DOCSLIB.ORG

The Local Group Timing Argument

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Local Group Timing Argument The Local Group Timing Argument •Real galaxies Milky Way (MW) Andromeda (M31) Indranil Banik ([email protected]) Supervisor: Hongsheng Zhao University of Saint Andrews MNRAS, 459 (2), 2237 – 2261 Governing Equations r In a homogeneous Universe: r a() t .. .. a GM()()r r GM r r r r MW MW M31 M 31 a 3 3 r rMW r r M 31 Can derive this from General Relativity (flat Universe assumed) Governing Equations r In a homogeneous Universe: r a() t .. .. a GM()()r r GM r r r r MW MW M31 M 31 a 3 3 r rMW r r M 31 Can derive this from General Relativity (flat Universe assumed) Model assumptions • All objects following Hubble flow at early time (no peculiar velocity) – spherical symmetry initially • Mass dominated by MW & M31 • MW – M31 orbit is radial (Sohn et. al., 2012) Local group axisymmetric • Test particles can’t start too close to MW or M31 – an equipotential is drawn which encloses the initial MW + M31 mass in a homogeneous Universe. Test particles starting within this equipotential are discarded. Close approaches • Particles that approach MW or M31 too closely are accreted and increase mass of accreting galaxy. • Force from MW and M31 is r -1 at short range (but r -2 at long range). This is to match their observed flat rotation curves. Model deficiencies • Interactions between LG dwarf galaxies not included. Would likely have caused a velocity dispersion of ~15 km/s (Kirby et. al., 2014) • Might be good to include M33 • Tides from distant galaxies might matter a little (though we included Cen A directly and regions too close to other massive galaxies were not included in the analysis) • Force from MW & M31 transitions from r -1 at short range to r -2 at long range, but exact recipe for transition somewhat arbitrary • Initial separation varied until final separation MW-M31 separation, Mpc 0.25 0.75 1.25 First step: MW–M31 trajectory = 0.783 Mpc (McConnachie, 2012) 0.5 0 1 0 2 Time since Big Bang, Gyr 4 6 8 10 12 14 •Real galaxies Milky Way (MW) Andromeda (M31) 2 1 0 -1 0.5 1 1.5 2 Gravity slows cosmic expansion vr H0 d Gravity slows cosmic expansion vr H0 d Gravity Input data • Data for LG galaxies from McConnachie (2012) • Targets selected same as in work of Peñarrubia et. al. (2014), but we excluded Andromeda 18. • Velocity field smooth near target galaxies, allowing well-defined velocity prediction. If this isn’t true, computer rejects target (rare). Satellite galaxies not included in analysis Analysis • 2D Newton-Raphson used to get test particle trajectory landing where an actual galaxy is • Velocity projected onto line of sight from MW to get galactocentric radial velocity (GRV) • Distance from MW increased by 1σ & analysis repeated to get uncertainty in GRV due to uncertainty in distance • Error due to GRV measurement added • σextra also added: extra variance. This is due to interactions between LG dwarf galaxies • Value reduced for M31 as it is hard to budge Observed GRV, km/s Best-fit model and observations -200 -100 100 200 300 -100 0 Model galactocentric radial velocity (GRV), km/s -50 0 50 100 150 200 250 Best-fit model and observations 300 s / 200 m k , V 100 R G σ d extra e 0 v r e s b -100 O -200 -100 -50 0 50 100 150 200 250 Model galactocentric radial velocity (GRV), km/s • How much extra dispersion do we need? Probability density 0.01 0.02 0.03 0.04 0.05 • 10 km/s less if M31 not treated specially 0 0 Results: