15938( 3) - 26-Jul-2019 12:31:02 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15938 Version: 3 Check-in Time: 26-Jul-2019 12:31:02 STScI Edit Number: 0 Title The NGC253 Satellite Luminosity Function: A Case Study for Low Density Environments ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Burcin Mutlu-Pakdil University of Arizona Y CoI: Prof. David J. Sand University of Arizona N CoI: Dr. Denija Crnojevic University of Tampa N CoI: Dr. Joshua D. Simon Carnegie Institution of Washington N CoI: Dr. Nelson Caldwell Smithsonian Institution Astrophysical N Observatory CoI: Mr. Paul Bennet Texas Tech University N CoI: Prof. Jay Strader Michigan State University N CoI: Prof. Anil C. Seth University of Utah N CoI: Prof. Puragra Guhathakurta University of California - Santa Cruz N CoI: Dr. Elisa Toloba University of the Pacific N ------------------------------------------------------------------------------------ Abstract The faint end of the galaxy luminosity function is a strong test for models of galaxy formation and evolution, but can only be studied in the most constraining "ultra-faint" regime in the nearest galaxies. Deep satellite counts around a limited sample of nearby Milky Way-mass galaxies show evidence for a large variation in the number of dwarfs. These results could reflect either stochastic variations in satellite populations or systematic changes with environmental density. The origin of these variations can help elucidate the poorly-understood physical processes that contribute to the evolution of low mass galaxies, such as reionization. This proposal requests 5 orbits of HST/ACS for two-band imaging of five new faint candidate dwarfs in the halo of NGC253 (D=3.5 Mpc), a Milky Way-mass spiral galaxy in a nearly isolated environment. This imaging will enable the measurement of distances, luminosities, metallicities, and star formation histories for these dwarfs, all of which can only be done with HST. The confirmation of these dwarfs will complete the first dwarf satellite census of NGC253 down to Mv ~ -7, testing cosmological predictions for the faint end of the satellite luminosity function in low density environments. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observations are going to be performed with ACS/WFC (primary) and WFC3/UVIS (parallel). We request imaging in F606W and F814W filters (broad V and I) for both instruments, in order to compute accurate TRGB distances for our targets and characterize their stellar content (star formation histories and metallicities), while optimizing the exposure times. The parallel pointings will allow us to observe a field region next to our targets. We will thus be able to estimate more precisely the number of background/foreground contaminants present in our ACS fields. 15938( 3) - 26-Jul-2019 12:31:02 - [ 2] Our goal is to obtain a minimum SNR of ~10 at ~1 mag below the TRGB in I band, assuming that the TRGB is found at M_I = ~-4.0 and M_V = ~-2.5, in order to derive precise distance measurements, structural properties and average metallicities. With the requested SNR, the photometric errors will be ~0.05 mag in magnitude and ~0.1 mag in color at the TRGB. We will obtain distance uncertainties as low as ~0.1 mag, corresponding to ~150 kpc at the distance of NGC253. Since the exact distances for our targets are unknown, the candidate NGC253 satellites are assumed to be at the distance of NGC253 (~3.5 Mpc). Given their low masses, these are expected to be metal-poor objects, thus having average colours of V - I ~ 1.5. At this distance, the TRGB is found at a magnitude of I ~ 24.2 and V ~ 25.7. The exposures to obtain the required SNR at 1 mag below the TRGB for both bands are ~ 1000 sec in F606W and ~ 1000 sec in F814W (as computed with the latest version of the ACS ETC), which result in one orbit per target. Each exposure will be split in two with a dither pattern in order to subsequently remove detector defects and improve the PSF sampling. We have checked that the charge transfer efficiency losses of ACS do not significantly affect our observations (at most 10% loss of flux). This program is resilient to two-gyro mode, we believe. Our visits are 1-orbit, and we have no ORIENT requirements (we have one visit with a loose ORIENT). Nor does this program have time constraints (other than the baseline excitement of the science!). We can also achieve our science goals with a longer acquisition time, if necessary. ------------------------------------------------------------------------------------ 15938( 3) - 26-Jul-2019 12:31:02 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC253-DW1 GALAXY, DWARF RA=00H47M34.9300S +/- 2", J2000 V = 17.4 SPHEROIDAL DEC=-26D23'19.70" +/- 2" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC253-DW3 GALAXY, DWARF RA=00H47M7.1770S +/- 2", J2000 V = 19.85 SPHEROIDAL DEC=-23D57'21.68" +/- 2" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC253-DW4 GALAXY, DWARF RA=00H53M49.0293S +/- 2", J2000 V = 19.8 SPHEROIDAL DEC=-25D28'28.43" +/- 2" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC253-DW5 GALAXY, DWARF RA=00H50M26.0148S +/- 2", J2000 V = 20.8 SPHEROIDAL DEC=-26D43'42.76" +/- 2" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC253-DW6 GALAXY, DWARF RA=00H47M27.1826S +/- 2", J2000 V = 21.2 SPHEROIDAL DEC=-25D13'7.55" +/- 2" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 15938( 3) - 26-Jul-2019 12:31:02 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.364 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 47.23 Angle_Between_Sides Center_Pattern NO Pattern_Comments: Two-point dither. No need to fill chip gap. ------------------------------------------------------------------------------------------------------------------------------------ 