrophysics Survey Up until the late 1970’s, most extragalactic spectroscopy was dependent on photographic plates, or photographic plates in contact with image intensifier tubes.
    [Show full text]
  • The HI Content and Extent of Low Surface Brightness Galaxies – Could LSB Galaxies Be Responsible for Damped Ly-Α Absorption?
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Extragalactic Gas at Low Redshift ASP Conference Series, Vol. , 2001 Mulchaey, et al. The HI Content and Extent of Low Surface Brightness Galaxies { Could LSB Galaxies be Responsible for Damped Ly-α Absorption? Karen O’Neil NAIC/Arecibo Observatory, HC3 Box 53995, Arecibo, PR 00612 [email protected] Abstract. Low surface brightness galaxies, those galaxies with a central surface brightness at least one magnitude fainter than the night sky, are often not included in discussions of extragalactic gas at z < 0.1. In this paper we review many of the properties of low surface brightness galaxies, in- cluding recent studies which indicate low surface brightness systems may contribute far more to the local HI luminosity function than previously thought. Additionally, we use the known (HI) gas properties of low sur- face brightness galaxies to consider their possible contribution to nearby damped Lyman-α absorbers. 1. Introduction - What is a LSB Galaxy? Typically, low surface brightness (LSB) galaxies are defined as those galaxies with an observed central surface brightness that is at least one magnitude fainter than the night sky. In the B band, this translates to µB(0) 22.6 – 23.0 mag 2 ≥ arcsec− . However, alternatives to this definition do exist. One common defini- tion is that a LSB galaxy is a galaxy whose inclination corrected central surface 2 brightness is µB(0) 23.0 mag arcsec− (Matthews, Gallagher, & van Driel 1999). Although it is≥ a more consistent definition, this second definition relies on understanding the dust properties and opacity of the studied galaxies.
    [Show full text]