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Description
We investigate the relation between star-formation activity and environment in six intermediate redshift clusters (z~0.25) out to large clustercentric distances (~4R_vir_). For that, we conducted a panoramic spectroscopic campaign with MOSCA at the Calar Alto observatory. We acquired spectra of more than 500 objects. Approximately 150 of these spectra were of galaxies that are members of the clusters. Other ~150 are field galaxies or galaxies belonging to groups, serendipitously found during the investigation. The rest of the spectra did not met the quality criteria or were stars. The wavelength range allows us to quantify the star formation activity by using the [OII] and the H{alpha} lines. This activity is examined in terms of the large-scale environment expressed by the clustercentric distance of the galaxies as well as on local scales given by the spatial galaxy densities. The suppression of the star-formation activity is observed at large clustercentric distances and low projected densities. Galaxies with current star-formation show similar activity, regardless of the environment, Therefore, the decline of the star-formation activity inside the investigated clusters is driven mainly by the significant change in the fraction of active versus passive populations. This suggests that the suppression of the star-formation activity occurs on short timescales. We also detect a significant population of red star-forming galaxies whose colors are consistent with the red-sequence of passive galaxies. They appear to be in an intermediate evolutionary stage between active and passive types.
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