extra variance 20 40 extra , km/s 60 80 100 Explaining σextra • Line of sight dispersion of 45 km/s implies dispersion of 80 km/s in 3D • LG dwarf galaxies rotate at << 50 km/s (more like 15 km/s, Kirby et. al., 2014) • Velocities more often above model than below Interactions between LG dwarf galaxies can’t easily account for the discrepancies • Looked carefully at tides and MW / M31 satellites ΛCDM does not match the observations Consider Modified Newtonian Dynamics (MOND) MW – M31 separation in ΛCDM c 1.25 p M , 1 n o i t a 0.75 r a p e 0.5 s 1 3 0.25 M - 0 W 0 2 4 6 8 10 12 14 M Time since Big Bang, Gyr • Past MW–M31 flyby not possible: gravity too weak • In any case, dynamical friction between dark matter halos would cause merger, not flyby Flyby inevitable under wide range of assumptions MW-M31 separation, Mpc 0.2 0.4 0.6 0.8 Modified Newtonian Dynamics 0 1 0 2 4 Time after Big Bang, Gyr 6 Astronomy & Astrophysics 557: L3 (2013) 8 10 M too high M just right M too low 12 14 Basic principle: gravitational slingshots • Heavy galaxy (e.g. MW) moves right at 5 km/s • Small object moving right at 1 km/s Relative speed = 4 km/s 5 km/s 1 km/s 4 km/s Basic principle: gravitational slingshots • Heavy galaxy (e.g. MW) moves right at 5 km/s • Small object moving right at 1 km/s Relative speed = 4 km/s • MW reverses relative velocity of object Object now moves at (5 + 4) km/s 5 km/s 4 km/s 1 km/s 4 km/s MOND • In this model, there was a close encounter between the MW & M31 in the past • This caused substantial dynamical heating of the Local Group Very high GRV’s occur as some LG galaxies flung out at high speed by fast-moving MW./.M31 (around time of their encounter) • Process also occurs in ΛCDM, but MW–M31 relative motion much slower as no close flyby Observed – predicted GRVs (ΛCDM) 0.8 GRV > 0 Never One GRV < 0 y galaxy t i 0.6 interacted with 15 km/s s MW / M31 n e Gaussian d y t i l 0.4 i b a b o r 0.2 P 0 0 20 40 60 80 100 120 140 |GRV|, km/s • Objects with ΔGRV < 0 roughly consistent Observed – predicted GRVs (ΛCDM) 0.8 GRV > 0 Never One GRV < 0 y galaxy t i 0.6 interacted with 15 km/s s MW / M31 n e Gaussian d Flung out y t i by MW l 0.4 i Flung out by M31 b a (~2× heavier b than MW) o r 0.2 P 0 0 20 40 60 80 100 120 140 |GRV|, km/s • Objects with ΔGRV < 0 roughly consistent • Not true for objects with ΔGRV > 0 Smooth velocity field Disturbed velocity field Distances from LG barycentre of observed ‘target’ galaxies Flung out by MW/M31 Timing Argument in MOND • Main difference: galaxies moving outwards very fast must all have been at ~same place at same time (i.e. close to Local Group barycentre at time of MW–M31 flyby) Galaxies furthest away now must have been flung out fastest (and still be going fastest) d = v Δt (elapsed time since flyby) v = d k 1 k t Distant objects going faster? • Not all objects flung out by MW or M31 Should see lots of objects with ΔGRV ≈ 0 BUT: some objects will follow ΔGRV d • Note: velocities plotted (ΔGRVs) are net of the best-fitting model (which at long range is ~a pure Hubble flow: a uniformly expanding Universe with v = H0d) DDO 99 s / KKH 98 DDO 190 100 DDO 125 m NGC 404 k UGC Leo P , Sextans B 8508 KKH 86 HIZSS V Tucana NGC 3109 NGC 55 UGC 9128 Sextans A NGC 300 IC 3104 R UGC 4879 KKR 3 KKR 25 GR 8 G 0 WLM UKS 2323-326 NGC 4163 Andromeda Aquarius ESO 294-G010 Sagittarius Antila IC 5152 IC 4662 Leo A -100 0 0.5 1 1.5 2 2.5 3 3.5 Distance from LG barycentre, Mpc •H0 = 67 km/s/Mpc (at d = 1 Mpc, v = H0d = 67 km/s