DOCSLIB.ORG

The M31 Dwarf Galaxy Population

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The M31 Dwarf Galaxy Population The M31 Dwarf Galaxy Population Marla Geha (Yale) Raja Guhathakurta (UCSC) Jason Kalirai (STScI) Steve Majewski (UVa) Roeland van der Marel (STScI) Racheal Beaton (UVa) Kirsten Howley (LLNL) Nhung Ho (Yale) Erik Tollerud (UCI/Yale) Google Sky IRAS map The M31 Dwarf Galaxy Population Marla Geha (Yale) 150 kpc Raja Guhathakurta (UCSC) Jason Kalirai (STScI) Steve Majewski (UVa) Roeland van der Marel (STScI) Racheal Beaton (UVa) Kirsten Howley (LLNL) Nhung Ho (Yale) Erik Tollerud (UCI/Yale) Google Sky IRAS map The M31 Dwarf Galaxy Population 150 kpc 31 M31 satellites And XXVIII And XXIX Bell et al. (2011) Slater et al. (2011) PAndAS Survey: Richardson et al. (2011) Local Group Dwarf Satellites Milky Way: 26 dwarf satellites M31: 31 (20) dwarf satellites (km/s) (km/s) _M31 _MW v v Dist_MW (kpc) Dist_M31 (kpc) McConnachie (2012) Local Group Dwarf Satellites M31 dSph MW dSph MW GC Faintest M31 satellite MV = -6.1 To this mag limit, M31 has 2.5x more PAndAS satellites than MW limit SDSS limit Quenched M31 Dwarf Satellites McConnachie (2012) Most MW/M31 satellites are quenched galaxies (no on- going SF, little to no HI). V / L HI M Distance (kpc) Environment and Quenched Dwarf Galaxies MG et al (2012): Quenched fractions as a function of distance to a massive host galaxy 0 out of 2950 quenched SDSS dwarf galaxies > 1.5 Mpc Below LMC stellar mass, *all* quenched galaxies found within ~4 rvir of a massive host. Keck/DEIMOS Observations of M31 Satellites Majority of work on M31 satellite kinematics and metallicities enabled by Keck/DEIMOS spectrograph: Chapman et al. 2005, Geha et al. 2006, Majewski et al. 2007, Kalirai et al. 2009, Letarte et al. 2009, Geha et al. 2010, Kalirai et al. 2010, Collins et al. 2010, Howley et al. 2012, Ho et al. 2012, Tollerud et al 2012 ✦ RGB stars selected from photometry. ✦ Typically Ca II triplet region, ∆v ~2-3 km/s. ✦ Radial velocities for ~hundred of RGB stars in one hour in good conditions. spatial -> wavelength -> A Quick Tour of M31’s Satellites LMC NGC 205 SMC Sgr For Leo I Scl NGC 205 Tidal radius (5’ = 1 kpc ) Geha et al. (2006) Simien & Prugniel (2000) velocity (km/s) velocity radius (arcmin) Inner rotation = 15 km s-1 Velocity turn-over at tidal radius (730 stars) NGC 205 on first passage? (Howley et al. 2008) A Quick Tour of M31’s Satellites LMC M32 NGC 205 SMC Sgr For Leo I Scl M32: Compact Elliptical with a Black Hole M32 has a central black hole 6 MBH = (2.4± 1.0) × 10 M⊙ : Goodman & Lee 1989; Bender, Kormendy & Dehnen 1996; van der Marel et al. 1998b; Joseph et al. 2001; Verolme et al. 2002; Tremaine et al. 2002; van der Marel et al. 1997; van den Bosch & de Zeeuw 2010 Based on kinematics within r_eff = 30” = 0.1 kpc Choi, Guhathakurta & Johnston (2002): Distorted M32 isophotes around 150”, consistent with tidal interactions. M32: Compact Elliptical with a Black Hole Howley et al. (2012) BH + M/L = 1.2 velocity (km/s) velocity sigma (km/s) sigma radius (arcmin) M32 kinematics appear well-behave out to large radius A Quick Tour of M31’s Satellites LMC M32 NGC 205 SMC NGC 147 Sgr NGC 185 For Leo I Scl NGC 147 and NGC 185: Normal dEs NGC 147 NGC 185 Keck/ DEIMOS HST WPFC2 spectroscopy HST ACS HST WFC3 NGC 147 and NGC 