Trends along Hubble Sequence
		• Roberts & Haynes 1994: – Masses from S0 to Scd roughly constant, then decrease, and M/L roughly the same – more next chapter – H I not significant in ellipticals (< 1 in 10000), but is in spirals (0.01 to 0.15 from Sa to Sm) – Total surface density decreases, H I surface density increases – Ellipticals are red, spirals are blue… – H II regions frequency increases monotonically along the sequence (Kennicutt et al. 1989) • Star formation rates appear key to these relations