12180( 3) - 01-Oct-2010 13:32:39 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12180 Version: 3 Check-in Time: 01-Oct-2010 13:32:39 STScI Edit Number: 1 Title The Holistic Evolution of Dwarf Galaxies: Internal and External Processes in NGC 6822 ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. John M. Cannon Macalester College CoI: Dr. Frank Bigiel University of California - Berkeley N CoI: Dr. Andrew A. Cole University of Tasmania N CoI: Dr. Erwin de Blok University of Cape Town N CoI: Dr. Andrew Dolphin Raytheon Company N CoI: Dr. Henry Lee Gemini Observatory, Southern Operations N CoI: Dr. Evan D. Skillman University of Minnesota - Twin Cities N CoI: Dr. Fabian Walter Max-Planck-Institut fur Astronomie, N Heidelberg CoI: Mr. Dan Weisz University of Minnesota - Twin Cities N ------------------------------------------------------------------------------------ Abstract Low-mass galaxy evolution is driven by both internal (e.g., star formation and feedback) and external (e.g., tidal interaction) processes; however, few nearby systems show evidence of both mechanisms operating in tandem. The Local Group dwarf galaxy NGC 6822 presents a unique opportunity to study important evolutionary processes because of proximity and timing: it harbors one of the largest known holes in its neutral ISM (a signpost of violent stellar feedback), and it appears to be undergoing a tidal interaction with a very low mass companion dwarf galaxy. To capitalize on this opportunity, we propose to undertake an ACS and WFC3 imaging study of the stellar populations throughout NGC 6822. We will study the role of both internal and external processes by sampling the stellar populations associated with the main body (using archival WFPC2 data), the giant HI hole, the companion dwarf galaxy, and the tidal material at the ends of the disk. From these data we will extract precise color magnitude diagrams; we will measure the full 13 Gyr star formation history of each field, with high time resolution (20-250 Myr) over the past 1 Gyr, and quantify the relative contributions of internal and external drivers of dwarf galaxy evolution. Specifically, we will study: 1) the nature of the companion object (differentiating between infalling gas and a genuine low-mass galaxy); 2) the energetics of giant HI hole creation; 3) the role of interactions in the system's evolution; 4) the nature of feedback in governing the star formation process; and 5) the patterns of star formation over time. We have optimized our field placements to extract the most information possible about the competing forces that drive galaxy evolution; in only six orbits, we will gain fundamental insights into the contributions of both internal and external processes that bear on the evolution of low-mass galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ To obtain detailed SFHs back to 1 Gyr, we need photometry deep enough to reach M_V = +2.5. The distance of NGC 6822 allows us to reach our requisite 12180( 3) - 01-Oct-2010 13:32:39 - [ 2] photometric depth quickly and eciently. A single 52-minute orbit per pointing will be used to obtain imaging in the F475W and F814W filters (ACS - all fields; WFC3 - non-overlapping fields) and in the F336W filter (WFC3 - overlapping fields). This provides exceptional quality photometry to the depth we require (e.g., S/N > 8, 13 for a star of M_V = +2.5 in the G and I bands, respectively, using either ACS or WFC3; S/N ~ 7 for a star of M_V +1 in the WFC3 U band). We request 6 pointings (3 each at two dierent roll angles), for a total of 6 orbits. NGC 6822 is close enough to allow efficient photometry, but yet distant enough that the ACS and WFC3 detectors can image a significant fraction of the galaxy in a modest number of orbits. We are interested in the nature of multiple stellar populations in various regions of the galaxy, and in how these populations are related. We will combine suciently deep archival WFPC2 pointings with these proposed ACS and WFC3 observations in order to study all regions of interest. