The program devoted 840 orbits to six cluster/blank field pairs (140 orbits each). The first four cluster/blank field pairs were observed with Director's Discretionary time in Cycles 21 and 22. After obtaining initial results from those data, observations of the final two cluster/blank field pairs were approved for execution in Cycle 23. For each cluster/parallel blank field, HST obtained WFC3/IR and ACS images simultaneously at a fixed position angle, then rolled and swapped camera positions roughly 6 months later.
The 140-orbit depth for each field was designed to achieve depths of AB ≈ 28.7-29 mag in optical (ACS) and NIR (WFC3) imaging. Limiting magnitudes are for 5-sigma detections of a point source within a 0.4" diameter aperture. For details, see Lotz et al. 2017.
| Cluster Name | z | Cluster | Parallel Field | HST FOV | Regions File | ||
|---|---|---|---|---|---|---|---|
| RA | Dec | RA | Dec | ||||
| Year 1: | |||||||
| Abell 2744 | 0.308 | 00:14:21.2 | -30:23:50.1 | 00:13:53.6 | -30:22:54.3 |
| regions |
| MACSJ0416.1-2403 | 0.396 | 04:16:08.9 | -24:04:28.7 | 04:16:33.1 | -24:06:48.7 |
| regions |
| Year 2: | |||||||
| MACSJ0717.5+3745 | 0.545 | 07:17:34.0 | +37:44:49.0 | 07:17:17.0 | +37:49:47.3 |
| regions |
| MACSJ1149.5+2223 | 0.543 | 11:49:36.3 | +22:23:58.1 | 11:49:40.5 | +22:18:02.3 |
| regions |
| Year 3: | |||||||
| Abell S1063 (RXCJ2248.7-4431) | 0.348 | 22:48:44.4 | -44:31:48.5 | 22:49:17.7 | -44:32:43.8 |
| regions |
| Abell 370 | 0.375 | 02:39:52.9 | -01:34:36.5 | 02:40:13.4 | -01:37:32.8 |
| regions |
The selection of these six clusters was based primarily on their predicted lensing strength*, their low/moderate zodiacal and Galactic backgrounds, their observability with ALMA and Mauna Kea, and their observability with HST and Spitzer. We've also looked at their suitability for deep radio observations, and their existing multi-wavelength data observations.
(* Lensing strengths were calculated by Dan Coe, Johan Richard, and Adi Zitrin, based on pre-HFF HST data.)
The parallel blank field positions are constrained by the availability of HST guide stars, which permit > 30-day windows of fixed roll-angle observations with both ACS and WFC3 at both the cluster and blank field positions. From the available locations, the final parallel field location was based primarily upon the ability to obtain very deep, high quality imaging in both HST and Spitzer. Therefore the avoidance of bright stars which would cause scattered light, saturated columns, and persistence took precedence over the avoidance of extended cluster structures.
Locations on the sky of the Frontier Fields are shown below.
