Galactic Astronomy [1 ed.] 0691004021, 0691025657, 9780691025650

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Copyright © 1998 by Princeton University Press Published by Princeton University Press, 41 William Street, Princeton, New Jersey 08540 In the United Kingdom: Princeton University Press, Chichester, West Sussex All Rights Reserved Library of Congress Cataloging-In-Publication Data Binney, James, 1950Galactic astronomy / James Binney and Michael Merrifield. p. cm.-{Princeton series in astrophysics) Includes bibliographical references and index. ISBN 0-691-00402-1 (cloth: alk. paper)-ISBN 0-691-02565-7 (pbk.: alk. paper) 1. Galaxies. 2. Milky Way. 3. Stars. I. Merrifield, Michael, 1964- . II. Title. III. Series. QB857.B522 1998 . 523.1----dc21 98-24385 The publisher would like to acknowledge the authors of this volume for providing the camera-ready copy from which this book was printed Princeton University Press books are printed on acid-free paper and meet the guidelines for permanence and durability of the Committee on Production Guidelines for Book Longevity of the Council on Library Resources http://pup. princeton.edu Printed in the United States of America 10987654321

]0 9 8 7 (Pbk.) ISBN-13: 978-0-691-02565-0 (Pbk) ISBN-l 0: 0-691-02565-7 (Pbk)

Contents Preface 1 Galaxies: an overview 1.1 Introduction 1.2 A brief history of galactic astronomy • Photometric models of the Milky Way 5 • The nature of the spiral nebulae 10 • Kinematic models of the Milky Way 15 • Stellar populations 20 • More recent developments 21

2 Astronomical Measurements 2.1 Positions, motions and coordinate systems • The equatorial system 27 • Galactic coordinates 30 • Parallax 31 • Proper motions 34 • Precession and nutation 35 • Astrometric systems 37 2.2 Distances determined from velocities • Radial velocities 39 • Distances from the moving• Secular parallaxes 42 cluster method 40 • Statistical parallaxes 45 2.3 Magnitudes and colors • Apparent magnitudes 47 • Colors 52 • Absolute magnitudes 56 • Absolute energy distributions and bolometric magnitudes 58 • Mass-to-light ratios 60 • Surface brightness and isophotal radii 61 2.4 Gravitational lensing 2.5 Archival data and catalogs t> On-line resources 71 Problems

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2

26 27

38

46

62 67 74

Contents

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3 The Properties of Stars

76

3.1 The masses of stars 76 • The Mass of the Sun 77 • Masses of binary stars 78 [> Visual binaries 78 [> Spectroscopic binaries 79 3.2 The radii of stars 82 • Phase interferometry 82 • Intensity' interferometry 83 • Speckle interferometry 83 • Lunar occultations 84 • Eclipsing binaries 84 • Astrophysical estimates 86 3.3 Classification of stars 87 [> Novae 87 [> Pulsars 87 • Classification of stellar spectra 88 [> The MK system 90 94 3.4 Physical interpretation of stellar spectra 102 3.5 Color-magnitude diagrams • Observed CM-diagrams 103 • Luminosity and color as functions of spectral class 104 • The physical properties of stars on the MS and RGB 109 3.6 The stellar luminosity function . 109 • Malmquist bias 111 • Lutz-Kelker Bias 115 • The general luminosity function 119 [> Cluster luminosity functions 119 [> Photometrically complete surveys 119 [> Proper-motion selected surveys 120 • The luminosity function of a given MK spectral class 127 • Catalogs of the nearby stars 130 3.7 Interstellar dust 131 • Extinction and reddening 133 [> Reddening-free indices 138 [> Polarization of starlight by dust 140 • Extinction of sightlines out of the Galaxy 140 Problems 143

4 Morphology of Galaxies 4.1 Morphological classification of galaxies • The Hubble sequence 149 • Effects of environment 157 • The galaxy luminosity function 162 [> The field galaxy luminosity function 162 [> The cluster galaxy luminosity function 165 [> The lu-

