11678( 3) - 22-May-2009 14:02:24 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11678 Version: 3 Check-in Time: 22-May-2009 14:02:24 STScI Edit Number: 0 Title Resolved H alpha star formation in two lensed galaxies at z=0.9 ------------------------------------------------------------------------------------ Type Cycle GO 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Jane R. Rigby Carnegie Institution of Washington ------------------------------------------------------------------------------------ Abstract We will obtain H alpha narrow-band images of two galaxies at z=0.912 that have been gravitationally lensed by the galaxy cluster Abell 2390. H alpha falls squarely into the F126N filter, and both galaxies fit in a single WFC3 field of view. Because these two galaxies are magnified by factors of 6.7 (+-0.4) and 12.6 (+-0.8), WFC3 IR pixels probe spatial scales of 150 and 80 pc. (Without lensing, the WFC3 pixels probe 1 kpc scales at these redshifts.) Thus, these two galaxies provide a rare chance to examine, in detail and at high S/N, the spatial distribution of star formation in average galaxies at z=1. After lensing deprojection, we will study the spatial distribution of star formation, the star-forming disk properties and nuclear contribution, as well as the distributioin of extinction (from the archival F55W to H-alpha ratio map). We will also compare integrated extinction--corrected H alpha to Spitzer-derived diagnostics of star formation rate. ------------------------------------------------------------------------------------ Observations Description ------------------------ We use two filters: F126N to capture H-alpha at z=0.912, and F125W as continuum. Because the wide filter will continuum-subtract the narrow filter, identical dither positions are required. The two target galaxies are separated by just 19", and thus fit easily in a single WFC3 field of view. Low background makes the F126N observations readnoise limited. To minimize readnoise, we use only 3 dither positions, and 3 long exposures in STEP200 mode. For pessimistic assumptions of H alpha distribution, the per-pixel F126N signal/noise ratios will be >4 and 6 for galaxies A and B. If H alpha is concentrated like the F814W light, then the S/N will be ~15 per pixel. We begin each orbit with an F126N exposure. In F125W, we avoid saturation of the brighter (J=17.31) target by limiting exposures to <400s. As such, we use STEP50 sampling, a good compromise since it avoids saturation and comes close to the sky/readnoise equality point. For each filter, we use 3 dither positions, separated by 7", with integer pixel steps, to step over bad pixels and other detector defects. In such a small program, we are not able to dither sufficiently to overcome the undersampled PSF. The benefits of 4-6 dither positions would be overwhelmed by the increased readnoise in F126N. 11678( 3) - 22-May-2009 14:02:24 - [ 2] Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 11678( 3) - 22-May-2009 14:02:24 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 A2390ARCS GALAXY, GRAVITATIONAL RA=21H53M34.4600S +/- 0.1", J2000 Z = J=17.31 and J=20.1 LENS, HIGH REDSHIFT DEC=+17D42'9.37" +/- 0.1" 0.912 GALAXY Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 11678( 3) - 22-May-2009 14:02:24 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 A2390ARCS WFC3/IR MULTIAC IR F126N NSAMP=14, SAMP-SEQ=STEP200 1 DEF POS TARG -4.995, -4.961 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 A2390ARCS WFC3/IR MULTIAC IR F126N NSAMP=14, SAMP-SEQ=STEP200 1 DEF POS TARG 0.0, 0.0 CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 A2390ARCS WFC3/IR MULTIAC IR F126N SAMP-SEQ=STEP200, NSAMP=14 1 DEF POS TARG 4.995, 4.961 CUM ------------------------------------------------------------------------------------------------------------------------------------ 4 A2390ARCS WFC3/IR MULTIAC IR F125W SAMP-SEQ=STEP50, NSAMP=12 1 DEF SAME POS AS 3 CUM ------------------------------------------------------------------------------------------------------------------------------------ 5 A2390ARCS WFC3/IR MULTIAC IR F125W SAMP-SEQ=STEP50, NSAMP=12 1 DEF SAME POS AS 2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 6 A2390ARCS WFC3/IR MULTIAC IR F125W SAMP-SEQ=STEP50, NSAMP=12 1 DEF SAME POS AS 2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 7 A2390ARCS WFC3/IR MULTIAC IR F125W SAMP-SEQ=STEP50, NSAMP=12 1 DEF SAME POS AS 1 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ A2390ARCS 1 WFC3/IR MULTIAC IR F126N none none none none 1 N/A CUM A2390ARCS 2 WFC3/IR MULTIAC IR F126N none none none none 1 N/A CUM A2390ARCS 3 WFC3/IR MULTIAC IR F126N none none none none 2 N/A CUM A2390ARCS 4 WFC3/IR MULTIAC IR F125W none none none none 2 N/A CUM A2390ARCS 5 WFC3/IR MULTIAC IR F125W none none none none 2 N/A CUM A2390ARCS 6 WFC3/IR MULTIAC IR F125W none none none none 2 N/A CUM A2390ARCS 7 WFC3/IR MULTIAC IR F125W none none none none 2 N/A CUM 11678( 3) - 22-May-2009 14:02:24 - [ 5] Summary Form for Proposal 11678 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=12, NSAMP=14, SAMP-SEQ=STEP200, SAMP-SEQ=STEP50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG -4.995, -4.961, POS TARG 0.0, 0.0, POS TARG 4.995, 4.961, SAME POS AS 1, SAME POS AS 2, SAME POS AS 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125W, F126N ------------------------------------------------------------------------------------------------------------------------------------ Target Names A2390ARCS ------------------------------------------------------------------------------------------------------------------------------------