We present COSMOS-Drift And SHift ( DASH ) , a Hubble Space Telescope WFC3 imaging survey of the COSMOS field in the H _ { 160 } filter .
The survey comprises 456 individual WFC3 pointings corresponding to an area of 0.49 deg ^ { 2 } ( 0.66 deg ^ { 2 } when including archival data ) and reaches a 5 \sigma point-source limit of H _ { 160 } = 25.1 ( 0 \farcs 3 aperture ) .
COSMOS-DASH is the widest HST/WFC3 imaging survey in H _ { 160 } filter , tripling the extragalactic survey area in the near-infrared at HST resolution .
We make the reduced H _ { 160 } mosaic available to the community .
We use this dataset to measure the sizes of 162 galaxies with \log ( M _ { \star } / M _ { \odot } ) > 11.3 at 1.5 < z < 3.0 , and augment this sample with 748 galaxies at 0.1 < z < 1.5 using archival ACS imaging .
We find that the median size of galaxies in this mass range changes with redshift as \langle { } r _ { eff } \rangle = ( 10.4 \pm 0.4 ) \times ( 1 + z ) ^ { ( -0.65 \pm 0.05 ) } kpc .
Separating the galaxies into star forming and quiescent galaxies using their restframe U - V and V - J colors , we find no statistical difference between the median sizes of the most massive star-forming and quiescent galaxies at \langle z \rangle = 2.5 : they are 4.9 \pm 0.9 kpc and 4.3 \pm 0.3 kpc respectively .
However , we do find a significant difference in the Sèrsic index between the two samples , such that massive quiescent galaxies have higher central densities than star forming galaxies .
We extend the size-mass analysis to lower masses by combining it with the 3D-HST/CANDELS sample of , and derive empirical relations between size , mass , and redshift .
Fitting a relation of the form r _ { eff } = A \times m _ { \star } ^ { \alpha } , with m _ { \star } = M _ { \star } / 5 \times 10 ^ { 10 } M _ { \odot } and r _ { eff } in kpc , we find \log A = -0.25 \log ( 1 + z ) +0.79 and \alpha = -0.13 \log ( 1 + z ) +0.27 .
We also provide relations for the subsamples of star forming and quiescent galaxies .
Our results confirm previous studies that were based on smaller samples or ground-based imaging .