Hubble Boldly Goes: The Frontier Fields Program

The Hubble Deep Field Initiative

Given the substantial advances made in this field over the past 15 years—and the costs—can Hubble offer the prospect of further transformative science from another deep-field survey? Or should we sit back, focus on consolidating our gains, and wait for Webb to bring the next breakthrough? That, in essence, was the question that prompted the Hubble Deep Field Initiative (HDFI). Following discussions with the Space Telescope Users Committee and the community, the Institute Director, Matt Mountain, chartered a science working group (SWG) chaired by James Bullock (UC Irvine) to examine how Hubble might extend our knowledge of the cosmic frontiers at high redshift. The SWG members were Mark Dickinson (NOAO), Steve Finkelstein (UT Austin), Adriano Fontana (INAF), Ann Hornschemeier-Cardiff (GSFC), Jennifer Lotz (STScI), Priya Natarajan (Yale), Alexandra Pope (UMass), Brant Robertson (UA), Brian Siana (UC Riverside), Jason Tumlinson (STScI), and Michael Woods-Vasey (Pittsburgh). As a secondary goal, the committee was asked to consider observations that would lay the groundwork for future Webb observations of the early universe.

Formally, the HDFI SWG was charged with the following tasks:

  • Define the science case and a set of science goals for a new set of ultra-deep-imaging fields with sensitivity depths comparable to those of the HUDF and the HUDF09 infrared follow-up. Provide an assessment of the urgency of pursuing this science.
  • Assess the prospects for near-field science that can be achieved with these deep-field observations.
  • Recommend the locations and number of fields that should be obtained to meet the science goals defined for the HDFI.
  • Recommend the suite of filters and exposure times necessary to accomplish the science goals defined for the HDFI.
  • Solicit input from the astronomical community in defining the science goals and recommendations described in the above tasks.
  • Produce a short (10–15 page) white paper describing the results of the above tasks by October 1, 2012.

The HDFI SWG was also constrained to identify a program that required no more than 800–1,000 orbits, which (like the HDF) could therefore be accommodated through DDT without impinging on GO allocations in Cycle 21 and succeeding cycles.

At the outset of the process, the community was asked to weigh in on the HDFI, and 32 white papers were received outlining a variety of techniques, programs, and constraints that the community felt should be taken into account. The SWG engaged in lively discussions through the summer and fall of 2012, thoroughly covering the pros and cons of a wide variety of programs, including duplicating the UDF at a different location, probing deeper within the UDF itself, adding deep grism observations in selected fields, obtaining blue/ultraviolet data in selected fields as a precursor for Webb, and using galaxy clusters as telescopes to probe the high-redshift universe. Those discussions resulted in a unanimous recommendation to the Director, and were summarized in the SWG’s report, submitted on November 21, 2012. The HDFI SWG report is available here.

After due deliberation, the Director decided to go ahead with the program, renaming it “Hubble Frontier Fields.” The observations of four galaxy clusters will be executed in Cycles 21 and 22, and, dependent on the results of an interim review, with observations of the final two clusters in Cycle 23. The HFF decision was announced in the Cycle 21 Call for Proposals, issued on December 5, 2012.