DOCSLIB.ORG

Galaxy Disks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Galaxy Disks Galaxy disks P.C. van der Kruit Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, the Netherlands ([email protected]) K.C. Freeman Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, ACT 2611, Australia ([email protected]) Keywords: disks in galaxies: surveys, luminosity distributions, mass distributions, disk sta- bility, warps and truncations, scaling laws, thick disks, chemical evolution, abundance gradients, formation, S0 galaxies Abstract The disks of disk galaxies contain a substantial fraction of their baryonic matter and angular momentum, and much of the evolutionary activity in these galaxies, such as the formation of stars, spiral arms, bars and rings and the various forms of secular evolution, takes place in their disks. The formation and evolution of galactic disks is therefore particularly important for understanding how galaxies form and evolve, and the cause of the variety in which they appear to us. Ongoing large surveys, made possible by new instrumentation at wavelengths from the ultraviolet (GALEX), via optical (HST and large groundbased telescopes) and infrared (Spitzer) to the radio are providing much new information about disk galaxies over a wide range of redshift. Although progress has been made, the dynamics and structure of stellar disks, including their truncations, are still not well understood. We do now have plausible estimates of disk mass-to-light ratios, and estimates of Toomre’s Q parameter show that they are just locally stable. Disks are mostly very flat and sometimes very thin, and have a range in surface brightness from canonical disks with a central surface brightness of about 21.5 B-mag arcsec−2 down to very low surface brightnesses. It appears that galaxy disks are not maximal, except possibly in the largest systems. Their HI layers display warps whenever HI can be detected beyond the stellar disk, with low-level star formation going on out to large radii. Stellar disks display abundance gradients which flatten at larger radii and sometimes even reverse. The existence of a well-defined baryonic (stellar + HI) Tully-Fisher relation hints at an approximately uniform baryonic to dark matter ratio. Thick disks are common in disk galaxies and their existence appears unrelated to the presence of a bulge component; they are old, but their formation is not yet understood. Disk formation was already advanced at redshifts of ∼ 2, but at that epoch disks were not yet quiescent and in full rotational equilibrium. Downsizing (the gradual reduction with time in the mass of the most actively star-forming galaxies) is now well-established. The formation and history of star formation in S0s is still not fully understood. The final version of this chapter as it will appear in Annual Reviews of Astronomy & Astrophysics, vol. 49 (2011), will have fewer figures and a somewhat shortened text. Contents 1 INTRODUCTION AND OVERVIEW 1 1.1 Historical Background . 1 1.2 Setting the Scene . 4 2 SURVEYS 4 3 STELLAR DISKS 6 3.1 Luminosity Distributions . 6 3.1.1 Exponential disks . 6 3.1.2 Three-dimensional distributions . 11 3.2 Stellar Kinematics, Stability and Mass . 11 3.2.1 Vertical dynamics . 11 3.2.2 Stellar velocity dispersions in the plane . 13 3.2.3 Origin of the constant scaleheight . 15 3.2.4 Mass distributions from stellar dynamics . 16 3.3 Age Gradients and Photometric M/L Ratios . 20 3.4 Global Stability, Bars and Spiral Structure . 21 3.5 The Flatness of Disks . 23 3.6 ‘Superthin’ Galaxies . 24 3.7 Warps in Stellar Disks . 25 3.8 Truncations . 25 3.9 Nuclei of Pure-Disk Galaxies . 29 4 HI DISKS 29 4.1 HI Distributions, Kinematics and Dynamics . 29 4.2 Dark Matter Halos . 32 4.3 Outer HI and Warps . 35 4.4 Dustlanes in Disks . 39 5 CHEMICAL EVOLUTION AND ABUNDANCE GRADIENTS 40 5.1 Gas-phase Abundance Gradients . 41 5.2 Stellar Abundance Gradients . 42 6 SCALING LAWS FOR DISK GALAXIES 44 6.1 The Tully-Fisher Law . 45 6.2 Scaling Laws involving the Galaxy Diameter . 47 6.3 The Mass-Metallicity Relation . 48 6.4 The Surface Density-Mass Relation . 48 6.5 Scaling Laws for Dark Matter Halos . 48 7 THICK DISKS 49 7.1 Statistics of Incidence . 49 7.2 Structure of Thick Disks . 49 7.3 Kinematics and Chemical Properties . 50 7.4 Relation of Thick Disk to the other Galactic Components . 52 7.5 Thick Disk Formation Scenarios . 52 8 FORMATION OF DISKS 53 8.1 Disk Formation Scenarios . 53 8.2 Disks at High Redshift . 55 8.3 Baryon Acquisition by Disk Galaxies . 