0Assigned ID: 3129
----- Attempting Submission 1 (Fri Mar 25 04:08:35 GMT 2022) -----
HST Phase I Proposal 3129 successfully submitted.
Receipt: # 3129-1
----- Attempting Submission 2 (Fri Mar 25 21:35:02 GMT 2022) -----FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser
FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser
FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser
FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser
FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser
FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser
FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser
FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browserWe added new orient constraints to one of our targets' observations to help with the placement of our parallel observations. There is a large galaxy in the field that could fall in our parallel WFC3 observation under certain conditions, which could have an impact on our science (i.e., the ability to assess the background around the dwarf galaxies).
The addition of the orient was recommended by the instrument team and approved by TTRB.-1785852579----- Attempting Submission 1 (Wed Jul 13 16:04:03 GMT 2022) -----
----- Attempting Submission 2 (Thu Aug 04 22:16:08 GMT 2022) -----I have discussed the warnings with the program coordinator, and we agreed that the WFC3 exposures are fine; the exposures are long, and targets being an extended source, there should be no concerns regarding CTE.Exploring The Plane of Satellites Around NGC253: A Case Study for Isolated EnvironmentsThe distribution of dwarf satellite galaxies is a strong test for models of galaxy formation and evolution, independent of the exact details of baryonic physics. The three observed planes of satellites known today (around the Milky Way, M31, and Centaurus A) constitute a main problem for the standard cosmological models, where satellite systems are expected to have a nearly isotropic distribution. As these three systems reside in rich galaxy groups, their specific local environment could be responsible for the observed satellite planes. Exploration of satellite planes in other galaxies, in different environments, is thus a critical first step in solving the 'plane of satellites' problem.
A spatially flattened dwarf satellite system has recently been proposed around NGC253 (D=3.5 Mpc), a Milky Way-mass spiral galaxy in an isolated environment. However, four faint dwarf candidates still lack distance measurements, and prevent us to draw a final conclusion on the true nature of this alleged plane of satellites (based on ten confirmed dwarf satellites). We request four orbits of HST/ACS in F606W and F814W to image these four NGC253 dwarf candidates in order to confirm their nature, precisely measure their distances, and study the 3D structure of the NGC253 dwarf satellite system as a whole. The results from this modest request will constrain the proposed plane of satellite galaxies in NGC253, an essential test for cosmological models in isolated environments.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, 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. 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. 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.Dr. Burcin Mutlu-Pakdil 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. She has recently completed an HST study of five faint and ultra-faint dwarf galaxies around NGC253 (Mutlu-Pakdil et al. 2022), and published two papers on HST observations of two Milky Way ultra-faint dwarf galaxies (Mutlu-Pakdil et al., 2019, 2020). Dr. David Sand is an expert in near field cosmology, and he has led and participated in several previous HST campaigns related to resolved stellar populations of dwarf galaxies that have led to several published results. 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). She led the dwarf galaxy search around CenA, and followed-up them with HST. She is an expert on TRGB distance measurements. Dr. Jones, Dr. Spekkens and Dr. Karunakaran are experts in low surface brightness galaxies. Dr. Jones recently published an HST study of two nearby ultra-diffuse galaxies, measuring their globular cluster content, and comparing that with models describing the formation of these unusual galaxies (Jones et al. 2021). He also led an HST study of two dwarf-like objects in the direction of the Virgo cluster (Jones et al. 2022). Dr. Paul Bennet 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).GalaxiesStellar Populations and the Interstellar Medium6falsefalsefalsefalsefalsefalsefalseSUPPORTEDGALAXYDWARF SPHEROIDALYESJ2000J2000GALAXYDWARF SPHEROIDALYESJ2000J2000GALAXYDWARF SPHEROIDALYESJ2000J2000GALAXYDWARF SPHEROIDALYESJ2000J2000ACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WACS/WFCImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WPOS-TARGDITHER0.364Two-point dither. 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