185: Normal dEs NGC 147 NGC 185 Vrot = 17 ± 2 km/s Vrot = 15 ± 5 km/s 8 reff Geha et al (2010) Geha et al. (2010) NGC 147 and NGC 185: Normal dEs HST/ACS: Geha et al. (2012) NGC 147 NGC 185 Intermediate + old stars Intermediate + old stars <age> ~ 7.5 Gyr <age> ~ 10 Gyr A Quick Tour of M31’s Satellites LMC M32 NGC 205 SMC NGC 147 Sgr NGC 185 For And II Leo I Scl Ho, MG, et al. (2012) And II vrad (km/s) 165 170 175 180 185 190 195 200 205 210 33.7 33.6 ) 33.5 o 33.4 (J2000) ( 33.3 33.2 Nonmember Member 33.1 19.3 19.2 19.1 19.0 18.9 18.8 (J2000) (o) Radius (kpc) Prolate or triaxial rotation: dynamically stable? And II M32 More M31 satellites with rotation as compared to MW A Quick Tour of M31’s Satellites LMC M32 NGC 205 SMC NGC 147 Sgr NGC 185 For And II Leo I Scl And V And XII And XII: MV = -6.2 sigma = ?? (2 member stars) CMD Velocity Velocity vs. radius Tollerud et al. (2012) See also poster by M. Collins! M31 vs. MW Satellite Systems from M. Collins MW M31 sigma (km/s) M31 vs. MW Satellite Systems McConnachie (2012) ) h Dynamical Mass (<r Dynamical MV MV MV The M31 Dwarf Galaxy Population The Milky Way satellite system provides strong constrain on cosmological models (number of satellites, central densities, ages/metallicities) M31 satellites now have competitive observational dataset -- M31 satellite system is similar to MW: -- Basic scaling relations -- Evidence for on-going tidal interactions/merging -- M31 satellite system is different to MW: -- Basic scaling relations -- Number of satellites -- Detailed properties.
Load more

Recommended publications
  • A Revised View of the Canis Major Stellar Overdensity with Decam And
    MNRAS 501, 1690–1700 (2021) doi:10.1093/mnras/staa2655 Advance Access publication 2020 October 14 A revised view of the Canis Major stellar overdensity with DECam and Gaia: new evidence of a stellar warp of blue stars Downloaded from https://academic.oup.com/mnras/article/501/2/1690/5923573 by Consejo Superior de Investigaciones Cientificas (CSIC) user on 15 March 2021 Julio A. Carballo-Bello ,1‹ David Mart´ınez-Delgado,2 Jesus´ M. Corral-Santana ,3 Emilio J. Alfaro,2 Camila Navarrete,3,4 A. Katherina Vivas 5 and Marcio´ Catelan 4,6 1Instituto de Alta Investigacion,´ Universidad de Tarapaca,´ Casilla 7D, Arica, Chile 2Instituto de Astrof´ısica de Andaluc´ıa, CSIC, E-18080 Granada, Spain 3European Southern Observatory, Alonso de Cordova´ 3107, Casilla 19001, Santiago, Chile 4Millennium Institute of Astrophysics, Santiago, Chile 5Cerro Tololo Inter-American Observatory, NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena, Chile 6Instituto de Astrof´ısica, Facultad de F´ısica, Pontificia Universidad Catolica´ de Chile, Av. Vicuna˜ Mackenna 4860, 782-0436 Macul, Santiago, Chile Accepted 2020 August 27. Received 2020 July 16; in original form 2020 February 24 ABSTRACT We present the Dark Energy Camera (DECam) imaging combined with Gaia Data Release 2 (DR2) data to study the Canis Major overdensity. The presence of the so-called Blue Plume stars in a low-pollution area of the colour–magnitude diagram allows us to derive the distance and proper motions of this stellar feature along the line of sight of its hypothetical core. The stellar overdensity extends on a large area of the sky at low Galactic latitudes, below the plane, and in the range 230◦ <<255◦.
