0 Assigned ID: 2613 ----- Attempting Submission 1 (Thu Sep 30 23:14:35 GMT 2021) ----- FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser 0 ----- Attempting Submission 1 (Tue Dec 14 19:28:20 GMT 2021) ----- The warning is about CTE issues due to a predicted low background level for the F814W UVIS exposures in Visit 4. The predicted background from APT is significantly lower than what we get from the ETC, and we have used the ETC value as recommended. The exposures include FLASH=1 to reach a background level of 20 e- according to the ETC. Unveiling the Source of Extreme Ionization in a Lensed Galaxy at z=2.6 Studies of the most highly ionized galaxies in the universe offer insights into the complex interplay between feedback, shocks, and radiative cooling, driven by extreme star formation or accreting supermassive black holes. We here propose eight orbits of broad and narrowband imaging of J1356-2313, a puzzling, newly discovered gravitationally lensed source at z=2.6 with the highly unusual combination of extreme high ionization UV line emission from O VI, N V, He II and C IV coupled with damped Lya absorption. Integral field spectroscopy of the kinematically narrow O VI emission reveals that it is gravitationally lensed into an arc, indicating a spatially extended source larger than an AGN narrow-line region; further, the line is kinematically inconsistent with a quasar outflow. The very high ionization emission lines may instead be a signature of catastrophic radiative cooling, which may suppress feedback in the most extreme starbursts. With the proposed broadband imaging, we will construct a lensing model and determine the intrinsic luminosity of the source and the structure of the emitting region(s). Modeling of the spectral energy distribution will offer further constraints on the nature of the ionizing source. We also propose narrowband imaging of the extremely strong and spatially extended O VI emission, which is fortuitously redshifted into the F373N filter. The spatial resolution of HST in combination with the magnification of gravitational lensing will provide an unprecedented map of extremely high ionization line emission in the distant universe, allowing tests of the emission mechanisms discussed above. The goal of this proposal is to use WFC3-UVIS/IR to obtain both broad (F606W, F814W, F125W, F160W) and narrow/medium-band (F373N and F390M) imaging of the gravitationally lensed galaxy J1356-2313. The program consists of 8 orbits, two in each of the narrow/medium filters and one in each of the broadband filters. Observations with each filter are configured as separate visits, so we have a total of six visits: two 2-orbit visits and four visits with one orbit each. For the F373N and F390M imaging we divide each orbit into three exposures using the UVIS-DITHER-LINE-3PT pattern, balancing considerations of cosmic ray rejection with the changes in efficiency, background and S/N from increasing the number of exposures. We mitigate CTE effects by using the UVIS-C1K1C-CTE aperture in order to place the target near one of the amplifiers, and further specify FLASH=16 in order to reach the recommended background level of 20 e-, based on calculations with the ETC. We also use the UVIS-C1K1C-CTE aperture for the broadband F606W and F814W observations. With one orbit and visit per filter, we divide these observations into four exposures per orbit with the UVIS-DITHER-BOX pattern in order to enable rejection of cosmic rays and detector artifacts. For the F814W observations the ETC predicts 19 background e-, and we therefore add FLASH=1 to reach the recommended level of 20. Note that this differs from the APT background prediction, which is lower and therefore recommends more FLASH. As advised by the APT warning, we use the ETC predictions. For the IR observations in F125W and F160W with larger pixels, we use a 4-point box dither followed by a 3-point line for a total of seven exposures at six 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 STEP50 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, and the seven exposures with two different exposure times enable the most efficient use of the full orbit. This program has no constraints on the roll angle or on the time of observations, so there are no specific impacts of reduced gyro operations. PI Prof. Dawn Erb has extensive experience in imaging and spectroscopy of high redshift galaxies. Most relevant to the work proposed here, she recently led a study combining WFC3 UVIS narrowband imaging of Lya emission in a gravitationally lensed galaxy with Keck spectroscopy in order to compare the spatial distributions of Lya and continuum emission at high resolution and assess the spatial origins of features observed in the spectrum (Erb et al 2019). We propose a similar analysis with the O VI emission from J1356-2313. Co-I Dr. Matthew Auger is an expert on gravitational lensing, and initially discovered and identified the unusual nature of J1356-2313. He has constructed lens models for large numbers of high redshift galaxies; those recently studied by our team include Berg et al 2018, Erb et al 2019, Citro et al 2021. Co-I Prof. Danielle Berg is an expert in the spectroscopy of galaxies, with particular expertise in the analysis of the most extreme and highly ionized sources. She has led or supervised a number of recent papers using photoionization modeling to try to identify the sources of high energy photons in the most extreme galaxies (Berg et al 2018, 2019, 2021; Olivier et al 2021). These efforts include modeling the contributions of shocks and AGN as well as star formation, so will be extremely relevant to the understanding of J1356-2313. Co-Is Dr. Annalisa Citro and Dr. Bethan James are experienced in the spectral analysis of gravitationally lensed sources (Citro et al 2021, James et al 2014, 2018). Co-I Prof. Max Pettini is one of the leading experts on the study is of gravitationally lensed galaxies, having pioneered the field with detailed analysis of the lensed galaxy MS1512-cB58 (Pettini et al 2001, 2002) and worked on many other analyses of lensed galaxies (e.g. Quider et al 2009, 2010, James et al 2014, 2018). References: Berg, D. A., Chisholm, J., Erb, D. K., et al. 2019, ApJ, 878, L3 Berg, D. A., Chisholm, J., Erb, D. K., et al. 2021, ApJ, in press. arXiv e-prints, arXiv:2105.12765 Berg, D. A., Erb, D. K., Auger, M. W., et al. 2018, ApJ, 859, 164 Citro, A., Erb, D. K., Pettini, M., et al. 2021, ApJ, in press. arXiv e-prints 2109.09748 Erb, D. K., Berg, D. A., Auger, M. W., et al. 2019, ApJ, 884, 7 James, B. L., Auger, M., Pettini, M., et al. 2018, MNRAS, 476, 1726 James, B. L., Pettini, M., Christensen, L., et al. 2014, MNRAS, 440, 1794 Olivier, G. M., Berg, D. A., Chisholm, J., et al. 2021, arXiv e-prints, arXiv:2109.06725 Pettini, M., Rix, S. A., Steidel, C. C., et al. 2002, ApJ, 569, 742 Pettini, M., Steidel, C. C., Adelberger, K. L., et al. 2000, ApJ, 528, 96 Quider, A. M., Pettini, M., Shapley, A. E., & Steidel, C. C. 2009, MNRAS, 398, 1263 Quider, A. M., Shapley, A. E., Pettini, M., et al. 2010, MNRAS, 402, 1467 Galaxies Supermassive Black Holes and Active Galaxies 3 false false false false false false false false SUPPORTED GALAXY EINSTEIN RING GRAVITATIONAL LENS HIGH REDSHIFT GALAXY J2000 J2000 WFC3/UVIS Imaging No No F373N WFC3/UVIS Imaging No No F390M WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 5 false POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 2 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 3 false POS-TARG DITHER 0.605 LINE false false 3 41.788 WFC3-IR-DITHER-LINE-3PT 4 false /Users/erbd/Dropbox/props/cycle29mid/OP-cache/J1356-phase2-v01.xml The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. 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