in a uniformly expanding Universe) Universe age ≈ 1 Mpc ÷ 67 km/s = 13.8 Gyr DDO 99 s / KKH 98 DDO 190 100 DDO 125 m NGC 404 k UGC Leo P , Sextans B 8508 KKH 86 HIZSS V Tucana NGC 3109 NGC 55 UGC 9128 Sextans A NGC 300 IC 3104 R UGC 4879 KKR 3 KKR 25 GR 8 G 0 WLM UKS 2323-326 NGC 4163 Andromeda Aquarius ESO 294-G010 Sagittarius Antila IC 5152 IC 4662 Leo A -100 0 0.5 1 1.5 2 2.5 3 3.5 Distance from LG barycentre, Mpc •H0 = 67 km/s/Mpc (at d = 1 Mpc, v = H0d = 67 km/s in a uniformly expanding Universe) Universe age ≈ 1 Mpc ÷ 67 km/s = 13.8 Gyr DDO 99 s / KKH 98 DDO 190 100 DDO 125 m NGC 404 k UGC Leo P , Sextans B 8508 KKH 86 HIZSS V Tucana NGC 3109 NGC 55 UGC 9128 Sextans A NGC 300 IC 3104 R UGC 4879 KKR 3 KKR 25 GR 8 G 0 WLM UKS 2323-326 NGC 4163 Andromeda Aquarius ESO 294-G010 Sagittarius Antila IC 5152 IC 4662 Leo A -100 0 0.5 1 1.5 2 2.5 3 3.5 Distance from LG barycentre, Mpc •H0 = 67 km/s/Mpc (at d = 1 Mpc, v = H0d = 67 km/s in a uniformly expanding Universe) Universe age ≈ 1 Mpc ÷ 67 km/s = 13.8 Gyr • Observe excess of ~40 km/s/Mpc in Local Group Flyby time ≈ 1 Mpc ÷ (67 + 40) km/s = 8.7 Gyr ago Other flyby time estimates 1 c p M , 0.8 n o i t a r 0.6 a p High e s ΔGRV 0.4 1 objects 3 ASP ConferenceM too low M - 0.2 Series,M vol just 230, right W Thick Timing M disk age p 87M (2001) too high 0 argument 0 2 4 6 8 10 12 14 Time after Big Bang, Gyr (billions of years) • All three age estimates agree, within errors Flyby ~7–9 Gyr ago (5–7 Gyr after Big Bang) Conclusions • ΛCDM does not describe the dynamics of Local Group galaxies very well (1128 models tried) • Distant LG galaxies with high radial velocities were flung out at high speed at ~same time as thick disk of MW formed (~5 Gyr after Big Bang) • More detailed lecture: www.youtube.com/watch?v=U3HTzJohNAw Constraining The Extra Variance ()v 2 1 2 Probability e 2 • View as equation in σ • At first, raising σ lowers χ2 and raises the probability.
Load more

Recommended publications
  • Distances to Local Group Galaxies
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Distances to Local Group Galaxies Alistair R. Walker Cerro Tololo Inter-American Observatory, NOAO, Casilla 603, la Serena, Chile Abstract. Distances to galaxies in the Local Group are reviewed. In particular, the distance to the Large Magellanic Cloud is found to be (m M)0 =18:52 0:10, cor- − ± responding to 50; 600 2; 400 pc. The importance of M31 as an analog of the galaxies observed at greater distances± is stressed, while the variety of star formation and chem- ical enrichment histories displayed by Local Group galaxies allows critical evaluation of the calibrations of the various distance indicators in a variety of environments. 1 Introduction The Local Group (hereafter LG) of galaxies has been comprehensively described in the monograph by Sidney van den Berg [1], with update in [2]. The zero- velocity surface has radius of a little more than 1 Mpc, therefore the small sub-group of galaxies consisting of NGC 3109, Antlia, Sextans A and Sextans B lie outside the the LG by this definition, as do galaxies in the direction of the nearby Sculptor and IC342/Maffei groups. Thus the LG consists of two large spirals (the Galaxy and M31) each with their entourage of 11 and 10 smaller galaxies respectively, the dwarf spiral M33, and 13 other galaxies classified as either irregular or spherical. We have here included NGC 147 and NGC 185 as members of the M31 sub-group [60], whether they are actually bound to M31 is not proven.