    [Show full text]
  • Complex Stellar Populations in Massive Clusters: Trapping Stars of a Dwarf Disc Galaxy in a Newborn Stellar Supercluster
    Mon. Not. R. Astron. Soc. 372, 338–342 (2006) doi:10.1111/j.1365-2966.2006.10867.x Complex stellar populations in massive clusters: trapping stars of a dwarf disc galaxy in a newborn stellar supercluster M. Fellhauer,1,3⋆ P. Kroupa2,3⋆ and N. W. Evans1⋆ 1Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA 2Argelander Institute for Astronomy, University of Bonn, Auf dem Hug¨ el 71, D-53121 Bonn, Germany 3The Rhine Stellar-Dynamical Network Accepted 2006 July 24. Received 2006 July 21; in original form 2006 April 27 ABSTRACT Some of the most-massive globular clusters of our Milky Way, such as, for example, ω Centauri, show a mixture of stellar populations spanning a few Gyr in age and 1.5 dex in metallicities. In contrast, standard formation scenarios predict that globular and open clusters form in one single starburst event of duration 10 Myr and therefore should exhibit only one age and one metallicity in its stars. Here, we investigate the possibility that a massive stellar supercluster may trap older galactic field stars during its formation process that are later detectable in the cluster as an apparent population of stars with a very different age and metallicity. With a set of numerical N-body simulations, we are able to show that, if the mass of the stellar supercluster is high enough and the stellar velocity dispersion in the cluster is comparable to the dispersion of the surrounding disc stars in the host galaxy, then up to about 40 per cent of its initial mass can be additionally gained from trapped disc stars.
    [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]
  • Midwife of the Galactic Zoo
    FOCUS 30 A miniature milky way: approximately 40 million light-years away, UGC 5340 is classified as a dwarf galaxy. Dwarf galaxies exist in a variety of forms – elliptical, spheroidal, spiral, or irregular – and originate in small halos of dark matter. Dwarf galaxies contain the oldest known stars. Max Planck Research · 4 | 2020 FOCUS MIDWIFE OF THE GALACTIC ZOO TEXT: THOMAS BÜHRKE 31 IMAGE: NASA, TEAM ESA & LEGUS Stars cluster in galaxies of dramatically different shapes and sizes: elliptical galaxies, spheroidal galaxies, lenticular galaxies, spiral galaxies, and occasionally even irregular galaxies. Nadine Neumayer at the Max Planck Institute for Astronomy in Heidelberg and Ralf Bender at the Max Planck Institute for Extraterrestrial Physics in Garching investigate the reasons for this diversity. They have already identified one crucial factor: dark matter. Max Planck Research · 4 | 2020 FOCUS Nature has bestowed an overwhelming diversity upon our planet. The sheer resourcefulness of the plant and animal world is seemingly inexhaustible. When scien- tists first started to explore this diversity, their first step was always to systematize it. Hence, the Swedish naturalist Carl von Linné established the principles of modern botany and zoology in the 18th century by clas- sifying organisms. In the last century, astronomers have likewise discovered that galaxies can come in an array of shapes and sizes. In this case, it was Edwin Hubble in the mid-1920s who systematized them. The “Hubble tuning fork dia- gram” classified elliptical galaxies according to their ellipticity. The series of elliptical galaxies along the di- PHOTO: PETER FRIEDRICH agram branches off into two arms: spiral galaxies with a compact bulge along the upper branch and galaxies with a central bar on the lower branch.
