0 Assigned ID: 609 ----- Attempting Submission 1 (Fri Apr 10 17:43:29 GMT 2015) ----- HST Phase I Proposal 609 (hst23_snells_sub.apt) successfully submitted. Receipt: # 609-1 ----- Attempting Submission 2 (Fri Apr 10 22:17:16 GMT 2015) ----- 0 ----- Attempting Submission 1 (Mon Jul 20 16:49:18 GMT 2015) ----- ----- Attempting Submission 2 (Wed May 18 19:08:00 GMT 2016) ----- We propose WFC3/UVIS imaging of newly-identified strong gravitational lenses from SNELLS, the "SINFONI Nearby Elliptical Lens Locator Survey", at the ESO VLT. Our novel approach uses IFU observations to search for lensed background line emitters behind very low redshift (z<0.06) massive ellipticals. The key characteristic of such nearby lenses is that the gravitional deflections are dominated by stellar mass, with only very small contributions from dark matter. As such, they provide uniquely robust constraints on the stellar mass-to-light ratio (M/L), and hence the initial mass function (IMF). To date, SNELLS has discovered two new lenses, SNL-1 at z=0.031 and SNL-2 at z=0.052. Analysing these systems, as well as the previously-known low-z lens ESO325-G004, we found that all three have M/L consistent with a standard MW-like IMF. This result is very surprising in the context of recent works which favour Salpeter or bottom-heavy IMFs in massive ellipticals. A major limitation of our present analysis is that SNL-1 and SNL-2 are two-image systems, and the arcs are unresolved in our ground-based observations. As a result, the lensing mass is degenerate with the component of external shear along the image separation axis. This degeneracy can be broken by measuring the tangential extent of the arcs (or more generally, the detailed structure of the lensed images). In this application, we propose HST observations which will spatially resolve the arcs, and greatly improve the robustness of our lensing mass estimates. The data will reduce the error on M/L by a factor ~5 and, combined with ongoing deep spectroscopy from the VLT, lead to tighter derived constraints on the IMF. The targets are two nearby (z=0.03,0.05) early-type galaxies behind which we have discovered multiply-imaged background line emitters. The aim of the observations is to measure accurate position, flux and size of the lensed images, for improved modelling of the lens system, narrowing the constraints on the stellar mass of the foreground galaxy. We observe each target in a blue bandpass (F336W or F390W, depending on target), to improve contrast between the star-forming background galaxy and the very red foreground galaxy. We also aquire imaging in a red bandpass (F814W), to help model the stellar mass distribution in the lens. The observation should be fairly straightforward, with a simple three-point offset pattern in each band for cosmic ray and detector defect rejection. We elected to use post-flash to mitigate CTE losses in the F336W observations (also for F814W where the exposures are short). This might not be strictly necessary for the primary science, because the "targets", i.e. the lensed sources, will sit on a substantial background (actually foreground!) of light from the lens galaxy. This also means that post-flash will not add significant extra noise for our purposes, and using it should improve the archival value of the data. ====================== Summary of changes since original Phase II submission: Added a roll-range restriction for SNL-1. Changed to C1K1C-CTE aperture to keep target close to the amplifier. Switched to the standard small 3-point line dither, instead of the large 1-arcsec dither as before. UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 12 false false false false SUPPORTED GALAXY ELLIPTICAL GRAVITATIONAL LENS Redshift is given for the lens galaxy; source redshfift is z=0.9 SNL-1 J2000 J2000 lens J=11.8, source U=25 GALAXY GRAVITATIONAL LENS LENTICULAR Redshift is given for the lens galaxy; source redshfift is z=2.0 SNL-2 J2000 J2000 lens J=11.9, source U=25 WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F390W WFC3/UVIS Imaging No No F814W 1463598187541 The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. /Users/rjsmith/astro/hst23/OP-cache/fix2-v03.xml Roll range restriction to avoid the brightest star (although would be on opposite corner of the field w.r.t the target). In practice, the orbit planner shows that for late 2016 this target can only be observed near 80 deg. Now using C1K1C-CTE window to place closer to amplifier and using small 3-point line-dither. (Tic-Visit :proposal-id 14210 :visit-id "03" :proposal-version -1 :trans-version "20150609" :date "18-May-2016 20:03:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1732464 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14210 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14210 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2973 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3307 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14210 :visit-id "03" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3084 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3307 :pcs-gap 0 ) true 2 0 1463590151739 The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. /Users/rjsmith/astro/hst23/OP-cache/fix2-v04.xml No roll-range restriction. Now using C1K1C-CTE window to place closer to amplifier and using small 3-point line-dither. (Tic-Visit :proposal-id 14210 :visit-id "04" :proposal-version -1 :trans-version "20150609" :date "18-May-2016 17:49:11.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1732464 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14210 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14210 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2872 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3213 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14210 :visit-id "04" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2984 :al-overhead-at-end 116 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3213 :pcs-gap 0 ) true 2 0