0 Assigned ID: 1677 ----- Attempting Submission 1 (Wed Mar 21 17:05:24 GMT 2018) ----- HST Phase I Proposal 1677 (lsqlens.apt) successfully submitted. Receipt: # 1677-1 ----- Attempting Submission 2 (Wed Mar 21 17:31:11 GMT 2018) ----- HST Phase I Proposal 1677 (lsqlens.apt) successfully submitted. Receipt: # 1677-2 ----- Attempting Submission 3 (Wed Mar 21 20:35:19 GMT 2018) ----- HST Phase I Proposal 1677 (lsqlens.apt) successfully submitted. Receipt: # 1677-3 See "proposal description" for the comments. I think everything should be fairly straightforward. -1428503001 ----- Attempting Submission 1 (Thu May 17 15:44:09 GMT 2018) ----- We request WFC3/UVIS imaging of a newly-discovered low-redshift strong-lensing elliptical galaxy. Nearby lenses provide uniquely-robust measurements of the stellar mass-to-light ratios, because their Einstein radii are small, so that lensing measures the stellar mass, with only small contributions from dark matter. Until recently, only three nearby elliptical lenses were known, and all yielded low M/L values consistent with a MW-like Initial Mass Function (IMF), in tension with the apparent presence of dwarf-enriched populations from modelling their spectra. The target of this observation is a new low-z lens, discovered in February 2018, during a systematic search for multiply-imaged line-emission behind massive galaxies in archival VLT/MUSE datacubes (Collier, Smith & Lucey 2018b). The system comprises an elliptical galaxy at z=0.066, with two very bright arcs formed by an emission line galaxy at z=0.192. The Einstein radius is 1.4", which projects to only ~2 kpc, minimizing the dark matter correction. A simple lensing analysis yields a stellar M/L ratio compatible with a MW-like IMF, in contrast to some studies which infer bottom-heavy IMFs in massive ellipticals. We now request HST observations to measure the resolved structure of the lensed images, and the inner luminosity profile of the lens itself, in order to constrain more complex mass models. We will fit models incorporating stellar and dark matter components, including stellar M/L gradients, constrained jointly by the MUSE kinematics and the pixel-level lensing. Among all the known low-z lenses, our target lens is the most suitable for this analysis, due to the bright and extended nature of its lensed arcs. -- From Phase I pdf: The two goals of our observation are: (1) to image the lensed arcs at HST resolution, so that we can use the internal structure of the source to better reconstruct the lens mass model; and (2) to define the inner luminosity profile for use in the lensing/dynamical modelling. Goal (1) is best addressed using a blue pass-band, to reach higher angular resolution, to harness the typically higher degree of "structure" in star-forming galaxies in the blue/UV, and to improve contrast against the red starlight of the foreground galaxy. For Goal (2), a red pass-band is preferred, to approximate the stellar mass as closely as possible (modulo M*/L variations). Note that a red-band image also helps in defining and subtracting the lens light distribution prior to modelling the lensed arcs. Hence we request observations in F390W (the most sensitive band lying largely short-ward of the lens 4000-Ang break) and in F814W (the most efficient red passband of WFC3/UVIS). In order to observe both bands, with four exposures per band (to yield cosmetically clean images) and with individual exposures long enough to avoid strong CTE losses, TWO orbits are required. With this strategy, the total exposure time will be ~3700sec in F390W and ~1300 sec in F814W; these are similar to the images of the SNELLS galaxies used in Collier et al. (2018a). As in our previous observations, we will use the UVIS2-C1K1C-CTE aperture to place the target near the read-out amplifiers to mitigate CTE effects. -- There is just one target to be observed, with 4xF390W (long) and 4xF814W (short) exposures. The target is a bright elliptical galaxy with gravitationally-lensed arcs. I've set an orient restriction to keep the r=13 star away from the edge of the FoV, to avoid scattered light problems (this doesn't seem to cost too much in schedulability). I'm using UVIS2-C1K1C-CTE aperture, and minimum flash suggested by the APT, to mitigate against CTE losses. (This is probably overkill, since the arcs sit on substantial diffuse light from the lens galaxy.) I've set up a dither pattern using POS-TARG entries. One pixel = 0.04 arcsec, so I'm using a 4-point dither box with sidelength (N+0.5)*0.04 arcsec, and N=5, so dithers are 0.22 pixels. Each orbit has two exposures, covering one diagonal of the dither box, in each band. Galaxies and the IGM Cosmology 3 false false false false false false false SUPPORTED GALAXY EINSTEIN RING ELLIPTICAL GRAVITATIONAL LENS YES J2000 J2000 WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F390W 1526571835315 /private/var/folders/dc/jc71fhpn0d154cd9s8ndyv9r0000gn/T/OPVisit2824239459102249501.xml The scheduling data was generated by CASM 26.0. CASM was run in Phase II mode. 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