    [Show full text]
  • The Large Scale Universe As a Quasi Quantum White Hole
    International Astronomy and Astrophysics Research Journal 3(1): 22-42, 2021; Article no.IAARJ.66092 The Large Scale Universe as a Quasi Quantum White Hole U. V. S. Seshavatharam1*, Eugene Terry Tatum2 and S. Lakshminarayana3 1Honorary Faculty, I-SERVE, Survey no-42, Hitech city, Hyderabad-84,Telangana, India. 2760 Campbell Ln. Ste 106 #161, Bowling Green, KY, USA. 3Department of Nuclear Physics, Andhra University, Visakhapatnam-03, AP, India. Authors’ contributions This work was carried out in collaboration among all authors. Author UVSS designed the study, performed the statistical analysis, wrote the protocol, and wrote the first draft of the manuscript. Authors ETT and SL managed the analyses of the study. All authors read and approved the final manuscript. Article Information Editor(s): (1) Dr. David Garrison, University of Houston-Clear Lake, USA. (2) Professor. Hadia Hassan Selim, National Research Institute of Astronomy and Geophysics, Egypt. Reviewers: (1) Abhishek Kumar Singh, Magadh University, India. (2) Mohsen Lutephy, Azad Islamic university (IAU), Iran. (3) Sie Long Kek, Universiti Tun Hussein Onn Malaysia, Malaysia. (4) N.V.Krishna Prasad, GITAM University, India. (5) Maryam Roushan, University of Mazandaran, Iran. Complete Peer review History: http://www.sdiarticle4.com/review-history/66092 Received 17 January 2021 Original Research Article Accepted 23 March 2021 Published 01 April 2021 ABSTRACT We emphasize the point that, standard model of cosmology is basically a model of classical general relativity and it seems inevitable to have a revision with reference to quantum model of cosmology. Utmost important point to be noted is that, ‘Spin’ is a basic property of quantum mechanics and ‘rotation’ is a very common experience.
    [Show full text]
  • Interpreting the Spitzer/IRAC Colours of 7 Z 9 Galaxies
    MNRAS 000,1–11 (2019) Preprint 15 July 2020 Compiled using MNRAS LATEX style file v3.0 Interpreting the Spitzer/IRAC Colours of 76 z 69 Galaxies: Distinguishing Between Line Emission and Starlight Using ALMA G. W. Roberts-Borsani1;2?, R. S. Ellis2 and N. Laporte3;4;2 1Department of Physics and Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USA 2Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK 3Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 4Cavendish Laboratory, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK Accepted XXX. Received YYY; in original form ZZZ ABSTRACT Prior to the launch of JWST, Spitzer/IRAC photometry offers the only means of studying the rest-frame optical properties of z >7 galaxies. Many such high redshift galaxies display a red [3.6]−[4.5] micron colour, often referred to as the “IRAC excess”, which has conven- tionally been interpreted as arising from intense [O III]+Hβ emission within the [4.5] micron bandpass. An appealing aspect of this interpretation is similarly intense line emission seen in star-forming galaxies at lower redshift as well as the redshift-dependent behaviour of the IRAC colours beyond z ∼7 modelled as the various nebular lines move through the two band- passes. In this paper we demonstrate that, given the photometric uncertainties, established stel- lar populations with Balmer (4000 Å rest-frame) breaks, such as those inferred at z >9 where line emission does not contaminate the IRAC bands, can equally well explain the redshift- dependent behaviour of the IRAC colours in 7.
    [Show full text]
  • Blue Straggler Stars in Galactic Open Clusters and the Effect of Field Star Contamination
    A&A 482, 777–781 (2008) Astronomy DOI: 10.1051/0004-6361:20078629 & c ESO 2008 Astrophysics Blue straggler stars in Galactic open clusters and the effect of field star contamination (Research Note) G. Carraro1,R.A.Vázquez2, and A. Moitinho3 1 ESO, Alonso de Cordova 3107, Vitacura, Santiago, Chile e-mail: [email protected] 2 Facultad de Ciencias Astronómicas y Geofísicas de la UNLP, IALP-CONICET, Paseo del Bosque s/n, La Plata, Argentina e-mail: [email protected] 3 SIM/IDL, Faculdade de Ciências da Universidade de Lisboa, Ed. C8, Campo Grande, 1749-016 Lisboa, Portugal e-mail: [email protected] Received 7 September 2007 / Accepted 19 February 2008 ABSTRACT Context. We investigate the distribution of blue straggler stars in the field of three open star clusters. Aims. The main purpose is to highlight the crucial role played by general Galactic disk fore-/back-ground field stars, which are often located in the same region of the color magnitude diagram as blue straggler stars. Methods. We analyze photometry taken from the literature of 3 open clusters of intermediate/old age rich in blue straggler stars, which are projected in the direction of the Perseus arm, and study their spatial distribution and the color magnitude diagram. Results. As expected, we find that a large portion of the blue straggler population in these clusters are simply young field stars belonging to the spiral arm. This result has important consequences on the theories of the formation and statistics of blue straggler stars in different population environments: open clusters, globular clusters, or dwarf galaxies.
