The Settling of Disc Galaxies at 0.5 < z < 2 from Galaxy Zoo CANDELS: Detailed Morphological Measurements of 50,000 Galaxies
Witnessing Disc Galaxy Evolution Through The Eyes of their Stellar Structures
Brooke D. Simmons
University of Oxford
Chris Lintott (Oxford), Kyle W. Willett (Minnesota), Karen L. Masters (ICG Portsmouth), Robert C. Nichol (ICG Portsmouth), Sandra M. Faber (UCO/Lick), Henry C. Ferguson (STScI), Jeyhan Kartaltepe (NOAO), the Galaxy Zoo team, the CANDELS team
Using detailed, quantified visual Galaxy Zoo morphologies of approximately 50,000 galaxies imaged by the Cosmic And Near-infrared Deep Extragalactic Legacy Survey (CANDELS), we report first results on the settling of massive disc galaxies from 0.5 < z < 2. The fraction of disc galaxies dynamically cold enough to support strong disc instabilities is constant from 1 < z < 2, in contrast to the vanishing fraction expected from extrapolation of previous rest-frame optical results to z = 1 but marginally consistent with the predictions of some simulations.

The full Galaxy Zoo CANDELS morphologies will also be released to the public: 85% of galaxies in the sample have redshifts 0.5 < z < 3, and they range in observed H-band surface brightness between 17.5 < µ < 27 mag/arcsec^2. Galaxy Zoo collects multiple independent classifications (typically 40) of each galaxy in the sample. After applying an iterative consensus-based classifier weighting scheme and correcting for the effects of varying image depth and distance, we report measurements of morphology along a variety of physically useful axes, such as clumpiness, spiral arm count and strength, bulge strength, and the presence of a bar instability. We demonstrate the utility of these classifications to the community by showing how these morphologies may be used to identify a population of completely featureless yet rotation-dominated disc galaxies.
13:30 - 15:00