56 9 S0 GALAXIES 58 References 61 1 INTRODUCTION AND OVERVIEW 1.1 Historical Background Disks are the most prominent parts of late-type spiral galaxies. The disk of our own Milky Way Galaxy stretches as a magnificent band of light from horizon to horizon, particularly from a dark site at southern latitudes, as in the Astronomy Picture of the Day for January 27, 2009 (Pacholka, 2009). Its appearance with the Galactic Center high in the sky is reminiscent of the beautiful edge-on spiral NGC 891 (Hawaiian Starlight, 1999), which can be regarded as a close twin to our Galaxy (van der Kruit, 1984). What might in hindsight be called the first study of the distribution of stars in a galaxy disk is William Herschel’s famous cross-cut of the ‘Sidereal System’ based on his ‘star gauges’ (“On the Construction of the Heavens”; Herschel, 1785), from which he concluded that the distribution of stars in space is in the form of a flattened system with the sun near its center. His counts, on which he based this ‘section’ of the system, were performed along a great circle on the sky almost perpendicular to the Galactic equator, crossing it at longitudes 45◦ and 225◦ and missing the poles by 5◦. Comparison to modern star counts shows that Herschel counted stars consistently down to magnitude V ∼ 15 (van der Kruit, 1986). It was the first description of the flattened nature of galactic disks. The next major step in the study of the distribution of stars in the Milky Way was that of Jacobus Kapteyn (Kapteyn & van Rhijn, 1920; Kapteyn, 1922). In spite of his deduction that interstellar extinction must have the effect of reddening of starlight with increasing distance, Kapteyn (1909a,b, 1914) was unable to establish the existence of interstellar absorption in a convincing way and was led to ignore it. As a result he ended up with a model for what we now know to be the Galactic disk that erroneously had the Sun located near its center. The proceedings ‘The Legacy of J.C. Kapteyn’ (van der Kruit & van Berkel, 2000) has a number of interesting studies of Kapteyn and astronomy in his time. Even before galaxies were established to be ‘Island universes’, spiral structure was discovered in 1845 by William Parsons, the Third Earl of Rosse. His famous drawing of M51 appears in many textbooks, popular literature and books on the history of astronomy. The importance of the disk and the development of spiral structure were the basis for the classification scheme that John Reynolds and Edwin Hubble developed; the background and early development of galaxy classification was described by Sandage (2005). Eventually the concept of Stellar Populations, first proposed by Baade (1944), led to the famous Vatican Symposium of 1957 (O’Connell, 1958), where a consistent picture was defined to interpret the presence of disk and halo populations in the context of the structure and formation of galaxies. Not long after that, the collapse picture of Eggen, Lynden-Bell & Sandage (1962) provided a working picture for the formation and evolution of the Galaxy and by implication of galaxies in general (Sandage, Freeman & Stokes, 1970). It was modified by Searle & Zinn (1978) to include extended evolution, whereby the outer globular clusters originated and underwent chemical evolution in separate fragments that fell into the Galaxy after the collapse of the central halo had been completed. The basic discrete two-component structure of the edge-on galaxy NGC 7814 led van der Kruit & Searle (1982b) to deduce that there are two discrete epochs of star formation, one before and the other after virialization of the spheroid and the formation of the disk. Two related important developments in understanding the properties of galaxies and their formation were the discovery of dark matter halos, and the appreciation of the role of hierarchical assembly of galaxies. The concepts of hierarchical assembly were already around in the early 1970s, and became widely accepted at a landmark symposium on the Evolution of Galaxies and Stellar Populations at Yale University in 1977 (Tinsley & Larson, 1977). The discovery of dark matter halos (see below) led to the two-stage galaxy formation model of White & Rees (1978), in which hierarchical clustering of the dark matter took place under the influence of gravity, followed 1 by collapse and cooling of the gas in the resulting potential wells. The Hubble Space Telescope made possible the high resolution imaging of galaxies at high redshift, and showed directly that merging and hierarchical assembly are significant in the formation of massive galaxies. The significance of internal secular evolution for the evolution of disks has become clear in recent years. The presence of oval distortions, bars and spiral structure can have a profound effect on the changing structure of disks, as has been extensively reviewed by Kormendy & Kennicutt (2004) and Kormendy (2007). The rotation of galaxies was discovered early in the twentieth century. For a historical introduction, see van der Kruit & Allen (1978), van der Kruit (1990, Ch.
