1	ASTR 5460, Mon. Nov. 8, 2004 The Formation of Galaxies and Large Scale Structures in the Universe Combes et al. chapter 12, also Longair (chapter 11-15) Other: exams due – any discussion? Observing Project reports not graded yet Discuss Proposal Project (another handout) Mini-TAC exercise for next week (handed out Wed.)
2	“Accelerating” into Cosmology
3	Issues of density contrast and growth of structure under gravitational instabilities
4	Recall: Spiral Galaxies -- Stability Jean’s criteria governs “small scale” collapse due to self-gravitation Treated as stability vs. perturbation in an infinite homogeneous medium in equilibrium For fluid with a pressure P = ρ₀v_s², then perturbations with λ > v_s(G ρ₀)^-1/2 = λ_J are unstable. Basically, does the disturbance have time to cross in a freefall time, t_ff = (Gρ)^-1/2?If so, then pressure forces are negligible. The sound crossing time is r/v_s, which gives the λ_J criteria For galaxies, we can write an effective pressure in terms of the velocity dispersion: λ > σ(G ρ₀)^-1/2 = λ_J
5	Jeans Mass and the Growth of Perturbations
6	Jeans Mass and the Growth of Perturbations
7	Longair’s take: Jean’s Instability
8	Longair’s take: Jean’s Instability
9	Jean’s Instability
10	Jeans Mass and the Growth of Perturbations
11	Jeans Mass and the Growth of Perturbations
12	Jeans Mass and the Growth of Perturbations
13	Jeans Mass and the Growth of Perturbations
14	Jean’s Instability in an Expanding Medium
15	Jeans Mass and the Growth of Perturbations
16	Jean’s Instability in an Expanding Medium
17	Other issues
18	Other issues
19	Including Radiation “Sea” of photons. Photon Energy Density is proportional to 1/R⁴. Note that the text has this WRONG. Photon number density changes as 1/R³, but wavelengths stretch out. Anyway, proceeding… Recall the linearized perturbation equation Set y = ρ_x/ρ_γ= R/R(t_eq) where there is an equilibrium time where the two densities are equal.
20	Including Radiation At this equilibrium time
21	What goes wrong with baryon-only cosmologies?
22	Dark Matter and Galaxy Formation
23	Hot Dark Matter
24	Cold Dark Matter
25	Structure Simulations
26	More Simulations From Combes et al., of CDM structure simulations. They kind of work.
27	Growth of Adiabatic Fluctuations Homogeneity scale is D>100 Mpc. What of smaller perturbations? Initial origin unknown. A power spectrum is postulated (as gravity does not have a characteristic scale): δρ/ρ = δM/M = AM ^–^α Significant perturbations on small scales would mean an excess of primordial black holes, and we don’t see much on the largest scales, which means alpha isn’t too large. Adjust the amplitude A to match observation.
28	Growth of Adiabatic Fluctuations Do perturbations affect entropy per baryon? If not, then they are adiabatic: δs/s = 3δT/T – δn_s/n_s = 0 δT/T=1/3 δρ/ρ Whereas for isothermal: T = constant δs/s = δn_s/n_s and no T fluctuations, and the photon to baryon ratio must vary Jeans mass is limit of growth vs. acoustic action When universe was radiation dominated sound speed was order of light speed (divided by root 3).
29	Growth of Adiabatic Fluctuations L_J ~ ct_exp ~ L_horizon This increases with the expansion, until recombination. At this time… Universe becomes matter dominated with density going as 1/R³ and 1/T_γ³. Sound speed goes as 1/R, and so Jeans’ mass goes as R^-3/2.
30	Growth of Adiabatic Fluctuations
31	Fluctuation Spectrum at Recombination Contrasting possible isothermal and adiabatic scenarios. See Rees (1984) for more details.
32	Spectrum of Initial Fluctuations
33	Evolution of a pertubation
34	Nonlinear Evolution Pancake model: HDM or adiabatic baryons you get a characteristic collapse scale. “Azita’s House of Pancakes.” Galaxies form from pancake fragmentation. Heirarchical scenarios. Isothermal fluctuations or CDM gives no cutoff at small scales. Some details in the text for particular cosmologies (which we will wait on). Numerical simulations pay a serious role here. More details in text, but we’re rush, rush, rush at this point. Feel the knowledge flooding your brain, but don’t drown!
35	What this might look like Movie simulation of galaxy formation via assembly of small pieces (courtesy of Space Telescope Science Institute):
36	The Hubble Deep Field
37	Evidence for “Hierarchical” Galaxy Formation from the HDF
38	Structure Simulations
39	Galaxies and the Exgal background DIRECTLY related to models by the fact of galaxy formation and evolution. Everything must be self-consistent or the model must be discarded.
40	Peculiar Velocities
41	Quest for Primordial Galaxies: Photometric/SED fitting
42	Photometric Vs. Spec. redshifts
43	Color-Color Diagram
44	UV Luminosity Density vs. z Cf. Boyle and Terlevich 1998 that compared quasars and stars. After Madau et al. 1996 (called the “Madau plot” even) Must reconcile with galaxy formation + evolution scenarios. Right? Highest redshifts unclear, but some rise and then steep fall off. Epoch of galaxy formation still unclear.
45	Coming up We’ve talked around the crux of things: cosmology. How does spacetime itself evolve? How is redshifted related to distance, look-back time, etc.? Will look at some specific formulations of distances and more (Hogg et al. pedagogical stuff) and classical formations, plus latest WMAP results.