Galaxy Formation
	• Thermal history of pregalactic gas can be worked out in detail (and we will do so!). • Density fluctuations tied to temperature fluctuations, revealed finally by COBE, but small. Lots more details to go into here later in course. • Two main ideas: top-down vs. bottom-up. • Need for dark matter (hot or cold) became apparent – normal matter needs help to collapse into galaxies.