2015ApJ...804..103K

We investigate the sizes of z ∼ 6-8 dropout galaxies using the complete data of the Abell 2744 cluster and parallel fields in the Hubble Frontier Fields program. By directly fitting light profiles of observed galaxies with lensing-distorted Sérsic profiles on the image plane with the glafic software, we accurately measure intrinsic sizes of 31 z ∼ 6-7 and 8 z ∼ 8 galaxies, including those as faint as M_UV~= -16.6. We find that half-light radii r_e positively correlates with UV luminosity at each redshift, although the correlation is not very tight. The largest (r_e > 0.8 kpc) galaxies are mostly red in UV color while the smallest (r_e < 0.08 kpc) ones tend to be blue. We also find that galaxies with multiple cores tend to be brighter. Combined with previous results at 2.5 ≲ z≲ 12, our result confirms that the average r_e of bright ((0.3-1)L_z=3^*) galaxies scales as r_e ∝ (1+z)^–m with m = 1.24 ± 0.1. We find that the ratio of r_eto virial radius is virtually constant at 3.3±0.1% over a wide redshift range, where the virial radii of hosting dark matter halos are derived based on the abundance matching. This constant ratio is consistent with the disk formation model by Mo et al. with j_d ∼ m_d, where j_d and m_d are the fractions of the angular momentum and mass within halos confined in the disks. A comparison with various types of local galaxies indicates that our galaxies are most similar to circumnuclear star-forming regions of barred galaxies in the sense that a sizable amount of stars are forming in a very small area.