DOCSLIB.ORG

A Dark Galaxy in the Virgo Cluster Imaged at 21-Cm

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Dark Galaxy in the Virgo Cluster Imaged at 21-Cm Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 15 December 2018 (MN LATEX style file v2.2) A Dark Galaxy in the Virgo Cluster Imaged at 21-cm. R. F. Minchin1, J. I. Davies1, M. J. Disney1, A. R. Marble2, C. D. Impey2, P. J. Boyce3, D. A. Garcia1, M. Grossi1, C. A. Jordan4, R. H. Lang1, S. Roberts1, S. Sabatini5, W. van Driel6 1 School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3YB, UK 2 Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721-0065, US 3 Planning Division, Cardiff University, Park Place, Cardiff, CF10 3UA, UK 4 Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire, SK11 9DL, UK 5 Osservatorio Astronomico di Roma, via Frascati 33, I-00040, Monte Porzio, Italy 6 Observatoire de Paris, GEPI, CNRS UMR 8111 and Universit´eParis 7, 5 place Jules Janssen, F-92195 Meudon Cedex, France 15 December 2018 ABSTRACT Dark Matter supposedly dominates the extragalactic, yet no totally dark structure of galactic proportions has ever been convincingly identified. Earlier (Minchin et al. 2005) we suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster at Jodrell Bank using single-dish observations (Davies et al. 2004), was probably such a dark galaxy because of its broad line-width (∼ 200 kms−1) unaccompanied by any visible gravitational source to account for it. Now we have managed to image VIR- GOHI 21 in the neutral-hydrogen line, and indeed we find what appears to be a dark, edge-on, spinning disc with the mass and diameter of a typical spiral galaxy. Moreover the disc has unquestionably interacted with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor invariably responsible for such a feature. Published numerical models (Vollmer, Huchtmeier & van Driel 2005) of NGC 4254 call for a close interaction ∼ 108 years ago with a perturber of ∼ 1011 solar masses. This we take as completely independent evidence for the massive nature of VIRGOHI 21. Key words: dark matter – galaxies: individual (VIRGOHI 21) – radio lines: galaxies arXiv:astro-ph/0508153v1 5 Aug 2005 1 INTRODUCTION terparts have been known about for many years; these in- clude high velocity clouds (Wakker & van Woerden 1997), Cold Dark Matter (CDM) models of galaxy formation the Leo Ring (Schneider et al. 1983), and various gas clouds predict many more dark matter halos than are ob- close to bright galaxies (Kilborn et al. 2000; Boyce et al. served as galaxies (Kauffmann, White & Guiderdoni 1993; 2001; Ryder et al. 2001). However, none of these objects Moore et al. 1999; D’Onghia & Lake 2004). Whether stars have the characteristics of a galaxy, i.e. detectable emission can form in dark matter halos depends critically on the frac- over galaxy sized spatial scales and a velocity structure con- tion of baryons (md) that can be trapped and retained by sistent with a rotating and gravitationally bound disc. each halo (for previous discussions about the existence and formation of dark galaxies see (Jimenez et al. 1997; Hawkins 1997; Verde et al. 2002)). Some of those that retain a small fraction of their original baryons (md < 0.05) are able to form stable gaseus disks, but because of the low gas den- In a previous paper (Minchin et al. 2005) we described sities they are not able to form stars. The physical state Jodrell Bank and Arecibo observations of VIRGOHI 21 an of the gas in the disc is very dependent on its density and HI source discovered during a survey of the Virgo cluster temperature with the latter influenced by the intensity of (Davies et al. 2004). VIRGOHI 21 has all of the HI charac- any ionising background. Models predict that galaxies can teristics of a typical rotating disc galaxy, but no detectable form with gas column densities that prohibit star formation optical emission. Our conclusion was that VIRGOHI 21 was yet provide some self shielding from the ionizing background an extremely promising candidate for the first dark galaxy. (Davies et al. in prep.). Such dark galaxies are potentially In this paper, we present high resolution HI observations detectable by blind 21cm surveys of the sky. of this source, which add to the conclusions drawn in the Objects detected at 21cm but with no optical coun- earlier paper that this is, indeed, a massive dark galaxy. c 0000 RAS 2 R. F. Minchin et al. 2 OBSERVATIONS AND ANALYSIS North and in particular to the South could either be part of the interaction or be clumps further out