Models of Disk Evolution: Confrontation with Observations

We present simple models for disk evolution based on two differentapproaches: a forward approach based on predictions generic to hierarchicalmodels for structure formation (e.g., Mo, Mao, & White 1998) and a backwardsapproach based on detailed modeling of the Milky Way galaxy (e.g., Bouwens,Cayon, & Silk 1997). We normalize these models to local observations andpredict high-redshift luminosities, sizes, circular velocities, and surfacebrightnesses. Both approaches yield somewhat similar predictions for size,surface brightness, and luminosity evolution though they clearly differ in theamount of number evolution. These predictions seem to be broadly consistentwith the high-redshift observations of Simard et al. (1999), suggesting thatthe B-band surface brightness of disks has indeed evolved by ~1.5 mag from z~0to z~1 similar to the models and is not an artifact of selection effects aspreviously claimed. We also find a lack of low surface brightness galaxies inseveral high redshift samples relative to model predictions based on localsamples (de Jong & van der Kruit 1994; Mathewson, Ford, & Buchhorn 1992).