GAMA: towards a physical understanding of galaxy formation

Abstract: The Galaxy And Mass Assembly (GAMA) project is the latest in a tradition of large galaxy redshift surveys, and is now underway on the 3.9m Anglo-Australian Telescope at Siding Spring Observatory. GAMA is designed to map extragalactic structures on scales of 1kpc - 1Mpc in complete detail to a redshift of z~0.2, and to trace the distribution of luminous galaxies out to z~0.5. The principal science aim is to test the standard hierarchical structure formation paradigm of Cold Dark Matter (CDM) on scales of galaxy groups, pairs, discs, bulges and bars. We will measure (1) the Dark Matter Halo Mass Function (as inferred from galaxy group velocity dispersions); (2) baryonic processes, such as star formation and galaxy formation efficiency (as derived from Galaxy Stellar Mass Functions); and (3) the evolution of galaxy merger rates (via galaxy close pairs and galaxy asymmetries). Additionally, GAMA will form the central part of a new galaxy database, which aims to contain 275,000 galaxies with multi-wavelength coverage from coordinated observations with the latest international ground- and space-based facilities: GALEX, VST, VISTA, WISE, HERSCHEL, GMRT and ASKAP. Together, these data will provide increased depth (over 2 magnitudes), doubled spatial resolution (0.7"), and significantly extended wavelength coverage (UV through Far-IR to radio) over the main SDSS spectroscopic survey for five regions, each of around 50 deg^2. This database will permit detailed investigations of the structural, chemical, and dynamical properties of all galaxy types, across all environments, and over a 5 billion year timeline.

• The paper provides a comprehensive analysis of the GAMA survey, emphasizing precise measurements of dark matter halo masses and the testing of the Cold Dark Matter paradigm.
• It employs an integrated methodology combining spectroscopic data and multi-wavelength imaging from both ground-based and spaceborne observatories.
• Preliminary findings reveal low star formation efficiency in low-mass halos and refined estimates of galaxy merger rates over the past 5 billion years.

Insights on the GAMA Survey

The paper by Driver et al., titled GAMA: Towards a Physical Understanding of Galaxy Formation, provides an exhaustive examination of the Galaxy and Mass Assembly (GAMA) survey. Conducted using the 3.9m Anglo-Australian Telescope, GAMA represents an ambitious effort to elucidate the processes of galaxy formation and evolution through one of the most comprehensive datasets available to date. This work places an emphasis on testing the Cold Dark Matter (CDM) paradigm by utilizing a multitude of observational and computational techniques. This review will dissect the primary scientific goals of the GAMA survey, key methodologies employed, as well as its current findings and future objectives.

Major Scientific Goals

The GAMA project focuses on several critical objectives:

1. Measuring the Dark Matter Halo Mass Function (HMF): By constructing extensive galaxy group catalogues, the survey aims to measure the HMF accurately down to systems on the scale of the Local Group. This aspect directly correlates with testing predictions of CDM-based simulations.
2. Understanding Baryonic Systematics: The survey endeavors to paint a complete picture of how baryonic matter (stars, dust, gas) interacts with dark matter across different scales, thereby enriching our understanding of star formation efficiency and feedback mechanisms.
3. Galaxy Merger Rates: Through the analysis of close galaxy pairs and structural asymmetries, GAMA seeks to quantify galaxy merger rates over the past 5 billion years.

Methodological Framework

The survey combines spectroscopic data from the Anglo-Australian Telescope's AAOmega spectrograph with extensive multi-wavelength imaging from facilities across four continents and three space missions. The integration of these datasets offers a robust approach for measuring numerous parameters critical to understanding galaxy assembly, such as velocity dispersions and baryonic content. GAMA's ambitious approach is underscored by its collaboration with both ground-based and spaceborne observatories, including UKIRT, VISTA, HERSCHEL, and ASKAP.

The complexities in deriving halo masses from the galaxy distribution require sophisticated algorithmic techniques, including the use of realistic mock galaxy catalogues to refine group membership and correct any methodological biases. Such approaches are essential to ascertain the dark matter halo distribution amid issues like observational depth and group-finding algorithm efficiency.

Early Outcomes and Implications

Preliminary observations from GAMA have revealed insights into the galaxy stellar mass function (GSMF), particularly highlighting inefficiencies in star formation across varying halo masses. These observations suggest that a mere 1% or less of baryonic mass in low-mass halos converts into stellar content, prompting questions regarding the distribution and fate of the remaining baryons.

GAMA's data also shed light on merger rates, utilizing high-resolution imaging and spectroscopy to observe ongoing and imminent mergers. The findings on merger rates provide a pathway to refine hierarchical growth models in cosmological simulations.

Future Directions

GAMA's focus on extending our understanding of galaxy structures and environments suggests significant implications for future observational and theoretical pursuits. As more instruments such as ALMA and JWST come online, GAMA aims to further extend its survey capacity in terms of depth and area coverage, aiming to bridge current observational gaps in galaxy formation studies.

The GAMA database offers tremendous potential for the upcoming detailed analysis of galaxy morphology, stellar populations, and halo environments. The project's dedication to regular data releases ensures that the wider astronomical community can actively participate and leverage this extensive observational resource, promoting new collaborations and advancements in astrophysical research.

In summation, the GAMA survey exemplifies a methodologically detailed study seeking to confront and explore the intricacies of galaxy formation and dark matter interactions. Its ongoing developments promise to significantly enrich the foundation of cosmological understanding, providing a detailed empirical framework that will influence both current and future studies in extragalactic astronomy.