in the disc. Note The new data were taken in March 2005 at the Westerbork the lack of connection between galaxy ‘C’ and VIRGOHI 21. Synthesis Radio Telescope (WSRT) in two full 12-hour syn- theses and reduced using the Miriad package. The data were flagged for shadowing and on two of the fourteen 25- metre antennae one polarisation was flagged due to problems 3 DISCUSSION with the gain. A spectral bandwidth of 10 MHz covered the 1 Combining the new data with the old, we argue: velocity range 930 - 3070 km s− . Removal of the noisier end (a) If attributed to gravitation, changes in velocity of channels left 230 useful channels of width 8.2 km s−1 each, 1 galactic size over galactic scales, as seen here, require masses giving a velocity resolution of 10 km s− over the range 980 −1 of galactic proportions. On dimensional grounds the veloc- to 2890 km s . Continuum removal was carried out in the −1 ity wrench ∆V (∼ 200 km s ) seen at VIRGOHI 21 over a UV plane using Uvlin. The standard source 3C147 was used 22 conservative length-scale ∆x (∼ 14 kpc ≃ 5×10 cm ≃ 3 ar- for calibration. Cleaning used a robust setting of 1, close to cmin at the Virgo Cluster distance of 16 Mpc (Minchin et al. normal weighting (Briggs 1995). The cleaned cube was gaus- 2 10−11 2005)) implies a mass M ≥ (∆V ) ∆x/G ≃ 10 so- sian smoothed spatially and Hanning smoothed in velocity, lar masses. More specifically the gravitational (free-fall) and then used for a second-pass deeper cleaning which gave 3 2 1 2 timescale (∆x) / /(GM) / needs to be ≤ ∆x/V , the time the final cube used in the analysis. The synthesised beam it takes for gas travelling at V (relative to M) to change was 99′′ × 30′′ in size (extended North-South) and the noise −1 −1 velocity by ∆V . And where ∆V ∼ V , as it appears to was 0.3 mJy beam channel , giving a 5σ column-density 2 1 19 2 be here (see Fig. 2b), M ≥ (∆V ) ∆x/G again. For non- to sources 25 km s− wide of 2×10 Hydrogen atoms cm− . gravitational alternatives see below. i Fig. 1a shows a neutral Hydrogen (H ) contour map of (b) The bridge between NGC 4254 and VIRGOHI 21 re- the field superimposed on a negative optical image. VIR- veals that they have interacted. According to published nu- GOHI 21 is the elongated structure in the centre (which is merical simulations (Vollmer et al. 2005) (below) the mor- at about 2000 km s−1). A faint bridge can be seen stretch- 1 phological peculiarities of NGC 4254 require a perturbing ing down to the prominent spiral NGC 4254 (2400 km s− ) 11 1 mass of ∼ 10 M⊙ – providing independent evidence that while the other two sources, NGC 4262 (1500 km s− , upper 11 −1 VIRGOHI 21 weighs ∼ 10 M⊙. The simulation implies an left) and the faint galaxy ‘C’ (1750 km s , immediately to interaction 3 × 108 years ago. As the projected length of the the left of VIRGOHI 21) appear unconnected. Fig. 1b shows bridge is 120 kpc this would imply it has been drawn out at the velocity-declination projection of the full 3 dimensional a projected speed of 390 km s−1, which is comparable to the data cube. Now NGC 4254 is at the bottom right while VIR- radial velocity difference between NGC 4254 and VIRGOHI GOHI 21 is the angular structure in the centre. C is to its 21 of 400 km s−1. left. Far more detail can be seen on an animation which is (c) NGC 4262, the spiral to the North-East, is not in- available at http://www.astro.cf.ac.uk/groups/galaxies, for volved. There is no bridge to it (see animation) and the instance the bridge is clear and obvious, as is the lack of any radial velocity difference between NGC 4254 and NGC 4262 connection between VIRGOHI 21 and either NGC 4262 or is too large (900 km s−1) to generate one. C. The apparent alignment of NGC 4262 with VIRGOHI 21 (d) If object C, the H i galaxy just to the east (left) of and NGC 4254 in Fig. 1b is a consequence of the particular VIRGOHI 21 (Fig. 2) were involved its mass, by (a), must be projection shown 11 ∼ 10 M⊙. However its measured H i velocity distribution 9 The ∼ 25 arcmin filamentary bridge stretches from the and size suggest a probable mass ≤ 10 M⊙, while it has a 8 6 low-velocity (western) edge of NGC 4254, falling gently in luminosity of only 10 L⊙ and a MHI of 4×10 M⊙. It is two −1 ◦ ′ radial velocity from 2250 km s at declination +14 20 to- orders of magnitude too undermassive and underluminous to −1 ◦ ′ wards 1900 km s at +14 41 where it is suddenly arrested. explain the dynamics of VIRGOHI 21, while there is no sign ◦ ′ Then at +14 46 it is abruptly wrenched upwards again to- of its interacting.
