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C.E. Covington, W.C. Keel (U. Ala.), I. Smail (Durham), F.N. Owen (NRAO), G.E. Morrison (IPAC), R.A. Windhorst, S.C. Odewahn (Arizona State U.)
We have used the KPNO 4m telescope and CCD Mosaic to measure H\alpha emission from the well-studied cluster Abell 851 (Cl 0939+4713) at z=0.40. H\alpha is a more reliable star-formation tracer than the more accessible [O II] \lambda 3727 doublet, and their comparison is relevant to estimates of star formation at higher redshift. A z-band image was used for continuum measurement. The greatest H\alpha EW values are found among low-luminosity compact systems. Comparing to local samples, and using the MORPHS Hubble types in the cluster core, Sbc and later spirals in Abell 851 have weaker H\alpha+[N II] emission than in nearby (field and Virgo) galaxies. This is broadly consistent with a picture in which star formation is quenched as spirals join the cluster. Earlier Hubble types (E-Sab) show, in addition, a tail of high-EW systems, indicating local and recent star-formation events. These are generally the same ones with mid-UV detections. These data also let us address the spatial distribution of strong-emission galaxies close to the cluster redshift out to a radius of 2.5 Mpc from the core.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.