Galaxy And Mass Assembly (GAMA) Survey

Updated 4 August 2025

Galaxy And Mass Assembly Survey (GAMA) is a large-scale, spectroscopic and multiwavelength program that provides a nearly complete census of galaxy properties in the low-redshift universe.
The survey integrates extensive photometry, SED fitting, and structural analysis across multiple bands to yield robust measurements of stellar mass, star formation, and environmental parameters.
Its high redshift completeness (≥98%) and advanced group cataloguing techniques underpin precise empirical scaling relations and detailed mappings of the cosmic web.

The Galaxy And Mass Assembly Survey (GAMA) is an extensive spectroscopic and multiwavelength imaging program operating primarily in the low-redshift universe. Founded on the 3.9-m Anglo-Australian Telescope with the AAOmega fibre-fed spectrograph, GAMA systematically targets galaxy populations in multiple sky regions to yield a highly complete (≥98%) census of galaxy properties over hundreds of square degrees, with a fundamental focus on the interplay between galaxy structure, star formation, environment, and cosmic web topology. Its design, technical implementation, and data products make GAMA a pivotal resource for studies in galaxy evolution, the large-scale structure of the universe, stellar mass assembly, and comparison with cosmological simulations.

1. Survey Footprint, Observing Strategy, and Data Acquisition

GAMA targets five regions on the sky, including three major equatorial strips (G09, G12, G15; each ~60 deg²) and two southern regions (G02, G23; ~56 and 51 deg² respectively), reaching a total coverage of ~286 deg² (Driver et al., 2010, Baldry et al., 2017). The main spectroscopic limits are $r < 19.8$ mag (with some regions slightly shallower), optimized for overlap with complementary surveys (SDSS, UKIDSS-LAS, GALEX, Herschel-ATLAS, KiDS, VIKING). The region selection achieves overlap with major extragalactic datasets (e.g., XXL X-ray, VIPERS), supporting panchromatic studies.

GAMA's observing campaign began in 2008, operating with a dual-arm spectrograph (blue arm 3720–4800 Å, red arm 4800–8850 Å; $R \approx 1300$ ), typically observing 318–366 objects per 2dF field. Redshifts are extracted using a two-stage automated and manual process, with a normalized quality (nQ) system calibrated via repeated "re-redshifting" and quantitative reliability assessment. The resulting velocity precision is 65–100 km s $^{-1}$ , with a redshift completeness exceeding 98% for the r-band selected main sample (Driver et al., 2010, Hopkins et al., 2013, Liske et al., 2015, Baldry et al., 2017).

Table: Main GAMA Regions and Survey Limits

Region	Area (deg²)	Main Flux Limit ( $r$ )
G09	60	$r<19.8$
G12	60	$r<19.8$
G15	60	$r<19.8$
G02	56	$r<19.8$
G23	51	$i<19.0$

2. Multiwavelength Photometry, Structural Analysis, and SEDs

GAMA builds matched-aperture photometric catalogues spanning ultraviolet (GALEX FUV, NUV), optical (SDSS $ugriz$ , VST KiDS $ugri$ ), near-infrared (UKIDSS-LAS, VIKING $YJHK_s$ ), mid-infrared (WISE $W1-W4$ ), and far-infrared (Herschel $P100$ to $S500$ ). Imaging data are mosaicked (SWARP) and source-extracted using pipelines such as SExtractor, PSFEx, and (since DR4) ProFound, delivering consistent segmentations and fluxes across all bands. Photometry is uniform and designed for accurate SED analyses and stellar mass estimation (Driver et al., 2010, Bellstedt et al., 2020).

Every galaxy is fitted in each optical/NIR band with a single- or double-component Sérsic model (GALFIT3), yielding parameters ( $n$ , $r_e$ , $q$ , $PA$ ) and total magnitudes. Sérsic fits are integrated to both infinity and $10R_e$ , with the latter preferred for robust total fluxes, especially for high- $n$ systems (Liske et al., 2015). This approach underpins stellar mass estimates (Taylor et al. calibration) and informs morphological analyses.

