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

Table of contents :
Title Page
Contents
Preface
1 Galaxies: an overview
1.1 Introduction
1.2 A brief history of galactic astronomy
2 Astronomical Measurements
2.1 Positions, motions and coordinate systems
2.2 Distances determined from velocities
2.3 Magnitudes and colors
2.4 Gravitational lensing
2.5 Archival data and catalogs
Problems
3 The Properties of Stars
3.1 The masses of stars
3.2 The radii of stars
3.3 Classification of stars
3.4 Physical interpretation of stellar spectra
3.5 Color-magnitude diagrams
3.6 The stellar luminosity function
3.7 Interstellar dust
Problems
4 Morphology of Galaxies
4.1 Morphological classification of galaxies
4.2 Surface Photometry of Galaxies
4.3 Photometry of Elliptical Galaxies
4.4 Photometry of Disk Galaxies
4.5 Globular cluster systems
4.6 Abnormal galaxies
Problems
5 Evolution of Stars and Stellar Populations
5.1 Stellar evolution and the CM diagram
5.2 Synthesis of the chemical elements
5.3 Models of chemical enrichment
5.4 Evolution of stellar populations
Problems
6 Star clusters
6.1 Globular clusters
6.2 Open clusters
Problems
7 The Cosmic Distance Scale
7.1 An introduction to cosmology
7.2 Absolute distance estimators
7.3 Relative distance estimators
7.4 Results
Problems
8 The Interstellar Media of Galaxies
8.1 How interstellar matter is detected
8.2 The ISM in Disk Galaxies
8.3 The ISM in elliptical galaxies
8.4 Intergalactic gas
Problems
9 The Milky Way's ISM
9.1 The kinematics of differential rotation
9.2 The large-scale distribution of H-I and CO
9.3 Other tracers of the ISM
9.4 The central disk
9.5 The nucleus
9.6 Small-scale structure of the ISM
Problems
10 Components of the Milky Way
10.1 Gross Structure from Surface Photometry
10.2 The bulge
10.3 Kinematics of stars near the Sun
10.4 The structure of the stellar disk
10.5 The halo
10.6 Galaxy models
10.7 Formation and evolution of the Milky Way
Problems
11 Stellar Kinematics in External Galaxies
11.1 Measuring the kinematics of external galaxies
11.2 The stellar kinematics of elliptical galaxies
11.3 The stellar kinematics of disk galaxies
Problems
Appendices
A: Gravitational deflection of light
B: Important astronomical catalogs
C: Richardson-Lucy deconvolution
D: Useful numbers
References
Index

Citation preview

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

xii 1 1

2

26 27

38

46

62 67 74

Contents

vi

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

296

306

Contents

viii

• 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

314

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

414

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

ix

429

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

x

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

535 536

549

570

580

594 597

603 606 609 616

624

643

xi

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

666

678

684

690 693 694

707

722

730

Appendices A

Gravitational deflection of light

732

B

Important astronomical catalogs

736

C

Richardson-Lucy deconvolution

743

D

Useful numbers

744

References

745

Index

777

Appendix D: Useful numbersl

744

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.