    [Show full text]
  • ガンマ線バーストと遠方宇宙・元素の起源� 井上 進�（理研） ＋共同研究者の皆様 Grbs, Blazars
    ProbingwithTMT the (more 時代のFirst than) Stars,GRBsGRB a forUVlittleで切り拓く超遠方宇宙� UNravelling Radiation, help from the B my DarkFields, friends Ages Dust… Mission� GeV Fermi ガンマ線バーストと遠方宇宙・元素の起源� 井上 進�（理研） ＋共同研究者の皆様 GRBs, blazars R. Salvaterra, T. R. Choudhury, A. Ferrara, B. Ciardi, R. Schneider 分子 ALMA (MNRAS in press, arXiv:0906.2495) Y. Inoue, M. Kobayashi, T. Totani, Y. Niinou (in prep.) z~30-6 ダスト ASTRO-H blazar HiZ-G GRB SPICA 再電離 金属 TMT submm R.ALMA Salvaterra,5@5 T.epoch R. Choudhury, of first starA. Ferrara, formation Inoue, （磁場）� Omukai & Ciardi, Benedetta MNRAS, Ciardi Firstsubmitted (MPA)Radiation (astro-ph/0502218) Fields,! FirstB. MagneticCiardi, R. Schneider Fields,lots of First theory Star Formation SKA K. Ichiki, K. KiyotomoTakahashi Ichiki (CfCP/NAOJ) but almost no observations!!! K. Omukai Keitaro Takahashi (Princeton) IceCube SKA CTA CTA “in an interstella burst i am back to reveal the universe” radio see - after T. Yorke also かなた outline� I. GRBs and the high-z Universe - overview: early excitement vs recent calming down - quasar contribution to reionization - gamma-ray probe of UV background *star formation rate, metal evolution, damping wings… -> later talks recent reviews: Space Sci. Rev. (2016) 202� II. neutron star mergers and r-process nucleosynthesis - potential of X-ray diagnostics cosmic dark ages -> cosmic dawn� - big bang� z~3600� - matter-rad. eq.� z~1000� - recombination� dark ages� z>~30� - first stars, galaxies, black holes… -> reionization z~8-10� z~6� - reion. ends - star formation � z~1-3 peak� z~0� adapted
    [Show full text]
  • The Dwarf Galaxy Abundances and Radial-Velocities Team (DART) Large Programme – a Close Look at Nearby Galaxies
    Reports from Observers The Dwarf galaxy Abundances and Radial-velocities Team (DART) Large Programme – A Close Look at Nearby Galaxies Eline Tolstoy1 The dwarf galaxies we have studied are nearby galaxies. The modes of operation, Vanessa Hill 2 the lowest-luminosity (and mass) galax- the sensitivity and the field of view are Mike Irwin ies that have ever been found. It is likely an almost perfect match to requirements Amina Helmi1 that these low-mass dwarfs are the most for the study of Galactic dSph galaxies. Giuseppina Battaglia1 common type of galaxy in the Universe, For example, it is now possible to meas- Bruno Letarte1 but because of their extremely low ure the abundance of numerous elements Kim Venn surface brightness our ability to detect in nearby galaxies for more than 100 stars Pascale Jablonka 5,6 them diminishes rapidly with increasing over a 25;-diameter field of view in one Matthew Shetrone 7 distance. The only place where we can shot. A vast improvement on previous la- Nobuo Arimoto 8 be reasonably sure to detect a large frac- borious (but valiant) efforts with single-slit Tom Abel 9 tion of these objects is in the Local spectrographs to observe a handful of Francesca Primas10 Group, and even here, ‘complete sam- stars per galaxy (e.g., Tolstoy et al. 200; Andreas Kaufer10 ples’ are added to each year. Within Shetrone et al. 200; Geisler et al. 2005). Thomas Szeifert10 250 kpc of our Galaxy there are nine low- Patrick Francois 2 mass galaxies (seven observable from The DART Large Programme has meas- Kozo Sadakane11 the southern hemisphere), including Sag- ured abundances and velocities for sev- ittarius which is in the process of merging eral hundred individual stars in a sample with our Galaxy.