Load more

Recommended publications
  • Pos(FRAPWS2016)027 ∗ -Elements, Fe and Heavier
    The chemical evolution of the Milky Way PoS(FRAPWS2016)027 Francesca Matteucci∗ Dipartimento di Fisica, Università di Trieste E-mail: [email protected] Emanuele Spitoni Dipartimento di Fisica, Università di Trieste E-mail: [email protected] Donatella Romano I.N.A.F. Osservatorio Astronomico di Bologna E-mail: [email protected] Alvaro Rojas-Arriagada Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile E-mail: [email protected] We will discuss some highlights concerning the chemical evolution of our Galaxy, the Milky Way. First we will describe the main ingredients necessary to build a model for the chemical evolution of the Milky Way. Then we will illustrate some Milky Way models which includes detailed stellar nucleosynthesis and compute the evolution of a large number of chemical elements, including C, N, O, α-elements, Fe and heavier. The main observables and in particular the chemical abun- dances in stars and gas will be considered. A comparison theory-observations will follow and finally some conclusions from this astroarchaeological approach will be derived. Frontier Research in Astrophysics - II 23-28 May 2016 Mondello (Palermo), Italy Speaker. ∗ © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/ Milky Way Francesca Matteucci 1. Introduction In the last years a great deal of spectroscopic data concerning a very large number of Galactic stars has appeared in the literature.
    [Show full text]
  • Set 4: Active Galaxies
    Set 4: Active Galaxies Phenomenology • History: Seyfert in the 1920’s reported that a small fraction (few tenths of a percent) of galaxies have bright nuclei with broad emission lines. 90% are in spiral galaxies • Seyfert galaxies categorized as 1 if emission lines of HI, HeI and HeII are very broad - Doppler broadening of 1000-5000 km/s and narrower forbidden lines of ∼ 500km/s. Variable. Seyfert 2 if all lines are ∼ 500km/s. Not variable. • Both show a featureless continuum, for Seyfert 1 often more luminous than the whole galaxy • Seyferts are part of a class of galaxies with active galactic nuclei (AGN) • Radio galaxies mainly found in ellipticals - also broad and narrow line - extremely bright in the radio - often with extended lobes connected to center by jets of ∼ 50kpc in extent Radio Galaxy 3C31, NGC 383 Phenomenology • Quasars discovered in 1960 by Matthews and Sandage are extremely distant, quasi-starlike, with broad emission lines. Faint fuzzy halo reveals the parent galaxy of extremely luminous object 38−41 11−14 - visible luminosity L ∼ 10 W or ∼ 10 L • Quasars can be both radio loud (QSR) and quiet (QSO) • Blazars (BL Lac) highly variable AGN with high degree of polarization, mostly in ellipticals • ULIRGs - ultra luminous infrared galaxies - possibly dust enshrouded AGN (alternately may be starburst) • LINERS - similar to Seyfert 2 but low ionization nuclear emission line region - low luminosity AGN with strong emission lines of low ionization species Spectrum . • AGN share a basic general form for their continuum emission • Flat broken power law continuum - specific flux −α Fν / ν .
