Major Topics. J.M. Lattimer AST 346, Galaxies, Part 1

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1 Major Topics 1. Introduction Stars, the Milky Way, Other Galaxies, Cosmology 2. The Galaxy and its Components Luminosity/Mass Functions, Distances, Clusters, Rotation 3. The Interstellar Medium Gas, Dust, Emission and Absorption 4. Galactic Dynamics Gravity, Encounters, Epicycles, Boltzmann Equation 5. The Local Group 6. Spiral and S0 Galaxies Starlight Distribution, Gas Motions, Spiral Structure, Bulges 7. Elliptical Galaxies Photometry, Motions, Dark Matter, Black Holes 8. Galaxy Groups and Clusters Galaxy Formation, Intergalactic Matter and Gravitational Lensing 9. The Large Scale Distribution of Galaxies Cosmology, Growth of Structure 10. Active Galaxies and Pre-Galactic History Active Galactic Nuclei, Jets, Intergalactic Clouds, the First Galaxies

2 Stars Main Sequence Spectra metal 4000Å break CH H neutral Balmer lines Balmer jump 3646Å H nearly totally ionized Paschen jump 8250Å

3 Stars A Dwarf, Giant and Supergiant Spectra Effect of gravity on line width the Stark effect broad Balmer lines narrow Balmer lines

4 Stars Basic Relations for Main Sequence Stars Masses between 0.08 M and 100 M Radii between 0.1 R and 25 R ( M R R M ) 0.7 ) 5 ( M M (M M M ), L L ( ) 3.9 L L M (M 10M M ) ( ) 2.2 M L 50L M (M 10M ) ( ) ( ) ( ) 2.5 ( M τ MS τ L M MS, M L 10Gyr M 10Gyr L ( ) [ ( )] 2 M M log(τ MS /Gyr) log M log M M V, = 4.83, M B, = 5.48, M K, = 3.31, M I, = 4.11 M bol, = 4.76, L = erg s 1, T eff, = 5780K L ) 5/7

5 Abundances [ ] [A/B] = log (A/B) 10 (A/B)

6 Photometry F BP = T 0 BP,λ F λ dλ F λeff T 0 BP,λ dλ F λeff λ BP Sky emission from La Palma m 2 m 1 = 2.5 log 10 ( F1 F 2 ) ( ) FV m BP = 2.5 log,0 λ BP 10 F BP F V, erg s 1 cm 2 Å 1 m BP = 21.1( ) λ +2.5 log BP 10 F BP log 10 F λeff T BP (λ) A0 F λ

Milky Way Disc stellar mass: 6 1010 M Halo stellar

Bulge stellar mass: 2 1010 M Bulge luminosity: 5

7 Milky Way Disc stellar mass: M Halo stellar mass: M M BH Disc luminosity: L Bulge stellar mass: M Bulge luminosity: L 8.5 kpc HI J.M. Lattimer AST 346, Galaxies, Part 1

8 Gas and Dust in the Milky Way Solar neighborhood: 1 star per 10 pc 3, 1 atom per cm 3 H II region: ionizing photons λ < 912 Å, E γ > 13.6 ev Emission timescale typically 10 8 s Collisional excitation A + B A + B, A A + hν Forbidden line: collisons rare (gas density low), timescale 1 s Fine structure transition: spin-orbit coupling in atoms, 1/137 2 less energy: far-infrared Hyperfine transition: nuclear spin coupling with electron spin, 2000 times less energy than fine structure: mm and radio Spin flip 21 cm radiation of H I. Takes about 11 Myr to spontaneously transition to ground state. Collision times of order thousands of years. Molecular emission from electronic, vibrational and rotational transitions CO emission (1.3 mm, 2.6 mm) is strongest after H 2 OH (1.7 GHz) and H 2 O (22 GHz) masing Continuum radiation (free-free or bremstrahlung, and synchotron) from ionized gas Dust absorption (optical and UV) and emission (infrared)

9 21 cm Emission Strength of 21 cm emission depends on collision rate. In general, rate = density cross section velocity. T 100 K. m H v 2 H/2 = 3kT /2, v H 1.6 km s 1 Cross section of a sphere with a radius equal to the Bohr radius a 0 = c/(αm e c 2 ) = /0.511 fm = 50Å is πa0 2. The inverse collision rate is ( ) ( nh πa0v 2 ) 1 1 cm K H = 3000 T n H yr. An H atom in the upper level (electron and proton spins aligned) spontaneously decays with a halflife of 11 Myr. Since the energy difference corresponding to 21 cm emission is much smaller than T, collisions drive the abundances of the two states to equilibrium. The population ratio upper/lower is 3. So the emission rate of 21 cm radiation is (3/44)n H photons per Myr, independent of T.