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12180( 3) - 01-Oct-2010 13:32:39 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6822-GRID GALAXY, MAGELLANIC RA=19H43M33.5007S +/- 0.1", J2000 V = 26 +/- 1 1 IRREGULAR DEC=-14D33'41.00" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6822-GRID GALAXY, MAGELLANIC RA=19H43M54.0219S +/- 0.1", J2000 V = 26 +/- 1 2 IRREGULAR DEC=-14D37'9.62" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6822-GRID GALAXY, MAGELLANIC RA=19H44M14.8717S +/- 0.1", J2000 V = 26 +/- 1 3 IRREGULAR DEC=-14D40'39.74" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6822-GRID GALAXY, MAGELLANIC RA=19H45M10.2455S +/- 0.1", J2000 V = 26 +/- 1 4 IRREGULAR DEC=-14D49'46.42" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6822-GRID GALAXY, MAGELLANIC RA=19H45M30.2646S +/- 0.1", J2000 V = 26 +/- 1 5 IRREGULAR DEC=-14D53'14.32" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6822-GRID GALAXY, MAGELLANIC RA=19H45M51.1279S +/- 0.1", J2000 V = 26 +/- 1 6 IRREGULAR DEC=-14D56'36.66" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 12180( 3) - 01-Oct-2010 13:32:39 - [ 4] Visit: 01 Visit Requirements: ORIENT 257.8D TO 257.85 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6822-GRI ACS/WFC ACCUM WFC F475W CR-SPLIT=2 1 1119 S PAR 3-4 WITH 1-2 D1 see below ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6822-GRI ACS/WFC ACCUM WFC F814W CR-SPLIT=2 1 1118 S D1 see below ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6822-GRI WFC3/UVI ACCUM UVIS F475W CR-SPLIT=2 1 400 S D1 S see below ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6822-GRI WFC3/UVI ACCUM UVIS F814W CR-SPLIT=2 1 300 S D1 S see below ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6822-GRI ACS/WFC ACCUM WFC F475W CR-SPLIT=2 1 1119 S PAR 7 WITH 5-6 D2 see below ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6822-GRI ACS/WFC ACCUM WFC F814W CR-SPLIT=2 1 1118 S D2 see below ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6822-GRI WFC3/UVI ACCUM UVIS F336W CR-SPLIT=2 1 2740 S D2 S see below ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6822-GRI ACS/WFC ACCUM WFC F475W CR-SPLIT=2 1 1119 S PAR 10 WITH 8-9 D3 see below ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC6822-GRI ACS/WFC ACCUM WFC F814W CR-SPLIT=2 1 1118 S D3 see below ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6822-GRI WFC3/UVI ACCUM UVIS F336W CR-SPLIT=2 1 2740 S D3 S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC6822-GRID1 1 ACS/WFC ACCUM WFC F475W none none none 1 1 423.0 S NGC6822-GRID1 1 ACS/WFC ACCUM WFC F475W none none none 2 1 463 S NGC6822-GRID1 2 ACS/WFC ACCUM WFC F814W none none none 1 1 883 S NGC6822-GRID1 2 ACS/WFC ACCUM WFC F814W none none none 2 1 463 S NGC6822-GRID1 3 WFC3/UVI ACCUM UVIS F475W none none none 1 1 600.0 S S 12180( 3) - 01-Oct-2010 13:32:39 - [ 5] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC6822-GRID1 3 WFC3/UVI ACCUM UVIS F475W none none none 2 1 600.0 S S NGC6822-GRID1 4 WFC3/UVI ACCUM UVIS F814W none none none 1 1 790.0 S S NGC6822-GRID1 4 WFC3/UVI ACCUM UVIS F814W none none none 2 1 474 S S NGC6822-GRID2 5 ACS/WFC ACCUM WFC F475W none none none 1 2 559.5 S NGC6822-GRID2 5 ACS/WFC ACCUM WFC F475W none none none 2 2 559.5 S NGC6822-GRID2 6 ACS/WFC ACCUM WFC F814W none none none 1 2 559 S NGC6822-GRID2 6 ACS/WFC ACCUM WFC F814W none none none 2 2 559 S NGC6822-GRID2 7 WFC3/UVI ACCUM UVIS F336W none none none 1 2 1370 S S NGC6822-GRID2 7 WFC3/UVI ACCUM UVIS F336W none none none 2 2 1370 S S NGC6822-GRID3 8 ACS/WFC ACCUM