    [Show full text]
  • Luminosity Functions for Old Stellar Systems
    LUMINOSITY FUNCTIONS FOR OLD STELLAR SYSTEMS by Peter Anthony Bergbusch L> ^ B.Sc., University of Saskatchewan, 1974 rACULTY 0 f GRADUATE STotd - M.Sc., University of Regina, 1984 „JL Dissertation submitted in partial fulfillment flr ' ^ DEAN of the requirements for the degree of P DOCTOR OF PHILOSOPHY in the Department of Physics and Astronomy We accept this dissertation as conforming to the required standard Dr. D.A. VandenBerg, Supervisor (Department of P’.ysics and Astronomy) Dr. F.D.A, Hartwick, Departmental Member (Dept, of Physics and Astronomy) Th'. O.J. Pritchet, Departmental Member (Department of Physics and Astronomy) Dr. R.D. McClure, Outside Member (Dominion Astrophysical Observatory) Dr. F.P. Robinsojv-Qutside Member (Department of Chemistry) Dr. II. Srivastava, Outside Member (Department of Mathematics) “ " / ■ —y — • r ----------------------- Dr. ( i.Ci . Fahlman, External Examiner (University of British Columbia) ©PETER ANTHONY BERGBUSCH, 1992 University of Victoria September 1992 All rights reserved. This dissertation may not be reproduced, in whole or in part, by mimeograph or other means, without the permission of the author. 11 Supervisor: Professor Don A, VandenBerg ABSTRACT The potential for luminosity functions (LFs) of post-turnoff stars to constrain basic cluster parameters such as age, metallicity, and helium abundance is examined in this di, sertation. A review of the published LFs for the globular cluster (GC) M92 suggests that the morphology of the transition from the main sequence to the red giant branch (ltGB) is sensitive to these parameters. In particular, a small bump in this region may provide an important age discriminant for GCs. A significant deficiency in the number of stars over a 2 mag interval, just below the turnoff, remains unexplained.
    [Show full text]
  • Download Article (PDF)
    Baltic Astronomy, vol. 24, 213{220, 2015 VELOCITY DISPERSION OF IONIZED GAS AND MULTIPLE SUPERNOVA EXPLOSIONS E. O. Vasiliev1;2;3, A. V. Moiseev3;4 and Yu. A. Shchekinov2 1 Institute of Physics, Southern Federal University, Stachki Ave. 194, Rostov-on-Don, 344090 Russia; [email protected] 2 Department of Physics, Southern Federal University, Sorge Str. 5, Rostov-on-Don, 344090 Russia 3 Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnij Arkhyz, Karachaevo-Cherkesskaya Republic, 369167 Russia 4 Sternberg Astronomical Institute, Moscow M. V. Lomonosov State University, Universitetskij pr. 13, 119992 Moscow, Russia Received: 2015 March 25; accepted: 2015 April 20 Abstract. We use 3D numerical simulations to study the evolution of the Hα intensity and velocity dispersion for single and multiple supernova (SN) explosions. We find that the IHα{ σ diagram obtained for simulated gas flows is similar in shape to that observed in dwarf galaxies. We conclude that collid- ing SN shells with significant difference in age are responsible for high velocity dispersion that reaches up to ∼> 100 km s−1. Such a high velocity dispersion could be hardly obtained for a single SN remnant. Peaks of velocity disper- sion in the IHα{ σ diagram may correspond to several isolated or merged SN remnants with moderately different ages. Degrading the spatial resolution in the Hα intensity and velocity dispersion maps makes the simulated IHα{ σ di- agrams close to those observed in dwarf galaxies not only in shape, but also quantitatively. Key words: galaxies: ISM { ISM: bubbles { ISM: supernova remnants { ISM: kinematics and dynamics { shock waves { methods: numerical 1.
    [Show full text]
  • The Extragalactic Distance Scale
    The Extragalactic Distance Scale Published in "Stellar astrophysics for the local group" : VIII Canary Islands Winter School of Astrophysics. Edited by A. Aparicio, A. Herrero, and F. Sanchez. Cambridge ; New York : Cambridge University Press, 1998 Calibration of the Extragalactic Distance Scale By BARRY F. MADORE1, WENDY L. FREEDMAN2 1NASA/IPAC Extragalactic Database, Infrared Processing & Analysis Center, California Institute of Technology, Jet Propulsion Laboratory, Pasadena, CA 91125, USA 2Observatories, Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena CA 91101, USA The calibration and use of Cepheids as primary distance indicators is reviewed in the context of the extragalactic distance scale. Comparison is made with the independently calibrated Population II distance scale and found to be consistent at the 10% level. The combined use of ground-based facilities and the Hubble Space Telescope now allow for the application of the Cepheid Period-Luminosity relation out to distances in excess of 20 Mpc. Calibration of secondary distance indicators and the direct determination of distances to galaxies in the field as well as in the Virgo and Fornax clusters allows for multiple paths to the determination of the absolute rate of the expansion of the Universe parameterized by the Hubble constant. At this point in the reduction and analysis of Key Project galaxies H0 = 72km/ sec/Mpc ± 2 (random) ± 12 [systematic]. Table of Contents INTRODUCTION TO THE LECTURES CEPHEIDS BRIEF SUMMARY OF THE OBSERVED PROPERTIES OF CEPHEID