GAMA enables detailed SED fitting using tools such as MAGPHYS or ProSpect, leveraging the homogeneous panchromatic coverage to extract star formation histories, dust masses, and energy distributions for $\sim$ 380,000 galaxies (Driver, 2012, Bellstedt et al., 2020).

3. Environmental Catalogs and Large-Scale Structure

GAMA constructs group catalogues (G $^3$ C) using iterative friends-of-friends (FoF) algorithms, calibrated with mock catalogues to ensure unbiased recovery of group multiplicity, mass, and membership (Liske et al., 2015, Baldry et al., 2017). Group environments are characterized by multiplicity, $N_{\mathrm{FoF}}$ , projected size, velocity dispersion, and dynamical mass proxies ( $M \sim R_{50} \sigma^2$ ), with robust estimates for centrals and satellites.

Large-scale structure within the survey is mapped using an adapted minimal spanning tree (MST) algorithm, identifying filaments (mean length $13\,h^{-1}$ Mpc, 643 filaments in three main fields), "tendrils" (coherent galaxy chains, $\sim10\,h^{-1}$ Mpc), and void galaxies (extremely flat two-point correlation function at $>20\,h^{-1}$ Mpc) (Alpaslan et al., 2013). The cosmic web topology is matched to Millennium Simulation-derived mocks with high fidelity, enabling direct comparisons between observations and simulations of higher-order distribution statistics beyond two-point correlations.

Table: Hierarchy of GAMA Structures

Structure	Definer	Scale
Filament	Group MST Links	$>10\,h^{-1}$ Mpc
Tendril	Galaxy MST (remnant)	$\sim10\,h^{-1}$ Mpc
Void	No MST links	Isolation ( $>10\,h^{-1}$ Mpc radius)

4. Galaxy, Group, and Cluster Properties

GAMA enables population-wide studies of galaxy morphology, mass functions, and environmental dependence. Visual classifications (phase II; 7556 objects) extend to $\log(M_\star/M_\odot)=8$ , with single Schechter functions fitting each morphological class. Spheroidal (E, S0-Sa) systems contribute $\sim70\%$ of the stellar mass budget, with disks (Sab-Scd, Sd-Irr) comprising the remainder; decomposition including bulge-to-total gives nearly equal partition (Moffett et al., 2015, Moffett et al., 2016).

Stellar mass functions for spheroid and disk components are robustly constrained, with the overall stellar mass density $\rho_\star = 2.5 \times 10^8\,M_\odot\,\mathrm{Mpc}^{-3}\,h_{0.7}$ (about 4% of baryons in stars). Spheroid mass fraction increases with group halo mass (transition near $\log(M_{\mathrm{halo}}/M_\odot)\sim12.5$ ), with satellites showing higher disk fractions in low-mass groups (Moffett et al., 2016).

Cluster detection combines Delaunay Tessellation Field Estimator (DTFE) and caustic mass analysis, recovering 113 clusters ( $10^{12}$ – $10^{16}\,\mathcal{M}_\odot$ ) compatible with Sunyaev-Zel'dovich Effect densities and spanning a broad mass range (Ibarra-Medel et al., 2014).

5. Physical Scaling Relations and Galaxy Evolution Diagnostics

GAMA's high quality spectroscopy ( $R\sim1300$ , $z$ accuracy $\sim65$ –$100$ km s $^{-1}$ ) and robust photometric catalogues underlie precise measurements of star formation, metallicity, and dust content (Hopkins et al., 2013, Driver, 2012).

