15258( 15) - 06-Aug-2018 21:10:43 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15258 Version: 15 Check-in Time: 06-Aug-2018 21:10:43 STScI Edit Number: 12 Title Galaxies at the Extremes: Ultradiffuse Galaxies in the Virgo Cluster ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Chris Mihos Case Western Reserve University Y CoI: Dr. Patrick Cote National Research Council of Canada N CoI: Dr. Patrick R. Durrell Youngstown State University Y CoI: Dr. John J. Feldmeier Youngstown State University N CoI: Dr. Laura Ferrarese Dominion Astrophysical Observatory N CoI: Dr. Paul Harding Case Western Reserve University N CoI: Dr. Eric W. Peng Peking University N CoI: Dr. Elisa Toloba University of the Pacific N CoI: Prof. Puragra Guhathakurta University of California - Santa Cruz N CoI: Prof. Laura Virginia Sales University of California - Riverside N CoI: Dr. Sungsoon Lim N ------------------------------------------------------------------------------------ Abstract The "ultradiffuse galaxies" (UDGs) recently discovered in massive galaxy clusters presents both challenges and opportunities for our understanding of galaxy evolution in dense clusters. Such large, low density galaxies should be most vulnerable to gravitational destruction within the cluster environment. Thus their presence in cluster cores argues either that they must be stabilized by massive dark halos or else be short-lived objects undergoing rapid transformation, perhaps leading to the formation of ultracompact dwarf galaxies (UCDs) if their destruction leaves only a compact nucleus behind. We propose deep imaging of four Virgo Cluster UDGs to probe their local environment within Virgo via accurate tip of the red giant branch (TRGB) distances. With a distance precision of 1 Mpc, we will accurately place the objects in the Virgo core, cluster outskirts, or intervening field. When coupled with our extant kinematic data, we can determine whether they are infalling objects or instead have already passed through the cluster core. We will also compare their compact nuclei to Virgo UCDs, and study their globular cluster (GC) populations in detail. Probing three magnitudes beyond the turnover in the GC luminosity function, we will construct larger and cleaner GC samples than possible with ground-based imaging, using the total mass and radial extent of the globular cluster systems to estimate the dark halo mass and tidal radius for each UDG. The new information provided by HST about the local environment and intrinsic properties of these Virgo UDGs will be used in conjunction with simulation data to study cluster-driven evolution and transformation of low density galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ The program is to obtain very deep F814W images of a single ultra-diffuse galaxy in the Virgo cluster, and to obtain photometry of very faint point 15258( 15) - 06-Aug-2018 21:10:43 - [ 2] sources over the entire FOV. We are using ACS as primary to get the larger FOV on the target galaxy, and using WFC3 in parallel to obtain a 'background' field necessary for our science goals. LOW-SKY is required due to the higher-than-average sky background for targets near the ecliptic plane, and our need to get high enough S/N for very faint point sources. Visit locations: For each of the three 2-orbit visits, we are using a small 4 pt ACS-WFC-DITHER-BOX pattern to properly sample the PSF. Between visits, we are using POS-TARGs to create a larger BOX pattern such that we cover the chip gap. The 4th part of this larger box (location 4) is a single orbit (2 exposures only), so I have made a custom DITHER-LINE to match the first two points of the small, subpixel DITHER-BOX pattern. Exposure times: All of our F814W observations are 2 images per orbit -- there will be 14 individual F814W images, so CR removal should be fine. We have left a few x10s of orbit visibilty open for schedulability. The single orbit in F475W will employ 4 primary+parallel images, but with unequal exposure times. Roll Angles: We are limited by the target availability for this object, as well as the need for all observations to be made at the same roll angle as the first Visit. We have chosen a rather restricted roll angle range so that we avoid (a) a bright star that lies to the E of VCC 615, and (b) such that the WFC3 parallel fields do not land on a region of bright stars. (the roll angle we used was chosen to co-incide with surprisingly small target visibility). FLASH: Due to the length of the exposures, we do not need post-FLASH for any of the F814W exposures in either camera. However, some of the shorter F475W exposures in Visit 05 will require some post-FLASH. To conservative determine the appropriate backgrounds, we used the ETC and assumed the faintest possible sky