Hao-Jing Yan

Size Evolution of the Most Massive Galaxies at 1.7 < z < 3 from GOODS NICMOS Survey Imaging

We measure the sizes of 82 massive (M ≥ 1011 M☉) galaxies at 1.7 ≤ z ≤ 3 utilizing deep HST NICMOS data taken in the GOODS North and South fields. Our sample is almost an order of magnitude larger than previous studies at these redshifts, providing the first statistical study of massive galaxy sizes at z > 2, confirming the extreme compactness of these systems. We split our sample into disk-like (n ≤ 2) and spheroid-like (n > 2) galaxies based on their Sersic indices, and find that at a given stellar mass disk-like galaxies at z ~ 2.3 are a factor of 2.6 ± 0.3 smaller than present-day equal-mass systems, and spheroid-like galaxies at the same redshifts are 4.3 ± 0.7 smaller than comparatively massive elliptical galaxies today. At z > 2 our results are compatible with both a leveling off, or a mild evolution in size. Furthermore, the high density (~2 × 1010 M☉ kpc−3) of massive galaxies at these redshifts, which are similar to present-day globular clusters, possibly makes any further evolution in sizes beyond z = 3 unlikely.

A surprisingly high pair fraction for extremely massive galaxies at z∼ 3 in the GOODS NICMOS survey

We calculate the major pair fraction and derive the major merger fraction and rate for 82 massive (M* > 1011xa0M⊙) galaxies at 1.7 1.5 to reliably measure their pair fraction history. We find strong evidence that the pair fraction of massive galaxies evolves with redshift. We calculate a pair fraction of fm= 0.29 ± 0.06 for our whole sample at 1.7 1011xa0M⊙ galaxy experiencing 1.7 ± 0.5 mergers between z= 3 and 0.