10 Dust Absorption Dust is about 1% of the interstellar mass, primarily in the form of silicates and carbon with sizes r d 0.1µm. For radiation with wavelengths smaller than this size, absorption and scattering are quite efficient, so the effective cross section is πrd 2. Long wavelength light is scattered less efficiently, κ λ 1, leading to preferential removal of blue light and reddenning. The number density n d of dust grains is df λ dx n d m d = 0.01n H m H, = κρf λ = F λ l, n d =.01 3n Hm H 4πρ d r 3 d which is about cm 3 if ρ d 1 g cm 3. For uniformly distributed dust, the flux is diminished with path length: ) pc l = ( ( n d πrd 2 ) 1 rd µm with l the mean free path. Thus, for a path length x l, F λ is decreased by a factor e. The column density of hydrogen over a path length x is ( N H = n H x = n ) ( ) H x 1 cm 3 cm 2. 1 kpc

11 Galactic and Sky Coordinates Sun-centered Galactic-centered

12 Other Galaxies 100 L MW, 300 kpc 10 L MW, 30 kpc 0.1 L MW

13 Galaxy Photometry Surface brightness I BP (x), measured in L BP pc 2 or mag BP arcsec 2. Observed area on galaxy is D 2, distance to galaxy is d, α 2 = (D/d) 2 is angular area observed on sky. I BP (x) = F BP(x) α 2 = L BP(x)/4πd 2 (D/d) 2 which is independent of d! Centers of galaxies: I B 18 mag arcsec 2 = 4000L B pc 2 or I R 16 mag arcsec 2. Galactic discs have I B 27 mag arsec 2 1 L B pc 2. For comparison, the background brightness of the night sky is about I B = 22.7 mag arsec 2. Sky emission Las Palma Sky emission Mauna Kea

14 Numbers of Galaxies Number of galaxies between luminosities L and L + dl (Schechter function): Φ(L)dL = n ( ) α ( ) L L exp dl L L L For the bandpass B J, α 0.5, n = 0.02h 3 Mpc Mpc 3, L h 2 L L. For α 1, total number Φ(L)dL for L 0. L The luminosity density in each luminosity interval dl is ρ L (L) = Φ(L)L which peaks near L. The total luminosity density is ρ L = 0 Φ(M) ρ M (M) Φ(L)LdL = n L Γ(α + 2) h L Mpc 3. For the K band, ρ L h L Mpc 3.

15 Hubble s Law V r = H 0 d, d = h 1 ( V r 100 km s 1 ) Mpc, h = H km s 1 Mpc 1 When d determined from V r, L h 2, n h 3, M V 2 r d h 1. Brightest galaxies in rich clusters V r = H 0 d + V pec dm V = 5d log 10 z V r cz d = 3h 1 z Gpc

16 Cosmic Parameters Hubble time t H = 1 H 0 = 9.78h 1 Gyr Age of universe in the standard model (Ω Λ = 0.7, Ω m = 0.3) Critical density t H = H 0 = 9.43h 1 Gyr ρ crit (now) = 3H2 0 8πG = h 2 g cm 3 = h 2 M Mpc 3

17 The Big Bang Planck epoch: t < s GR predicts gravitational singularity before this, but quantum effects prevent it. Grand unification epoch: s < t < s Gravitation separates from the fundamental gauge interactions Inflationary epoch: s < t < s Universe flattened by homogenous, isotropic rapid expansion, triggered by separation of strong force from electroweak forces, resulting in a primordial spectrum of nearly scale-invariant fluctuations. Potential energy of the inflation field decays into a hot, relativistic plasma. Electroweak epoch: s < t < s Production of W and Z bosons and Higgs bosons. Baryogenesis Universe becomes asymmetric with respect to baryons and anti-baryons. Why?