background (MU_V=22.6 for target at 13 degrees ecliptic latitude), and no Earthshine or airglow. For 410S exposures in F475W this becomes 9 e-/pixel (http://etc.stsci.edu/etc/results/WFC3UVIS.im.1012759/). Thus we will need a post-FLASH of 3 e- for the shorter WFC3 F475W exposures. For the ACS, using these same (rather optimistic) conditions, we find a minimum of 19 e-/pixel in the 365s exposures (http://etc.stsci.edu/etc/results/ACS.im.1012739/), requiring a post-FLASH of 1.0 e- for the shorter ACS exposures ------------------------------------------------------------------------------------ 15258( 15) - 06-Aug-2018 21:10:43 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 3 VCC-615 GALAXY, LSB RA=12H23M2.7869S, J2000 V = 29 DEC=+12D01'10.55" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 15258( 15) - 06-Aug-2018 21:10:43 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.265 Line_Spacing 0.187 Coordinate_Frame POS-TARG Pattern_Orient 20.67 Angle_Between_Sides 69.05 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.262 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 20.67 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15258( 15) - 06-Aug-2018 21:10:43 - [ 5] Visit: 01 (VCC 615 - I - location 1) Visit Requirements: ORIENT 116D TO 125 D On Hold Comments: Additional Comments: F814W images, 2 exposures per orbit in DITHER-BOX pattern. Location 1 of 4 different POST TARGS for each of the 4 F814W-related visits. Small ORIENT range dictated by limited target visibility and need to avoid a few bright stars both E and S of the galaxy 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 VCC-615 ACS/WFC ACCUM WFCENTER F814W 1 1200 S POS TARG 0.00, 0.00; (4800 S) LOW-SKY; GS ACQ SCENARIO SINGLE; PATTERN 1 1-2; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS-CENT F814W 1 1200 S S ER (4800 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 | ------------------------------------------------------------------------------------------------------------------------------------ VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 1 none none none 1 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 2 none none none 1 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 3 none none none 2 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 4 none none none 2 N/A ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 1 none none none 1 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 2 none none none 1 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 3 none none none 2 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 4 none none none 2 N/A S TER 15258( 15) - 06-Aug-2018 21:10:43 - [ 6] Visit: 02 (VCC 615 - I - location 2) Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: F814W images, 2 exposures per orbit in DITHER-BOX pattern. Location 2 of 4 different POST TARGS for each of the 4 F814W-related visits. This field X-1" of Visit 01. 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 VCC-615 ACS/WFC ACCUM WFCENTER F814W 1 1200 S POS TARG -0.98, 0.00; (4800 S) LOW-SKY; GS ACQ SCENARIO SINGLE; PATTERN 1 1-2; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS-CENT F814W 1 1200 S S ER (4800 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 | ------------------------------------------------------------------------------------------------------------------------------------ VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 1 none none none 1 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 2 none none none 1 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 3 none none none 2 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 4 none none none 2 N/A ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 1 none none none 1 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 2 none none none 1 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 3 none none none 2 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 4 none none none 2 N/A S TER 15258( 15) - 06-Aug-2018 21:10:43 - [ 7] Visit: 03 (VCC 615 - I - location 3) Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: F814W images, 2 exposures per orbit in DITHER-BOX pattern. Location 3 of 4 different POST TARGS for each of the 4 F814W-related visits. This field Y+3" from Visit 01, in order to cover 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 VCC-615 ACS/WFC ACCUM WFCENTER F814W 1 1200 S POS TARG 0.00, 2.94; (4800 S) LOW-SKY; GS ACQ SCENARIO SINGLE; PATTERN 1 1-2; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS-CENT F814W 1 1200 S S ER (4800 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 | ------------------------------------------------------------------------------------------------------------------------------------ VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 