Load more

Recommended publications
  • Wimps and Machos ENCYCLOPEDIA of ASTRONOMY and ASTROPHYSICS
    WIMPs and MACHOs ENCYCLOPEDIA OF ASTRONOMY AND ASTROPHYSICS WIMPs and MACHOs objects that could be the dark matter and still escape detection. For example, if the Galactic halo were filled –3 . WIMP is an acronym for weakly interacting massive par- with Jupiter mass objects (10 Mo) they would not have ticle and MACHO is an acronym for massive (astrophys- been detected by emission or absorption of light. Brown . ical) compact halo object. WIMPs and MACHOs are two dwarf stars with masses below 0.08Mo or the black hole of the most popular DARK MATTER candidates. They repre- remnants of an early generation of stars would be simi- sent two very different but reasonable possibilities of larly invisible. Thus these objects are examples of what the dominant component of the universe may be. MACHOs. Other examples of this class of dark matter It is well established that somewhere between 90% candidates include primordial black holes created during and 99% of the material in the universe is in some as yet the big bang, neutron stars, white dwarf stars and vari- undiscovered form. This material is the gravitational ous exotic stable configurations of quantum fields, such glue that holds together galaxies and clusters of galaxies as non-topological solitons. and plays an important role in the history and fate of the An important difference between WIMPs and universe. Yet this material has not been directly detected. MACHOs is that WIMPs are non-baryonic and Since extensive searches have been done, this means that MACHOS are typically (but not always) formed from this mysterious material must not emit or absorb appre- baryonic material.
    [Show full text]
  • Dark Energy and Dark Matter
    Dark Energy and Dark Matter Jeevan Regmi Department of Physics, Prithvi Narayan Campus, Pokhara [email protected] Abstract: The new discoveries and evidences in the field of astrophysics have explored new area of discussion each day. It provides an inspiration for the search of new laws and symmetries in nature. One of the interesting issues of the decade is the accelerating universe. Though much is known about universe, still a lot of mysteries are present about it. The new concepts of dark energy and dark matter are being explained to answer the mysterious facts. However it unfolds the rays of hope for solving the various properties and dimensions of space. Keywords: dark energy, dark matter, accelerating universe, space-time curvature, cosmological constant, gravitational lensing. 1. INTRODUCTION observations. Precision measurements of the cosmic It was Albert Einstein first to realize that empty microwave background (CMB) have shown that the space is not 'nothing'. Space has amazing properties. total energy density of the universe is very near the Many of which are just beginning to be understood. critical density needed to make the universe flat The first property that Einstein discovered is that it is (i.e. the curvature of space-time, defined in General possible for more space to come into existence. And Relativity, goes to zero on large scales). Since energy his cosmological constant makes a prediction that is equivalent to mass (Special Relativity: E = mc2), empty space can possess its own energy. Theorists this is usually expressed in terms of a critical mass still don't have correct explanation for this but they density needed to make the universe flat.
