The GLASS data yield spatially resolved Hα fluxes for all star-forming galaxies in the core (< 1 Mpc) of the clusters. In addition, each cluster is observed at two different position angles. These two orientations allow us to mitigate the impact of contamination from overlapping spectra, and reliably measure for the first time the relative position of the Hα emission with respect to the continuum.
In Vulcani et al. (2015) we present a pilot study characterizing the spatial distribution of the Hα emission in cluster galaxies beyond the local universe based on WFC3-IR data.
We analyze two of the ten clusters in the GLASS sample. We select MACS0717.5+3745 and MACS1423.8+2404 because they are at similar redshift (z~0.55), so as to minimize evolutionary effects and differences in the sensitivity/selection function, and are in very different dynamical states, so as to span the range of expected environments. We use use foreground and background galaxies as field control sample.
Both in clusters and in the field, Hα is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside out growth. In ∼ 20% of the cases, the Hα emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the Hα emission and that of the continuum are offset by less than 1 kpc.
The diversity of morphologies and sizes observed in Hα illustrates the complexity of the environmental process that regulate star formation.