1 none none none 1 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 2 none none none 1 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 3 none none none 2 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 4 none none none 2 N/A ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 1 none none none 1 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 2 none none none 1 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 3 none none none 2 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 4 none none none 2 N/A S TER 15258( 15) - 06-Aug-2018 21:10:43 - [ 8] Visit: 04 (VCC 615 - I - location 4) Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: SIngle orbit visit in F814W (2 exposures per orbit, much like previous 3 visits), using a 2 point DITHER-LINE to mimic first half of DITHER-BOX. Location 4 of 4 different POST TARGS for each of the 4 F814W-related visits. This field Y+3" from Visit 02, in order to cover 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 VCC-615 ACS/WFC ACCUM WFCENTER F814W 1 1200 S POS TARG -0.98, 2.984; (2400 S) LOW-SKY; GS ACQ SCENARIO SINGLE; PATTERN 2 1-2; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS-CENT F814W 1 1200 S S ER (2400 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 | ------------------------------------------------------------------------------------------------------------------------------------ VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 1 none none none 1 N/A VCC-615 1 ACS/WFC ACCUM WFCENTER F814W 2 none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 1 none none none 1 N/A S TER ANY 2 WFC3/UVI ACCUM UVIS-CEN F814W 2 none none none 1 N/A S TER 15258( 15) - 06-Aug-2018 21:10:43 - [ 9] Visit: 05 (VCC 615 - B - location 1) Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: F475W observations - single orbit. Small sub-pixel 4 point DITHER BOX used, input as POS-TARGS due to different post-FLASH values for different exposures. Exposures 1 and 4 are shorter in order to fit 4 dithered images in a single orbit. 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 VCC-615 ACS/WFC ACCUM WFCENTER F475W 1 365 S (365 LOW-SKY; GS ACQ SCENARIO S) SINGLE; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS-CENT F475W FLASH=3.0 1 410 S (410 S ER S) ------------------------------------------------------------------------------------------------------------------------------------ 3 VCC-615 ACS/WFC ACCUM WFCENTER F475W 1 660 S (660 POS TARG 0.247, 0.094; S) LOW-SKY; PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS-CENT F475W 1 700 S (700 S ER S) ------------------------------------------------------------------------------------------------------------------------------------ 5 VCC-615 ACS/WFC ACCUM WFCENTER F475W 1 660 S (660 POS TARG 0.124, 0.232; S) LOW-SKY; PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS-CENT F475W 1 700 S (700 S ER S) ------------------------------------------------------------------------------------------------------------------------------------ 7 VCC-615 ACS/WFC ACCUM WFCENTER F475W 1 365 S (365 POS TARG -0.124, 0.138; S) LOW-SKY; PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS-CENT F475W FLASH=3.0 1 410 S (410 S ER 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 | ------------------------------------------------------------------------------------------------------------------------------------ VCC-615 1 ACS/WFC ACCUM WFCENTER F475W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS-CEN F475W none none none none 1 N/A S TER VCC-615 3 ACS/WFC ACCUM WFCENTER F475W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS-CEN F475W none none none none 1 N/A S TER VCC-615 5 ACS/WFC ACCUM WFCENTER F475W none none none none 1 N/A ANY 6 WFC3/UVI ACCUM UVIS-CEN F475W none none none none 1 N/A S TER VCC-615 7 ACS/WFC ACCUM WFCENTER F475W none none none none 1 N/A 15258( 15) - 06-Aug-2018 21:10:43 - [ 10] 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 8 WFC3/UVI ACCUM UVIS-CEN F475W none none none none 1 N/A S TER 15258( 15) - 06-Aug-2018 21:10:43 - [ 11] Summary Form for Proposal 15258 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS-CENTER, WFCENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=3.0 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO SINGLE, LOW-SKY, ORIENT 116D TO 125 D, PAR 2 WITH 1, PAR 4 WITH 3, PAR 6 WITH 5, PAR 8 WITH 7, PATTERN 1 1-2, PATTERN 2 1-2, POS TARG -0.124, 0.138, POS TARG -0.98, 0.00, POS TARG -0.98, 2.984, POS TARG 0.00, 0.00, POS TARG 0.00, 2.94, POS TARG 0.124, 0.232, POS TARG 0.247, 0.094, SAME ORIENT AS 01 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, VCC-615 ------------------------------------------------------------------------------------------------------------------------------------