    [Show full text]
  • Resolving the Radio Loud/Radio Quiet Dichotomy Without Thick Disks David
    Resolving the radio loud/radio quiet dichotomy without thick disks David Garofalo Department of Physics, Kennesaw State University, Marietta GA 30060, USA Abstract Observations of radio loud active galaxies in the XMM-Newton archive by Mehdipour & Costantini show a strong anti-correlation between the column density of the ionized wind and the radio loudness parameter, providing evidence that jets may thrive in thin disks. This is in contrast with decades of analytic and numerical work suggesting jet formation is contingent on the presence of an inner, geometrically thick disk structure, which serves to both collimate and accelerate the jet. Thick disks emerge in radiatively inefficient disks which are associated with sub-Eddington as well as super-Eddington accretion regimes yet we show that the inverse correlation between winds and jets survives where it should not, namely in a luminosity regime normally attributed to radio quiet active galaxies which are modeled with thin disks. This along with other lines of evidence argues against thick disks as the foundation behind the radio loud/radio quiet dichotomy, opening up the possibility that jetted versus non jetted black holes may be understood within the context of radiatively efficient thin disk accretion. 1. Introduction Sikora et al (2007) explored the inverse correlation between radio loudness and Eddington accretion rate for a large sample of active galaxies (AGN) including Seyfert galaxies and LINERs, optically selected quasars, FRI radio galaxies, FRII quasars, and broad line radio galaxies. Despite a clear dichotomy in radio loudness between objects referred to as radio loud and those as radio quiet, the data was insufficiently detailed to shed light on the jet-disk connection near the Eddington limit where we traditionally model the radio quiet subset of the AGN family.
    [Show full text]
  • Powerful Jets from Radiatively Efficient Disks, a Decades-Old Unresolved Problem in High Energy Astrophysics
    galaxies Article Powerful Jets from Radiatively Efficient Disks, a Decades-Old Unresolved Problem in High Energy Astrophysics Chandra B. Singh 1,*,†, David Garofalo 2,† and Benjamin Lang 3 1 South-Western Institute for Astronomy Research, Yunnan University, University Town, Chenggong, Kunming 650500, China 2 Department of Physics, Kennesaw State University, Marietta, GA 30060, USA; [email protected] 3 Department of Physics & Astronomy, California State University, Northridge, CA 91330, USA; [email protected] * Correspondence: [email protected] † These authors contributed equally to this work. Abstract: The discovery of 3C 273 in 1963, and the emergence of the Kerr solution shortly thereafter, precipitated the current era in astrophysics focused on using black holes to explain active galactic nuclei (AGN). But while partial success was achieved in separately explaining the bright nuclei of some AGN via thin disks, as well as powerful jets with thick disks, the combination of both powerful jets in an AGN with a bright nucleus, such as in 3C 273, remained elusive. Although numerical simulations have taken center stage in the last 25 years, they have struggled to produce the conditions that explain them. This is because radiatively efficient disks have proved a challenge to simulate. Radio quasars have thus been the least understood objects in high energy astrophysics. But recent simulations have begun to change this. We explore this milestone in light of scale-invariance and show that transitory jets, possibly related to the jets seen in these recent simulations, as some have proposed, cannot explain radio quasars. We then provide a road map for a resolution.
