16284( 5) - 25-Sep-2020 21:03:09 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16284 Version: 5 Check-in Time: 25-Sep-2020 21:03:09 STScI Edit Number: 2 Title Imaging of an apparent ''globular cluster galaxy'' ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Shany Danieli Institute For Advanced Study Y CoI: Prof. Pieter van Dokkum Yale University N CoI: Prof. Aaron Romanowsky San Jose State University N CoI: Zili Shen Yale University N CoI: Prof. Charlie Conroy Harvard University N CoI: Prof. Roberto G. Abraham University of Toronto N CoI: Prof. Jean P. Brodie University of California - Santa Cruz N CoI: Dr. Johnny P Greco The Ohio State University N CoI: Jonah Gannon Swinburne University of Technology N ------------------------------------------------------------------------------------ Abstract Recently a remarkable low surface brightness galaxy, NGC5846-UDG1, was discovered in archival ground-based CFHT data. The galaxy has a low stellar mass (~10^8 solar masses), a large size (r_e=1.8 kpc), and an unprecedented number of compact sources that resemble globular clusters. Keck spectroscopy confirms the association of the globular clusters and the diffuse light: they are at a common radial velocity of ~2000 km/s, close to the group velocity of ~1900 km/s. Based on the current ground-based imaging and spectroscopic data the galaxy might have up to 30% of its light in the form of globular clusters, significantly higher than any other galaxy known to date. Taking diffusion of low mass clusters into account, it is possible that the galaxy consisted solely of ~100 globular clusters when it formed. Here we request 2 WFC3/UVIS orbits to study this extreme galaxy along with its unusual globular cluster system. With WFC3/UVIS we will measure the sizes, colors, ellipticities and luminosity function of the clusters. These properties will be compared to the globular cluster systems of other galaxies (and in particular other Ultra Diffuse Galaxies), to determine whether NGC5846-UDG1's globular clusters have similarities to those in other galaxies or represent something entirely new. We will also use the data to better determine the structure and morphology of this enigmatic galaxy in order to put further constraints on its dynamical state. ------------------------------------------------------------------------------------ Observations Description ------------------------ The program is ought to obtain F606W and F475W imaging of a single ultra-diffuse galaxy which seems to host an outstanding number of bright globular clusters. The goal is to obtain photometry of these compact point sources over the entire WFC3/UVIS field of view. Instrumental setup: We will use WFC3/UVIS, and the F606W and F475W filters. The F606W filter is the primary filter for selecting globular clusters, with the F475W - F606W colors of compact objects helping (in conjunction with their sizes and the Keck spectroscopy) to distinguish them from background galaxies. 16284( 5) - 25-Sep-2020 21:03:09 - [ 2] A single pointing is sufficient as the candidate fits well inside the UVIS field of view. Total orbits and observing strategy: the target is observed for two orbits in a single visit, with one orbit per filter in two filters (F606W and F475W). We have no ORIENT constraints. We will be using the WFC3-UVIS-MOS-DITH-LINE pattern with 2 primarty points and 2 sub-pattern points. This allows both dithering over the chip gap and includes a secondary pattern which adds a sub-pixel dither to each of the primary steps. Apertures and POSTARGs: the galaxy is observed near UVIS2 with a slight shift from the chip center. ------------------------------------------------------------------------------------ 16284( 5) - 25-Sep-2020 21:03:09 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5846-UDG1 GALAXY, LSB RA=15H05M20.2900S, J2000 V = 2000 V = 25.0 DEC=+01D48'46.60" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 16284( 5) - 25-Sep-2020 21:03:09 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-MOS-DITH-LINE WFC3-UVIS-MOS-DITH-LINE Pattern_Purpose DITHER DITHER Number_Of_Points 2 2 Point_Spacing 2.4 0.119 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.754 33.606 Angle_Between_Sides Center_Pattern YES NO ------------------------------------------------------------------------------------------------------------------------------------ 16284( 5) - 25-Sep-2020 21:03:09 - [ 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 NGC5846-UDG WFC3/UVI ACCUM UVIS2 F606W 1 590 S POS TARG 1 S (2360 S) 1.9149547243532645, 6.104351303643155; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5846-UDG WFC3/UVI ACCUM UVIS2 F475W 1 585 S POS TARG 1 S see below 0.11424270911157405, (2349 S) 5.958445254507281; PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC5846-UDG1 1 WFC3/UVI ACCUM UVIS2 F606W 1 1 none none 1 N/A S NGC5846-UDG1 1 WFC3/UVI ACCUM UVIS2 F606W 1 2 none none 1 N/A S NGC5846-UDG1 1 WFC3/UVI ACCUM UVIS2 F606W 2 1 none none 1 N/A S NGC5846-UDG1 1 WFC3/UVI ACCUM UVIS2 F606W 2 2 none none 1 N/A S NGC5846-UDG1 2 WFC3/UVI ACCUM UVIS2 F475W 1 1 none none 2 594.0 S S NGC5846-UDG1 2 WFC3/UVI ACCUM UVIS2 F475W 1 2 none none 2 N/A S NGC5846-UDG1 2 WFC3/UVI ACCUM UVIS2 F475W 2 1 none none 2 N/A S NGC5846-UDG1 2 WFC3/UVI ACCUM UVIS2 F475W 2 2 none none 2 N/A S 16284( 5) - 25-Sep-2020 21:03:09 - [ 6] Summary Form for Proposal 16284 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2, POS TARG 0.11424270911157405, 5.958445254507281, POS TARG 1.9149547243532645, 6.104351303643155 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC5846-UDG1 ------------------------------------------------------------------------------------------------------------------------------------