A silver bullet for the sources of reionization

A silver bullet for the sources of reionization Recent discoveries of z>6 galaxies have given us the first glimpse of the Universe shortly after the era of reionization. The questions arose whether these first galaxies can be made responsible for the reionization process, and how long did it last. Neither observations nor theory provide a clean answer. In particular observations give results that are barely mutually consistent and need to be further tested. Observing high redshift (z>7) sources is in general difficult, mostly due to the high luminosity distance to these objects, and partly due to the lower expected stellar masses compared to objects at moderate redshifts. We propose to use one of the most massive, merging cluster 1E0657-56 (z=0.295) as a cosmic telescopes to efficiently probe the high-redshift universe. The gravitational potential well of this cluster provides several magnitudes of magnification, enabling study of intrinsically lower luminosity galaxies.As we discuss in the proposal, due to its highly elongated mass distribution and ideal redshift the bullet cluster is a prime candidate for this study. We propose deep WFC3 (awarded as NICMOS) and WFPC2 observations; with much reduced observing time compared to e.g. NICMOS UDF we expect an order of magnitude more (~5 candidates) z>7 objects. They will also likely be multiply imaged, and since the geometry of images depends upon the redshift, we will be able to confirm their nature, thereby not requiring (often prohibitive at these magnitudes) spectroscopic follow-up. This will enable us to count high-redshift sources and constrain their luminosity function; a task made possible with the help of gravitational lensing even in the pre-JWST era.

The goal of this program is to identify and study high-redshift (z>7) objects with the help of the magnifying power of one of the most massive and most elongated clusters. The use of HST is critical to this program for two reasons: (1) sensitivity and depth are absolutely crucial for this project and HST's IR cameras are more sensitive than a ground-based 8m telescope (2) the search for and identification of multiply imaged sources can only be done through exquisite resolution of the space based imaging. The WFPC2 part of the program has been executed, the remaining NICMOS exposures have been transferred to WFC3/IR observations. Required Area: This program requires two pointings with WFC3. For the two pointings we do not require specific roll-angles, however *****we will need to change the pointing positions depending on the roll-angle****** by no more than 20arcsec. Slight preference is given to positions angles of 70-110deg or 250-290 deg. Required Filters: We request observations in WFC3-IR/F110W and WFC3-IR/F160W. Dithering - The 10 orbits in WFC3/F110W and F160W are split into 2 visits, 5 orbits each. Each of the 2 visits has 20 exposures, 10 pairs of exposures for two filters (half-orbit in F110W and F160W each). 5 orbits are used to implement 4-point WFC3-DITHER-BOX-MED dithering pattern and the last pair is used in the centre. Corresponding pixel positions of the dither pattern are (0,0),(20,7.5),(12.5,20), (-7.5,12.5), (6.25,8.25). Same dither pattern is repeated for the second visit. COSMOLOGY 12 false 0.0 0.0 false false false false false false SUPPORTED CLUSTER OF GALAXIES GRAVITATIONAL LENS RICH CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 06 58 27.4000 -55 56 47.00 J2000 CLUSTER OF GALAXIES GRAVITATIONAL LENS RICH CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 06 58 27.4000 -55 56 47.00 J2000 CLUSTER OF GALAXIES GRAVITATIONAL LENS RICH CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 06 58 27.4000 -55 56 47.00 J2000 NIC3 Imaging No No F110W NIC3 Imaging No No F160W WFPC2 Imaging No F814W POS-TARG DITHER 0.559017 LINE 0.559017 false false 143.1301 4 26.56505 WFPC2-BOX 1

false

POS-TARG DITHER 3.394 LINE false false 2 45.0 LINE 2

false

Same orient constraint links visits (01 02 03) The scheduling data was generated by CASM 17.2. 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CASM was run in Phase II mode. 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