0----- Attempting Submission 1 (Thu Jul 23 07:03:10 GMT 2015) -----The Lowest Luminosity Star-Forming GalaxyWe propose ACS/WFC imaging of the newly discovered Milky Way satellite galaxy Eridanus II. Eri II is unique among nearby dwarfs in that it appears to contain young stars but has no detected gas, and it is located just beyond the transition radius around the Milky Way inside of which star formation is rapidly quenched. With a luminosity of only 54000 Lsun, Eri II is likely the lowest luminosity star-forming galaxy yet found, surpassing Leo T. This combination of properties makes Eri II a key target for studying the mechanisms by which low-mass galaxies are quenched, and it will provide new insight into why some dwarfs are able to continue forming stars for a Hubble time while other seemingly similar objects are not. We will use a deep HST color-magnitude diagram to derive the star formation history of the galaxy, confirming the existence of its young population, measuring the age of its oldest stars, and determining whether its star formation has been continuous or episodic.This program will obtain straightforward deep imaging with one ACS tile on the galaxy and one parallel WFC3 tile just outside the galaxy. The individual exposures will be dithered to resample the PSF, reduce detector artifacts, and dither the gap.
The 4 2-orbit F814W visits each contain a 2x2 resampling of the PSF, with each visit stepping by 40% of the detector gap in ACS.
The 2 2-orbit F606W visits each contain a 2x2 resampling of the PSF, with each visit offset stepping by 120% of the detector gap in ACS. A 5th 1-orbit F606W visit obtains the 1st and 3rd steps in the PSF resampling, and falls between the two larger offsets of the detector gap.
All visits should execute at the same orient to maximize the field coverage obtained at the greatest depth.RESOLVED STELLAR POPULATIONS12falsefalsefalsefalse0.00.00.0SUPPORTEDGALAXYDWARF SPHEROIDALJ2000ACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WHst Same orient constraint links visits (01 02 03 04 05 06 07)The scheduling data was generated by CASM 23.2.CASM was run in Phase II mode./stanford/jsimon/proposals/hst/cycle23/eri2/phase2/OP-cache/14234-v01.xml4-point dither for PSF combined with larger dither by -0.6 gap(Tic-Visit
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