15938( 3) - 26-Jul-2019 12:31:02 - [ 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 NGC253-DW1 ACS/WFC ACCUM WFC1 F606W 1 650 S PATTERN 1 1-2; PAR 2 see below WITH 1 (1030 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS1 F606W 1 350 S S (1090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC253-DW1 ACS/WFC ACCUM WFC1 F814W 1 450 S PATTERN 1 3-4; PAR 4 see below WITH 3 (1053 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS1 F814W 1 360 S S see below (1213 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC253-DW1 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 295.0 S NGC253-DW1 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 735.0 S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 2 none none none 1 740.0 S S NGC253-DW1 3 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 705.0 S NGC253-DW1 3 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 348.0 S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 1 742.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 1 471.0 S S 15938( 3) - 26-Jul-2019 12:31:02 - [ 6] Visit: 02 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 NGC253-DW3 ACS/WFC ACCUM WFC1 F606W 1 650 S PATTERN 1 1-2; PAR 2 see below WITH 1 (1026 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS1 F606W 1 350 S S (1090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC253-DW3 ACS/WFC ACCUM WFC1 F814W 1 450 S PATTERN 1 3-4; PAR 4 see below WITH 3 (1049 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS1 F814W 1 360 S S see below (1208 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC253-DW3 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 293.0 S NGC253-DW3 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 733.0 S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 2 none none none 1 740.0 S S NGC253-DW3 3 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 703.0 S NGC253-DW3 3 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 346.0 S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 1 742.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 1 466.0 S S 15938( 3) - 26-Jul-2019 12:31:02 - [ 7] Visit: 03 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 NGC253-DW4 ACS/WFC ACCUM WFC1 F606W 1 650 S PATTERN 1 1-2; PAR 2 see below WITH 1 (1030 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS1 F606W 1 350 S S (1090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC253-DW4 ACS/WFC ACCUM WFC1 F814W 1 450 S PATTERN 1 3-4; PAR 4 see below WITH 3 (1053 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS1 F814W 1 360 S S see below (1213 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC253-DW4 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 295.0 S NGC253-DW4 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 735.0 S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 2 none none none 1 740.0 S S NGC253-DW4 3 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 705.0 S NGC253-DW4 3 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 348.0 S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 1 742.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 1 471.0 S S 15938( 3) - 26-Jul-2019 12:31:02 - [ 8] Visit: 04 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 NGC253-DW5 ACS/WFC ACCUM WFC1 F606W 1 650 S PATTERN 1 1-2; PAR 2 see below WITH 1 (1030 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS1 F606W 1 350 S S (1090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC253-DW5 ACS/WFC ACCUM WFC1 F814W 1 450 S PATTERN 1 3-4; PAR 4 see below WITH 3 (1053 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS1 F814W 1 360 S S see below (1213 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC253-DW5 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 295.0 S NGC253-DW5 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 735.0 S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 2 none none none 1 740.0 S S NGC253-DW5 3 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 705.0 S NGC253-DW5 3 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 348.0 S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 1 742.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 1 471.0 S S 15938( 3) - 26-Jul-2019 12:31:02 - [ 9] Visit: 05 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 NGC253-DW6 ACS/WFC ACCUM WFC1 F606W 1 650 S PATTERN 1 1-2; PAR 2 see below WITH 1 (1030 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS1 F606W 1 350 S S (1090 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC253-DW6 ACS/WFC ACCUM WFC1 F814W 1 450 S PATTERN 1 3-4; PAR 4 see below WITH 3 (1053 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS1 F814W 1 360 S S see below (1213 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC253-DW6 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 295.0 S NGC253-DW6 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 735.0 S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS1 F606W 2 none none none 1 740.0 S S NGC253-DW6 3 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 705.0 S NGC253-DW6 3 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 348.0 S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 1 742.0 S S ANY 4 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 1 471.0 S S 15938( 3) - 26-Jul-2019 12:31:02 - [ 10] Summary Form for Proposal 15938 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS1, WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PAR 2 WITH 1, PAR 4 WITH 3, PATTERN 1 1-2, PATTERN 1 3-4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, NGC253-DW1, NGC253-DW3, NGC253-DW4, NGC253-DW5, NGC253-DW6 ------------------------------------------------------------------------------------------------------------------------------------