The evolving demographics of the red sequence since z=1
Witnessing Disc Galaxy Evolution Through The Eyes of their Stellar Structures
Thomas Melvin
ICG, University of Portsmouth
Galaxy Zoo team
In the local universe we observe a bimodal galaxy population, with galaxies tending to be either part of the blue cloud or the red sequence. As we observe galaxies towards higher redshifts, this bimodality becomes less distinct. Here, we
combine photometric and spectroscopic data from the Cosmic Evolution Survey (COSMOS) with visual morphological classifications from Galaxy Zoo: Hubble to explore how the demographics of the red sequence have evolved over the last
eight billion years. Since z=1, the fraction of galaxies in the red sequence has remained steady (~30-40% of all galaxies). However, the red sequence has become almost a magnitude redder over this time period, with the mean colour
rising from 4.8 at z=1.0 to 5.5 at z=0.2. The morphologies of the red sequence over this time has also changed, with the red sequence consisting of more disks, and barred disks, as the universe has aged. We propose that this growth in red
disk galaxies is due to the disk population becoming more mature, and disk-dominated by secular evolution (i.e. through stellar bars). This work indicates that not all galaxies in the red sequence are ellipticals formed by a major merger process, and thus slower processes, like secular evolution, can move galaxies onto the red sequence in ways which do not drastically alter their morphologies.
13:30 - 15:00