18 The Big Bang Quark epoch: s < t < 10 6 s Fundamental particles acquire mass (Higgs mechanism), quarks too hot to bind into hadrons Hadron epoch: 10 6 s < t < 1 s Quark-gluon plasma cools and hadrons form, neutrinos decouple. Lepton epoch: 1 s< t < 10 s Majority of hadrons and anti-hadrons annihilate, leaving leptons and anti-leptons to dominate mass, which themselves finally annihilate. Small residues of hadrons and leptons survive. Photon epoch: 10 s< t < 0.38 Myr Universe energy dominated by photons Nucleosynthesis: 3 m< t <20 m Protons and neutrons fuse, neutrons decay, forming D and He, Li, and Be isotopes.

Nucleosynthesis Neutrons are more massive than protons by 1.293 MeV, resulting in a proton excess: n/p = e (1.293 MeV/kT ). Neutrinos decouple at t = 1 s, T = 0.8 MeV.

Therefore n/p = 1/7 and He/H=1/12. By mass, Y /X = 1/3. Y is insensitive to n B, but D/H is very sensitive. D forms easily, but He requires weak interactions.

19 Nucleosynthesis Neutrons are more massive than protons by MeV, resulting in a proton excess: n/p = e (1.293 MeV/kT ). Neutrinos decouple at t = 1 s, T = 0.8 MeV. Neutrons freeze out with n/p 1/5. Neutrons have a finite lifetime, τ n 886 s. After 20 minutes, when fusion terminates, only 1/4 are left. These become bound in He nuclei. Therefore n/p = 1/7 and He/H=1/12. By mass, Y /X = 1/3. Y is insensitive to n B, but D/H is very sensitive. D forms easily, but He requires weak interactions. If n B is relatively small, D/H becomes large. If n B is relatively large, D/H becomes small. Thus, D/H is a sensitive measure of Ω B. Abundances of other light nuclei like 3 He, 6 Li and 7 Li can also be used to estimate n B. The estimates of all but 7 Li converge on 0.02 < Ω B h 2 <

38 Myr Protons and electrons form neutral H, opacity decreases, photons decouple and form the CMB. Now redshifted by factor 1 + z 1100 to 2.73 K.

20 The Big Bang Matter domination: t < 0.07 Myr Jeans length falls below fluctuation masses and smallest structures form. Cold dark matter dominates (but when did that form?). Recombination: t = 0.38 Myr Protons and electrons form neutral H, opacity decreases, photons decouple and form the CMB. Now redshifted by factor 1 + z 1100 to 2.73 K. Dark ages: 150 Myr < t < 500 Myr Only emitted radiation is 21 cm. Structure formation, reionization: 500 Myr< t < 1 Gyr Quasars and Pop III stars (not yet observed) form and re-ionize surroundings. Sub-galactic object with z = 10.2, t = 480 Myr, observed Jan Star-forming galaxies observed at t = 500 Myr.

21 The CMB fluctuations The small fluctuations in the CMB remaining after subtraction of the Doppler effect are acoustic oscillations due to a competition between the gravitational attraction of the baryons and the smoothing of photons. The angular scale of the first peak depends on the curvature of the universe. The next peak depends on n B. The third peak depends on the dark matter density. They depend on Ω Λ and Ω B. Ω Λ = 0.7, Ω m = 0.3 Ω Λ = 0.85, Ω m = 0.15 Ω Λ = 0, Ω m = 0.3

22 The CMB and the Sun The radiation from the CMB is far larger than that from the extragalactic background at IR, optical, UV, X-ray and γ-ray energies. The CMB is uniform to within 1 part in 10 5 with the exception (besides the annual motion of the Earth about the Sun) of a dipole anisotropy in the direction l = 265, b = 48, with an amplitude of 0.1% (hottest in that direction). The higher temperature represents a Doppler blue shift ( T (θ) = T CMB 1 + V ) c cos θ. This gives V = 370 km s 1. After correction for the solar motion in the Galaxy and the Milky Way s motion relative to nearby galaxies, one has V pec 600 km s 3. The origin of this large motion is not understood.

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Astr 2320 Thurs. May 7, 2015 Today s Topics Chapter 24: New Cosmology Problems with the Standard Model Cosmic Nucleosynthesis Particle Physics Cosmic

Astr 2320 Thurs. May 7, 2015 Today s Topics Chapter 24: New Cosmology Problems with the Standard Model Cosmic Nucleosynthesis Particle Physics Cosmic Inflation Galaxy Formation 1 Chapter 24: #3 Chapter