    [Show full text]
  • The Milky Way Tomography with SDSS I. Stellar Number Density
    The Astrophysical Journal, 673:864Y914, 2008 February 1 A # 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE MILKY WAY TOMOGRAPHY WITH SDSS. I. STELLAR NUMBER DENSITY DISTRIBUTION Mario Juric´,1,2 Zˇ eljko Ivezic´,3 Alyson Brooks,3 Robert H. Lupton,1 David Schlegel,1,4 Douglas Finkbeiner,1,5 Nikhil Padmanabhan,4,6 Nicholas Bond,1 Branimir Sesar,3 Constance M. Rockosi,3,7 Gillian R. Knapp,1 James E. Gunn,1 Takahiro Sumi,1,8 Donald P. Schneider,9 J. C. Barentine,10 Howard J. Brewington,10 J. Brinkmann,10 Masataka Fukugita,11 Michael Harvanek,10 S. J. Kleinman,10 Jurek Krzesinski,10,12 Dan Long,10 Eric H. Neilsen, Jr.,13 Atsuko Nitta,10 Stephanie A. Snedden,10 and Donald G. York14 Received 2005 October 21; accepted 2007 September 6 ABSTRACT Using the photometric parallax method we estimate the distances to 48 million stars detected by the Sloan Digital Sky Survey (SDSS) and map their three-dimensional number density distribution in the Galaxy. The currently avail- able data sample the distance range from 100 pc to 20 kpc and cover 6500 deg2 of sky, mostly at high Galactic lati- tudes (jbj > 25). These stellar number density maps allow an investigation of the Galactic structure with no a priori assumptions about the functional form of its components. The data show strong evidence for a Galaxy consisting of an oblate halo, a disk component, and a number of localized overdensities. The number density distribution of stars as traced by M dwarfs in the solar neighborhood (D < 2 kpc) is well fit by two exponential disks (the thin and thick disk) with scale heights and lengths, bias corrected for an assumed 35% binary fraction, of H1 ¼ 300 pc and L1 ¼ 2600 pc, and H2 ¼ 900 pc and L2 ¼ 3600 pc, and local thick-to-thin disk density normalization thick(R )/thin(R ) ¼ 12%.
    [Show full text]
  • The Age of the Galaxy's Thick Disk
    The Ages of Stars Proceedings IAU Symposium No. 258, 2008 c 2009 International Astronomical Union E.E. Mamajek, D.R. Soderblom & R.F.G. Wyse, eds. doi:10.1017/S1743921309031676 The age of the Galaxy’s thick disk Sofia Feltzing1† and Thomas Bensby2 1 Lund Observatory, Box 43, SE-22100, Lund, Sweden email: [email protected] 2 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile email: [email protected] Abstract. We discuss the age of the stellar disks in the solar neighborhood. After reviewing the various methods for age dating, we discuss current estimates of the ages of both the thin- and the thick disks. We present preliminary results for kinematically-selected stars that belong to the thin- as well as the thick disk. All of these dwarf and sub-giant stars have been studied spectroscopically and we have derived both elemental abundances as well as ages for them. A general conclusion is that in the solar neighborhood, on average, the thick disk is older than the thin disk. However, we caution that the exclusion of stars with effective temperatures around 6500 K might result in a biased view of the full age distribution for the stars in the thick disk. Keywords. Galaxy: structure, Galaxy: disk, kinematics and dynamics, solar neighborhood, Hertzsprung-Russell diagram, stars: late-type 1. Introduction The age of a stellar population can be determined in several ways. For groups of stars, isochrones may be fitted to the stellar sequence in the Hertzsprung-Russell diagram (HRD; see, e.g., Schuster et al.
    [Show full text]
  • The Galaxy in Context: Structural, Kinematic & Integrated Properties
    The Galaxy in Context: Structural, Kinematic & Integrated Properties Joss Bland-Hawthorn1, Ortwin Gerhard2 1Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006, Australia; email: [email protected] 2Max Planck Institute for extraterrestrial Physics, PO Box 1312, Giessenbachstr., 85741 Garching, Germany; email: [email protected] Annu. Rev. Astron. Astrophys. 2016. Keywords 54:529{596 Galaxy: Structural Components, Stellar Kinematics, Stellar This article's doi: 10.1146/annurev-astro-081915-023441 Populations, Dynamics, Evolution; Local Group; Cosmology Copyright c 2016 by Annual Reviews. Abstract All rights reserved Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It is the only galaxy whose formation history can be stud- ied using the full distribution of stars from faint dwarfs to supergiants. The oldest components provide us with unique insight into how galaxies form and evolve over billions of years. The Galaxy is a luminous (L?) barred spiral with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo. Based on global properties, it falls in the sparsely populated \green valley" region of the galaxy colour-magnitude dia- arXiv:1602.07702v2 [astro-ph.GA] 5 Jan 2017 gram. Here we review the key integrated, structural and kinematic pa- rameters of the Galaxy, and point to uncertainties as well as directions for future progress. Galactic studies will continue to play a fundamen- tal role far into the future because there are measurements that can only be made in the near field and much of contemporary astrophysics depends on such observations. 529 Redshift (z) 20 10 5 2 1 0 1012 1011 ) ¯ 1010 M ( 9 r i 10 v 8 M 10 107 100 101 102 ) c p 1 k 10 ( r i v r 100 10-1 0.3 1 3 10 Time (Gyr) Figure 1 Left: The estimated growth of the Galaxy's virial mass (Mvir) and radius (rvir) from z = 20 to the present day, z = 0.
