Can Minor Merging Account for the Size Growth of Quiescent Galaxies? New Results from the CANDELS Survey
(44 votes over all institutions)
The presence of extremely compact galaxies at z~2 and their subsequent growth in physical size has been the cause of much puzzlement. We revisit the question using deep WFC3/IR data to probe the rest-frame optical structure of 935 host galaxies selected with 0.4<z 10^10.7 Msol using optical and near-infrared photometry in the UKIRT Ultra Deep Survey and GOODS-South fields of the CANDELS survey. At each redshift, the most compact sources are those with little or no star formation, and we find that the mean size of these systems grows by a factor of 3.5 +- 0.3 over this redshift interval. The new data are sufficiently deep to enable us to identify companions to these hosts whose stellar masses are ten times smaller, while still yielding suitably accurate photometric redshifts to define a likely physical association. By searching for faint companions around 404 quiescent hosts within a projected physical annulus 10 < R < 30 kpc/h, we estimate the minor merger rate over the redshift range 0.4 < z 0.1 may explain most of the size evolution observed at z >~ 1 if a relatively short merger timescale is assumed, but the rapid growth seen at higher redshift likely requires additional physical processes.
