0 ----- Attempting Submission 1 (Fri Jan 31 21:04:43 GMT 2025) ----- ----- Attempting Submission 2 (Mon Mar 10 20:09:46 GMT 2025) ----- Building the Last Bridge Between the PHAT & PHATTER Surveys and Carbon Star Cosmology The Hubble Tension refers to a >5 sigma difference between local and cosmological measurements of the present expansion rate of our universe, the Hubble constant (H0). This tension hints at the possibility of undiscovered physics undermining the canonical standard model of our universe. Probing the Hubble Tension necessitates intense scrutiny of the Cepheid-based distance ladder, which currently provides the strongest constraints on direct H0 measurements. Possibly the most powerful approach to test systematics in the Cepheid-based steps of the distance ladder is to develop and use independent standard candles to measure distances to galaxies. To date, agreement with another candle, the tip of the red giant branch (TRGB), has been elusive. The J-region Asymptotic Giant Branch (JAGB) is a new standard candle that can provide independent relative distances between nearby systems, as well as crosscheck Cepheid systematics at > 30 Mpc. The Panchromatic Hubble Andromeda Treasury (PHAT) and PHAT Triangulum Extended Region (PHATTER) were HST multi-cycle programs that mapped a third of the star forming disk in M31 and central ~0.1 deg2 region of M33 and are unequivocally the best testing grounds for characterizing and standardizing the JAGB via cross calibration with other standard candles. However, there currently exists no F110W observations of the outer disk in NGC 4258 that can be used to measure JAGB distances with PHAT & PHATTER. We propose to fill in this gap and observe the outer disk of NGC 4258 in the HST WFC3/IR F110W filter. This cycle is the last that will enable tying the PHAT & PHATTER legacies to Carbon star cosmology. This program will observe multipel fields in NGC 4258 in the WFC3 F110W filter to observe JAGB stars. These fields will overlap with one of the existing NGC 4258 fields, which will provide the F814W observations needed to differentiate these JAGB stars via color cuts. 6 false false false false false false SUPPORTED GALAXY SPIRAL This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 POS-TARG DITHER DITHER 4 1.908 WFC3-IR-DITHER-BOX-MIN false 74.653 false 1.095 1.716 3 41.788 POS-TARG LINE 18.528 2 true Hst Same orient constraint links visits (01 02 03 04) The scheduling data was generated by CASM 33.0. CASM was run in Phase II mode. 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