Galaxy And Mass Assembly (GAMA): end of survey report and data release 2 (1506.08222v1)

Abstract: The Galaxy And Mass Assembly (GAMA) survey is one of the largest contemporary spectroscopic surveys of low-redshift galaxies. Covering an area of ~286 deg^2 (split among five survey regions) down to a limiting magnitude of r < 19.8 mag, we have collected spectra and reliable redshifts for 238,000 objects using the AAOmega spectrograph on the Anglo-Australian Telescope. In addition, we have assembled imaging data from a number of independent surveys in order to generate photometry spanning the wavelength range 1 nm - 1 m. Here we report on the recently completed spectroscopic survey and present a series of diagnostics to assess its final state and the quality of the redshift data. We also describe a number of survey aspects and procedures, or updates thereof, including changes to the input catalogue, redshifting and re-redshifting, and the derivation of ultraviolet, optical and near-infrared photometry. Finally, we present the second public release of GAMA data. In this release we provide input catalogue and targeting information, spectra, redshifts, ultraviolet, optical and near-infrared photometry, single-component S\'ersic fits, stellar masses, H$\alpha$-derived star formation rates, environment information, and group properties for all galaxies with r < 19.0 mag in two of our survey regions, and for all galaxies with r < 19.4 mag in a third region (72,225 objects in total). The database serving these data is available at http://www.gama-survey.org/.

• The paper provides a comprehensive end-of-survey report demonstrating high redshift completeness (98.5%) using advanced spectroscopic techniques.
• The study introduces the automated redshift code Autoz, which outperforms previous methods with a mere 0.2% error rate on high-quality redshifts.
• The DR2 data release offers detailed multi-band photometry and galaxy environment measures for over 72,000 galaxies, enabling robust studies of galaxy evolution.

Overview of the Galaxy And Mass Assembly (GAMA) Survey: End of Survey Report and Data Release 2

The paper "Galaxy And Mass Assembly (GAMA): end of survey report and data release 2" provides a comprehensive account of the GAMA survey, a large spectroscopic campaign targeting galaxies in the low-redshift universe. This second major data release (DR2) follows the successful completion of GAMA's first phase, GAMA-I, and includes significant extensions and enhancements over the first data release (DR1).

GAMA is designed to test the Cold Dark Matter (CDM) model and paper galaxy evolution by integrating data from multiple ground-based and space-borne facilities. The survey's main scientific objectives include measuring the dark matter halo mass function, probing star formation efficiency and feedback, and quantifying the recent galaxy merger rate. These goals hinge on GAMA's ability to provide high-quality spectroscopic data alongside extensive multi-wavelength photometry for a large sample of galaxies.

Survey Design and Execution

GAMA spans approximately 286 square degrees over five survey regions. The spectroscopic campaign was executed using the AAOmega spectrograph on the Anglo-Australian Telescope (AAT), targeting galaxies down to a limiting magnitude of $r < 19.8$. The survey includes novel approaches in data acquisition, such as frequent visits to the same sky areas, ensuring high redshift completeness and excellent spatial coverage.

The campaign achieved a remarkable redshift completeness of 98.5% in its equatorial regions (G09, G12, and G15) by overcoming challenges such as adverse weather conditions and instrumental limitations. The GAMA methodology focuses on recovering redshifts even for complex regions, such as crowded galaxy groups, which are critical for understanding large-scale structures.

Redshift Analysis and Quality Control

Redshifts for the GAMA survey were primarily determined using the semi-automated code, {\sc runz}, with subsequent validation through re-redshifting campaigns. An alternative automated redshift code, {\sc Autoz}, was developed and proved superior to {\sc runz} in terms of precision and reliability. This fully automated method enhances the robustness of redshift determination, with {\sc Autoz} achieving an impressive incorrectness fraction of just 0.2% among high-quality ($nQ\ge3$) redshifts.

Multi-Wavelength Photometry

DR2 includes comprehensive photometry derived from several imaging surveys spanning wavelengths from the ultraviolet to the infrared. Key to this is aperture-matched multi-band photometry obtained from SDSS and UKIDSS imaging data, supplemented by GALEX FUV and NUV photometry for star formation studies. Significant improvements over previous photometric releases are achieved by homogenizing data and employing updated convolution and extraction techniques to mitigate varying seeing conditions.

Data Release 2: Access and Content

GAMA DR2 releases a wealth of data products for 72,225 galaxies, including spectra, redshifts, environment measures, and group catalogues. Each dataset is structured within a modular system dubbed Data Management Units (DMUs), enabling efficient access and interpretation. The release primarily covers the three equatorial survey regions, offering unprecedented detail on galaxy properties, environments, and group memberships.

DR2 is accessible via a dedicated web portal and includes tools for data exploration such as SQL querying, Single Object Viewer for detailed inspection, and an organized file server for data downloads. Future data releases will extend the available data to include deeper samples and additional galaxy attributes, providing an essential resource for studies in cosmology and galaxy evolution.

Conclusion

The GAMA survey exemplifies a major achievement in the field of astrophysics, combining extensive spectroscopic data with a rich set of multi-wavelength observations. By addressing critical scientific questions about galaxy formation and evolution, GAMA stands as a pivotal contributor to our understanding of the cosmos, while also offering rich datasets for the broader research community through its public data releases. Future plans include expanding the scope of covered data and ensuring all findings are disseminated for collaborative scientific advancements.