0 Assigned ID: 1257 ----- Attempting Submission 1 (Sat Jan 30 11:42:25 GMT 2016) ----- HST Phase I Proposal 1257 (HSTprop_MC_NEW_FEB2016.apt) successfully submitted. Receipt: # 1257-1 SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE 0 ----- Attempting Submission 1 (Sat Apr 09 21:05:21 GMT 2016) ----- ----- Attempting Submission 2 (Wed Apr 20 08:25:38 GMT 2016) ----- We want to assure that grism observations are done in the same way the image obtained before, or that the image following the grism observation is done with the exact same pointing as the grism. This should be done for all pairs of exposures essentially. We have recently discovered the most luminous Lyman-alpha (Lya) emitter ever found in the era of re-ionization ('CR7', z = 6.6, L(Lya)=10^43.9 erg/s; Sobral et al. 2015, ApJ, 808, 139), with extreme Lya rest-frame EW (>200A). Ground-based near-infrared spectroscopy reveals the presence of a strong HeII164nm emission line with narrow FWHM (~130 km/s), high rest-frame EW (~80 A) and the absence of metal lines down to limits which have never been seen before (e.g. HeII/CIII]>2.5 and HeII/OIII]>3.0). Current ground-based data, limited by atmospheric OH lines, already imply a metallicity of at least <0.003 solar and exclude 'normal' AGN. CR7 must therefore host a unique, very hot ionising source (~100kK or higher), which may be explained by i) very low metallicity WR stars, ii) a direct collapse black hole (DCBH) or iii) a PopIII-like stellar population. HST/WFC3 observations reveal that i) CR7 consists of three components (A, B, C) which are separated by ~5 projected kpc and ii) the brightest (A) coincides with the Lya peak and HeII emission. Our new CLOUDY modelling exploring a wide physical parameter space clearly shows that high ionisation N, O and C lines can place strong constraints on the metallicity and physical conditions of the ionised ISM of CR7. Only WFC3 Grism observations on HST can achieve the required sensitivies to test if CR7 is "metal free" (<10^-4 solar). Constraining the metallicity and the ionised ISM is absolutely key towards unveiling the nature of this source and its ISM, testing both the PopIII and DCBH interpretations. We aim to use the unique capabilities of WFC3 to further unveil the nature of CR7 by looking for faint metal lines which can be compared directly with the strong HeII1640 emission. We will use the WFC3 grism to look for any weak emission line which could be an indication that the source is not completely metal-free (or obtain stringent line limits that will imply that the source needs to be completely metal-free). The 141 Grism has the necessary resolution (R~130 at 1.1-1.6 um) to separate all our target lines at z=6.6. Exposure times: ----------------- We use the WFC3IR spectroscopic exposure time calculator to find that in order to achieve our science goals with the WFC3 grism (detect any of NIV1487, CIV1549, OIII]1664, NIII]1750 and CIII]1909 with >0.4x10^-17 erg/s/cm^-2; 3 sigma), we require 12.8 ks. Note that this means that if all lines apart from HeII remain undetected, at the 1 sigma level, the source must be virtually metal free. Observations with the WFC3 grism will consist (our target is visible for 54 minutes per orbit) of a guide-star acquisition (6 min), two un-dispersed science exposures (4.8 minutes) and one science exposure of 40 minutes (per orbit). Filter changes, camera set-ups and readouts will add an extra 4.8 minutes. Thus, in order to achieve the necessary S/N, we require 5 orbits with the WFC3 grism. We will assure (with our WFC3 imaging) that the dispersed light does not overlap with any bright source in the field of view, and that we disperse it in angles which also avoid the overlap of components within CR7 (PA angles 28+-180 and 97+-180). Angles needed to avoid/minimise contamination: ----------------- We will observe the source with 2 different dispersion angles of 28 and 97 deg. We assume these to be PA_DISPERSION angles. We thus compute, for WFC/IR grism ORIENT = (PA_DISPERSION+225.37). This results in ORIENT angles of i) 253.37 (73.37 also possible - dispersion on the opposite direction but along the same angle) and ii) 322.37 (142.37 with the dispersion in the opposite direction). Orbit / visit strategy: ----------------- Each visit consists of 2 orbits + a final one. In these 2 orbits 4 dithered exposures in WFC3/G141 will be obtained, along with 4 direct images taken at the same positions. We follow the simple pattern direct, grism, offset, direct, grism, offset, ... Dithering strategy: --------------- We use POS-TARG offsets to enable rejection of hot/bad pixels and to improve sampling of the PSF. The pattern is: POS-TARG: (0,0) (1.355,0.424) (0.881,1.212) (-0.474,0.788) pixels: (0,0) (10.0,3.5) (6.5,10.0) (-3.5,6.5) This is a larger version of the standard WFC3-IR-DITHER-BOX-MIN pattern, which has only 1-2 pixel offsets between pointings. As some bad pixels come in clumps we prefer a slightly larger pattern. No attempt is made to dither over the "dead spot", as large dithers introduce large differential distortion. Fluxes: --------------- We already know the relevant flux-densities accurately (and many limits), allowing for an accurate estimate of the exposure times without uncertain extrapolations. For our grism observations, the most relevant information is the HeII1640A line-flux:4x10^-17 erg/s/cm^-2. From our X-SHOOTER observations (Sobral et al. 2015), we already have some strong line limits, such as HeII/CIII]1909>2.5 and HeII/OIII]1663>3. We aim to improve these limits by at least a factor of ~3-4, to reach line limits between HeII and lines such as NIV1487, CIV1549, OIII]1664, NIII]1750 and CIII]1909 of >10 (3 sigma) - all separated at the resolution of the grism at z=6.6. Given the strong ionising source, if all these lines are undetected at that level, the source must be virtually metal-free. In order to achieve such limits, we require to detect any emission line with >0.4x10^-17 erg/s/cm^-2 from 1.10-1.65um at >3 sigma. Our observations will also result in a HeII >50 sigma detection, sufficient to characterise its spatial extent and deep enough to look for any emission from clumps B and C in CR7 (our ALMA observations will also provide key information for those). We note that because we already have WFC3 imaging, we can assure the best choice of dispersion angles that assure that sources do not overlap with the three clumps and that the clumps do not overlap between themselves (PA angles 28+-180 and 97+-180). ISM IN EXTERNAL GALAXIES 12 false false false false false false SUPPORTED GALAXY EMISSION LINE NEBULA HIGH REDSHIFT GALAXY LYMAN ALPHA CLOUD NLR YES J2000 J2000 f_Lya = 1.7e-16 erg/s/cm2, f_heII1640 = 4e-17 erg/s/cm2 WFC3/IR Spectroscopic No No G141 1461140641126 The scheduling data was generated by CASM 24.0. CASM was run in Phase II mode. /private/var/folders/tr/3vdhk00s1xgb66tkbt_cv81r0000gn/T/OPVisit6495867258487332148.xml (Tic-Visit :proposal-id 14495 :visit-id "01" :proposal-version -1 :trans-version "20160129" :date "20-Apr-2016 09:24:00.0" :trans-errors '(:WARNINGS 6 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 2071632 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14495 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14495 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2836 :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 3210 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14495 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2886 :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 3210 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14495 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2885 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3210 :pcs-gap 0 ) true 3 0 1461140602063 The scheduling data was generated by CASM 24.0. 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