    [Show full text]
  • The Galactic Thick Disk: an Observational Perspective
    Chemical Abundances in the Universe: Connecting First Stars to Planets Proceedings IAU Symposium No. 265, 2009 c International Astronomical Union 2010 K. Cunha, M. Spite & B. Barbuy, eds. doi:10.1017/S1743921310000761 The Galactic Thick Disk: An Observational Perspective Bacham E. Reddy Indian Institute of Astrophysics, Bengaluru, 560034, email: [email protected] Abstract. In this review, we present a brief description of observational efforts to understand the Galactic thick disk and its relation to the other Galactic components. This review primarily focused on elemental abundance patterns of the thick disk population to understand the pro- cess or processes that were responsible for its existence and evolution. Kinematic and chemical properties of disk stars establish that the thick disk is a distinct component in the Milky Way, and its chemical enrichment and star formation histories hold clues to the bigger picture of understanding the Galaxy formation. Keywords. stars: FGK dwarfs, Stars: abundances, Stars: Kinematics, Galaxy: disk 1. Introduction Deciphering the history of the birth and the growth of the Milky Way Galaxy is one of the major outstanding astrophysical problems. Detailed studies of our Galaxy would help to gain insights into the formation and evolution of other galaxies, and thereby large scale structure formation in the universe. As inhabitants, we have much better access to our Galaxy to resolve its building blocks: the stars. The properties of stars that constitute the Galaxy are clues to the processes involved in the making of the Milky Way Galaxy we see today. The observational data on stellar motions and photospheric abundances played decisive roles in the progression of our understanding of the Galaxy.
    [Show full text]
  • Thick Disks and Halos of Spiral Galaxies M 81, NGC 55 and NGC 300
    A&A 431, 127–142 (2005) Astronomy DOI: 10.1051/0004-6361:20047042 & c ESO 2005 Astrophysics Thick disks and halos of spiral galaxies M 81, NGC 55 and NGC 300 N. A. Tikhonov1,2, O. A. Galazutdinova1,2, and I. O. Drozdovsky3,4 1 Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR 369167, Russia e-mail: [email protected] 2 Isaac Newton Institute of Chile, SAO Branch, Russia 3 Spitzer Science Center, Caltech, MC 220-6, Pasadena, CA 91125, USA 4 Astronomical Institute, St. Petersburg University, 198504, Russia Received 9 January 2004 / Accepted 28 September 2004 Abstract. By using images from the HST/WFPC2/ACS archive, we have analyzed the spatial distribution of the AGB and RGB stars along the galactocentric radius of nearby spiral galaxies M 81, NGC 300 and NGC 55. Examining color–magnitude diagrams and stellar luminosity functions, we gauge the stellar contents of the surroundings of the three galaxies. The red giant population (RGB) identified at large galactocentric radii yields a distance of 3.85 ± 0.08 Mpc for M 81, 2.12 ± 0.10 Mpc for NGC 55, and 2.00±0.13 Mpc for NGC 300, and a mean stellar metallicity of −0.65, −1.25, and −0.87 respectively. We find that there are two number density gradients of RGB stars along the radius, which correspond to the thick disk and halo components of the galaxies. We confirm the presence of a metallicity gradient of evolved stars in these galaxies, based on the systematic changes of the color distribution of red giant stars.
