We present a study of the spatial distribution and kinematics of star-forming galaxies in 30 massive clusters at 0.15 { < } z { < } 0.30 , combining wide-field Spitzer 24 \mu m and GALEX NUV imaging with highly-complete spectroscopy of cluster members .
The fraction ( f _ { SF } ) of star-forming cluster galaxies rises steadily with cluster-centric radius , increasing fivefold by 2 r _ { 200 } , but remains well below field values even at 3 r _ { 200 } .
This suppression of star formation at large radii can not be reproduced by models in which star formation is quenched in infalling field galaxies only once they pass within r _ { 200 } of the cluster , but is consistent with some of them being first pre-processed within galaxy groups .
Despite the increasing f _ { SF } –radius trend , the surface density of star-forming galaxies actually declines steadily with radius , falling { \sim } 15 { \times } from the core to 2 r _ { 200 } .
This requires star-formation to survive within recently accreted spirals for 2–3 Gyr to build up the apparent over-density of star-forming galaxies within clusters .
The velocity dispersion profile of the star-forming galaxy population shows a sharp peak of 1.44 \sigma _ { \nu } at 0.3 r _ { 500 } , and is 10-35 % higher than that of the inactive cluster members at all cluster-centric radii , while their velocity distribution shows a flat , top-hat profile within r _ { 500 } .
All of these results are consistent with star-forming cluster galaxies being an infalling population , but one that must also survive { \sim } 0 .5–2 Gyr beyond passing within r _ { 200 } .
By comparing the observed distribution of star-forming galaxies in the stacked caustic diagram with predictions from the Millennium simulation , we obtain a best-fit model in which SFRs decline exponentially on quenching time-scales of 1.73 { \pm } 0.25 Gyr upon accretion into the cluster .