SDSS-IV MaNGA IFS Galaxy Survey --- Survey Design, Execution, and Initial Data Quality

Abstract: The MaNGA Survey (Mapping Nearby Galaxies at Apache Point Observatory) is one of three core programs in the Sloan Digital Sky Survey IV. It is obtaining integral field spectroscopy (IFS) for 10K nearby galaxies at a spectral resolution of R~2000 from 3,622-10,354A. The design of the survey is driven by a set of science requirements on the precision of estimates of the following properties: star formation rate surface density, gas metallicity, stellar population age, metallicity, and abundance ratio, and their gradients; stellar and gas kinematics; and enclosed gravitational mass as a function of radius. We describe how these science requirements set the depth of the observations and dictate sample selection. The majority of targeted galaxies are selected to ensure uniform spatial coverage in units of effective radius (Re) while maximizing spatial resolution. About 2/3 of the sample is covered out to 1.5Re (Primary sample), and 1/3 of the sample is covered to 2.5Re (Secondary sample). We describe the survey execution with details that would be useful in the design of similar future surveys. We also present statistics on the achieved data quality, specifically, the point spread function, sampling uniformity, spectral resolution, sky subtraction, and flux calibration. For our Primary sample, the median r-band signal-to-noise ratio is ~73 per 1.4A pixel for spectra stacked between 1-1.5 Re. Measurements of various galaxy properties from the first year data show that we are meeting or exceeding the defined requirements for the majority of our science goals.

An Overview of the SDSS-IV MaNGA IFS Galaxy Survey

The MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) survey is a significant component of the Sloan Digital Sky Survey IV (SDSS-IV), focusing on obtaining detailed integral field spectroscopy (IFS) of 10,000 nearby galaxies. The survey targets a substantial wavelength range from 3622 to 10,354 Å with a spectral resolution of $R\sim2000$. This initiative aims to address fundamental questions concerning galaxy formation and evolution by deriving precise measurements of various galaxy properties, including star formation rates, gas metallicity, stellar populations, and kinematics.

Survey Design and Execution

The survey's design is guided by stringent science requirements. It incorporates a uniform sample selection methodology that ensures consistent spatial coverage of galaxies across effective radii. The principal science goals necessitate measuring physical quantities such as star formation rates and gas metallicity with high precision, which drive the survey's depth and observational strategies.

MaNGA employs multiple integral field unit (IFU) configurations to achieve spatial resolution and coverage goals across different galaxy types and sizes. Two primary samples—Primary and Secondary—are established to cover galaxies up to 1.5 and 2.5 effective radii, respectively, ensuring comprehensive spatial sampling necessary for quantifying radial gradients in galaxy properties.

Initial Data Quality and Observational Challenges

The survey's observational strategy capitalizes on the unique capabilities of the SDSS 2.5m telescope, implementing a dither pattern to ensure optimal spatial sampling across fiber bundles. Key elements of MaNGA's data quality control include consistent flux calibration utilizing standard stars and managing chromatic differential atmospheric refraction.

Despite challenges such as varying seeing conditions and instrument flexure, MaNGA achieves remarkable data quality, highlighted by near-Poisson-limited sky subtraction and highly accurate flux calibration across its extensive spectral coverage. The survey successfully delivers spatially-resolved galaxy spectra that allow measurement of essential parameters like stellar age and metallicity gradients.

Implications and Future Directions

The comprehensive dataset provided by MaNGA opens the door to a multitude of research avenues, enabling profound insights into galaxy dynamics, evolution, and the underlying processes governing these transformations. The approach reflects a balance between sample size and observational depth, potentially setting a standard for future large-scale spectroscopic surveys of galaxies.

MaNGA's impact extends beyond its immediate findings; it sets a foundation for cross-collaboration with other surveys, enriching the observational landscape with integrated multi-wavelength datasets. Looking ahead, MaNGA’s methodology and dataset will undoubtedly drive further advances in theoretical models and simulations, refining our understanding of galaxy physics in cosmological contexts.

In summary, the MaNGA survey represents a significant advance in the field of galaxy spectroscopy, providing a wealth of high-quality, spatially-resolved data that meets its science objectives. The robust design and execution of this survey will remain a cornerstone for ongoing research and future exploration of galactic phenomena.