15874( 4) - 24-Sep-2019 14:07:07 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15874 Version: 4 Check-in Time: 24-Sep-2019 14:07:07 STScI Edit Number: 1 Title Ultra-Diffuse Galaxy Formation through Interactions ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kristine Spekkens Royal Military College of Canada Y CoI: Prof. David J. Sand University of Arizona N CoI: Mr. Paul Bennet Texas Tech University N CoI: Prof. Dennis Zaritsky University of Arizona N CoI: Dr. Denija Crnojevic University of Tampa N CoI: Ananthan Karunakaran Queen's University N ------------------------------------------------------------------------------------ Abstract We request D-configuration HI observations as well as HST data to image two ultra-diffuse galaxies (UDGs) which are associated with tidal material connected to a larger galaxy halo. These dwarfs provide evidence that UDGs can form via galaxy interactions, although it is not clear whether they are normal dwarf galaxies that have been `puffed up' during the interaction or if they are tidal dwarf galaxies, the dark matter-free stellar aggregations that can result from gas-rich major galaxy encounters. Alternatively, these galaxies may have formed as UDGs through some other mechanism, and are now being stripped by a larger galaxy halo. The deep VLA observations are essential for spatially correlating HI emission with each dwarf and its stream, which would bolster the tidal dwarf galaxy hypothesis. The HST observations will allow for a detailed morphological analysis of each interacting dwarf and its stellar stream, and will also measure their globular cluster content -- a powerful discriminant between these formation scenarios. The proposed observations will point to one of the formation mechanisms of the mysterious class of UDGs. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observations are going to be performed with the ACS/WFC (primary) and WFC3/UVIS (parallel). We request imaging in F555W and F814W filters for both instruments in order to both measure the detailed morphology of each ultra-diffuse dwarf (along with its stellar stream) and their globular cluster (GC) content. The parallel WFC3 pointings will allows us to observe a field region next to our ultra-diffuse galaxy targets and will be invaluable to characterize the 'background' of points sources with consistent magnitudes and colors as the GCs we wish to identify. Each target/visit is two orbits, with the first orbit devoted to F555W and the second to F814W. We use a standard four-point dither box for each orbit, with sub-pixel dithers in order to get closer to the native resolution of ACS. This is vital, as one method we will use to identify globular clusters is to measure slight deviations from a true point source. Most globular clusters at the distance to our targets will be very slightly resolved, and we will use a 15874( 4) - 24-Sep-2019 14:07:07 - [ 2] standard 'concentration index' to identify them (basically, the difference in magnitude between two apertures). We have implemented some loose ORIENTs in order to include some portion of the stream associated with each dwarf, and its connection to the main parent galaxy. This program is relatively resilient to two-gyro mode, we believe. Our visits are 2-orbits, and we have loose ORIENT constraints. Nor does this program have time constraints (other than the baseline excitement of the science!). We can also achieve our science goals with a longer acquisition time, if necessary. Note that this dataset was requested through the joint NRAO program. We will also be acquiring VLA HI observations of the two ultradiffuse galaxy targets in this proposal to get a more complete picture and narrow down the formation scenarios of these two remarkable galaxies. We do not require concurrent VLA and HST imaging. ------------------------------------------------------------------------------------ 15874( 4) - 24-Sep-2019 14:07:07 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2708DW1 GALAXY, DWARF RA=08H56M12.7000S, J2000 V = 19.3 SPHEROIDAL DEC=-03D25'14.80" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5631DW1 GALAXY, DWARF RA=14H26M13.6000S, J2000 V = 20.5 SPHEROIDAL DEC=+56D31'50.20" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 15874( 4) - 24-Sep-2019 14:07:07 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.262 