The morphological demographics of galaxies in the Advanced Camera for Surveys Hubble Ultra Deep parallel fields

We present a morphological analysis of distant field galaxies using the deep Advanced Camera for Surveys images from the public parallel Near-Infrared Camera and Multi-Object Spectrometer observations of the Hubble Ultra Deep Field obtained in the F435W (B-435), F606W (V-606), F775W (i(775)), and F850LP (z(850)) filters. We morphologically segregate galaxies using a combination of visual classification and objective machine-based selection. We use the asymmetry (A) and central concentration (C) parameters to characterize galaxies up to z(850,AB) < 25 mag. We take advantage of the multicolor data set and estimate redshifts for our sample using the Bayesian photometric redshift, which enables us to investigate the evolution of their morphological demographics with redshift. Using a template fitting model and a maximum likelihood approach, we compute the star formation rate (SFR) for galaxies up to z similar or equal to 1.3 and its contributions from different morphological types. We report that spiral galaxies are the main providers to the total SFR. The E/S0 contribution flattens out at z similar or equal to 1, while the irregular/peculiar (Irr/Pec) galaxy populations continuously rise to match the spiral contribution at z similar or equal to 1:0. We use the i(775) - z850 and V606 - i(775) color-magnitude diagrams to constrain the galaxies' formation histories and find that E/S0s show both a population of luminous red galaxies in place at z similar to 1.2 and a bluer and fainter population resembling that of Irr/Pec at similar redshifts.