0 Assigned ID: 764 ----- Attempting Submission 1 (Fri Apr 07 19:11:32 GMT 2017) ----- 0 ----- Attempting Submission 1 (Tue Jul 18 21:59:33 GMT 2017) ----- ----- Attempting Submission 2 (Tue Sep 19 23:00:34 GMT 2017) ----- ----- Attempting Submission 3 (Fri Sep 22 21:05:00 GMT 2017) ----- ----- Attempting Submission 4 (Tue Jan 30 19:08:03 GMT 2018) ----- We propose to use four HST/ACS orbits to obtain follow-up imaging and resolved photometry of two candidate dwarf galaxies in the halos of Local Volume LMC analogs, which have been discovered as part of our ground-based MADCASH survey: MADCASH-1, which is a satellite of NGC 2403 (D = 3.2 Mpc), and MADCASH-2, near NGC 4214 (D = 2.9 Mpc). These are the faintest dwarf satellites known around host galaxies of Large Magellanic Cloud stellar mass outside the Local Group. We will measure accurate TRGB distances to confirm their associations with their host galaxies, derive their structural parameters, and assess their stellar populations. These two dwarf galaxies, the first of their kind around LMC analogs, are vital probes of dwarf evolution in different environments. Both of these MADCASH dwarfs are at luminosities intermediate between the "classical" Milky Way dwarf galaxies and the "ultra-faint" dwarfs. The proposed observations will resolve individual stars in these systems of small angular size, allowing us to quantify the relative presence of ancient stellar populations and younger, more metal-enriched stars, and to measure their physical properties. We will compare these to the Milky Way classical and ultra-faint dwarfs to place these systems in a broader context and assess similarities or differences between these "dwarfs around dwarfs" and Local Group satellites. Our observing strategy is to obtain deep imaging in two filters (ACS/WFC F606W and F814W) in order to (a) confirm the association of two new dwarf galaxies (MADCASH-1 and MADCASH-2) with their putative LMC-analog hosts via accurate TRGB distances, (b) assess their stellar populations and star formation histories, and (c) derive their structural parameters (size, luminosity, ellipticity, and position angle) via resolved photometry. To accomplish these goals, we require deep, precise photometry with S/N~5 at least 2 magnitudes below the RGB tip in the target galaxies. Our choices of filters and exposure times are motivated by numerous studies and HST programs similar to ours (e.g., Williams et al. 2013, Dalcanton et al. 2009, Radburn-Smith et al. 2011). For low metallicity systems, the TRGB can be easily distinguished (using, e.g., a Sobel edge detection filter) due to the quick cutoff at M_I = -4.0 mag if the imaging in the I band (F814W) is sufficiently deep. The use of the V band (F606W) allows us to minimize galaxy contamination using photometric colors, and to use the detected member stars of each galaxy to assess their stellar populations and derive their structural parameters. We will use one orbit per filter per target galaxy, splitting the observing time into exposures of 1415/1272 sec (for MADCASH-1/MADCASH-2) in F606W and 1484/1341 sec in F814W, requiring a total of 4 HST orbits. Each exposure will be split into a two-line dither pattern to cover the ACS/WFC chip gap and facilitate cosmic ray removal. Each of the two galaxy candidates is small enough to fit onto one of the ACS/WFC chips, and given the lack of nearby bright stars, any HST orientation angle is sufficient for observing these targets. However, for MADCASH-1, we have placed limitations on the orientation in order to avoid placing nearby very bright stars onto the WFC3/UVIS chip during parallel observations. Our requested parallel observations with WFC3/UVIS will obtain neighboring fields from which we will assess the contribution of background sources. We note that these filters are similar to the g- and i-band filters we are using for our Subaru/HSC survey. These proposed parallel observations will thus provide an ancillary benefit by allowing us to use the deeper, higher-resolution HST data in regions of the WFC3/UVIS field of view well beyond our dwarf galaxy targets to assess the veracity of our star/galaxy classification in the ground-based MADCASH imaging, and improve our techniques in order to reduce the contamination from unresolved background galaxies. Stellar Populations 6 false false false false false false false SUPPORTED GALAXY DWARF SPHEROIDAL Note: V~20 is the total integrated magnitude of the dwarf galaxy. MADCASH-J074238+652501-DW J2000 J2000 GALAXY DWARF SPHEROIDAL Note: V~19 is the total integrated magnitude of the dwarf galaxy. 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 3.034 LINE false false 4 85.29 ACS-WFC-DITHER-LINE 1 false 1517338690130 The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. 1542086646000 257.01178488844005 (Tic-Visit :proposal-id 15228 :visit-id "01" :proposal-version -1 :trans-version "20170613" :date "30-Jan-2018 11:58:09.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 4583776 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15228 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15228 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3213 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3546 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15228 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3324 :al-overhead-at-end 0 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3546 :pcs-gap 0 ) true 2 0 1545081126726 /Users/jcarlin/Dropbox/local_volume_dwarfs/hst15228/OP-cache/PhaseII_resub_HST15228_17Dec2018-v02.xml The scheduling data was generated by CASM 26.2.2. 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