International Herald Tribune, November 1, 1907

Transcription

1 Recently reports have been current in certain newspapers that Mr. Thomas A. Edison, the inventor, has at last perfected the storage battery, and that within a few months electrically propelled vehicles, costing little to buy and next to nothing to maintain, will be on the market. The same story has appeared regularly for years and yet matters do not appear to have advanced much. International Herald Tribune, November 1, 1907

2 Recently reports have been current in certain newspapers that Mr. Thomas A. Edison, the inventor, has at last perfected the storage battery, and that within a few months electrically propelled vehicles, costing little to buy and next to nothing to maintain, will be on the market. The same story has appeared regularly for years and yet matters do not appear to have advanced much. International Herald Tribune, November 1, 1907

3 Galaxies Mid 18th century, Kant and Wright suggested that the Milky Way is a finite system of stars. Turns out this is accurate. Kant went on to suggest that the very faint elliptical nebulae might be similar collections of stars, well beyond the boundaries of the Milky Way. He called these Island Universes. Immanuel Kant ( ) Nebulae Virgo Cluster of Galaxies sky.google.com

4 Charles Messier cataloged 103 fuzzy objects while looking for comets. This is still referred to as the Messier Catalog. Objects are given as M#, such as those below. It contains planetary nebulae, spiral and elliptical nebulae. Charles Messier ( ) Virgo Cluster of Galaxies sky.google.com

5 Charles Messier cataloged 103 fuzzy objects while looking for comets. This is still referred to as the Messier Catalog. Objects are given as M#, such as those below. It contains planetary nebulae, spiral and elliptical nebulae. M91 Charles Messier ( ) M90 M88 M86 M84 M87 M58 M89 Virgo Cluster of Galaxies sky.google.com

6 Cataloging Nebulae Herschel expanded the cataloging of nebulae, succeeded by his son, Sir John Herschel, included objects in the Southern Hemisphere (viewed from South Africa). Their New General Catalog (NGC) contains nearly 8000 objects, but the nature of these objects was an open question. William Herschel Sir John Herschel In 1845, William Parsons, built the Leviathan, telescope with 72-inch (1.8m) collecting power. William Parsons Third Earl of Rosse ( )

7 Cataloging Nebulae Parsons showed that some nebulae have spiral structure (henceforth known as spiral nebulae ). He argued they may be rotating. This was confirmed later by Vesto Slipher in 1912 who saw rotation in the Doppler-shifts of a spectral lines in these objects.

8 Cataloging Nebulae Parsons showed that some nebulae have spiral structure (henceforth known as spiral nebulae ). He argued they may be rotating. This was confirmed later by Vesto Slipher in 1912 who saw rotation in the Doppler-shifts of a spectral lines in these objects. HST Image

9 The Nature of Galaxies The Great Shapley-Curtis Debate At beginning of 20th century, half the astronomers thought the nebulae were objects in the Milky Way Galaxy. half thought they were Island Universes. On April 26, 1920 at the National Academy of Sciences in Washington, DC, Harlow Shapley (Mt. Wilson Observatory) debated Heber D. Curtis ( , Lick Observatory). Shapley - Nebulae are members of our Galaxy Major point: If Andromeda nebulae were as large as the Milky Way (100 kpc), then its angular size (3 o x 1 o ) would imply such a great distance (2 Mpc) that the nova he observed in Andromeda would be much, much more luminous than anything observed in the Milky Way. Curtis - Nebulae are Island Universes like the Milky Way Novae showed that spiral nebulae are at least 150 kpc away to have same luminosities as those in the Milky Way. Doppler velocities (> km/s) of spiral nebulae implied they would not remain bound to the Galaxy. If transverse velocities were just as high and they are in the Galaxy, we should be able to measure their proper motion (which we can t).

10 The Nature of Galaxies The Great Shapley-Curtis Debate Debate was settled by Edwin Hubble in Using the new 100-inch telescope on Mt. Wilson (Caltech), he detected Cepheid Variable stars in M31 (Andromeda Nebula). He measured the distance to Andromeda to be 285 kpc - well outside the Milky Way. (Current measurement is 770 kpc.) Spiral Nebulae (and Elliptical Nebulae) are Island Universes, other galaxies like the Milky Way. Edwin Hubble Hubble went on in his paper Extra-Galactic Nebulae to propose that galaxies (nebulae) be classified as ellipticals, spirals, and irregulars. This is today known as the Hubble Sequence.

11 Hubble arranged his sequence on a tuning fork diagram. Originally he (incorrectly) hypothesized that galaxies evolved from the Left to the Right of this sequence. Early types Later types Hubble went on in his paper Extra-Galactic Nebulae to propose that galaxies (nebulae) be classified as ellipticals, spirals, and irregulars. This is today known as the Hubble Sequence.

12 Hubble subdivided spiral sequences into Sa, Sab, Sb, Sbc, Sc (Scd, Sd), and SBa, SBab, SBb, SBbc, SBc (SBcd, SBd). Two characteristics dictate this (1) the bulgeto-disk ratio and (2) how tighltly wound the spiral arms are. Spirals with high bulge-to-disk ratios (Lbulge/Ldisk > 0.3) and tightly wound arms are the a subclass. The lower sequence has nuclear bars.

13 Hubble subdivided spiral sequences into Sa, Sab, Sb, Sbc, Sc (Scd, Sd), and SBa, SBab, SBb, SBbc, SBc (SBcd, SBd). Two characteristics dictate this (1) the bulgeto-disk ratio and (2) how tighltly wound the spiral arms are. Spirals with high bulge-to-disk ratios (Lbulge/Ldisk > 0.3) and tightly wound arms are the a subclass. The lower sequence has nuclear bars. Irregulars: galaxies lacking organized structure.

