The role of stellar mass and environment for cluster blue fraction, AGN fraction and star formation indicators from a targeted analysis of Abell 1691


  • Kevin A. Pimbblet,

    Corresponding author
    1. Monash Centre for Astrophysics (MoCA), Monash University, Clayton, Victoria, Australia
    • School of Physics, Monash University, Clayton, Victoria, Australia
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  • Peter C. Jensen

    1. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria, Australia
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We present an analysis of the galaxy population of the intermediate X-ray luminosity galaxy cluster, Abell 1691, from Sloan Digital Sky Survey (SDSS) and Galaxy Zoo data to elucidate the relationships between environment and galaxy stellar mass for a variety of observationally important cluster populations that include the Butcher–Oemler blue fraction, the active galactic nucleus (AGN) fraction and other spectroscopic classifications of galaxies. From 342 cluster members, we determine a cluster recession velocity of 21257 ± 54 km s−1 and velocity dispersion of math formula km s−1 and show that although the cluster is fed by multiple filaments of galaxies it does not possess significant sub-structure in its core. We identify the AGN population of the cluster from a Baldwin, Phillips & Terlevich diagram and show that there is a mild increase in the AGN fraction with radius from the cluster centre that appears mainly driven by high-mass galaxies [log(stellar mass) > 10.8]. Although the cluster blue fraction follows the same radial trend, it is caused primarily by lower mass galaxies [log(stellar mass) < 10.8]. Significantly, the galaxies that have undergone recent starbursts or are presently starbursting but dust-shrouded [spectroscopic e(a) class galaxies] are also nearly exclusively driven by low-mass galaxies. We therefore suggest that the Butcher–Oemler effect may be a mass-dependent effect. We also examine red and passive spiral galaxies and show that the majority are massive galaxies, much like the rest of the red and spectroscopically passive cluster population. We further demonstrate that the velocity dispersion profiles of low- and high-mass cluster galaxies are different. Taken together, we infer that the duty cycle of high- and low-mass cluster galaxies is markedly different, with a significant departure in star formation and specific star formation rates observed beyond r200 and we discuss these findings.