Recently , a small sample of six z \sim 9 - 10 candidates was discovered in CANDELS that are \sim 10 - 20 \times more luminous than any of the previous z \sim 9 - 10 galaxies identified over the HUDF/XDF and CLASH fields .
We measure the sizes of these candidates to map out the size evolution of galaxies from the earliest observable times .
Their sizes are also used to provide a valuable constraint on whether these unusual galaxy candidates are at high redshift .
Using galfit to derive sizes from the CANDELS F160W images of these candidates , we find a mean size of 0 \farcs 13 \pm 0 \farcs 02 ( or 0.5 \pm 0.1 kpc at z \sim 9 - 10 ) .
This handsomely matches the 0.6 kpc size expected extrapolating lower redshift measurements to z \sim 9 - 10 , while being much smaller than the 0 \farcs 59 mean size for lower-redshift interlopers to z \sim 9 - 10 photometric selections lacking the blue IRAC color criterion .
This suggests that source size may be an effective constraint on contaminants from z \sim 9 - 10 selections lacking IRAC data .
Assuming on the basis of the strong photometric evidence that the Oesch et al .
2014 sample is entirely at z \sim 9 - 10 , we can use this sample to extend current constraints on the size-luminosity , size-mass relation , and size evolution of galaxies to z \sim 10 .
We find that the z \sim 9 - 10 candidate galaxies have broadly similar sizes and luminosities as z \sim 6 -8 counterparts with star-formation-rate surface densities in the range of \Sigma _ { SFR } = 1 - 20 M _ { \odot } ~ { } yr ^ { -1 } kpc ^ { -2 } .
The stellar mass-size relation is uncertain , but shallower than those inferred for lower-redshift galaxies .
In combination with previous size measurements at z=4-7 , we find a size evolution of ( 1 + z ) ^ { - m } with m = 1.0 \pm 0.1 for > 0.3 L ^ { * } _ { z = 3 } galaxies , consistent with the evolution previously derived from 2 < z < 8 galaxies .