Line_Spacing 0.192 Coordinate_Frame POS-TARG Pattern_Orient 18.39 Angle_Between_Sides 68.14 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15874( 4) - 24-Sep-2019 14:07:07 - [ 5] Visit: 01 Visit Requirements: ORIENT 110D TO 140 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2708DW1 ACS/WFC ACCUM WFC1 F555W 1 600 S PATTERN 1 1-2; PAR 2 see below WITH 1 (2115 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS1 F555W FLASH=2.0 1 355 S S see below (2225 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2708DW1 ACS/WFC ACCUM WFC1 F814W 1 600 S PATTERN 1 3-4; PAR 4 see below WITH 3 (2187 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS1 F814W FLASH=3.0 1 369 S S see below (2243 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC2708DW1 1 ACS/WFC ACCUM WFC1 F555W 1 none none none 1 360.0 S NGC2708DW1 1 ACS/WFC ACCUM WFC1 F555W 2 none none none 1 700.0 S NGC2708DW1 1 ACS/WFC ACCUM WFC1 F555W 3 none none none 1 700.0 S NGC2708DW1 1 ACS/WFC ACCUM WFC1 F555W 4 none none none 1 355.0 S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 1 none none none 1 430.0 S S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 2 none none none 1 720.0 S S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 3 none none none 1 720.0 S S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 4 none none none 1 N/A S NGC2708DW1 3 ACS/WFC ACCUM WFC1 F814W 1 none none none 2 378.0 S NGC2708DW1 3 ACS/WFC ACCUM WFC1 F814W 2 none none none 2 718.0 S NGC2708DW1 3 ACS/WFC ACCUM WFC1 F814W 3 none none none 2 718.0 S NGC2708DW1 3 ACS/WFC ACCUM WFC1 F814W 4 none none none 2 373.0 S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 2 426.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 2 724.0 S S 15874( 4) - 24-Sep-2019 14:07:07 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ ANY 4 WFC3/UVI ACCUM UVIS1 F814W 3 none none none 2 724.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 4 none none none 2 369.0 S S 15874( 4) - 24-Sep-2019 14:07:07 - [ 7] Visit: 02 Visit Requirements: ORIENT 190D TO 300 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5631DW1 ACS/WFC ACCUM WFC1 F555W 1 600 S GS ACQ SCENARIO BASE1B3; see below PATTERN 1 1-2; PAR 2 (2359 S) WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS1 F555W FLASH=2.0 1 355 S S see below (2449 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC5631DW1 ACS/WFC ACCUM WFC1 F814W 1 600 S PATTERN 1 3-4; PAR 4 see below WITH 3 (2435 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS1 F814W FLASH=2.0 1 369 S S see below (2497 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC5631DW1 1 ACS/WFC ACCUM WFC1 F555W 1 none none none 1 421.0 S NGC5631DW1 1 ACS/WFC ACCUM WFC1 F555W 2 none none none 1 761.0 S NGC5631DW1 1 ACS/WFC ACCUM WFC1 F555W 3 none none none 1 761.0 S NGC5631DW1 1 ACS/WFC ACCUM WFC1 F555W 4 none none none 1 416.0 S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 1 none none none 1 481.0 S S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 2 none none none 1 771.0 S S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 3 none none none 1 771.0 S S ANY 2 WFC3/UVI ACCUM UVIS1 F555W 4 none none none 1 426.0 S S NGC5631DW1 3 ACS/WFC ACCUM WFC1 F814W 1 none none none 2 440.0 S NGC5631DW1 3 ACS/WFC ACCUM WFC1 F814W 2 none none none 2 780.0 S NGC5631DW1 3 ACS/WFC ACCUM WFC1 F814W 3 none none none 2 780.0 S NGC5631DW1 3 ACS/WFC ACCUM WFC1 F814W 4 none none none 2 435.0 S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 2 472.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 2 790.0 S S 15874( 4) - 24-Sep-2019 14:07:07 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ ANY 4 WFC3/UVI ACCUM UVIS1 F814W 3 none none none 2 790.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 4 none none none 2 445.0 S S 15874( 4) - 24-Sep-2019 14:07:07 - [ 9] Summary Form for Proposal 15874 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS1, WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=2.0, FLASH=3.0 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO BASE1B3, ORIENT 110D TO 140 D, ORIENT 190D TO 300 D, PAR 2 WITH 1, PAR 4 WITH 3, PATTERN 1 1-2, PATTERN 1 3-4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, NGC2708DW1, NGC5631DW1 ------------------------------------------------------------------------------------------------------------------------------------