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arXiv · 1603.00462

The nature of H-alpha star-forming galaxies at z~0.4 in and around Cl 0939+4713: the environment matters

David Sobral·Andra Stroe·Yusei Koyama·Behnam Darvish·João Calhau·Ana Afonso·Tadayuki Kodama·Fumiaki Nakata
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Abstract

Cluster star-forming galaxies are found to have an excess of Far-Infrared emission relative to H-alpha (Ha), when compared to those in the field, which could be caused by intense AGN activity, dust and/or declining star formation histories. Here we present spectroscopic observations of Ha emitters in the Cl 0939+4713 (Abell 851) super-cluster at z=0.41, using AF2+WYFFOS on the WHT. We measure [OII], Hbeta (Hb), [OIII], Ha and [NII] for a sample of 119 Ha emitters in and around the cluster. We find that 17+-5% of the Ha emitters are AGN, irrespective of environment. For star-forming galaxies, we obtain Balmer decrements, metallicities and ionisation parameters with different methods, individually and by stacking. We find a strong mass-metallicity relation at all environments, with no significant dependence on environment. The ionisation parameter declines with increasing stellar mass for low-mass galaxies. Ha emitters residing in intermediate environments show the highest ionisation parameters (along with high [OIII]/Ha and high [OIII]/[OII] line ratios, typically twice as large as in the highest and lowest densities), which decline with increasing environmental density. Dust extinction (A$_{Hα}$) correlates strongly with stellar mass, but also with environmental density. Star-forming galaxies in the densest environments are found to be significantly dustier (A$_{Hα}$~1.5-1.6) than those residing in the lowest density environments (A$_{Hα}$~0.6), deviating significantly from what would be predicted given their stellar masses.

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David Sobral, Andra Stroe, Yusei Koyama, Behnam Darvish, João Calhau, Ana Afonso, Tadayuki Kodama, Fumiaki Nakata. 2016-03-01. The nature of H-alpha star-forming galaxies at z~0.4 in and around Cl 0939+4713: the environment matters. https://doi.org/10.1093/mnras%2Fstw534

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