Jan 082013

Our implementation team here at STScI has been hard at work selecting the final cluster targets.  We have asked for input from the community to find the best candidates, and you all have responded!

Very few of our final cluster candidates will be ones that meet all of our criteria, but the most important considerations are, in order:

  1. observable with HST
  2. strong lenser
  3. low to moderate zodiacal background
  4. observable with ALMA

Here, lensing strength is determined by estimating the number of z ~ 10 galaxies at 27th magnitude within the WFC3 field of view, based on one or more mass models for the cluster. (Many thanks to Johan Richard, Adi Zitrin, and Dan Coe for helping to calculate these numbers.)

The plot below shows many of the clusters being considered and where they lie in relation to the high background regions of the galaxy and ecliptic.  A few have already been eliminated based on this.  Also shown is the visibility limit of ALMA.  Everything below the dashed line can be observed with ALMA, which is one of our more important considerations.

cluster selection map

You can see just how many of these clusters lie in the same region of the sky.  This presents scheduling difficulties for HST.  Ideally, we would like to have our six clusters evenly distributed across the sky, but that is looking unlikely.

You can also see the UDF (mostly overwritten), in the middle of this grouping of clusters.  Also notice that many of the legacy fields do not meet all of the criteria we are using now.

If you have ideas for great lensing clusters, check out our website for the current list being considered.  If your favorite isn’t listed there, send it to us quickly at frontierfields@stsci.edu!  We will finalize this list by next week!

Elizabeth Barker
Frontier Fields team member (and official blogger)

 Posted by at 2:54 pm