Assigned ID: 273 ----- Attempting Submission 1 (Fri Feb 25 03:44:31 GMT 2011) ----- HST Phase I Proposal 273 (HeII_hst_cycle19.v0.5.pdf.apt) successfully submitted. ----- Attempting Submission 1 (Wed Jul 06 17:11:33 GMT 2011) ----- HST Phase II Proposal 12487 (HeII_HST_cycle19.phaseii.apt) successfully submitted. ----- Attempting Submission 2 (Wed Jul 06 17:34:24 GMT 2011) ----- HST Phase II Proposal 12487 (HeII_HST_cycle19.phaseii.apt) successfully submitted. ----- Attempting Submission 3 (Wed Jul 06 17:47:19 GMT 2011) ----- Probing Population III Star Formation in a z=7 Galaxy We propose to carry out deep WFC-3/F132N narrow-band imaging of the galaxy BDF-521 (z = 7.008+/-0.002) to measure the strength of He II 1640 emission line in this young galaxy at the end of reionization epoch. He II 1640 emission, if detected, will provide the first direct evidence of massive Population III (metal free) star formation in the early Universe. In a pilot program in Cycle-17, we obtained narrow-band imaging centered on HeII for the galaxy IOK-1 at z=6.96, and found the He II flux to be 1.2+/-1.0 x 10^-18 ergs s^-1 cm^-2, corresponding to a 1-sigma upper limit of 2 M_sun/yr in Pop-III star formation rate (SFR) assuming a top-heavy IMF. This sensitivity is 2.5x deeper than for the best previous ground-based measurement, and illustrates the power of HST narrow-band imaging in probing the earliest star formation. In this cycle, we will continue this effort by targeting galaxy BDF-521 at z=7.01 using F132N which covers the HeII emission at the galaxy redshift. The ground based photometry implies that BDF-521 has an extremely blue continuum slope with f_lambda ~ lambda^-4, the bluest among all confirmed galaxies at z>6, suggestive of either extremely low metallicity and/or a complete lack of dust. Therefore, BDF-521 is the most promising candidate for Pop-III detection. This new HST observations will be able to detect or place the most stringent upper limit of 0.6 M_sun/yr on the Pop-III SFR (1 sigma). We will also use short F125W and F160W broad-band observations to measure the rest-frame UV flux of BDF-521 in order to estimate its overall SFR, confirm the blue UV slope, and quantify the morphology, as well as provide continuum subtraction for narrow-band imaging.
We will image in three filters with WFC3/IR: (1) 11-orbit exposure in F132N. (2) 2-orbit exposure in F125W. (3). 2-orbit exposure in F160W. We will divide the program into four visits. In the first visit, we will observe: (1). Two orbits F125W. (2). Two orbits F160W. We will do the same 4-point dither sequence with ~1450sec exposures to populate the 2-orbit F125W and F160W observations. In the second and third visits, we will observe: Four orbits in F132N. We will carry out a 4-point dither sequence with orbit-long (~2800sec) exposures in the narrow F132N band. This will bring the images to being background-limited. In the fourth visit, we will do: three orbits in F132N. We will carry out a 3-point dither sequence with orbit-long(~2800sec) exposures in the narrow F132N band. We will do a small POS-TARG offset for the third and the fourth visits and repeat the same sequence. COSMOLOGY 12 false 0.0 0.0 false false false false SUPPORTED GALAXY HIGH REDSHIFT GALAXY J2000 J2000 Y_AB=25.86; J_AB>26.5; K_AB>26.0 WFC3/IR Imaging No No F132N WFC3/IR Imaging No No F125W POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false POS-TARG DITHER 0.605 LINE false false 3 41.788 WFC3-IR-DITHER-LINE-3PT 2 false /Users/iraf/Documents/Latex_code/proposal/OP-cache/HeII_HST_cycle19-v01.xml The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. 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