Science Keywords: Select from 2 to 5 items. Science Keywords is a required field. Spectral Element 1 is a required field. Spectral Element 1 is a required field. Spectral Element 1 is a required field. Spectral Element 1 is a required field. Spectral Element 1 is a required field. Spectral Element 1 is a required field. 0 Assigned ID: 1230 ----- Attempting Submission 1 (Wed Sep 07 14:07:11 GMT 2016) ----- Joint Spitzer/HST Main galaxy targets are very low surface brightness and do not show up well in DSS images. 338506063 ----- Attempting Submission 1 (Wed Oct 05 21:12:42 GMT 2016) ----- Ultra-diffuse Galaxies in Clusters and the Field: Masses and Stellar Populations Ultra-diffuse galaxies (UDGs) were recognized only last year as a novel class of galaxies, with luminosities like dwarfs but sizes like giants. Although some UDGs appear to be just unusually extended dwarfs, others show evidence of being very different and unexpected: their dark matter halos are overmassive by factors of ~10, with one UDG even being arguably a "failed Milky Way." These exotic galaxies might be a byproduct of environmental processes within galaxy clusters, but UDGs have also now been found in the field. It is crucial for understanding their origins to test if UDGs have the same properties in cluster and field environments. Here we propose studying the stellar populations (ages and metallicities) of seven UDGs using Spitzer/IRAC 3.6- and 4.5-micron imaging combined with optical photometry, along with mass estimation of three of the UDGs using HST/ACS imaging to provide globular cluster number counts and colors (proxies for halo mass). This ultra low surface brightness photometry in the near infrared, on an important new class of galaxies, could become a legacy result from the Spitzer mission. The technical goal of the observations is to detect globular cluster candidates around ultra-diffuse galaxies (UDGs), with 5-sigma point-source detection limits of F606W = 27.7, F814W = 27.2. We will observe each of 3 UDGs in 2 filters, with 1 orbit per filter. The same orientation is used for both filters. We will use a large+small 4-point dither pattern to remove chip gap, hot pixels, and cosmic rays. Galaxies 6 false false false false false false SUPPORTED GALAXY LSB UNDESIGNATED Low surface brightness galaxy, diameter ~ 20 arcsec. J2000 J2000 GALAXY LSB UNDESIGNATED Low surface brightness galaxy, diameter ~ 40 arcsec. PG1133+4755 J2000 J2000 GALAXY LSB UNDESIGNATED Low surface brightness galaxy, diameter ~ 40 arcsec. PG1327+4637 J2000 J2000 ACS/WFC Imaging No No ACS/WFC Imaging No No ACS/WFC Imaging No No ACS/WFC Imaging No No ACS/WFC Imaging No No ACS/WFC Imaging No No POS-TARG DITHER DITHER 2 3.034 Large dither over gap combined with 2-point hot-pixel dither subpattern. LINE false false 0.145 2 85.29 POS-TARG ACS-WFC-DITHER-LINE 47.23 2 true The scheduling data was generated by CASM 24.2. 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CASM was run in Phase II mode. 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