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HST Frontier Fields
Frequently Asked Questions

Frequently Asked Questions:

  1. When will the HST data be taken? When will it be made public?

    The HST Frontier Field observations of the first four clusters + parallel fields will begin in Cycle 21, and continue through Cycle 22. The observations of the last two clusters will be done in Cycle 23, contingent upon the success of the initial observations.

    All raw data will be publicly immediately upon its entry into MAST (typically within 24 hours of observation). STScI will provide science-ready reduced data products (such as combined drizzled images) to the community soon after the raw data are obtained.

  2. Who will do the science?

    This is a Director's Discretionary program designed to enable cutting-edge science for the astronomical community, in the tradition of the Hubble Deep Fields and Ultra Deep Field. All scientific analyses -- including but not limited to that related to the primary science goals -- are open to the community. Funding to support these analyses can be requested as Archival Research programs in response to the HST Call for Proposals.

  3. What kinds of data products will be released by STScI?

    All raw data will be publicly available as soon as it has been ingested into MAST (typically with 24 hours of observation). In addition, STScI will provide science-ready combined, distortion-corrected mosaics in all the filters, astrometrically registered and drizzled onto a common pixel scale, soon after the raw data are obtained.

  4. Can I propose for HST Archival, Theory, GO programs in Cycle 21? Can a Legacy Archival proposal request funding for the entire Frontier Fields program (6 clusters)? How many archival datasets are expected?

    Yes, archival and theory proposals based upon the planned Cycle 21 observations are permitted. GO proposals to obtain additional HST data in the Frontier Fields are also permitted.

    Legacy Archival programs are allowed to be multi-year projects, therefore they may request funding for analysis of the full Frontier Fields dataset. Multi-year projects will be funded on a yearly basis, with continued funding beyond the first year subject to a performance review.

    The STScI final combined drizzled images and weight maps will consist of one dataset per filter per pointing per cluster = (3 ACS filters + 4 WFC3/IR filters) x 2 pointings x 6 clusters = 84 datasets total. The raw datasets are the number of visits x the number of filters/cameras per visit. Each pointing will have 35 visits per camera. Each visit will be 2 orbits long with a single filter per camera. See the table below (last question) for the number of orbits per filter/camera.

  5. How did you choose your fields? Why didn't you pick Abell XXXX? Where are the parallel blank fields?

    Based on the recommendations of the SWG, the clusters were judged by the following primary critera:

    • their lensing strength (defined as the expected number of high redshift galaxies magnified to H ∼ 27 within a WFC3/IR FOV)
    • the zodiacal background
    • the Galactic extinction
    • observability with HST, Spitzer, and JWST
    • observability with ALMA
    • existence of HST images and other supporting data

    Many strong lensing clusters did not meet the IR background or observability criteria; conversely, many interesting clusters in optimal parts of the sky were not as powerful gravitational telescopes as the selected objects.

    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.

  6. What are the Frontier Field clusters?

    All six cluster fields have been chosen. These are MACS0717.5+3745, Abell 370, Abell 2744, MACS0416.1-2403, MACSJ1149.5+2223 and RXCJ2248.7-4431.

  7. Which clusters will be go first?

    The first year of observations will be of Abell 2744 and MACSJ0416.1-2403, the second year observations will be of MACSJ0717.5+3745 and MACSJ1149.5+2223, and contingent upon the success of the first two years of observations, the third year observations will be of RXCJ2248.7-4431 and Abell 370.

  8. What filters and exposure times are planned?

    We will observe the same filter set to the same depths for both the cluster and blank field positions.

    The current planned orbital breakdown is:

    • ACS/WFC:
      • F435W - 18 orbits
      • F606W - 10 orbits
      • F814W - 42 orbits
    • WFC3/IR:
      • F105W - 24 orbits
      • F125W - 12 orbits
      • F140W - 12 orbits
      • F160W - 22 orbits
    • Two ~1300s exposures per orbit per filter. Two orbits per visit.

    These exposures are expected to reach ~5-sigma SNR for a point source with total aperture-corrected ABmag ~28.7-29.0. (See Table 2-4 in HDFI SWG report for details).

    The orbit allocation across the filters may be tweaked to account for field variation in Galactic extinction, and have not been finalized.

  9. Will the Spitzer Space Telescope observe the Frontier Fields?

    Yes, SST will devote up to ~1000 hours of DD time to the Frontier Fields. Each selected field has been confirmed as observable with Spitzer, and detailed planning for IRAC channel 1 and 2 observations are underway. Additional Spitzer GO proposals for these fields will also be welcomed.

  10. Can I propose for additional HST data?

    Yes. GO proposals for complementary data for any of the Frontier Fields are welcome.

  11. I don't know anything about lensing. How do I use this data to study distant galaxies? How do I learn more?

    Preliminary (but high-quality) lensing and magnification maps of the Frontier Field clusters will be made available to the community prior to the Frontier Field observations through our call for Lensing Map Proposals.

    STScI is also hosting a Cluster Lensing Workshop April 15-17, 2013, followed by a 1-day seminar on April 18th specifically to address the Frontier Field data challenges. The conference and Frontier Fields seminar will be webcast.

  12. I'm a lensing expert. What is this Lensing Map Proposal opportunity? Can I propose for both this and a regular HST archival proposal?

    In order to level the playing field for non-lensing expert, STScI will fund up several groups to provide high-quality magnification maps of the Frontier Fields prior to the Frontier Field observation, based on existing (HST) data.

    Funding through this Lensing Map Request for Proposals is possible only for U.S. Principal Investigators at one of the following types of U.S. institutions: universities, nonprofit research institutions, private for-profit organizations, and Federal employees. Funding will be issued as a firm fixed-price contract.

    Proposals for this effort are due Feb 15, 2013, and are to be free-format of the proposer's choice, with no page limits, but must contain the elements listed in the Request for Proposals. Please see the Request for Proposals for details.

    HST Cycle 21 Archival proposals to analyze the new Frontier Fields data -- including the creation of new/updated magnification maps based on the discovery of new multiply-imaged systems -- are also strongly encouraged.

  13. What about transient science with the Frontier Fields data?

    The detection of transient objects was not identified as a top science priority for the Frontier Fields. However, we are examining ways of making the Frontier Fields observations amenable to transient science, provided this does not place an undue burden on the HST scheduling system. The modifications being considered include optimizing the order of the filters and the length of the observing window at each roll angle.

    Here are the numbers for the duration of each observing window and their separation, based on a *preliminary* schedule.

    Cluster Window 1 Window 2 Start of Window 1 - Start of Window 2
    Abell 2744 48 days 59 days 200 days
    MACSJ0416.1-2403 34 days 40 days 200 days
    MACSJ0717.5+3745 76 days 69 days 146 days
    MACSJ1149.5+2223 56 days 63 days 156 days
    RXCJ2248.7-4431 46 days 50 days 200 days
    Abell 370 69 days 69 days 220 days

    So the main cluster field will have 70 orbits of WFC3/IR observations spread out over 40-70 days, then 70 orbits of ACS/optical observations spread out over 40-70 days ~5-7 months later.