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  • AAS 2016 abstracts

    GZH data and catalog

    K.W. Willett et al.

    The Galaxy Zoo project uses crowdsourced visual classifications to create large and statistically robust catalogs of detailed galaxy morphology. We present initial results for the Galaxy Zoo: Hubble dataset, which includes 169,944 images of galaxies selected from the AEGIS, COSMOS, GEMS, and GOODS surveys. The galaxies span a redshift range of \(0<z<2.5\), with a median of \(z\sim0.7\). The classification scheme distinguishes between bulge-dominated and disk-dominated galaxies, as well as identifying kpc-scale features including galactic bars, spiral arms, irregular structure, and mergers. In addition, we also measure the geometry and relative positions of clumpy structures that are unique to high-redshift star-forming galaxies. Visual classifications are calibrated using a set of \(z\simeq0.05\) SDSS images that are processed to appear as they would at a variety of simulated redshifts using Hubble; this measures the morphological bias for galaxies as a function of changing the apparent size and brightness, without overcorrecting for effects such as an evolving \(L^\star\). We present a new technique for debiasing the morphologies based on a simple parametric model of surface brightness and distance, which adjusts the threshold for detecting feature or disk-dominated galaxies in fainter galaxies and at higher redshifts. We demonstrate the effectiveness of this technique for bulge/disk separation, and discuss its applications and limitations for smaller physical sub-structures. We also present preliminary results analyzing the evolution of disk sub-structure as a function of cosmic time. All the above data will be included in the upcoming release of the full Galaxy Zoo: Hubble catalog.

    GZ multi-wavelength morphologies

    K.W. Willett et al.

    The Galaxy Zoo project uses crowdsourced visual classifications to generate robust catalogs of detailed galaxy morphology. We present results from a study of how kpc-scale galaxy morphology changes as a function of observed wavelength. This includes classifications of color-composite \(gri\) images from the SDSS, as well as individual single-band images of each of the \(ugriz\) bands for a sample of 1000 disk galaxies. We supplement these with near-infrared color-composite images from UKIDSS in the \(YHK\) bands. The range in observed wavelength isolates the effect of different stellar populations, discrete UV-bright star forming regions, and dust clouds on morphology. We show that the fraction of galactic bars detected peaks in the \(i\)-band for optical images, although the overall bar fraction is relatively flat for all bands in \(griz\) between 41% and 56%. Optical \(u\)-band images show a much higher rate of disks where the bar is undetected, at only 13%. We show that there is a mild (?) correlation between bar fraction and bar length in optical bands, both as a function of absolute size and as a fraction of the total disk diameter. In near-infrared wavelengths, bars are detected at slightly lower fractions than in optical; the data show that this is frequently driven by misclassification of barred face-on disks as edge-on disks, where the lack of contrast between the bar and the outer edge of the disk in the near-infrared drives the confusion. Overall, the detection of bars in disks is shown not to be a strong function of wavelength over the majority of the stellar blackbody emission between \(400-2000\) nm.

    Galaxy Zoo Hubble: First results of the redshift evolution of disk fraction in the red sequence

    M.A. Galloway et al.

    [in progress: Sentences of what we already know and why we care] [this is so vague oh my goodness] add: Couple of lines (maybe steal from Kyle) describing GZH

    The transition of galaxies from the blue cloud to the red sequence is commonly linked to a morphological transformation from disk to elliptical structure. However, the correlation between color and morphology is not one-to-one, as evidenced by the existence of a significant population of red disks. As this stage in a galaxy’s evolution is likely to be transitory, the mechanism by which red disks are formed offers insight to the processes that trigger quenching of star formation and the galaxy’s position on the star-forming sequence. To study the population of disk galaxies in the red sequence as a function of cosmic time, we utilize data from the Galaxy Zoo: Hubble project, which uses crowdsourced visual classifications of images of galaxies selected from the AEGIS, COSMOS, GEMS, and GOODS surveys. We construct a large sample of over 10,000 disk galaxies spanning a wide (\(0 < z < 1.0\)) redshift range. We use this sample to examine the change in the fraction of disks in the red sequence with respect to all disks from \(z\sim1\) to the present day. Preliminary results confirm that the fraction of disks in the red sequence decreases as the Universe evolves. We discuss the quenching processes which may explain this trend, and which morphological transformations are most affected by it.

    -role of /lifetime of disk phase as they evolve from SF to passive -how that relates to their position on the SF sequence -using GZ to look at relative role of bulge prominence as it relates to disks on/off the red sequence -does what kind of disk it is matter for its position on RS or time it takes to get there or what mass is there? How do bars/bulges move along the RS? -results show the fraction of disks on the RS falls over cosmic time to present day, use GZH to probe which types of disks are added to RS -role of mass vs environmental vs morphological quenching