Galaxy Zoo: Quantitative Visual Morphological Classifications for 48,000 galaxies from CANDELS

TL;DR

This paper presents detailed visual morphological classifications for 48,000 galaxies from the CANDELS survey, using Galaxy Zoo data to analyze galaxy features and compare with previous classifications, providing depth-corrected and consensus-based results.

Contribution

It introduces a large-scale, consensus-based visual classification method for galaxies, incorporating depth corrections and comparisons with prior classifications, enhancing morphological analysis at high redshift.

Findings

High agreement with previous classifications

Depth-corrected classifications enable consistent analysis across surveys

Identification of a sample of featureless disks at 1 < z < 3

Abstract

We present quantified visual morphologies of approximately 48,000 galaxies observed in three Hubble Space Telescope legacy fields by the Cosmic And Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and classified by participants in the Galaxy Zoo project. 90% of galaxies have z < 3 and are observed in rest-frame optical wavelengths by CANDELS. Each galaxy received an average of 40 independent classifications, which we combine into detailed morphological information on galaxy features such as clumpiness, bar instabilities, spiral structure, and merger and tidal signatures. We apply a consensus-based classifier weighting method that preserves classifier independence while effectively down-weighting significantly outlying classifications. After analysing the effect of varying image depth on reported classifications, we also provide depth-corrected classifications which both preserve the information in the deepest observations and also enable the use of classifications at comparable depths across the full survey. Comparing the Galaxy Zoo classifications to previous classifications of the same galaxies shows very good agreement; for some applications the high number of independent classifications provided by Galaxy Zoo provides an advantage in selecting galaxies with a particular morphological profile, while in others the combination of Galaxy Zoo with other classifications is a more promising approach than using any one method alone. We combine the Galaxy Zoo classifications of "smooth" galaxies with parametric morphologies to select a sample of featureless disks at 1 < z < 3, which may represent a dynamically warmer progenitor population to the settled disk galaxies seen at later epochs.