15850( 3) - 29-Jul-2019 11:40:47 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15850 Version: 3 Check-in Time: 29-Jul-2019 11:40:47 STScI Edit Number: 1 Title An accurate age for the enigmatic galaxy NGC1052-DF2 ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Pieter van Dokkum Yale University Y CoI: Prof. Charlie Conroy Harvard University N CoI: Mrs. Shany Danieli Yale University N CoI: Prof. Aaron Romanowsky San Jose State University N CoI: Prof. Jean P. Brodie University of California - Santa Cruz N CoI: Dr. Diederik Kruijssen Zentrum fur Astronomie - Universitat N Heidelberg CoI: Prof. Roberto G. Abraham University of Toronto N CoI: Dhruba Dutta Chowdhury Yale University N ------------------------------------------------------------------------------------ Abstract The galaxy NGC1052-DF2 has been the subject of intense debate in the literature. Not only does it seem to have a very low dark matter content, it also has a peculiar population of very bright globular clusters that make up 3% of the total light. A central question is when the galaxy and its unusual globular clusters were formed. The best constraints have come from optical spectroscopy of the bright globular clusters. The clusters have a metallicity of [Fe/H]=-1.4 and an apparent age of 9 Gyr, consistent with constraints on the metallicity and age of the diffuse light. However, these age measurements are only lower limits, due to the unknown contribution of blue horizontal branch (BHB) stars to the integrated light. If the BHB branch is as strong as in Milky Way globular clusters of the same metallicity, the true age of the globular clusters, and the galaxy, could be 13 Gyr - predating the formation of the massive elliptical galaxy NGC1052. The objective of this proposal is to measure the contribution of hot stars to the integrated light by obtaining F225W UV imaging of NGC1052-DF2 and its globular clusters with UVIS. The F225W-F814W color is sensitive to hot stars and breaks the degeneracy between age and the strength of the BHB. This measurement will pin down the formation epoch of the galaxy, currently only constrained to be at least ~9 Gyr ago; determine whether the globular clusters all have identical UV properties or show variation in their F225W-F814W colors like luminous Milky Way clusters; and test the hypothesis that a significant fraction of the diffuse light comes from disrupted globular clusters. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program aims to obtain 3 orbits of UV F225W imaging of the galaxy NGC1052-DF2 and its globular clusters. The 3 orbits are organized in a single visit. Within each orbit two exposures are obtained, with an exposure time of ~1350 seconds per exposure and a standard chip gap dither between the two exposures. A 10 electron post flash is used to mitigate CTE effects. Large POS_TARGs (of ~25'') are used in between 15850( 3) - 29-Jul-2019 11:40:47 - [ 2] each orbit (so before the first exposure, before the third, and before the fifth) to obtain reliable photometry of the diffuse light. There are no timing or orientation constraints. ------------------------------------------------------------------------------------ 15850( 3) - 29-Jul-2019 11:40:47 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1052-DF2 GALAXY, DWARF RA=02H41M46.7200S, J2000 V = 21 expected F225W of clusters = SPHEROIDAL DEC=-08D24'10.80" 26-26.5 Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 15850( 3) - 29-Jul-2019 11:40:47 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-GAP-LINE Pattern_Purpose MOSAIC Number_Of_Points 2 Point_Spacing 2.414 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.759 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15850( 3) - 29-Jul-2019 11:40:47 - [ 5] Visit: 01 Visit Requirements: 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 NGC1052-DF2 WFC3/UVI ACCUM UVIS-CENT F225W FLASH=10.0 1 1000 S POS TARG -25, 30; GS ACQ S ER see below SCENARIO BASE1B3; (2670 S) PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1052-DF2 WFC3/UVI ACCUM UVIS-CENT F225W FLASH=10.0 1 1000 S POS TARG 20, 15; PATTERN S ER see below 1 2 (2700 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1052-DF2 WFC3/UVI ACCUM UVIS-CENT F225W FLASH=10.0 1 1000 S POS TARG -10, -25; S ER see below PATTERN 1 3 (2700 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC1052-DF2 1 WFC3/UVI ACCUM UVIS-CEN F225W 1 none none none 1 1335.0 S S TER NGC1052-DF2 1 WFC3/UVI ACCUM UVIS-CEN F225W 2 none none none 1 1335.0 S S TER NGC1052-DF2 2 WFC3/UVI ACCUM UVIS-CEN F225W 1 none none none 2 1350.0 S S TER NGC1052-DF2 2 WFC3/UVI ACCUM UVIS-CEN F225W 2 none none none 2 1350.0 S S TER NGC1052-DF2 3 WFC3/UVI ACCUM UVIS-CEN F225W 1 none none none 3 1350.0 S S TER NGC1052-DF2 3 WFC3/UVI ACCUM UVIS-CEN F225W 2 none none none 3 1350.0 S S TER 15850( 3) - 29-Jul-2019 11:40:47 - [ 6] Summary Form for Proposal 15850 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS-CENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=10.0 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO BASE1B3, PATTERN 1 1, PATTERN 1 2, PATTERN 1 3, POS TARG -10, -25, POS TARG -25, 30, POS TARG 20, 15 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F225W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1052-DF2 ------------------------------------------------------------------------------------------------------------------------------------