    [Show full text]
  • HST-ACS Photometry of the Isolated Dwarf Galaxy VV124=UGC 4879
    A&A 533, A37 (2011) Astronomy DOI: 10.1051/0004-6361/201117275 & c ESO 2011 Astrophysics HST-ACS photometry of the isolated dwarf galaxy VV124=UGC 4879 Detection of the blue horizontal branch and identification of two young star clusters, M. Bellazzini1,S.Perina1, S. Galleti1, and T. Oosterloo2 1 INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: [email protected] 2 Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands Received 17 May 2011 / Accepted 9 July 2011 ABSTRACT We present deep V and I photometry of the isolated dwarf galaxy VV124=UGC 4879, obtained from archival images taken with the Hubble Space Telescope – Advanced Camera for Surveys. In the color-magnitude diagrams of stars at distances greater than 40 from the center of the galaxy, we clearly identify a well-populated, old horizontal branch (HB) for the first time. We show that the distribution of these stars is more extended than that of red clump stars. This implies that very old and metal-poor populations 4 dominate in the outskirts of VV124. We also identify a massive (M = 1.2 ± 0.2 × 10 M) young (age = 250 ± 50 Myr) star cluster 3 (C1), as well as another of younger age (C2, ∼<30 ± 10 Myr) with a mass similar to classical open clusters (M ≤ 3.3 ± 0.5 × 10 M). Both clusters lie at projected distances less than 100 pc from the center of the galaxy.
    [Show full text]
  • IRFM T$ {\Sf\Sl Eff}$ Calibrations for Cluster and Field Giants in the Vilnius, Geneva, RI$ {\Sf\Sl (C)}$ and DDO Photometric Sy
    A&A 417, 301–316 (2004) Astronomy DOI: 10.1051/0004-6361:20031764 & c ESO 2004 Astrophysics IRFM Teff calibrations for cluster and field giants in the Vilnius, Geneva, RI(C) and DDO photometric systems I. Ram´ırez1,2 and J. Mel´endez1,3 1 Seminario Permanente de Astronom´ıa y Ciencias Espaciales, Universidad Nacional Mayor de San Marcos, Ciudad Universitaria, Facultad de Ciencias F´ısicas, Av. Venezuela s/n, Lima 1, Per´u 2 Department of Astronomy, The University of Texas at Austin, RLM 15.202A, TX 78712-1083, USA 3 Department of Astronomy, California Institute of Technology, MC 105–24, Pasadena, CA 91125, USA Received 2 May 2003 / Accepted 19 November 2003 Abstract. Based on a large sample of disk and halo giant stars for which accurate effective temperatures derived through the InfraRed Flux Method (IRFM) exist, a calibration of the temperature scale in the Vilnius, Geneva, RI(C) and DDO photometric systems is performed. We provide calibration formulae for the metallicity-dependent Teff vs. color relations as well as grids of intrinsic colors and compare them with other calibrations. Photometry, atmospheric parameters and reddening corrections for the stars of the sample have been updated with respect to the original sources to reduce the dispersion of the fits. Application of our results to Arcturus leads to an effective temperature in excellent agreement with the value derived from its angular diameter and integrated flux. The effects of gravity on these Teff vs. color relations are also explored by taking into account our previous results for dwarf stars. Key words.
    [Show full text]
  • The Evening Sky
    I N E D R I A C A S T N E O D I T A C L E O R N I G D S T S H A E P H M O O R C I . Z N O e d b l A a r , a l n e O , g N i C R a , Z p s e u I l i C l r a i , R I S C f R a O o s C t p H o L u r E e E & d H P a ( o T F m l O l s u i D R NORTH x ” , N M n E a A o n O X g d A H a x C P M T e r . I o P Polaris H N c S L r y E E e o P Z t n “ n E . EQUATORIAL EDITION i A N H O W T M “ R e T Y N H h E T ” K E ) W S . T T E U W B R N The Evening Sky Map W D E T T . FEBRUARY 2011 WH r A e E C t M82 FREE* EACH MONTH FOR YOU TO EXPLORE, LEARN & ENJOY THE NIGHT SKY O s S L u K l T Y c E CASSIOPEIA h R e r M a A S t A SKY MAP SHOWS HOW i s η M81 Get Sky Calendar on Twitter S P c T s k C A l e e E CAMELOPARDALIS R d J Sky Calendar – February 2011 a O http://twitter.com/skymaps i THE NIGHT SKY LOOKS s B y U O a H N L s D e t A h NE a I t I EARLY FEB 9 PM r T T f S p 1 Moon near Mercury (16° from Sun, morning sky) at 17h UT.