WFC F475W none none none 1 3 559.5 S NGC6822-GRID3 8 ACS/WFC ACCUM WFC F475W none none none 2 3 559.5 S NGC6822-GRID3 9 ACS/WFC ACCUM WFC F814W none none none 1 3 559 S NGC6822-GRID3 9 ACS/WFC ACCUM WFC F814W none none none 2 3 559 S NGC6822-GRID3 10 WFC3/UVI ACCUM UVIS F336W none none none 1 3 1370 S S NGC6822-GRID3 10 WFC3/UVI ACCUM UVIS F336W none none none 2 3 1370 S S 12180( 3) - 01-Oct-2010 13:32:39 - [ 6] Visit: 02 Visit Requirements: ORIENT 77.8D TO 77.85 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6822-GRI ACS/WFC ACCUM WFC F475W CR-SPLIT=2 1 1119 S PAR 3 WITH 1-2 D4 see below ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6822-GRI ACS/WFC ACCUM WFC F814W CR-SPLIT=2 1 1118 S D4 see below ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6822-GRI WFC3/UVI ACCUM UVIS F336W CR-SPLIT=2 1 2740 S D4 S see below ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6822-GRI ACS/WFC ACCUM WFC F475W CR-SPLIT=2 1 1119 S PAR 6 WITH 4-5 D5 see below ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6822-GRI ACS/WFC ACCUM WFC F814W CR-SPLIT=2 1 1118 S D5 see below ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6822-GRI WFC3/UVI ACCUM UVIS F336W CR-SPLIT=2 1 2740 S D5 S see below ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6822-GRI ACS/WFC ACCUM WFC F475W CR-SPLIT=2 1 1119 S PAR 9-10 WITH 7-8 D6 see below ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6822-GRI ACS/WFC ACCUM WFC F814W CR-SPLIT=2 1 1118 S D6 see below ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC6822-GRI WFC3/UVI ACCUM UVIS F336W CR-SPLIT=2 1 400 S D6 S see below ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6822-GRI WFC3/UVI ACCUM UVIS F814W CR-SPLIT=2 1 300 S D6 S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC6822-GRID4 1 ACS/WFC ACCUM WFC F475W none none none 1 1 559.5 S NGC6822-GRID4 1 ACS/WFC ACCUM WFC F475W none none none 2 1 559.5 S NGC6822-GRID4 2 ACS/WFC ACCUM WFC F814W none none none 1 1 559 S NGC6822-GRID4 2 ACS/WFC ACCUM WFC F814W none none none 2 1 559 S NGC6822-GRID4 3 WFC3/UVI ACCUM UVIS F336W none none none 1 1 1370 S S 12180( 3) - 01-Oct-2010 13:32:39 - [ 7] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC6822-GRID4 3 WFC3/UVI ACCUM UVIS F336W none none none 2 1 1370 S S NGC6822-GRID5 4 ACS/WFC ACCUM WFC F475W none none none 1 2 559.5 S NGC6822-GRID5 4 ACS/WFC ACCUM WFC F475W none none none 2 2 559.5 S NGC6822-GRID5 5 ACS/WFC ACCUM WFC F814W none none none 1 2 559 S NGC6822-GRID5 5 ACS/WFC ACCUM WFC F814W none none none 2 2 559 S NGC6822-GRID5 6 WFC3/UVI ACCUM UVIS F336W none none none 1 2 1370 S S NGC6822-GRID5 6 WFC3/UVI ACCUM UVIS F336W none none none 2 2 1370 S S NGC6822-GRID6 7 ACS/WFC ACCUM WFC F475W none none none 1 3 423 S NGC6822-GRID6 7 ACS/WFC ACCUM WFC F475W none none none 2 3 463 S NGC6822-GRID6 8 ACS/WFC ACCUM WFC F814W none none none 1 3 883 S NGC6822-GRID6 8 ACS/WFC ACCUM WFC F814W none none none 2 3 463 S NGC6822-GRID6 9 WFC3/UVI ACCUM UVIS F336W none none none 1 3 600 S S NGC6822-GRID6 9 WFC3/UVI ACCUM UVIS F336W none none none 2 3 600 S S NGC6822-GRID6 10 WFC3/UVI ACCUM UVIS F814W none none none 1 3 790 S S NGC6822-GRID6 10 WFC3/UVI ACCUM UVIS F814W none none none 2 3 474.0 S S 12180( 3) - 01-Oct-2010 13:32:39 - [ 8] Summary Form for Proposal 12180 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 257.8D TO 257.85 D, ORIENT 77.8D TO 77.85 D, PAR 10 WITH 8-9, PAR 3 WITH 1-2, PAR 3-4 WITH 1-2, PAR 6 WITH 4-5, PAR 7 WITH 5-6, PAR 9-10 WITH 7-8 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F336W, F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6822-GRID1, NGC6822-GRID2, NGC6822-GRID3, NGC6822-GRID4, NGC6822-GRID5, NGC6822-GRID6 ------------------------------------------------------------------------------------------------------------------------------------