WFC3 Early Release Science (ERS) Observations

The GOODS (North and South) fields are two major fields observed by the CANDELS program. The GOODS-N field will be fully covered by CANDELS near-IR observations, while only ~70% of the GOODS-S field area will be observed by CANDELS near-IR observations. The main reason is that the remaining ~30% of the area in the GOODS-S field was already observed by the Wide Field Camera 3 (WFC3) Early Release Science (ERS) observations. Today, I will summarize these ERS observations.

The multiwavelength 10-band color image of the entire ERS mosaic in the GOODS-South field combines a broad range of colors, from the ultraviolet, through visible light, and into the near infrared. Such a detailed multi-color view of the universe has never before been assembled in such a combination of color, clarity, accuracy, and depth. Credit: NASA, ESA, R. Windhorst, S. Cohen, M. Mechtley, and M. Rutkowski, R. O'Connell, P. McCarthy, N. Hathi, R. Ryan, H. Yan, and A. Koekemoer.

The Scientific Oversight Committee (SOC) was constituted in 1998 to oversee the science definition and the technical development of the WFC3. In recognition of their effort during 11 years of WFC3 development, the STScI director allocated ~210 orbits (~300 hours) of the HST time to the SOC to do challenging science programs designed to test key capabilities of the WFC3. To this effect, the SOC distributed these orbits equally between two major programs, to investigate (1) nearby galaxies and (2) distant galaxies. The combination of these two programs is referred to as the 'WFC3 Early Release Science (ERS) Program." I will only talk about the 'distant galaxies' program, as it is most relevant to the CANDELS program. The 'distant galaxies' program was allocated 104 orbits (~150 hours).

I got involved in this program through my PhD advisor, Rogier Windhorst, who is a member of the SOC. Myself, Seth Cohen, Russell Ryan, and few SOC members were involved in planning this 'distant galaxies' program. The GOODS-S field was chosen because of the availability of extensive ancillary data in this field. The primary goal of the ERS program was to showcase capabilities of the WFC3, so we planned 3 sets of observations: ultraviolet imaging (total 40 orbits), near-infrared imaging (total 60 orbits), and near-infrared grism (low resolution spectroscopy, total 4 orbits). The ultraviolet and near infrared imaging covers the full ERS field (~45 arcmin²), while the grism observations cover only ~1/10th of the ERS field.

Multiwavelength postage stamps of objects with interesting morphological structure
in the 10-band ERS color images of the GOODS-South field: from left
to right, high signal-to-noise detections of ERS galaxies resembling the main
cosmological parameters w, λ and ρ respectively. These images illustrate the rich and
unique morphological information available in the 10-band panchromatic ERS data set.
Credit: Rogier Windhorst and WFC3 SOC

These observations are being used for various science goals, including identifying and understanding passive galaxies, star-forming galaxies at intermediate redshifts, high redshift galaxies, emission-line galaxies, and galaxy morphology/mergers at various redshifts. These data are also useful to identify faint red stars in our own galaxy. Details of ERS observations are in Windhorst et al. 2011. The intermediate depth ERS observations are excellent complementary data to the CANDELS wide shallow and the CANDELS deep observations. CANDELS team is generating a large near-infrared mosaic in the GOODS-S field, which will include ERS as well as CANDELS datasets in a single image. Keep coming back for more results from these datasets.