0 Assigned ID: 243 ----- Attempting Submission 1 (Thu Apr 04 19:11:18 GMT 2019) ----- HST Phase I Proposal 243 (McQ_HST27_NIR_TRGB_v1.apt) successfully submitted. Receipt: # 243-1 ----- Attempting Submission 2 (Fri Apr 05 15:20:23 GMT 2019) ----- 0 ----- Attempting Submission 1 (Thu Jul 25 15:45:28 GMT 2019) ----- Calibrating the Tip of the Red Giant Branch Distance Indicator in the Near-Infrared The tip of the red giant branch (TRGB) method is the most accurate and least expensive distance indicator for nearby galaxies. HST has delivered TRGB distances to 100's of nearby galaxies, supporting innumerable astrophysical measurements and providing a new, independent route to a precision measurement of the Hubble constant, H_0. TRGB distances are primarily measured from I-band (F814W) observations as the I-band luminosities of the stars at the tip of the red giant branch have little dependency on stellar age and only a modest dependency on metallicity; this metallicity dependency is well-understood and corrected for in the I-band TRGB calibration. In the near-infrared (NIR), the TRGB is ~2 mag brighter. With the NIR capabilities of HST and JWST, accurate distances to nearby galaxies are possible with greater efficiency and to larger distances. There is already momentum in the H_0 community to pursue NIR TRGB distances using HST as a stepping stone to JWST. However, models show that the TRGB has a greater dependency on both stellar age and metallicity in the NIR. Thus, without a foundational investment in empirically calibrating the NIR TRGB and robustly testing the calibration, existing and planned NIR TRGB programs are vulnerable to systematic biases. We propose observations of 8 fields in 4 nearby galaxy halos with the ACS F814W and the WFC3 F110W and F160W filters to calibrate the NIR TRGB. We will quantify the sensitivity of the NIR TRGB to age and metallicity variations, while simultaneously characterizing the stellar content of galaxy halos. Such a calibration is urgently needed before undertaking NIR TRGB distance work with JWST. The primary goals of this proposal are to measure the tip of the red giant branch (TRGB) distances to 4 spiral galaxies using optical imaging from the ACS camera of the halo stars, use those distances to calibrate the TRGB in the infrared imaging from the WFC3 camera, and characterize the stellar content of the halos. Orbit allocation = 8 orbits (1 orbit for 2 fields per galaxy) which include 8 primary ACS orbits and 8 coordinated parallel WFC3 orbits. All primary visits include 1-orbit with the ACS/WFC. The orbit is split between the F606W filter and the F814W filter with a small 2 pixel offset in pointing. The small pointing offset is implemented using the POS-TARG of X=0.474 and Y=0.424 specificed in the WFC3 manual as the 2-point line dither offset equivalent of a 3.5 pixel shift in the WFC3 IR detector. We use the larger WFC3 IR shift (rather than the ACS dither) to ensure we are moving off hot pixels in both cameras. We do not intend to cover the chip gap with our dither pattern. The coordinated parallel observations are to be obtained with the WFC3 IR camera split between the F110W and F160W filters. The visits are requested within specific orientation ranges. The primary observations are of a field in the halo of each target galaxy. The orientation ranges have been chosen such that the coordinated parallels image a second field in halo of the target galaxy. For the second visit for the target galaxy, the cameras are placed on the opposite fields, ensuring that both halo fields on each galaxy are observed with each camera. PI Kristen McQuinn and Co-Is Evan Skillman, Andrew Dolphin have deep experience as a team measuring the TRGB distances to nearby galaxies using the optical I-band filter (McQuinn et al. 2013, 2014, 2016a,b, 2017, 2018). They have also recently modelled the NIR TRGB using stellar evolution libraries and quantified the expected, theoretical TRGB sensitivity to changes in stellar content (McQuinn, Boyer, Skillman, Dolphin 2019). Andrew Dolphin was involved with the calibration of the TRGB in the HST filters and developed the Maximum Likelihood code to identify the TRGB using photometry and consideration of the incompleteness of the data measured by artificial star tests. Our team has the skills needed to perform a careful calibration of the NIR TRGB and deliver the calibration in a timely manner (i.e., before it is needed for JWST programs). Stellar Populations Galaxies and the IGM 0 false true false false true false false SUPPORTED GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. 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