    [Show full text]
  • Dark Radiation from the Axino Solution of the Gravitino Problem
    21st of July 2011 Dark radiation from the axino solution of the gravitino problem Jasper Hasenkamp II. Institute for Theoretical Physics, University of Hamburg, Hamburg, Germany [email protected] Abstract Current observations of the cosmic microwave background could confirm an in- crease in the radiation energy density after primordial nucleosynthesis but before photon decoupling. We show that, if the gravitino problem is solved by a light axino, dark (decoupled) radiation emerges naturally in this period leading to a new upper 11 bound on the reheating temperature TR . 10 GeV. In turn, successful thermal leptogenesis might predict such an increase. The Large Hadron Collider could en- dorse this opportunity. At the same time, axion and axino can naturally form the observed dark matter. arXiv:1107.4319v2 [hep-ph] 13 Dec 2011 1 Introduction It is a new opportunity to determine the amount of radiation in the Universe from obser- vations of the cosmic microwave background (CMB) alone with precision comparable to that from big bang nucleosynthesis (BBN). Recent measurements by the Wilkinson Mi- crowave Anisotropy Probe (WMAP) [1], the Atacama Cosmology Telescope (ACT) [2] and the South Pole Telescope (SPT) [3] indicate|statistically not significant|the radi- ation energy density at the time of photon decoupling to be higher than inferred from primordial nucleosynthesis in standard cosmology making use of the Standard Model of particle physics, cf. [4,5]. This could be taken as another hint for physics beyond the two standard models. The Planck satellite, which is already taking data, could turn the hint into a discovery. We should search for explanations from particle physics for such an increase in ra- diation [6,7], especially, because other explanations are missing, if the current mean values are accurate.
    [Show full text]
  • Collider Signatures of Axino and Gravitino Dark Matter
    2005 International Linear Collider Workshop - Stanford, U.S.A. Collider Signatures of Axino and Gravitino Dark Matter Frank Daniel Steffen DESY Theory Group, Notkestrasse 85, 22603 Hamburg, Germany The axino and the gravitino are extremely weakly interacting candidates for the lightest supersymmetric particle (LSP). We demonstrate that either of them could provide the right amount of cold dark matter. Assuming that a charged slepton is the next-to-lightest supersymmetric particle (NLSP), we discuss how NLSP decays into the axino/gravitino LSP can provide evidence for axino/gravitino dark matter at future colliders. We show that these NLSP decays will allow us to estimate the value of the Peccei–Quinn scale and the axino mass if the axino is the LSP. In the case of the gravitino LSP, we illustrate that the gravitino mass can be determined. This is crucial for insights into the mechanism of supersymmetry breaking and can lead to a microscopic measurement of the Planck scale. 1. INTRODUCTION A key problem in cosmology is the understanding of the nature of cold dark matter. In supersymmetric extensions of the Standard Model, the lightest supersymmetric particle (LSP) is stable if R-parity is conserved [1]. An electrically and color neutral LSP thus appears as a compelling solution to the dark matter problem. The lightest neutralino is such an LSP candidate from the minimal supersymmetric standard model (MSSM). Here we consider two well- motivated alternative LSP candidates beyond the MSSM: the axino and the gravitino. In the following we introduce the axino and the gravitino. We review that axinos/gravitinos from thermal pro- duction in the early Universe can provide the right amount of cold dark matter depending on the value of the reheating temperature after inflation and the axino/gravitino mass.
    [Show full text]
  • Axion Dark Matter from Higgs Inflation with an Intermediate H∗
    Axion dark matter from Higgs inflation with an intermediate H∗ Tommi Tenkanena and Luca Visinellib;c;d aDepartment of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA bDepartment of Physics and Astronomy, Uppsala University, L¨agerhyddsv¨agen1, 75120 Uppsala, Sweden cNordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden dGravitation Astroparticle Physics Amsterdam (GRAPPA), Institute for Theoretical Physics Amsterdam and Delta Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands E-mail: [email protected], [email protected], [email protected] Abstract. In order to accommodate the QCD axion as the dark matter (DM) in a model in which the Peccei-Quinn (PQ) symmetry is broken before the end of inflation, a relatively low scale of inflation has to be invoked in order to avoid bounds from DM isocurvature 9 fluctuations, H∗ . O(10 ) GeV. We construct a simple model in which the Standard Model Higgs field is non-minimally coupled to Palatini gravity and acts as the inflaton, leading to a 8 scale of inflation H∗ ∼ 10 GeV. When the energy scale at which the PQ symmetry breaks is much larger than the scale of inflation, we find that in this scenario the required axion mass for which the axion constitutes all DM is m0 . 0:05 µeV for a quartic Higgs self-coupling 14 λφ = 0:1, which correspond to the PQ breaking scale vσ & 10 GeV and tensor-to-scalar ratio r ∼ 10−12. Future experiments sensitive to the relevant QCD axion mass scale can therefore shed light on the physics of the Universe before the end of inflation.
