The hydrogen Lyman-alpha line is arguably the most important signature of galaxies undergoing their first violent burst of star formation. Although Lya photons are easily destroyed by dust, candidate Lya emitters have been detected at z>5. Thus the line can potentially be used to probe galaxy formation and evolution, as long as the astrophysical processes that regulate the escape of Lya photons from star-forming galaxies are well understood. We request 15 orbits for imaging in Lya and the FUV continuum with ACS/SBC, and in the H-beta/H-alpha ratio (proxy for dust extinction) with WFC3/UVIS, a sample of isolated non-AGN face-on spirals for which our team previously obtained and analyzed COS FUV spectroscopy of the central regions. Each target shows a different Lya profile, i.e., pure absorption, P-Cygni like, and multiple-emission. From the COS data, we already know the starburst phase and H I gas velocity. The images would greatly increase the impact of our spectroscopic study by enabling us to 1) conclusively determine if Lya photons escape through dust-holes, 2) assess the relative importance of dust extinction, ISM kinematics, and starburst phase in regulating the Lya escape, 3) clarify what we can really learn from the Lya equivalent width, and 4) provide constraints on the dust extinction to Lya 3D radiative transfer models. Ultimately this program will inform our understanding of the Lya escape at high redshift by providing spatially resolved views of the local conditions within star-forming galaxies that favor escape. FUV Observations. We require nine orbits to observe three galaxies with ACS/SBC in the three filters F125LP, F140LP, and F150LP (one orbit per filter). Since the total FUV continuum fluxes of our galaxies are within a factor of a few, using equal exposures for each object in all filters is a reasonable observing strategy. Our objects have redshifts high enough to move Lyα into the F125LP filter bandpass, the use of which will eliminate contamination by the geocoronal Lyα emission produced by the Earth’s exosphere, however, this filter does not block the weaker O I λ1304 and λ1356 lines, so we will require observations with F125LP to be made during shadow time, which the on-line exposure time calculator (ETC) shows effectively eliminates the O I background. The duration of shadow time is half of the visibility window. The ETC shows that the other two filters are unaffected by geocoronal light, so they have no orbital restrictions. We will synthesize bandpass filters by forming subtracted images, F125 - F140 and F140 - F150, which we refer to as S132 and S141 respectively (since they have central wavelengths of 1320 Å and 1410 Å, respectively). The S141 and F150 images will contain mostly continuum, while the S131 image will contain continuum and any Lyα emission that might be present. We require two continuum band images (S141 and F150) to provide an estimate of the continuum present in the S131 image. The use of two continuum bands provides a means to estimate both amplitude and slope differences in the spectral energy distributions (SEDs), which improves the accuracy of the continuum flux estimation in the S131 bandpass over that provided by a single continuum image, with which we could only account for amplitude. The observations in each filter will be divided into three sub-exposures for small-scale dithering, which will enable artifact rejection and provide a better sampling of the point spread function (PSF). We intend to split the observation of F125LP and one of the other filters into two orbits to accommodate the shadow only observations. Our calculations for the number of orbits take into consideration the exposure and overhead times. The unrestricted visibility times corresponding to the declinations of our targets are 54 to 55 minutes. In the 54 minute case, allowing for 6 minutes of target acquisition, 3 minutes for filter changes, and 0.6 minutes for the pointing pattern, we arrive at a total on target orbital integration time of 44.4 min = 2664 s. We used our COS spectra to derive the expected sensitivity for detecting Lyα emission using these filters. We find that a Lyα emission line with an EW of 20 Å will produce approximately 10% of the flux in the S132 bandpass. We also find that none of our targets will exceed the MAMA local or global countrate limits