145 146

minosity function divided by morphological type. 167

• The Local Group 169 4.2 Surface Photometry of Galaxies 172 • The night sky 173 • Effect of seeing 176 • Deprojecting galaxy images 179 4.3 Photometry of Elliptical Galaxies 185 • Radial surface-brightness profiles of elliptical galaxies 185 [> cD galaxies 186 [> Dwarf elliptical galaxies 190

Contents

vii

Centers of elliptical galaxies 191 • Color and line-strength gradients in elliptical galaxies 193 • Shapes of elliptical galaxies 194 [> Ellipticity 194 [> Deviations from ellipses 199 [> Fine structure 201 • Correlations among global parameters of elliptical galaxies 204 [> The Dn 0"0 correlation 209 [> Dwarf ellipti~al galaxies 209 4.4 Photometry of Disk Galaxies 210 • Overall shapes of • Photometric effects of dust 211 disk galaxies 212 • Bulge-disk decomposition 214 • Shapes of bulges 222 • Color and metallicity gradients in disk galaxies 223 • Spiral structure in disk galaxies 224 • Barred galaxies 228 [> Vertical structure of bars 231 [> Rings in SB galaxies 233 [> Dust lanes in SB galaxies 234 [> Lop-sidedness in SB galaxies 234 4.5 Globular cluster systems 235 • Globular cluster luminosity function 236 • Specific frequency of globular clusters 237 • Radial density profiles and shapes 238 • Color distributions 239 4.6 Abnormal galaxies 241 • Starbursting systems 241 • Systems with active galactic nuclei 244 • Host galaxies of AGN 250 • The unified model of AGN 251 Problems 255 [>

5 Evolution of Stars and Stellar Populations 5.1 Stellar evolution and the eM diagram • Placing models in the CM diagram 262 • Features in the CM diagram 263 • Characteristic initial masses 267 • Bounding curves in the CM diagram 274 • Dependence of CM diagrams upon metallicity 276 • The cosmic helium abundance 279 • Simple numerical relations 279 • Star formation 281 • The initial mass function 283 • Pulsating stars 287 [> Classical Cepheid variables 289 [> Mira variables 292 [> W Virginis stars 293 [> RR Lyrae stars 293 5.2 Synthesis of the chemical elements • Basic nuclear physics 296 • Metal production at Mi < Mup 301 • Supernovae 302 [> Metal production by core-collapse supernovae 303 [> Metal production by type Ia supernovae 305 5.3 Models of chemical enrichment

258 259

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• The closed-box model 306 • The leaky-box model 308 • The accreting-box model 313 5.4 Evolution of stellar populations • Analytical results 315 • Numerical models of population evolution 317 Problems

6 Star clusters

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324 327

327 6.1 Globular clusters • Globular cluster stellar photometry 332 • Color-magnitude diagrams 334 I> The main sequence and subgiant branch 335 I> The horizontal branch 337 • Comparison with Theoretical CM diagrams 339 • Globular cluster ages 344 I> Turnoff point ages 344 I> Isochrone fitting 345 I> The .6. V method 346 I> The .6. (B - V) method 347 I> Comparison with the age of the Universe 348 I> Variations in age 349 • Metallicities of globular clusters 350 I> W Cen 351 • The third parameter problem 352 I> Variations in helium abundance 353 I> Variations in other element abundances 353 I> Other candidates 354 • Luminosity functions 354 • Binary stars 359 • Stellar remnants 361 I> White dwarfs 361 I> Neutron stars 362 • Radial profiles 363 I> Large-scale properties 365 I> Luminosity segregation 367 I> Central cusps 369 • Kinematics 371 I> Velocities of individual stars 371 I> Integrated-light kinematics 374 I> Proper motions 375 6.2 Open clusters 377 • Color-magnitude diagrams 381 • The ages and demise of open clusters 384 • Structure and kinematics 386 • Luminosity function 389 Problems 392

7 The Cosmic Distance Scale 7.1 An introduction to cosmology 7.2 Absolute distance estimators • The Baade-Wesselink method 399 I> Application to su• The Sunyaev-Zel"dovich effect 403 pernovae 402 • Distances from time delays 405 I> The ring around Supernova 1987A 406 I> Gravitational lens time delays 407 • Water-maser proper-motions by VLBI 410 7.3 Relative distance estimators • Luminosities of variable stars 415 • Luminosity functions 415 I> Globular clusters 4161> Planetary nebulae 417