    [Show full text]
  • Modified Newtonian Dynamics
    Faculty of Mathematics and Natural Sciences Bachelor Thesis University of Groningen Modified Newtonian Dynamics (MOND) and a Possible Microscopic Description Author: Supervisor: L.M. Mooiweer prof. dr. E. Pallante Abstract Nowadays, the mass discrepancy in the universe is often interpreted within the paradigm of Cold Dark Matter (CDM) while other possibilities are not excluded. The main idea of this thesis is to develop a better theoretical understanding of the hidden mass problem within the paradigm of Modified Newtonian Dynamics (MOND). Several phenomenological aspects of MOND will be discussed and we will consider a possible microscopic description based on quantum statistics on the holographic screen which can reproduce the MOND phenomenology. July 10, 2015 Contents 1 Introduction 3 1.1 The Problem of the Hidden Mass . .3 2 Modified Newtonian Dynamics6 2.1 The Acceleration Constant a0 .................................7 2.2 MOND Phenomenology . .8 2.2.1 The Tully-Fischer and Jackson-Faber relation . .9 2.2.2 The external field effect . 10 2.3 The Non-Relativistic Field Formulation . 11 2.3.1 Conservation of energy . 11 2.3.2 A quadratic Lagrangian formalism (AQUAL) . 12 2.4 The Relativistic Field Formulation . 13 2.5 MOND Difficulties . 13 3 A Possible Microscopic Description of MOND 16 3.1 The Holographic Principle . 16 3.2 Emergent Gravity as an Entropic Force . 16 3.2.1 The connection between the bulk and the surface . 18 3.3 Quantum Statistical Description on the Holographic Screen . 19 3.3.1 Two dimensional quantum gases . 19 3.3.2 The connection with the deep MOND limit .
    [Show full text]
  • Review of Cold Dark Matter in Astrophysics. Content: Preliminaries: Einstein Equation of Hubble Expansion
    J. Steinberger Nov. 2004 Review of Cold Dark Matter in Astrophysics. Content: Preliminaries: Einstein equation of Hubble expansion. Big Bang Nucleo Synthesis. Formation of CDM “Halos” Galactic rotation curves. Measurement of Ωm using x-ray measurements of galaxy clusters. Measurement of Ωm using gravitational lensing. Why neutralinos are hopeful candidates for CDM. 1. Astrophysical preliminaries; Einstein-Friedman equation for a homogeneous universe. Definition of Ωm . Metric of homogeneous universe. a is the scale, x, y and z are “comoving” coordinates, that is, they do not change with the expansion of the universe: ds2 = dt2 + a(t)2(dx2 + dy2 + dz2) Einstein (Friedmann) equation for homogeneous universe: H(t) ≡ ((da/dt)/a)2 = 8πG/3*ρ(t) + Λ , where H is the hubble expansion parameter, ρ is the energy density and Λ is the “cosmological constant”. For relativistic matter, that is kT >> mc2, the variation of ρ with a is as a-4, 4 ρrad = ρrad,0(a0/a) . Subscript zero, here and in the following, refers to the present universe. For nonrelativistic matter, that is kT << mc2, the variation of ρ with a is as a- 3 3 , ρm = ρm,0(a0/a) . Only in recent times, that is for a0/a < ≈ 2, has the cosmological constant term become important; before it was negligible. In the early universe the energy density was dominated by radiation, now it is dominated by non relativistic matter. After cold matter domination, 2 2 3 H(t) = H0 (Ωm(a0/a(t)) + ΩΛ); Ωm+ΩΛ = 1. Ωm is the sum of baryonic matter and cold dark matter: Ωm = Ωb + Ωcdm.
