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Rights statement: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astnomical Society following peer review. The version of record David Sobral, Andra Stroe, Yusei Koyama, Behnam Darvish, João Calhau, Ana Afonso, Tadayuki Kodama, and Fumiaki Nakata The nature of Hα star-forming galaxies at z ∼ 0.4 in and around Cl 0939+4713: the environment matters MNRAS (June 01, 2016) Vol. 458 3443-3454 doi:10.1093/mnras/stw534 first published online March 7, 2016 is available online at:http://mnras.oxfordjournals.org/content/458/4/3443

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

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Journal publication date 1/06/2016 Monthly Notices of the Royal Astronomical Society 4 458 12 3443-3454 Published 7/03/16 English

### 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$_{H\alpha}$) correlates strongly with stellar mass, but also with environmental density. Star-forming galaxies in the densest environments are found to be significantly dustier (A$_{H\alpha}$~1.5-1.6) than those residing in the lowest density environments (A$_{H\alpha}$~0.6), deviating significantly from what would be predicted given their stellar masses.

### Bibliographic note

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astnomical Society following peer review. The version of record David Sobral, Andra Stroe, Yusei Koyama, Behnam Darvish, João Calhau, Ana Afonso, Tadayuki Kodama, and Fumiaki Nakata The nature of Hα star-forming galaxies at z ∼ 0.4 in and around Cl 0939+4713: the environment matters MNRAS (June 01, 2016) Vol. 458 3443-3454 doi:10.1093/mnras/stw534 first published online March 7, 2016 is available online at:http://mnras.oxfordjournals.org/content/458/4/3443