期刊
ASTRONOMICAL JOURNAL
卷 150, 期 1, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-6256/150/1/19
关键词
atmospheric effects; methods: observational; surveys; techniques: imaging spectroscopy
资金
- Summer Undergraduate Research Program at the Dunlap Institute, University of Toronto
- Leverhulme Trust
- Alfred P. Sloan Foundation
- Center for High-Performance Computing at the University of Utah
- Carnegie Institution for Science
- Carnegie Mellon University
- Chilean Participation Group
- Harvard-Smithsonian Center for Astrophysics
- Instituto de Astrofisica de Canarias
- Johns Hopkins University
- Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo
- Lawrence Berkeley National Laboratory
- Leibniz Institut fur Astrophysik Potsdam (AIP)
- Max-Planck-Institut fur Astrophysik (MPA Garching)
- Max-Planck-Institut fur Extraterrestrische Physik (MPE)
- Max-Planck-Institut fur Astronomie (MPIA Heidelberg)
- National Astronomical Observatory of China
- New Mexico State University
- New York University
- Ohio State University
- Pennsylvania State University
- Shanghai Astronomical Observatory
- United Kingdom Participation Group
- Universidad Nacional Autonoma de Mexico
- University of Arizona
- University of Colorado Boulder
- University of Portsmouth
- University of Utah
- University of Washington
- University of Wisconsin
- Vanderbilt University
- Yale University
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is an integral-field spectroscopic survey that is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV). MaNGA's 17 pluggable optical fiber-bundle integral field units (IFUs) will observe a sample of 10,000 nearby galaxies distributed throughout the SDSS imaging footprint (focusing particularly on the North Galactic Cap). In each pointing these IFUs are deployed across a 3(degrees) field; they yield spectral coverage 3600-10300 angstrom at a typical resolution R similar to 2000, and sample the sky with 2 diameter fiber apertures with a total bundle fill factor of 56%. Observing over such a large field and range of wavelengths is particularly challenging for obtaining uniform and integral spatial coverage and resolution at all wavelengths and across each entire fiber array. Data quality is affected by the IFU construction technique, chromatic and field differential refraction, the adopted dithering strategy, and many other effects. We use numerical simulations to constrain the hardware design and observing strategy for the survey with the aim of ensuring consistent data quality that meets the survey science requirements while permitting maximum observational flexibility. We find that MaNGA science goals are best achieved with IFUs composed of a regular hexagonal grid of optical fibers with rms displacement of 5 mu m or less from their nominal packing position; this goal is met by the MaNGA hardware, which achieves 3 mu m rms fiber placement. We further show that MaNGA observations are best obtained in sets of three 15 minute exposures dithered along the vertices of a 1.44 arcsec equilateral triangle; these sets form the minimum observational unit, and are repeated as needed to achieve a combined signal-to-noise ratio of 5 angstrom(-1) per fiber in the r-band continuum at a surface brightness of 23 AB arcsec(-2). In order to ensure uniform coverage and delivered image quality, we require that the exposures in a given set be obtained within a 60 minute interval of each other in hour angle, and that all exposures be obtained at airmass less than or similar to 1.2 (i.e., within 1-3 hr of transit depending on the declination of a given field).
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