    [Show full text]
  • An Observer's Guide to the (Local Group) Dwarf Galaxies: Predictions for Their Own Dwarf Satellite Populations
    An observer's guide to the (Local Group) dwarf galaxies: predictions for their own dwarf satellite populations The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Dooley, Gregory A. et al. “An Observer’s Guide to the (Local Group) Dwarf Galaxies: Predictions for Their Own Dwarf Satellite Populations.” Monthly Notices of the Royal Astronomical Society 471, 4 (August 2017): 4894–4909 © 2018 The Author(s) As Published http://dx.doi.org/10.1093/MNRAS/STX1900 Publisher Oxford University Press (OUP) Version Author's final manuscript Citable link https://hdl.handle.net/1721.1/121369 Terms of Use Creative Commons Attribution-Noncommercial-Share Alike Detailed Terms http://creativecommons.org/licenses/by-nc-sa/4.0/ MNRAS 000,1{21 (2017) Preprint 6 September 2017 Compiled using MNRAS LATEX style file v3.0 An observer's guide to the (Local Group) dwarf galaxies: predictions for their own dwarf satellite populations Gregory A. Dooley1?, Annika H. G. Peter2;3, Tianyi Yang4, Beth Willman5, Brendan F. Griffen1 and Anna Frebel1, 1Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 2CCAPP and Department of Physics, The Ohio State University, Columbus, OH 43210, USA 3Department of Astronomy, The Ohio State University, Columbus OH 43210, USA 4Institute of Optics, University of Rochester, Rochester, New York, 14627, USA 5Steward Observatory and LSST, 933 North Cherry Avenue, Tucson, AZ 85721, USA Accepted by MNRAS 2017 July 22. Received 2017 July 22; in original 2016 September 27 ABSTRACT A recent surge in the discovery of new ultrafaint dwarf satellites of the Milky Way has 3 6 inspired the idea of searching for faint satellites, 10 M < M∗ < 10 M , around less massive field galaxies in the Local Group.
    [Show full text]
  • Draft181 182Chapter 10
    Chapter 10 Formation and evolution of the Local Group 480 Myr <t< 13.7 Gyr; 10 >z> 0; 30 K > T > 2.725 K The fact that the [G]alactic system is a member of a group is a very fortunate accident. Edwin Hubble, The Realm of the Nebulae Summary: The Local Group (LG) is the group of galaxies gravitationally associ- ated with the Galaxy and M 31. Galaxies within the LG have overcome the general expansion of the universe. There are approximately 75 galaxies in the LG within a 12 diameter of ∼3 Mpc having a total mass of 2-5 × 10 M⊙. A strong morphology- density relation exists in which gas-poor dwarf spheroidals (dSphs) are preferentially found closer to the Galaxy/M 31 than gas-rich dwarf irregulars (dIrrs). This is often promoted as evidence of environmental processes due to the massive Galaxy and M 31 driving the evolutionary change between dwarf galaxy types. High Veloc- ity Clouds (HVCs) are likely to be either remnant gas left over from the formation of the Galaxy, or associated with other galaxies that have been tidally disturbed by the Galaxy. Our Galaxy halo is about 12 Gyr old. A thin disk with ongoing star formation and older thick disk built by z ≥ 2 minor mergers exist. The Galaxy and M 31 will merge in 5.9 Gyr and ultimately resemble an elliptical galaxy. The LG has −1 vLG = 627 ± 22 km s with respect to the CMB. About 44% of the LG motion is due to the infall into the region of the Great Attractor, and the remaining amount of motion is due to more distant overdensities between 130 and 180 h−1 Mpc, primarily the Shapley supercluster.
