Sizing up Lyman-alpha and Lyman Break Galaxies

Understand

We show that populations of high redshift galaxies grow more luminous as they grow in linear size.

• This is because the brightness per unit area has a distinct upper limit due to the self-regulating nature of star-formation.
• As a corollary, we show that the observed increase in characteristic luminosity of Lyman Break Galaxies (L*) with time can be explained by their increase in size, which scales as 1/H(z).
• In contrast, Lyman-alpha selected galaxies have a characteristic, constant, small size between redshift z=2.25 and 6.5.