    [Show full text]
  • Tidal Dwarf Galaxies and Missing Baryons
    Tidal Dwarf Galaxies and missing baryons Frederic Bournaud CEA Saclay, DSM/IRFU/SAP, F-91191 Gif-Sur-Yvette Cedex, France Abstract Tidal dwarf galaxies form during the interaction, collision or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons”, known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this article, I use “dark matter” to refer to the non-baryonic matter, mostly located in large dark halos – i.e., CDM in the standard paradigm. I use “missing baryons” or “dark baryons” to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”. 1. Introduction: the formation of Tidal Dwarf Galaxies A Tidal Dwarf Galaxy (TDG) is, per definition, a massive, gravitationally bound object of gas and stars, formed during a merger or distant tidal interaction between massive spiral galaxies, and is as massive as a dwarf galaxy [1] (Figure 1).
    [Show full text]
  • Monster Black Hole Found in Tiny Galaxy Discovery Hints at Twice As Many Supermassive Black Holes in the Nearby Universe As Previously Thought
    NATURE | NEWS Monster black hole found in tiny galaxy Discovery hints at twice as many supermassive black holes in the nearby Universe as previously thought. Ron Cowen 17 September 2014 Artist's impression by V. Beckmann/ESA/NASA/SPL Matter falling into supermassive black holes can get so hot that it emits X-rays. Astronomers have for the first time found strong evidence for a giant black hole in a Lilliputian galaxy. The finding suggests that supermassive black holes could be twice as numerous in the nearby Universe as previously estimated, with many of them hidden at the centres of small, seemingly nondescript galaxies known as ultra-compact dwarfs. Anil Seth of the University of Utah in Salt Lake City and his colleagues report the findings on 17 September in Nature1. The team became intrigued by the ultra-compact dwarf galaxy M60-UCD1, some 16.6 million parsecs (54 million light years) from Earth, in part because its X-ray emissions suggested that it might house a black hole. Images taken with the Hubble Space Telescope showed that the galaxy harboured a high concentration of mass at its centre, but the team had no idea how heavy the putative black hole might be. To weigh the beast, the researchers measured the velocity of stars whipping about the galaxy’s centre using an infrared spectrometer on the Gemini North telescope atop Mauna Kea in Hawaii. The high velocity of the stars is best explained by a central black hole that tips the scales at 21 million times the Sun’s mass, concluded Seth’s team.
    [Show full text]
  • The Satellite Distribution of the Galaxy Therefore Ence for Orbits in the Plane of the Disk (Brainerd 2005)
    Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 29 June 2018 (MN LATEX style file v2.2) The satellite distribution of M31 A. W. McConnachie1,2 & M. J. Irwin1 1Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, U.K. 2Department of Physics and Astronomy, University of Victoria, Victoria, B.C. V8P 5C2, Canada 29 June 2018 ABSTRACT The spatial distribution of the Galactic satellite system plays an important role in Galactic dynamics and cosmology, where its successful reproduction is a key test of simulations of galaxy halo formation. Here, we examine its representative nature by conducting an analysis of the 3-dimensional spatial distribution of the M31 subgroup of galaxies, the next closest system to our own. We begin by a discussion of distance estimates and incompleteness concerns, before revisiting the question of membership of the M31 subgroup. We constrain this by consideration of the spatial and kinematic properties of the putative satellites. Comparison of the distribution of M31 and Galac- tic satellites relative to the galactic disks suggests that the Galactic system is probably modestly incomplete at low latitudes by ≃ 20 %. We find that the radial distribution of satellites around M31 is more extended than the Galactic subgroup; 50% of the Galactic satellites are found within ∼ 100kpc of the Galaxy, compared to ∼ 200kpc for M31. We search for “ghostly streams” of satellites around M31, in the same way others have done for the Galaxy, and find several, including some which contain many of the dwarf spheroidal satellites. The lack of M31-centric kinematic data, however, means we are unable to probe whether these streams represent real physical associ- ations.
    [Show full text]