15417( 2) - 08-Dec-2017 15:11:51 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15417 Version: 2 Check-in Time: 08-Dec-2017 15:11:51 STScI Edit Number: 0 Title Globular clusters and dark matter in the Virgo ultra-diffuse galaxy VLSB-B ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Eric W. Peng Peking University Y CoI: Dr. Elisa Toloba University of the Pacific N CoI: Prof. Puragra Guhathakurta University of California - Santa Cruz N CoI: Dr. Chris Mihos Case Western Reserve University N CoI: Dr. Patrick R. Durrell Youngstown State University N CoI: Dr. Patrick Cote National Research Council of Canada N CoI: Prof. Laura Virginia Sales University of California - Riverside N CoI: Dr. Sungsoon Lim Peking University N ------------------------------------------------------------------------------------ Abstract Ultra-diffuse galaxies (UDGs) are low surface brightness galaxies with low stellar masses, but sizes more like L* galaxies. UDGs could be "failed galaxies" that have been extremely inefficient at forming stars, and thus extremely dark matter dominated. We have identified the galaxy VLSB-B in the nearby Virgo cluster as one of the lowest surface brightness UDGs, and have very recently obtained velocities of candidate satellite globular clusters (GCs) in an effort to measure its dynamical mass. A preliminary measurement of the velocity dispersion of VLSB-B's GCs indicates that it could have one of the highest dark matter fractions for a galaxy of its mass. VLSB-B's systemic velocity is close to zero, however, making confusion between its GCs and Milky Way foreground stars a problem. GCs at Virgo distance are mostly point sources from the ground, but are easily distinguished from stars by HST. We propose to use HST/WFC3 for one orbit to image VLSB-B and definitively separate GCs from foreground stars by spatially resolving the GCs. Coupled with our ground-based spectroscopy, we will then have a clean measurement of VLSB-B's dynamical mass. The imaging will also be used to study the GC system of this unique galaxy. ------------------------------------------------------------------------------------ Observations Description ------------------------ The primary goal of our program is to obtain a clean, deep sample of globular clusters (GCs) in VLSB-B by spatially resolving them. We use WFC/UVIS with the F606W filter in a 3-point line dither pattern that fills the CCD gap. We also use ACS/WFC with F606W in parallel to observe a neighboring field in the Virgo cluster core that includes VCC 1077. ------------------------------------------------------------------------------------ 15417( 2) - 08-Dec-2017 15:11:51 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 VLSB-B GALAXY, DWARF RA=12H28M11.6540S, J2000 V = 26.0 SPHEROIDAL, LSB DEC=+12D43'7.19" Reference Frame: ICRS Comments: Targeting faint, marginally resolved globular clusters in a low surface brightness galaxy. ------------------------------------------------------------------------------------------------------------------------------------ 15417( 2) - 08-Dec-2017 15:11:51 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 2.4 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15417( 2) - 08-Dec-2017 15:11:51 - [ 4] Visit: 01 (VLSB-B) Visit Requirements: ORIENT 125D TO 136 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 VLSB-B WFC3/UVI ACCUM UVIS2-FIX F606W 1 848 S PATTERN 1 1-2; PAR 2 S (2544 S) WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 VLSB-B ACS/WFC ACCUM WFC F606W 1 753 S see below (2269 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 | ------------------------------------------------------------------------------------------------------------------------------------ VLSB-B 1 WFC3/UVI ACCUM UVIS2-FI F606W 1 none none none 1 N/A S X VLSB-B 1 WFC3/UVI ACCUM UVIS2-FI F606W 2 none none none 1 N/A S X VLSB-B 1 WFC3/UVI ACCUM UVIS2-FI F606W 3 none none none 1 N/A S X VLSB-B 2 ACS/WFC ACCUM WFC F606W 1 none none none 1 763.0 S VLSB-B 2 ACS/WFC ACCUM WFC F606W 2 none none none 1 N/A VLSB-B 2 ACS/WFC ACCUM WFC F606W 3 none none none 1 N/A 15417( 2) - 08-Dec-2017 15:11:51 - [ 5] Summary Form for Proposal 15417 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-FIX, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 125D TO 136 D, PAR 2 WITH 1, PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names VLSB-B ------------------------------------------------------------------------------------------------------------------------------------