    [Show full text]
  • First Stellar Spectroscopy in Leo P
    LJMU Research Online Evans, CJ, Castro, N, Gonzalez, OA, Garcia, M, Bastian, N, Cioni, M-RL, Clark, JS, Davies, B, Ferguson, AMN, Kamann, S, Lennon, DJ, Patrick, LR, Vink, JS and Weisz, DR First stellar spectroscopy in Leo P http://researchonline.ljmu.ac.uk/id/eprint/10138/ Article Citation (please note it is advisable to refer to the publisher’s version if you intend to cite from this work) Evans, CJ, Castro, N, Gonzalez, OA, Garcia, M, Bastian, N, Cioni, M-RL, Clark, JS, Davies, B, Ferguson, AMN, Kamann, S, Lennon, DJ, Patrick, LR, Vink, JS and Weisz, DR (2019) First stellar spectroscopy in Leo P. Astronomy and Astrophysics, 622. ISSN 0004-6361 LJMU has developed LJMU Research Online for users to access the research output of the University more effectively. Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Users may download and/or print one copy of any article(s) in LJMU Research Online to facilitate their private study or for non-commercial research. You may not engage in further distribution of the material or use it for any profit-making activities or any commercial gain. The version presented here may differ from the published version or from the version of the record. Please see the repository URL above for details on accessing the published version and note that access may require a subscription. For more information please contact [email protected] http://researchonline.ljmu.ac.uk/ A&A 622, A129 (2019) Astronomy https://doi.org/10.1051/0004-6361/201834145 & c ESO 2019 Astrophysics First stellar spectroscopy in Leo P C.
    [Show full text]
  • The Rotation of the Halo of NGC6822 Determined from the Radial Velocities of Carbon Stars
    The rotation of the halo of NGC6822 determined from the radial velocities of carbon stars { Graham Peter Thompson { Centre for Astrophysics Research School of Physics, Astronomy and Mathematics University of Hertfordshire Submitted to the University of Hertfordshire in part fulfilment of the requirements of the degree of Master of Philosophy in Astrophysics Supervisor: Professor Sean G. Ryan { April 2016 { Declaration I hereby certify that this dissertation has been written by me in the School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, Hertfordshire, and that it has not been submitted in any previous application for a higher degree. The core of the dissertation is based on original work conducted at the University of Hertfordshire, and some of the ideas for further work are drawn from topics studied during an earlier Master of Science. All material in this dissertation which is not my own work has been properly acknowledged. { Graham Peter Thompson { ii Acknowledgements I thank Professor Ryan for his invaluable support and patient guidance as my super- visor, throughout this study. His incisive questioning, thoughtful comments, helpful suggestions and, at times, hands-on assistance throughout the study, preparation of a paper to MNRAS and the writing of this dissertation have been invaluable. I thank also Dr Lisette Sibbons, whose work on the spectral classification of carbon stars in NGC 6822 was the genesis of my study. Dr Sibbons was responsible for the acquisition and reduction of the spectra I used in the study. She also provided me with background information related to the stars in the sample, and general advice.
    [Show full text]
  • Perseus I and the NGC 3109 Association in the Context of the Local Group Dwarf Galaxy Structures
    MNRAS 440, 908–919 (2014) doi:10.1093/mnras/stu321 Advance Access publication 2014 March 15 Perseus I and the NGC 3109 association in the context of the Local Group dwarf galaxy structures Marcel S. Pawlowski‹ and Stacy S. McGaugh Department of Astronomy, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA Accepted 2014 February 13. Received 2014 February 13; in original form 2014 January 8 ABSTRACT The recently discovered dwarf galaxy Perseus I appears to be associated with the dominant Downloaded from plane of non-satellite galaxies in the Local Group (LG). We predict its velocity dispersion and those of the other isolated dwarf spheroidals Cetus and Tucana to be 6.5, 8.2 and 5.5 km s−1, respectively. The NGC 3109 association, including the recently discovered dwarf galaxy Leo P, aligns with the dwarf galaxy structures in the LG such that all known nearby non-satellite http://mnras.oxfordjournals.org/ galaxies in the northern Galactic hemisphere lie in a common thin plane (rms height 53 kpc; diameter 1.2 Mpc). This plane has an orientation similar to the preferred orbital plane of the Milky Way (MW) satellites in the vast polar structure. Five of seven of these northern galaxies were identified as possible backsplash objects, even though only about one is expected from cosmological simulations. This may pose a problem, or instead the search for local backsplash galaxies might be identifying ancient tidal dwarf galaxies expelled in a past major galaxy encounter. The NGC 3109 association supports the notion that material preferentially falls towards the MW from the Galactic south and recedes towards the north, as if the MW were moving through a stream of dwarf galaxies.
    [Show full text]