of 50 counts s-1 pixel-1 and 2 x 105 counts s-1, respectively. The left panels in Fig. 1 show the COS/G130M spectra of the central regions of our spirals, and the transmission curves of the proposed SBC filters. The right legend of the left panels provides the KISSR ID, redshift, oxygen abundance relative to solar (12+log[O/H]=8.69, Asplund et al. 2009), extinction in the V band (Av), and flux and equivalent width of the Lyα line (the EW is uncorrected for the stellar Lyα; this correction is expected to be <5 Å for ages of <107 Myr, see Fig. 3 of Valls-Gabaud 1993). Optical Observations. We require six orbits to image the above three galaxies with WFC3/UVIS in three filters (one for Hβ, one for the continuum, and one for Hα). The specific filters for each target are specified in the right panels of Fig. 1, where we also show the SDSSS spectra of our targets, which corresponds to the COS pointings, and were taken with a 3” aperture, well matched to the COS aperture of 2.5” in diameter. The Hα images will be contaminated with the adjacent [N II] lines, and in the case of KISSR 298, with the [S II] doublet. The central regions of the images can be corrected using the Hα/[Ν ΙΙ] and Hα/[S II] ratios given by the SDSS spectra. For the rest of the galaxy, we will apply a statistical correction as in Ly et al. (2011). We note the absence of strong emission lines within the bandpass of the off-line filter F621M, to be used for the continuum subtraction. The scaling of the off-line image will be determined by the offset of its bandpass with respect to the relevant emission line. The reduced field of view of the quad filters is a non-issue, since unvignetted (66”x66”), it is still larger than the FOV of SBC (35”x30”), which we propose to use for the Lyα imaging. We will use four dithered exposures in each filter in order to reject cosmic rays, mask detector artifacts, and resample the PSF. In order to reduce the overhead time, we plan to only use a UVIS subarray of ¼ of the area of a full-frame image. We used the SDSS spectra to derive the expected sensitivity for detecting the Hα and Hβ emission lines with the filters of Fig. 1. We find that Hα and Hβ, with EWs derived from the spectra, will produce approximately the following fluxes in their bandpasses. Hα: 32%, 34%, and 11%; Hβ 9%, 20% and 7 %, for KISSR 218, KISSR 1084, and KISSR 298, respectively. Allowing for 6 minutes for the guide-star acquisition, ~10.4 minutes of overhead time per filter (2.6 min for filter change, camera set-up, and readout of the 1st exposure; 3 x 2.1 min = 6.3 min for readout of the 2nd, 3rd, and, 4th exposures; and 3 x 0.5 min = 1.5 min to offset between dither points), and adopting and unrestricted visibility time of 54 minutes, the total on target orbital integration time per filter is 5.6 min = 336 s = (54 min – 6 min – 3 x 10.4 min) / 3, which is shorter than the buffering time of 348 s and qualifies as a short exposure, therefore, in one orbit, we are dominated by the overhead. The quad filters require an additional minute of overhead time, in order to place them in the correct quadrant, reducing the integration time to 4.6 minutes = 276 seconds. One orbit per target is insufficient to achieve S/N>5 in Hα and Hβ in the central regions of our targets, for an extraction aperture of 0.5”, therefore, we request two orbits per target for the optical. ISM IN EXTERNAL GALAXIES 12 false 0.0 0.0 false false false false SUPPORTED GALAXY DISK This object was generated by the targetselector and retrieved from the SIMBAD database. IRAS-13068+2937 J2000 J2000 FUV_1500 [cgs]=8.3e-16 (COS) GALAXY DISK This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 FUV_1500 [cgs]=3.3E-16 (COS) GALAXY DISK This object was generated by the targetselector and retrieved from the SIMBAD database. IRAS-16471+2950 J2000 J2000 FUV_1500 [cgs]=4.4E-16 (COS) ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP WFC3/UVIS Imaging No No FQ492N WFC3/UVIS Imaging No No F621M WFC3/UVIS Imaging No No F665N WFC3/UVIS Imaging No No F502N WFC3/UVIS Imaging No No F621M WFC3/UVIS Imaging No No F673N WFC3/UVIS Imaging No No FQ508N WFC3/UVIS Imaging No No F621M WFC3/UVIS Imaging No No F680N POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 2 false The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. 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