394 396 399

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Contents • Novae and supernovae 419 I> Novae 419 I> Type Ia supernovae 420 • Distances from galaxy kinematics 422 I> Spiral galaxies 422 I> Elliptical galaxies 425 • Surface brightness fluctuations 426 7.4 Results • Distances within the Local Group 432 I> Distance to the Galactic center 432 I> Distance to the Large Magellanic Cloud 434 I> Distance to M31 435 • Distances beyond the Local Group 437 I> Distance to the Virgo Cluster 437 I> Peculiar velocity field 439 • The asymptotic Hubble constant 441 • The deceleration parameter and cosmic density 444 I> Standard candles and rulers 444 I> Peculiar velocity field 447 Problems

8 The Interstellar Media of Galaxies

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449 451

8.1 How interstellar matter is detected 452 • Absorption of starlight 452 • Extreme UV and xray observations 459 • Optical emission lines 463 I> Hydrogen lines 463 I> Metal lines 464 • Radio observations 468 I> The 21-cm line of atomic hydrogen 471 I> Rotation transitions of heteronuclear molecules 474 I> Synchrotron radiation 478 I> Radio-frequency bremsstrahlung and recombination lines 480 I> Dispersion and Rotation Measures 481 • ,-ray emission 482 • Radiation by dust 483 8.2 The ISM in Disk Galaxies 488 • Global measures 493 I> ill and H2 in disk galaxies 493 I> Radio-continuum and IR luminosities 496 • Radial density profiles 498 • Azimuthal distributions 500 I> Bars and oval distortions 500 I> Spiral structure 500 I> Lop-sidedness 502 • Velocity fields of disks 505 I> Circular-speed curves 507 I> Kinematic warps 510 I> Oval distortions 512 • SO galaxies 513 • Metalliciti~s of disk galaxies 516 • Magnetic fields 520 • Star formation in disk galaxies 522 8.3 The ISM in elliptical galaxies 525 • X-ray emitting plasma 525 • Cool gas in ellipticals 527 8.4 Intergalactic gas 530 • The Magellanic Stream 530 Problems 533

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Conten.ts

9 The Milky Way's ISM 9.1 The kinematics of differential rotation • The naive (l, v) plot 536 I> Radii and distances from the (l, v) plot 540 • Non-circular motion and the (l, v) plot 541 I> Axisymmetric expansion 541 I> Oval distortions 542 I> Spiral structure 544 I> Random motions 546 9.2 The large-scale distribution of HI and CO • The 21-cm line in emission 549 I> Measuring the spin temperature 553 • CO lines in emission 554 • The Milky Way's circular-speed curve 555 • Radial distributions of HI and CO 559 • Evidence for spiral structure 561 • Vertical distributions of HI and CO 562 I> The middle disk 563 I> The outer disk 565 9.3 Other tracers of the ISM • Diffuse infrared emission 570 • Pulsars and the Galactic magnetic field 574 • Diffuse Ha radiation 576 • Diffuse synchrotron and ,,),-radiation 577 • Diffuse X-rays 579 9.4 The central disk • 21-cm observations 580 • Observations in lines of CO and CS 586 • A dynamical model of the central disk 588 9.5 The nucleus 9.6 Small-scale structure of the ISM • Molecular gas in the Galaxy 598 I> X from virial masses 601 I> X from ,,),-rays 601 I> X from Av 602 Problems

10 Components of the Milky Way 10.1 Gross Structure from Surface Photometry • The Galaxy at optical wavelengths 614 10.2 The bulge • Integrated surface photometry 616 • Evidence for a bar from individual stars 619 • Age and metallicity of the bulge 621 • Bulge kinematics 622 10.3 Kinematics of stars near the Sun • The solar motion 624 • Random velocities of stars 629 I> Vertex deviation 630 I> The Schwarzschild distribution 632 I> Star streams 634 I> Causes of vertex deviation 636 • The Oort constants 637 I> Estimating the Oort constants 641 10.4 The structure of the stellar disk • Ages and metallicities of nearby stars 643 I> Correlations between abundances 643 I> Correlations between age and