    [Show full text]
  • THE SPATIAL STRUCTURE of an ACCRETION DISK Shawn Poindexter,1 Nicholas Morgan,1 and Christopher S
    The Astrophysical Journal, 673:34Y38, 2008 January 20 # 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE SPATIAL STRUCTURE OF AN ACCRETION DISK Shawn Poindexter,1 Nicholas Morgan,1 and Christopher S. Kochanek1 Received 2007 June 29; accepted 2007 October 5 ABSTRACT Based on the microlensing variability of the two-image gravitational lens HE 1104Y1805 observed between 0.4 and 8 m, we have measured the size and wavelength-dependent structure of the quasar accretion disk. Modeled as a À power law in temperature, T / R , we measure a B-band (0.13 m in the rest frame) half-light radius of R1/2;B ¼ þ6:2 ; 15 þ0:21 6:7À3:2 10 cm (68% confidence level) and a logarithmic slope of ¼ 0:61À0:17 (68% confidence level) for our standard model with a logarithmic prior on the disk size. Both the scale and the slope are consistent with simple thin 15 disk models where ¼ 3/4 and R1/2;B ¼ 5:9 ; 10 cm for a Shakura-Sunyaev disk radiating at the Eddington limit þ0:03 with 10% efficiency. The observed fluxes favor a slightly shallower slope, ¼ 0:55À0:02, and a significantly smaller size for ¼ 3/4. Subject headings: accretion, accretion disks — gravitational lensing — quasars: individual (HE 1104Y1805) 1. INTRODUCTION we analyze 13 yr of photometric data in 11 bands from the mid-IR to B band using the methods of Kochanek (2004) to measure A simple theoretical prediction for thermally radiating thin ac- the wavelength-dependent structure of this quasar modeled as cretion disks well outside the inner disk edge is that the temper- 1/ À3/4 apowerlawRk / k .WeassumeaflatÃCDM cosmological ature diminishes with radius as T / R (Shakura & Sunyaev À1 À1 model with M ¼ 0:3andH0 ¼ 70 km s Mpc and report 1973).
    [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]
  • Lecture 6 Recap Lecture
    Introduction to Astronomy Galaxies Lecture 6 Recap Lecture Peder Norberg [email protected] Introduction to Astronomy PHYS1081 Lecture Summary 1. The Milky Way: mapping the Galaxy. 2. Galaxies - Morphology: the Hubble Sequence, Spiral and Elliptical galaxies 3. Galaxies - Distances: The Cosmic Distance Ladder 4. Clusters and superclusters. 5. Active galaxies, Quasars & Gamma-ray bursts Lecture 6 By the end of this lecture, we will have revisited: Our Galaxy: The Milky Way Galaxy Morphologies Galaxy Transformations Active Galaxies and Black Holes Redshifts and Distances Large Scale Structure: Groups, Clusters & Superclusters Masses of Clusters Gravity Galaxy Cluster Galaxy AGN Forces on a particle in 2 V GM (< R) 2 GM (< R) a = = V = a circular orbit: centripetal R R2 R Virial Theorem for 2 2 KE T = PE T σ R groups of stars / M E galaxies: 2 2 / G σ = (vi − v ) Kinetic and potential GM v2 2GM = R = energy of a particle: r 2 S c2 Our Galaxy: The Milky Way The Milky Way The structure of the Galaxy The Sun’s position within the Galaxy What lurks at the Galactic Centre? Galactic rotation, Dark halos and Dark Matter Future of our Galaxy… The Milky Way @ different wavelengths Optical Far-IR IR Structure of the Milky Way Our galaxy has been mapped using star counts and emission from HI gas: - The Disk is about 30 kpc across and only 0.6 kpc thick (contains Pop I+II stars) - The Bulge is about 2 kpc across (Pop II stars) - The Halo is a diffuse structure that 3 kpc reaches out to 100 kpc radius (Pop II) - There is a “thick” disk of Pop II stars (thickness ~2-3kpc) Several spiral arms (6) in disk: not a “fixed” pattern, but density waves.
    [Show full text]