OBSERVING STRATEGY FOR THE SDSS-IV/MaNGA IFU GALAXY SURVEY

By D. Law, R. Yan, M. Bershady, K. Bundy, B. Cherinka, N. Drory, N. MacDonald, J. Sánchez-Gallego, D. Wake, A. Weijmans and 5 more. 2015

246 citations recorded by the source corpus.

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° field; they yield spectral coverage 3600−10300 Å at a typical resolution R ∼ 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 μm or less from their nominal packing position; this goal is met by the MaNGA hardware, which achieves 3 μm 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 Å−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 ≲ 1.2 ?> (i.e., within 1–3 hr of transit depending on the declination of a given field).

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/903391911ed2113e4d6fee338d232f5102723022

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Citations in the corpus

The Fifteenth Data Release of the Sloan Digital Sky Surveys: First Release of MaNGA-derived Quantities, Data Visualization Tools, and Stellar Library (2018, background): “Over its planned five years of operations MaNGA aims to get data for ∼10,000 nearby galaxies (Law et al. 2015; Yan et al. 2016b,a; and see Wake et al. (2017) for details on the sample selection).”
SDSS-IV MaNGA : the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements (2016, methodology): “The observations are done with a dithering scheme to achieve a complete spatial coverage and near critical sampling of the PSF (Law et al. 2015).”
SDSS IV MaNGA – metallicity and nitrogen abundance gradients in local galaxies (2017, methodology): “A three-point dithering pattern is used during observations to compensate for light loss and create a uniform point spread function (PSF, Law et al. 2015).”
Target Selection for the SDSS-IV APOGEE-2 Survey (2017, unknown): “For MaNGA observing details, see Law et al. (2015).”
SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs (2016, methodology): “A three point dithering pattern is applied to compensate for light loss between fibres and to obtain a uniform circular point spread function (PSF, Law et al. 2015).”
SDSS-IV/MaNGA: SPECTROPHOTOMETRIC CALIBRATION TECHNIQUE (2015, background): “As simulated by Law et al. (2015), if each exposure has a dither-dependent systematic flux calibration error with an RMS of 5%, a 1% pixel-to-pixel error in the reconstructed data cube would result.”
THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3 (2015, background): “Ongoing spatially-resolved spectroscopic surveys, such as the SDSS-IV/MaNGA IFU (Law et al. 2015) and SAMI (Bryant et al. 2015) galaxy surveys, will provide a dataset capable of unraveling the relative contributions of HII regions and diffuse ionized gas to global galaxy spectra.”
THE DATA REDUCTION PIPELINE FOR THE SDSS-IV MaNGA IFU GALAXY SURVEY (2016, methodology): “As detailed by Law et al. (2015), this integration time is a compromise between the minimum time necessary to reach background limited performance in the blue while simultaneously minimizing astrometric drift due to differential atmospheric refraction (DAR) between the individual exposures.”