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603 606 609 616

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Contents abundance 644 • The old disk clusters 651 • Star counts and the thick disk 651 [> The thick disk 654 • The local mass density of the disk 656 • Distribution of the youngest stars 664 10.5 The halo • The globular cluster system 666 • Field halo stars 670 [> Kinematically selected samples 673 10.6 Galaxy models [> The local circular speed 679 [> Mass models 680 [> Starcount models 682 [> Kinematic models 683 [> Dynamical models 683 10.7 Formation and evolution of the Milky Way • Formation scenarios 684 • Models of the chemical evolution 'of the Milky Way 688 [> Chemical evolution of the halo 688 [> Pre-enrichment 688 Problems

11 Stellar Kinematics in External Galaxies 11.1 Measuring the kinematics of external galaxies • Mean velocities and velocity dispersions 697 • Analysis of line profiles 700 • Position-velocity diagrams and data cubes 705 11.2 The stellar kinematics of elliptical galaxies • Large-scale properties 707 [> Major-axis kinematics 707 [> Detection of dark halos 712 [> Kinematic mapping 713 • Core properties 716 [> Decoupled cores 716 [> Detection of central black holes 717 11.3 The stellar kinematics of disk galaxies • Bulge kinematics 723 • Disk kinematics 724 [> Rotational motion 725 [> Random motions 727 Problems

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Appendices A

Gravitational deflection of light

732

B

Important astronomical catalogs

736

C

Richardson-Lucy deconvolution

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D

Useful numbers

744

References

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Index

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Appendix D: Useful numbersl

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Appendix D: Useful numbers 1 Physical constants Gravitational constant Speed of light Permeability of space Permittivity of space Planck's constant Boltzmann's constant Electron charge Electron volt Proton mass Electron mass Bohr magneton Stefan-Boltzmann constant Thomson cross-section Astronomical Constants Astronomical unit Parsec

G = 6.672(4) X 10- 11 m 3 kg- l s-2 8 C = 2.99792458 X 10 m s-1 (by definition) /-£0 = 4'JI" X 10- 7 H m- l (by definition) EO

= (/-£oc 2)-1

= 8.85418 X 10-12 Fm- l

6.62618(4) X 10- 34 J s n 1.054589(6) x 10-34 J s l 1.38066(4) x 10- 23 J K8.61733 X 10- 5 eV e = 1.602189(5) x 10- 19 coulomb eV = 1.602189(5) X 10- 19 J mp = 1.672649(9) x 10- 27 kg me = 9.10953(5) x 10- 31 kg /-£B = en/2me = 9.27408 x 10- 24 JT-l h= = k= =

0"

O"T

= 'JI"2k 4 /(60n 3 c2 ) = 5.6703(7) x 10-8 W m- 2 K- 4 = e4/(6'JI"E5 m ;c4) = 6.65245(6) x 10- 29 m 2

1 AU = 1pc = = 1 yr = Ho = HOI =

1.49597892(1) X 1011 m 648000/'JI" AU 3.08567802(2) X 1016 m 3.1558149984 X 107 s 100hkms- l Mpc- l where 0.5;S h;S 1 9.78h- l X 109 yr = 1.989(2) X 1030 kg = 1.32712497(1) X 1020 m 3 s-2 = 6.9599(7) X 108 m = 3.826(8) X 1026 W

1 sidereal year (1900.0) Hubble constant Hubble time Solar mass M0 G M0 Gaussian constant Solar radius R0 Solar luminosity (bolometric) L0 Escape speed from Sun v* = J2G M0/ R0 = 617.5 km s-l Solar absolute magnitude Mv = +4.83 MB = +5.48 Earth mass ME!) = 5.976(4) X 1024 kg

Useful relations 1 km S-l ~ 1 pc per million years (actually 1.023) 1 radian = 20p 265 arcsec 1 Taken from Allen (1973), Lang (1980) and Particle Data Group (1984). Numbers given in parentheses indicate one· standard deviation uncertainty in the last digits of the preceding number.