Galaxies and Cosmology

The problem of when and how galaxies formed continues to occupy large amounts of telescope and computer simulation time. Galaxies are complex stellar systems with numerous physical processes. These processes include star formation, stellar dynamics, gas dynamics, and includes the role of the dark matter which is their major constituent. Having forming galaxies can interact with their environment and other galaxies. Outright mergers may occur leading to the formation of a new galaxy. Extragalactic research is a dominant theme in Australian astronomy, and is carried out within almost every university and government research group.

Groups within Australian that work on galaxies & cosmology include:

  • The Astronomy and Astrophysics group at the Australian National University employ an observational approach to study galaxy morphology and galaxy formation. The twin Gemini telescopes on Mauna Kea and Cerro Pachon enable researchers to look back in time on the formation of other galaxies and compare observations to theoretical models of galaxy formation.
  • The Astrophysics Group at ANU’s Mathematical Sciences Institute are currently involved in using dark matter models of the early universe to study the impact of the first generation of stars and black holes on the re-ionisation of the Universe. This study is expected to elucidate the processes that are important in determining the morphology of the universe as it emerges from the “dark ages”. The group is also involved in investigating the origin of Type Ia Supernovae, and the limitations in their use as standard candles for probing the large scale structure of the universe.
  • The Galaxy formation and Cosmology group at Swinburne University’s Centre for Astrophysics and Supercomputing take a different approach, utilizing advanced computer technology and specially developed computer code to model galactic evolution. They employ a broad range of complementary approaches to modeling the formation of galaxies, each with their own unique strengths including: Collisionless Dark Matter, Adaptive Mesh Refinement, Gravitational Tree N-body + SPH and Semi-Analytical Models.
  • The Extragalactic Group at Swinburne is studying galaxy formation and evolution via observation and modelling. The group regularly obtains observations on some of the world’s best telescopes (including Hubble Space Telescope, Keck, Gemini and Parkes). These observations allow astronomers to probe the role of environment in galaxy evolution, and to identify the epoch of galaxy assembly.
  • The University of Melbourne is engaged in several theoretical investigations of galactic structure, including a first-principles analysis of the statistical mechanics of self-gravitating systems (with implications for the origin of the de Vaucouleurs profile in merger remnants), and the origin of the magnetic field in galaxy clusters (as inferred from Faraday rotation measure data acquired with the VLA and Australia Telescope National Facility). There is also an active program in the study of HI in nearby galaxies, including the determination of the HI mass function, the Tully-Fisher Relation, and the distribution of HI in groups and clusters of galaxies. The group also uses gravitational lensing to study a wide range of topics, including the dark matter halos of galaxies, microlensing and other areas of statistical lensing.
  • The Astrophysics Group at the University of Sydney is using data from SUMSS and NVSS in conjunction with the 2dF and 6dF galaxy redshift surveys, to explore the radio luminosity functions of both AGN and starburst galaxies and their evolution with redshift. SUMSS and NVSS data are also being used, together with optical, infrared and ATCA radio data, to identify and study the most distant and the largest radio galaxies.
  • Analytic calculations, simulations, and observations of gravitational lens systems are all undertaken at the University of Sydney. The lensed sources range from galaxies and quasars, to massive stars and gamma-ray bursters, with the common feature that they are all cosmologically distant. The work is aimed at using gravitational lensing to explore the distant Universe — both the sources in it, and its matter content. In particular, the nature and distribution of the dark matter are key questions which are under investigation.

Galaxy Distribution in the Zone of Avoidance:

Galaxies observed towards the band of the Milky Way become progressively fainter approaching the galactic equator due to foreground dust extinction. Almost 25% of the sky is obscured at visible wavelengths. Deep optical and infrared searches result in a considerable reduction of the Zone of Avoidance (ZOA), however the other methods are required to image behind the remaining opaque regions.

Since 1997 the Parkes radio telescope has been conducting a blind all sky survey at 21cm using the Multibeam receiver. The Milky Way is transparent to the 21cm line of neutral hydrogen, allowing the detection of H1-rich galaxies in the zone. With sensitivities down to 3mJy and a velocity range of -12000 to 12,700 km s-1 the survey detected galaxies well beyond the Great Attractor region.

PASA Invited Review:
Mapping the Hidden Universe: The Galaxy Distribution in the Zone of Avoidance

Galaxy Redshift Surveys:

The primary aim of galaxy redshift surveys is to map out the large-scale structure of the nearby universe and characterize the interplay between cosmological structure and galaxy properties. Such surveys include the 2dF Galaxy Redshift Survey, completed in 2002 with spectra and redshifts for over 220,000 galaxies, the WiggleZ survey (completed in 2010 with 240,000 galaxies) and the Galaxy And Mass Assembly (GAMA) survey, begun in 2008, and aiming to obtain spectra for 375,000 galaxies by the end of 2012. These surveys have provided fundamental measurements of the density of ordinary baryonic matter, dark matter, neutrinos and dark energy, along with a progressively more detailed understanding of galaxies and how they have evolved over cosmic history. The 6dF Galaxy Survey (6dFGS) has mapped the nearby universe over nearly half the sky producing a new catalogue of 125,071 galaxies. A peculiar velocity survey of 11,000 galaxies is measuring galaxy masses and bulk motions. The 6dFGS is also used to study the large scale distribution and clustering statistics of the nearby universe, in addition to galaxy properties such as mass and luminosity.

HIPASS:

The HI Parkes All-Sky Survey (HIPASS) is the first all-sky survey of HI-rich galaxies. It has used the Multibeam receiver on the Parkes radio telescope to map the entire southern sky and 40% of the northern sky in the 21-cm line. The southern sky catalogue, HICAT, is now complete and contains over 4300 galaxies. This is being used to study local large-scale structure. The survey of a collaboration between the University of Melbourne, ATNF, RSAA, the University of Sydney, Swinburne University, the AAO, the University of Queensland, Cardiff University, Jodrell Bank, the University of New Mexico and the University of Colorado.

The Milky Way & the Local Group:

The Milky Way and Local Group are active areas of research in Australia. The Southern skies afford us with a clear view into the inner Milky Way, of the Large and Small Magellanic Clouds, the Magellanic Bridge and Stream.

Using the Australia Telescope Compact Array in conjunction with the Parkes Multibeam, a small team of Australian and overseas astronomers are involved in a large-scale survey of the neutral hydrogen in the Southern Milky Way. The Southern Galactic Plane Survey (SGPS) is a survey of the 21 cm line emission in 235 sq-deg of the Galactic plane covering a narrow, 2 deg strip from Galactic longitude 253 degrees through longitude 360 and up to a longitude of 20 degrees. The second phase of the survey covers another 100 sq-deg region centered on the Galactic Centre. With an angular resolution of ~2 arcmin and a sensitivity limit of ~1 K, the survey is more than an order of magnitude better than previous surveys of this region. The survey is being used to understand the structure and dynamics of the neutral interstellar medium.

The Magellanic System is the object of many studies in Australia. The LMC, SMC and the various gaseous extrusions which result from their mutual interaction, and from their interaction with the Milky Way, are being studied in detail with the Parkes telescope and the Australia Telescope Compact Array.

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