0 Assigned ID: 5106 ----- Attempting Submission 1 (Sun Mar 24 03:39:58 GMT 2024) ----- HST Phase I Proposal 5106 successfully submitted. Receipt: # 5106-1 ----- Attempting Submission 2 (Mon Mar 25 15:06:13 GMT 2024) ----- As requested, patterns are specified (no need to fill the chip gaps). We dropped the parallel observations because of buffer dump considerations. -1877773250 ----- Attempting Submission 1 (Sat Aug 03 06:28:18 GMT 2024) ----- HST Phase II Proposal 17798 successfully submitted. Receipt: # 17798-1 ----- Attempting Submission 2 (Wed Aug 14 21:21:26 GMT 2024) ----- The Local Group satellite dwarf galaxies are often used as benchmarks for testing galaxy formation and evolution theories on the smallest scales because they are the lowest-mass galaxies for which detailed observations are available. However, most of these dwarfs have been affected by the Local Group environment. If we want to understand the physical mechanisms driving the evolution of low-mass galaxies, we must study pristine isolated dwarf galaxies beyond the Local Group as a control sample. Unfortunately, identifying such galaxies in the field is extremely challenging due to their extreme faintness. To date, Tucana B is the only known isolated, ultra-faint dwarf galaxy that is independent of group dynamics but close enough at 1.4 Mpc to be studied with resolved stars. With only one system, it is challenging to draw broad conclusions about the lowest-mass galaxies evolving in isolation. We request two orbits of HST/ACS imaging (F606W+F814W) to follow up two new nearby isolated faint dwarf galaxies (Cetus B and Hydrus A) discovered in ground-based surveys. The galaxies are likely just beyond the edge of the Local Group, with apparent morphologies and colors strikingly similar to Tucana B. HST imaging is essential to the determination of high-precision distances, measurement of basic physical properties, and measurement of star formation histories of these two newly discovered faint dwarfs. The requested observations will put these two galaxies into context with other dwarf galaxies in and beyond the Local Group, providing a rare opportunity to assess the impact of environment on low-mass systems. The observations are going to be performed with ACS/WFC (primary) and WFC3/UVIS (parallel) to match previous observations of faint dwarfs beyond the Local Group (e.g. Weisz et al. 2014, Hargis et al. 2020, Danieli et al. 2017, Bennet et al. 2019, Crnojevic et al. 2019, Mutlu-Pakdil et al 2022). 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, 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. Given the small size of each target (<1 arcmin), one pointing is sufficient to cover the entire spatial extent of each galaxy. Each dwarf will be placed on one of the ACS/WFC chips, and small dithers between exposures will remove detector defects and improve the PSF sampling. Given that the possible distance range for our targets is ~1-3 Mpc, we use existing HST ACS data of Local Volume dwarfs at <3 Mpc (NGC253 dwarfs [GO-14259, GO-15938], CenA dwarfs [GO-13856], MADCASH dwarfs [GO-15228]) to guide our observational request and ensure that the depth is sufficient for the science goals of this proposal. The archival ACS data for similar limiting magnitudes were obtained with 2 CR-SPLIT exposures of 1200 sec in F606W and 900 sec in F814W. The required exposure times nicely fit into one orbit per object after taking into account realistic overheads. With these exposures, the achieved SNR given by the ACS ETC is ~10 at 1 mag below the TRGB for both bands (assuming a distance of 3~Mpc), with a limiting magnitude of ~27 in F814W, thus fulfilling our requirements. This translates into only a total of three orbits for our three dwarfs. We have checked that the charge transfer efficiency losses of ACS do not significantly affect our observations (at most 10% loss of flux). Our visits are 1-orbit, and we have no ORIENT requirements. Nor does this program have time constraints (other than the baseline excitement of the science!). Dr. Burcin Mutlu-Pakdil has led (and participated in) several previous HST campaigns related to resolved stellar populations of dwarf galaxies that have led to published results. Some we highlight below. She is an expert in near field cosmology and has expertise in HST data reduction for ACS and WFC3 which are the primary and parallel instruments used in this proposal. Most recently, she has completed an HST study of eight faint and ultra-faint dwarf galaxies around NGC253 at 3.5 Mpc (Mutlu-Pakdil et al. 2022,2024). Dr. David Sand has been PI and co-PI of over 10 successful HST proposals, and is an expert in near field cosmology. He has extensive experience with HST imaging and has published numerous papers on faint and diffuse dwarf galaxies. Dr. Denija Crnojevic is an expert in near field cosmology and has led several previous HST observing campaigns leading to 5 papers published over the past decade based on HST data (e.g., Crnojevic et al. 2010, 2013, 2014, 2016, 2019). Dr. Jones, Dr. Spekkens and Dr. Karunakaran are experts in low surface brightness galaxies in both visible light as well as in their gas content. Recently Dr. Jones published an HST study of two nearby ultra-diffuse galaxies (Jones et al. 2021), and also led an HST study of two dwarf-like objects in the direction of the Virgo cluster (Jones et al. 2022). Dr. Paul Bennet is a postdoctoral researcher who has led two previous M101-focused HST dwarf galaxy campaigns leading to two papers (Bennet et al. 2019, 2020), along with a recently completed study of two isolated dwarf galaxies in the Local Volume (Bennet et al. 2021). Dr. Catherine Fielder is an expert in the spectral energy distribution of Milky Way-like galaxies. She is currently leading an HST program studying the globular cluster populations of ultra-diffuse galaxies. Dr. Dennis Zaritsky is an expert on low-mass galaxies and ultra-diffuse galaxies, and Richard Donnerstein is an expert on low-surface brightness galaxy detection algorithms. Dr. Amandine Doliva-Dolinsky is an expert in ultra-faint dwarf galaxies and deep imaging. Dr. Laura Hunter is an expert on dwarf galaxies and their HI contents. She is currently leading an HST program on timescales of stellar feedback in blue galaxies. Galaxies Stellar Populations and the Interstellar Medium 6 false false false false false false false false SUPPORTED GALAXY DWARF SPHEROIDAL YES J2000 J2000 GALAXY DWARF SPHEROIDAL YES J2000 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W POS-TARG DITHER 0.364 Two-point dither. No need to fill chip gap. LINE false false 2 47.23 ACS-WFC-DITHER-LINE 1 false 1723670105978 /Users/burcinmutlu/Desktop/OP-cache/C32_phase2_2_DSAND-v01.xml The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 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