The Structures of Distant Galaxies I: Galaxy Structures and the Merger Rate to z~3 in the Hubble Ultra-Deep Field

Abstract

This paper begins a series in which we examine the structures of distant galaxies to directly determine the history of their formation modes. We start this series by examining the structures of z_F850LP < 27 galaxies in the Hubble Ultra-Deep field, the deepest high-resolution optical image taken to date. We investigate a few basic features of galaxy structure using this image. These include: (1) The agreement of visual eye-ball classifications and non-parametric quantitative (CAS, Gini/M_20) methods; (2) How distant galaxy quantitative structures can vary as a function of rest-frame wavelength; and (3) The evolution of distant galaxy structures up to z~3. One of our major conclusions is that the majority of galaxies with z_850 < 27 are peculiar in appearance, and that galaxy assembly is rapidly occurring at these magnitudes, even up to the present time. We find a general agreement between galaxy classification by eye and through quantitative methods, as well as a general agreement between the CAS and the Gini/M_20 parameters. We find that the Gini/M_20 method appears to find a larger number of galaxy mergers than the CAS system, but contains a larger contamination from non-mergers. We furthermore calculate the merger rate of galaxies in the UDF up to z~3, finding an increase with redshift as well as stellar mass, confirming previous work in the Hubble Deep Field. We find that massive galaxies with M_{*} > 10^10 M_0 undergo 4.3_+0.8^-0.8 major galaxy mergers at z < 3, with all of this merging occurring at z > 1.

MNRAS, submitted

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• Globular Cluster Systems in Nearby Dwarf Galaxies: I. HST/ACS Observations and Dynamical Properties of Globular Clusters at Low Environmental Density
• A Surprisingly High Pair Fraction for Extremely Massive Galaxies at z ~ 3 in the GOODS NICMOS Survey
• Is the Gini coefficient a stable measure of galaxy structure?
• A Comparison of Galaxy Merger History Observations and Predictions from Semi-Analytic Models
• Evidence for Morphology and Luminosity Transformation of Galaxies at High Redshifts
• Merger and Ring Galaxy Formation Rates at z<=2
• Constraining Star Formation and AGN in z~2 Massive Galaxies using High Resolution MERLIN Radio Observations
• On the Onset of Stochasticity in $\Lambda$CDM Cosmological Simulations
• Classification of Extremely Red Objects in the Hubble Ultra Deep Field