    [Show full text]
  • Neutralino Dark Matter Detection in Split Supersymmetry Scenarios
    SISSA 95/2004/EP FSU–HEP–041122 Neutralino Dark Matter Detection in Split Supersymmetry Scenarios A. Masiero1, S. Profumo2,3 and P. Ullio3 1 Dipartimento di Fisica ‘G. Galilei’, Universit`adi Padova, and Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Via Marzolo 8, I-35131, Padova, Italy 2 Department of Physics, Florida State University 505 Keen Building, FL 32306-4350, U.S.A. 3 Scuola Internazionale Superiore di Studi Avanzati, Via Beirut 2-4, I-34014 Trieste, Italy and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34014 Trieste, Italy E-mail: [email protected], [email protected], [email protected] Abstract We study the phenomenology of neutralino dark matter within generic supersym- arXiv:hep-ph/0412058v2 19 Jan 2005 metric scenarios where the Gaugino and Higgsino masses are much lighter than the scalar soft breaking masses (Split Supersymmetry). We consider a low-energy model-independent approach and show that the guidelines in the definition of this general framework come from cosmology, which forces the lightest neutralino to have a mass smaller than 2.2 TeV. The testability of the framework is addressed by discussing all viable dark matter detection techniques. Current data on cos- mic rays antimatter, gamma-rays and on the abundance of primordial 6Li already set significant constraints on the parameter space. Complementarity among future direct detection experiments, indirect searches for antimatter and with neutrino telescopes, and tests of the theory at future accelerators, such as the LHC and a NLC, is highlighted. In particular, we study in detail the regimes of Wino-Higgsino mixing and Bino-Wino transition, which have been most often neglected in the past.
    [Show full text]
  • Dark Matter Candidates
    SLAC Summer Institute on Particle Physics (SSI04), Aug. 2-13, 2004 Dark Matter Candidates Edward A. Baltz KIPAC, Stanford University, P.O. Box 20450, MS 29, Stanford, CA 94309, USA It is now widely accepted that most of mass–energy in the universe is unobserved except by its gravitational effects. Baryons make only about 4% of the total, with “dark matter” making up about 23% and the “dark energy” responsible for the accelerated expansion of the universe making up the remainder. We focus on the dark matter, which is the primary constituent of galaxies. We outline the observed properties of this material, enumerating some candidates covering 90 orders of magnitude in mass. Finally, we argue that the weak scale (100 GeV) is relevant to new physics, including the dark matter problem. 1. THE DARK MATTER PROBLEM Cosmological parameter estimation, based on cosmic microwave background anisotropies measured by the WMAP satellite [1] and based on the power spectrum of galaxy density fluctuations measured by the SDSS collaboration [2] indicates that most of matter in the universe is unobserved save by gravity. Approximately 4% of the cosmological energy density is accounted for by baryons, 23% by the dark matter discussed in this lecture, with the remainder being the “dark energy” responsible for the observed accelerated expansion of the universe. The dark matter is the primary component of cosmological structures at the dwarf galaxy scale and larger. The dark matter and dark energy are of unknown composition. In this lecture we discuss the physics of dark matter, and enumerate a list of candidates, not meant to be exhaustive.
    [Show full text]
  • How Cold Dark Matter Theory Explains Milgrom's
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Submitted to Astrophysical Journal Letters How Cold Dark Matter Theory Explains Milgrom's Law Manoj Kaplinghat1 and Michael Turner1;2;3 ABSTRACT Milgrom noticed the remarkable fact that the gravitational effect of dark mat- ter in galaxies only becomes important where accelerations are less than about 8 2 10− cm s− cH . This forms the basis for his Modified Newtonian Dynamics ∼ 0 (MOND), an alternative to particle dark matter. We show that in the Cold Dark Matter (CDM) theory of structure formation Milgrom’s Law comes about auto- matically, owing to the scale-free character of the density perturbations, baryonic dissipation and numerical coincidences. With the evidence for CDM mounting, and at the same time problems for MOND becoming more numerous, it appears that Milgrom’s Law is an accident rather than an important clue to the dark- matter puzzle. Subject headings: cosmology: dark matter—galaxies: dynamics 1. Introduction The dark-matter mystery has been with us since Zwicky noticed that the gravitational action of luminous matter is not sufficient to hold clusters together (Zwicky 1933; Smith 1936). Rubin and others brought the problem closer to home by showing that spiral galaxies like our suffer the same problem (see e.g., Knapp & Kormendy, 1987). While the leading explanation for the dark matter problem today is slowly moving, weakly interacting “nonlu- minous” elementary particles remaining from the earliest moments – cold dark matter (see 1Department of Astronomy and Astrophysics, The University of Chicago, 5640 S.