14 Ellipticals

15 Spirals

16 Spirals

17 Barred Spirals

18 Irregulars

19 Rotation Curves of Spiral Galaxies Spiral galaxies do rotate. Measure rotation curve by measuring doppler shifted light from spectral lines as a function of galacticentric distance. Redshifted Wavelength Blueshifted 656 nm (Hα)

20 Rotation Curves of Spiral Galaxies Clemens 1985, ApJ, 295, 422 Rotation curve for our Galaxy. Strange thing is... rotation curve is flat beyond the Solar circle, R0 = 8.5 kpc.

21 Rotation Curves of Spiral Galaxies Observations! v ~ constant (r 0 )

22 Rotation Curves of Spiral Galaxies Rubin, Thonnard, & Ford, 1978, ApJ, 225, L107 Vera Rubin (b1928) Responsible for most of the work on the galaxy rotation rate problem.

23 This is the Dark Matter distribution in galaxies. Navarro-Frenk-White (NFW) profile: For Spiral Galaxies, we can extend the relation between Mass and Velocity over the whole galaxy using the maximum rotational velocity, V, at R=size of galaxy: 2

24 Rotation Curves of Spiral Galaxies There is a relationship between the Maximum rotation velocity and the Galaxy s Absolute Magnitude (Luminosity).

25 Rotation Curves of Spiral Galaxies There is a relationship between the Maximum rotation velocity and the Galaxy s Absolute Magnitude (Luminosity). This relation is now referred to as the Tully- Fisher Relation, after Brent Tully and Richard Fisher who first determined it in They derived: MB = log10 ( vmax ) (Sa) MB = log10 ( vmax ) (Sb) MB = log10 ( vmax ) (Sc) As with other quantities, this relation is tightened when using Infrared magnitudes: MH = -9.50( log10 VR ) Rubin et al. 1985, ApJ, 289, 81

26 Rotation Curves of Spiral Galaxies Rubin et al. 1985, ApJ, 289, 81

27 Rotation Curves of Spiral Galaxies Milky Way Rubin et al. 1985, ApJ, 289, 81

28 Rotation Curves of Spiral Galaxies Milky Way Vera Rubin, measuring spectra Rubin et al. 1985, ApJ, 289, 81

29 Luminosity-Metallicity Relation Zaritsky, Kennicutt, Huchra 1994, ApJ, 420, 87 Milky Way Sun Metallicity of stars Sun Metallicity (metal fraction) of gas More luminous galaxies have high metallicities. The more luminous galaxies have had more metal enrichment.

30 More luminous means more mass to first order. Higher-mass galaxies have had more metal enrichment. Mass-Metallicity Relation Tremonti et al. 2004, ApJ, 613, 898

31 Ellipticals

32 Elliptical Galaxies M 87 Giant Elliptical Mass ~ 3 x M Size is ~10 x diameter of Milky Way

33 Elliptical Galaxies Recall that the gravitational potential of a collection of points with total mass M and radius R is: And the Kinetic energy is : Where σ 2 is the velocity dispersion (average velocity of all particles in all dimensions). Using the Virial Theorem 2K + U = 0, and solving for the velocity dispersion: Solving for the Mass gives: What the heck is σ? This is the velocity dispersion, which is the average of radial velocities in a galaxy.

34 Elliptical Galaxies What the heck is σ? This is the velocity dispersion, which is the average of radial velocities in a galaxy. elliptical galaxy (made of lots of stars on radial, keplerian orbits) telescope continuum Normally, measure velocity dispersion in only 1-degree of freedom, so the mass will be: flux Δλ Absorption line: many stars at different velocities wavelength λ0

35 Elliptical Galaxies Recall that the gravitational potential of a collection of points with total mass M and radius R is: And the Kinetic energy is : Where σ 2 is the velocity dispersion (average velocity of all particles in all dimensions). Using the Virial Theorem 2K + U = 0, and solving for the velocity dispersion: Assume that the Mass-to-light ratio is constant over the galaxy: Introduce the surface brightness (luminosity per area), and assume its constant (not necessarily true, but OK for now) : Combining the above two relations gives: Solving for L gives:

36 Elliptical Galaxies All elliptical galaxies have a relationship between their central radial-velocity dispersion, σ, and their absolute magnitude. This is the Faber-Jackson relation, L ~ σ 4. Dwarf Ellipticals Mass ~ M Diameter ~ 1-10 kpc Normal Ellipticals Mass ~ M Diameter ~ kpc cd Ellipticals Mass ~ M Diameter ~ kpc Sandra Faber b This is a consequence of the Virial Theorem.

37 giant & normal Ellipticals dwarf Ellipticals cd Ellipticals Tighter fit to the data uses the radius (size) of the galaxy. This is the fundamental plane of elliptical galaxies. L ~ σ 2.65 re The effective radius is related to the surface brightness, which is not constant over all types of Ellipticals. You can rewrite the fundamental plane as re ~ σ 1.24 Ie -0.82

38 Supermassive Blackholes in Galaxies M 87 Giant Elliptical Mass ~ 3 x M Size is ~10 x diameter of Milky Way

39 Supermassive Blackholes in Galaxies M 87 Giant Elliptical Mass ~ 3 x M Size is ~10 x diameter of Milky Way Jet of material emitted by nucleus

40 Supermassive Blackhole in M87 rotational velocity velocity dispersion, σ FWHM / 2.35 Macchetto et al Modeling gives Virial Mass of (3.2+/-0.9) x 10 9 M within r < 0.05 = 3.5 pc. (This density is 1.8 x 10 7 M pc -3. Recall, the solar neighborhood has 0.05 M pc -3.)