Phase 2 revised May 2009 at STScI's request, due to non-availability of MIF modes. I switched from 2 to 3 exposures in F126N for better CR subtraction (after discussion w P. McCarthy.) Also shifted time from F125W to F126N, motivated by a new (brighter) estimate of the continuum flux; this mitigates the higher RN in F126N from 3 vs 2 dithers. ----- Attempting Submission 1 (Tue Jul 01 17:09:46 GMT 2008) ----- ----- Attempting Submission 2 (Fri May 22 00:31:36 GMT 2009) ----- Assigned ID: 280 ----- Attempting Submission 1 (Fri Mar 07 06:06:01 GMT 2008) ----- Phase I Proposal 280 (a2390.apt) successfully submitted. ----- Attempting Submission 2 (Fri Mar 07 06:27:18 GMT 2008) ----- Resolved H alpha star formation in two lensed galaxies at z=0.9 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.
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. UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 12 false 0.0 0.0 false false false false false SUPPORTED GALAXY GRAVITATIONAL LENS HIGH REDSHIFT GALAXY J=17.31 and J=20.1 J2000 21 53 34.0800 +17 42 13.20 J2000 WFC3/IR Imaging No No F126N WFC3/IR Imaging No No F125W The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /private/tmp/OPVisit7336.xml (Tic-Visit :proposal-id 11678 :visit-id "01" :proposal-version -1 :trans-version "20090130" :date "21-May-2009 17:24:20.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1688656 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11678 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11678 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2910 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11678 :visit-id "01" :orbit-number 2 :pcs-time 195 :si-vis-utilization 3032 :al-overhead-at-end 0 :internal-dur-at-end 516 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 2 0