0 Assigned ID: 1667 ----- Attempting Submission 1 (Wed Mar 21 03:34:07 GMT 2018) ----- HST Phase I Proposal 1667 (J1059-MC.apt) successfully submitted. Receipt: # 1667-1 ----- Attempting Submission 2 (Wed Mar 21 04:06:10 GMT 2018) ----- 0 ----- Attempting Submission 1 (Thu May 31 20:09:36 GMT 2018) ----- While thousands of galaxies have now been observed at the peak epoch of star formation, only the rare and highly magnified gravitationally lensed sources in conjunction with high resolution HST imaging enable the study of star formation at sub-kpc scales. We propose multiwavelength WFC3 imaging of J1059+4251 at z=2.79, the brightest galaxy-scale gravitational lens discovered to date. With F606W imaging obtained only a month ago, we have discovered that the source is magnified by an extraordinary factor of ~130, with multiple knots of star formation on scales of ~50 pc in the source plane. We therefore now request imaging in three additional filters in order to constrain the stellar populations across the source. These data will enable measurements of the stellar mass surface density, the star formation rate and specific star formation rate, the surface density of star formation, and the age and reddening of the stellar populations, all on ~50 pc spatial scales. With these results we will test models of star formation at high redshift by determining the fraction of the total star formation arising in clumps with sizes << 1 kpc, and relate the properties of the star-forming regions to spectroscopic measurements of galactic outflows in order to determine whether the outflows are locally or globally sourced. The unprecedented brightness of J1059+4251 will make it one of the preeminent laboratories for the study of star formation in the high redshift universe, and high resolution, multiwavelength HST imaging will be an essential component of that work. The scientific returns of these observations will be maximized if they are taken during Cycle 25 via the mid-cycle program. The goal of this program is to obtain multi-band imaging of the bright, gravitationally lensed arc SDSSJ1059+4251. Our primary concern is to optimize the spatial sampling, and we will therefore use a 4-point box dither for the UVIS observations. For the IR observations with larger pixels, we will use a 4-point box dither followed by a 3-point line for a total of 7 exposures at 6 different positions. The repeated position, corresponding to the first exposure in each dither pattern, will enable a consistency check of the slightly different exposure times of the two patterns, and the combination of the two patterns will improve the sub-pixel sampling over either pattern alone. We will use the STEP100 sampling sequence in order to obtain good sampling on both the lensed arc and on PSF stars to be used for the de-lensing model. The dither sequences will also enable rejection of detector artifacts and cosmic rays. Galaxies and the IGM 3 false false false false false false false SUPPORTED GALAXY GRAVITATIONAL LENS HIGH REDSHIFT GALAXY J2000 J2000 WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER 0.572 WFC3-IR-DITHER-BOX-MIN 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 2 false POS-TARG DITHER 0.605 WFC3-IR-DITHER-BOX-MIN false false 3 41.788 WFC3-IR-DITHER-LINE-3PT 3 false 1527796494644 /private/var/folders/84/24ddy5tj4y12p1f1zh6lxkl80000gp/T/OPVisit3309107141641419733.xml The scheduling data was generated by CASM 26.0. CASM was run in Phase II mode. 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