    [Show full text]
  • Non-Baryonic Dark Matter
    FR9703177 Institut Universite Claude Bernard de Physique IN2P3 - CNRS Nucleaire de Lyon LYCEN 9643 D6cembre 1996 Non-Baryonic Dark Matter Ecole Internationale de Cosmologie, Casablanca, 1-10 decembre 1996 I. Berk&s Institut de Physique Nucleaire de Lyon, IN2P3/CNRS, Universite Claude Bernard, F-69622 Villeuibanne Cedex, France 43, Boulevard du 11 Novembre 1918 - 69622 V1LLEURBANNE Cedex - France NON-BARYONIC DARK MATTER. (*) I. Berkes IPNL, Universite Lyon I et IN2P3, F-69622 VILLEURBANNE CEDEX Abstract. This article discusses the nature of the dark matter and the possibility of the detection of non-baryonic dark matter in an underground experiment. Among the useful detectors the low tem­ perature bolometers are considered in some detail. Resume. Get article expose les differences hypotheses sur la nature de la matiere noire, et la possibility de la detection de la matidre noire non-baryonique dans une experience souterraine. Parmi les de- tecteurs envisages 1'accent est mis sur les bolometres travaillant h. basse temperature. 1) Galactic dark matter. The best known star in our Galaxy is the Sun. Its mass is about Mo=2xl0 j0 kg, and it radiates a power of L©=3.8x10W. The ratio of these two quantities is Mo/Lo = 5200 kg/W. In our Galaxy masses for binary stars can be determined from their relative movement. It comes out, that while M and L vary strongly from a star to another, the ratio M/L varies only slightly for stars in the main sequence. So, the luminosity may be used as a mesure o the mass of a star, super-giants, white dwarfs, black holes and other exoti objects excepted.
    [Show full text]
  • Mainly Axion Cold Dark Matter in the Minimal Supergravity Model
    Preprint typeset in JHEP style - HYPER VERSION Mainly axion cold dark matter in the minimal supergravity model Howard Baera, Andrew D. Boxa and Heaya Summya aDept. of Physics and Astronomy, University of Oklahoma, Norman, OK 73019, USA E-mail: [email protected], [email protected],[email protected] Abstract: We examine the minimal supergravity (mSUGRA) model under the assump- tion that the strong CP problem is solved by the Peccei-Quinn mechanism. In this case, the relic dark matter (DM) abundance consists of three components: i). cold axions, ii). warm axinos from neutralino decay, and iii). cold or warm thermally produced axinos. To > 6 sustain a high enough re-heat temperature (TR ∼ 10 GeV) for many baryogenesis mech- anisms to function, we find that the bulk of DM should consist of cold axions, while the admixture of cold and warm axinos should be rather slight, with a very light axino of mass ∼ 100 keV. For mSUGRA with mainly axion cold DM (CDM), the most DM-preferred parameter space regions are precisely those which are least preferred in the case of neu- tralino DM. Thus, rather different SUSY signatures are expected at the LHC in the case of mSUGRA with mainly axion CDM, as compared to mSUGRA with neutralino CDM. Keywords: Supersymmetry Phenomenology, Supersymmetric Standard Model, Dark Matter. 1. Introduction The cosmic abundance of cold dark matter (CDM) has been recently measured to high precision by the WMAP collaboration[1], which lately finds 2 ΩCDM h = 0.110 ± 0.006, (1.1) where Ω = ρ/ρc is the dark matter density relative to the closure density, and h is the scaled Hubble constant.
    [Show full text]