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STScI Webcast

2018 Cold Science Colloquia

Quantifying the Evolution of Galaxy Distributions

Presented by: Jennifer Lotz (STScI/JHU)
Category: Science Colloquia   Duration: 30 minutes   Broadcast date: January 17, 2018
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Jennifer Lotz (STScI) – Quantifying the Evolution of Galaxy Distributions Abstract: We present a powerful new empirical methodology for tracking the evolution of galaxy distributions over cosmic time. With the PanSTARRS Optical Galaxy Survey (POGS) and CANDELS galaxy samples, we compute the size vs. stellar mass distributions at 0 < z < 3 including measurement and photz error estimates. We adapt the “Exterme Gaussian Mixture Modelling” technique for noisy data distributions (Bovy et al. 2009) to reconstruct the intrinsic size-mass galaxy distributions at each redshift with a combination of ~ 50 Gaussian mixture models. We determine which galaxies at a given epoch are evolving most strongly by computing the delta Likelihood that each galaxy is drawn from the empirically-derived size-mass GMM for the earlier/later epoch. After correcting for completeness and volume, we find that delta Likelihood (~ delta number density per unit time) generally increases from z~3 to z~0, consistent with the appearance of new galaxies over cosmic time. The stellar mass of most rapidly appearing population shifts from 5x10^10 Msun at z~2.5 to ~10^10 Msun at z~0.5. At z>1, the change in likelihood for both red and blue galaxies is strongly correlated with size, with large, massive galaxy populations appearing very rapidly between 1.5 < z < 3. Only small star-forming galaxies at z> 2, small quiescent galaxies at z ~1.5, and massive quiescent galaxies at z~0.5 have decreasing likelihoods (disappearing with time). We explore the implications for galaxy assembly, mergers and quenching in the evolution of the size-mass distribution.

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Jennifer Lotz's presentation PDF document (.pdf)