16082( 2) - 12-Mar-2020 18:12:26 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16082 Version: 2 Check-in Time: 12-Mar-2020 18:12:26 STScI Edit Number: 0 Title A new enigmatic population of over-luminous globular clusters in an ultra-diffuse galaxy ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Oliver Mueller University of Basel, Department of Physics Y CoI: Prof. Francine Marleau Universitat Innsbruck, Institut fur N Astronomie CoI: Dr. Pierre-Alain Duc Observatoire Astronomique de Strasbourg N CoI: Dr. Remco van der Burg European Southern Observatory - Germany N CoI: Mr. Jeremy Fensch European Southern Observatory - Germany N CoI: Dr. Adriano Agnello University of Copenhagen, Niels Bohr N Institute CoI: Dr. Patrick R. Durrell Youngstown State University Y CoI: Ms. Melina Poulain Universitat Innsbruck, Institut fur N Astronomie CoI: Dr. Rebecca Habas Universite de Strasbourg I N CoI: Dr. Ruben Sanchez-Janssen United Kingdom Astronomy Technology Centre N CoI: Dr. Eric Emsellem European Southern Observatory - Germany N CoI: Prof. Sanjaya Paudel Yonsei University N CoI: Dr. Sungsoon Lim University of Tampa N ------------------------------------------------------------------------------------ Abstract As part of a systematic survey with MegaCam/CFHT, we have identified an ultra-diffuse galaxy (UDG) with an excess of globular cluster (GC) candidates in the galaxy grop NGC 5846, dubbed MATLAS-2019. A large fraction of the GCs have been confirmed with follow-up MUSE spectroscopy, all of which are over-luminous with a luminosity one magnitude brighter than what is expected from the GC luminosity function. Many of the properties of MATLAS-2019 - e.g., the number of GCs, the brightness of the GC population, and an apparent lack of dark matter - are similar to the heavily discussed UDGs NGC1052-DF2 and NGC1052-DF4. The controversial nature of these two galaxies is due, in part, to uncertainties in their distances and the fact that they reside in the same field; the confirmation of a similar object in an independent group with an unambiguous distance will bring much desired and needed additional data to the discussion. We propose follow-up of MATLAS-2019 with HST, employing two-band ACS imaging to trace the full population of GCs three magnitudes below the peak of the GC luminosity function. The HST observation, combining depth, color-information, and its superior image quality, will give us an accurate estimate of the total number of GCs. With that we can test whether the UDG hosts an exceptionally large number of GCs, but with a regular GC function, or it contains a population consisting of only over-luminous GCs. Both cases pose a conundrum for our understanding of GC and galaxy formation. ------------------------------------------------------------------------------------ Observations Description ------------------------ F606W/F814W imaging of a single ultra-diffuse galaxy. Limited to 4 exposures of 16082( 2) - 12-Mar-2020 18:12:26 - [ 2] equal length for the single orbit requested/allocated. Use of small DITHER LINE as we do not require filling in the chip gap, but we do need two exposures in each filter to facilitate CR and hot pixel removal. We have created a dither of 7.5 pixels x 6.5 pixels, or spacing 0.504" at an angle of 42.11 degrees. Data to be used to obtain magnitudes and colors of most (marginally-resolved) globular cluster candidates in this galaxy. We have cntered the galaxy on aperture WFC1 in order to avoid chip gap running through galaxy. We have a wide range of possible ORIENT values, chosen only to to avoid a very brgiht (V=13) star to the NE of the target galaxy, and also to avoid a pair of V=15-16 stars SE and SW of the target galaxy. All are far from the galaxy, but we are maximizing the amount of the FOV available for background corrections. Relaxing the roll angles to allow the V=15-16 stars will not change the schedulability very much. Reduced Gyro mode: We do not expect large complication if less than 3 gyros are available for the observations, reducing the effective time available for observations. Our program allows for manyu possible roll angles, which means there are many months of schedulability available. ------------------------------------------------------------------------------------ 16082( 2) - 12-Mar-2020 18:12:26 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MATLAS2019 GALAXY, DWARF RA=15H05M20.1600S, J2000 V = 17 +/- 0.3 ELLIPTICAL DEC=+01D48'45.29" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 16082( 2) - 12-Mar-2020 18:12:26 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.504 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 42.11 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 16082( 2) - 12-Mar-2020 18:12:26 - [ 5] Visit: 01 Visit Requirements: ORIENT 283D TO 354 D; ORIENT 242D TO 263 D; ORIENT 102D TO 218 D On Hold Comments: Additional Comments: 2xF606W + 2xF814W images of target galaxy. Center galaxy on WFC1 to be sure no GC candidates fall outside FOV, or on chip gap. 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 MATLAS2019 ACS/WFC ACCUM WFC1 F606W 1 515 S PATTERN 1 1 (1030 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 MATLAS2019 ACS/WFC ACCUM WFC1 F814W 1 515 S PATTERN 1 2 (1030 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 | ------------------------------------------------------------------------------------------------------------------------------------ MATLAS2019 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 N/A MATLAS2019 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 N/A MATLAS2019 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 N/A MATLAS2019 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 N/A 16082( 2) - 12-Mar-2020 18:12:26 - [ 6] Summary Form for Proposal 16082 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 102D TO 218 D, ORIENT 242D TO 263 D, ORIENT 283D TO 354 D, PATTERN 1 1, PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names MATLAS2019 ------------------------------------------------------------------------------------------------------------------------------------