We present the 2012 Hubble Ultra Deep Field campaign (UDF12), a large 128-orbit Cycle 19 HST program aimed at extending previous WFC3/IR observations of the UDF by quadrupling the exposure time in the F105W filter, imaging in an additional F140W filt
er, and extending the F160W exposure time by 50%. The principal scientific goal of this project is to determine whether galaxies reionized the universe; our observations are designed to provide a robust determination of the star formation density at $z$$,gtrsim,$8, improve measurements of the ultraviolet continuum slope at $z$$,sim,7,-,$8, facilitate the construction of new samples of $z$$,sim,9,-,$10 candidates, and enable the detection of sources up to $z$$,sim,$12. For this project we committed to combining these and other WFC3/IR imaging observations of the UDF area into a single homogeneous dataset, to provide the deepest near-infrared observations of the sky currently achievable. In this paper we present the observational overview of the project, motivated by its scientific goals, and describe the procedures used in reducing the data as well as the final products that are produced. We have used the most up up-to-date methods for calibrating and combining the images, in particular paying attention to correcting several instrumental effects. We release the full combined mosaics, comprising a single, unified set of mosaics of the UDF, providing the deepest near-infrared blank-field view of the universe obtained to date, reaching magnitudes as deep as AB$,sim,$30 in the near-infrared, and yielding a legacy dataset on this field of lasting scientific value to the community.
This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black ho
les at $zsim1.5-8$, and to study Type Ia SNe beyond $z>1.5$. Five premier multi-wavelength sky regions are selected, each with extensive multiwavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and UVIS channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers sim125 square arcminutes within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of sim800 square arcminutes across GOODS and three additional fields (EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up to date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including CTE degradation for ACS, removal of electronic bias-striping present in ACS data after SM4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.
