Star formation trends in high-redshift galaxy surveys: the elephant or the tail?

Star formation rate and accummulated stellar mass are two fundamental physical quantities that describe the evolutionary state of a forming galaxy. Two recent at-tempts to determine the relationship between these quantities, by interpreting a sam-ple of star-forming galaxies at redshift of z ∼ 4, have led to opposite conclusions. We use a model galaxy population to investigate possible causes for this discrepancy and conclude that minor errors in the conversion from observables to physical quantities can lead to major misrepresentation when applied without awareness of sample se-lection. We also investigate, in a general way, the physical origin of the correlation between star formation rate and stellar mass within hierarchical galaxy formation theory.