The host haloes of Lyman-break galaxies and submillimetre sources

We use the observed sizes and star formation rates of Lyman-break galaxies (LBGs) to understand their properties expected in the hierarchical scenario of galaxy formation. The observed size distribution constrains the masses (or circular velocities) of the host haloes of LBGs from below, because small haloes can only host galaxies with small sizes. The observed star formation distribution constrains the masses from above, because the number density of massive haloes in duty cycle is too low to host all the observed galaxies. Assuming a flat CDM model with a cosmological constant (Omega (Lambda) = 0.7), we find that consistency with observations requires the circular velocities of LBG host haloes to be in the range 100-300 km s(-1). The star formation in these haloes is efficient; a large fraction of all the gas in them can form stars on a time-scale of about 10-20 per cent of the Hubble time at redshift of 3. The predicted comoving correlation length of these objects is similar to3 h(-1) Mpc, and the predicted velocity dispersion of their stellar contents is typically 70 km s(-1). The same prescription applied to larger haloes in the CDM cosmogony predicts the existence of galaxies with star formation rates of similar to 1000 M-circle dot yr(-1) at redshift z similar to 3. We explore the possibility of identifying these galaxies to be the bright submillimetre (submm) sources detected by SCUBA. The model predicts that the host haloes of these submm sources are massive, with typical circular velocity of similar to 350 km s(-1). The typical star formation timescale in these systems is about 10 per cent of the Hubble time at redshift 3, and the comoving number density of galaxies (in their duty cycle) is 10(-5)-10(-4) h(3) Mpc(-3). These galaxies are predicted to be strongly correlated, with a comoving correlation length of similar to7 h(-1) Mpc. They are also predicted to be strongly correlated with LBG population at the same redshift, with a cross-correlation length of 4-5 h(-1) Mpc. The descendants of the bright submm sources should reside in clusters of galaxies at the present time, and it is likely that these objects are the progenitors of giant ellipticals.