Key empirical relations include:

The mass–metallicity ( $M$ – $Z$ ) relation: $12+\log(\mathrm{O}/\mathrm{H}) = -10.8297 + 3.6478\,x - 0.16706\,x^2$ , $x=\log(M_\star/M_\odot)$ .
The star-forming main sequence (SFMS) for late-type ungrouped galaxies: $\log_{10} \,\mathrm{SFR}\ (\mathrm{M}_\odot\,\mathrm{yr}^{-1}) = 0.93\,\log_{10}(M_\star/\mathrm{M}_\odot) - 9.08$ , intrinsic scatter $\sim0.29$ dex (Cluver et al., 2020).
The Fundamental Plane for star-forming galaxies: $\log(M_\star)\! =\! 1.3764\,[12\!+\!\log(\mathrm{O}/\mathrm{H})] + 0.6073\log(\mathrm{SFR}) - 2.5499$ , $\sim0.2$ dex scatter, holding to $z\sim3.5$ (Lara-Lopez et al., 2013).

GAMA provides strong evidence for bimodal or environmentally modulated quenching. At high stellar masses ( $M_\star>10^{10.5}M_\odot$ ), quenching is primarily mass-driven (virial shock heating, AGN feedback), while at lower masses, environmental (e.g., stripping, harassment) mechanisms in groups increase the population of passive galaxies (Penny et al., 2015, Cluver et al., 2020). Void and non-void galaxies show similar colour–mass and mid-IR properties; quenching correlates most strongly with galaxy mass, not large-scale environment (Penny et al., 2015).

6. Data Releases, Accessibility, and Legacy Science

GAMA data releases (DR1, DR2, DR3, and DR4 forthcoming) provide public access to core catalogs, spectra, multi-band photometry, morphological parameters, environmental measures, and ancillary data (e.g. SED fitting, WISE/Herschel cross-matches). Primary access is via http://www.gama-survey.org, with tools for querying, visualization, and bulk download (Driver et al., 2010, Baldry et al., 2017).

DR3 includes 154,809 sources with secure redshifts, expanded southern sky coverage (G02), and extended spectroscopic redshifts for Herschel-ATLAS fillers to $r<20.6$ mag, supporting deep far-IR galaxy science (Baldry et al., 2017). DR4 assimilates the full KiDS and VIKING imaging, ProFound-derived photometry and segmentation, and advanced source classification, supporting state-of-the-art photometric accuracy and SED analyses (Bellstedt et al., 2020).

Table: Key GAMA Data Products by Release

Release	Coverage & Features	High-Value Additions
DR1	Year 1 spectroscopic, $r$ limits	Public redshifts, spectra
DR2	$r < 19.0/19.4$ , Sersic fits, groups	G $^{3}$ C, Single Object Viewer
DR3	G02, Herschel-ATLAS fillers to $r$ =20.6	XXL/VIPERS overlap, autoz
DR4	Full KiDS/VIKING, improved photometry	ProFound pipeline, 20-band SEDs

7. Impact and Future Prospects

GAMA is a benchmark for multiwavelength extragalactic surveys, providing absolute measures for stellar/dust/gas content, group and cluster identification, and a robust empirical anchor for galaxy evolution and cosmological models. Its high completeness, depth, environmental metrics, and panchromatic coverage enable detailed studies of the baryonic assembly of galaxies, environmental transformation, and black hole scaling relations (e.g., low-mass AGN detections in dwarfs, median $M_{BH} \sim 10^{6.2} M_\odot$ (Salehirad et al., 2022)).

The forthcoming assimilation of next-generation radio data (ASKAP), deeper imaging, and continued public data releases will reinforce GAMA as a reference survey for theoretical and observational extragalactic research, including constraining the dark matter halo mass function, the star formation quenching efficiency, the detailed structure of the cosmic web, and the demographics of active galactic nuclei.

References: (Driver et al., 2010, Lara-Lopez et al., 2012, Driver, 2012, Hopkins et al., 2013, Lara-Lopez et al., 2013, Alpaslan et al., 2013, Cluver et al., 2014, McNaught-Roberts et al., 2014, Ibarra-Medel et al., 2014, Holwerda et al., 2015, Liske et al., 2015, Driver, 2015, Penny et al., 2015, Moffett et al., 2015, Moffett et al., 2016, Baldry et al., 2017, Bellstedt et al., 2020, Cluver et al., 2020, Riggs et al., 2021, Salehirad et al., 2022)