‘Galaxy Metabolism' was the second in the annual ‘Southern Cross Astrophysics Conference Series’ (http://www.aao.gov.au/AAO/southerncross/), supported by the Anglo-Australian Observatory and the Australia Telescope National Facility. It was held at the Australian National Maritime Museum in Darling Harbour, Sydney, from 22 to 26 June 2009, and was attended by 91 delegates from around the world.

Over the past decade, both the star formation history and stellar mass density in galaxies spanning most of cosmic history have been well constrained. This provides the backdrop and framework within which many detailed investigations of galaxy growth are now placed. The mass-dependent and environment-dependent evolution of galaxies over cosmic history is now the focus of several surveys. Many studies are also exploring the role of gas infall and outflow in driving galaxy evolution, and the connection of these processes to massive star formation within galaxies.

The aims of ‘Galaxy Metabolism’ were to bring together the global constraints on galaxy evolution, at both low and high redshift, with detailed studies of well-resolved systems, to define a clear picture of our understanding of galaxy metabolism: How do the processes of ingestion (infall), digestion (ISM physics, star formation) and excretion (outflow) govern the global properties of galaxies; how do these change over a galaxy's lifetime; and are the constraints from nearby well resolved studies consistent with those from large population surveys at low and high redshift?

The conference was a great success, with an extensive variety of topics covered spanning many aspects of galaxy evolution, and brought together eloquently in a comprehensive conference summary by Warrick Couch. The four papers by De Lucia (2010), Cole (2010), Vlajić (2010) and Stocke et al. (2010) presented in this special collection of PASA are just a sampling of the depth and variety of the resentations given during the conference.

We review our recent studies of the globular cluster system of NGC 5128. First, we have obtained low-resolution, high signal-to-noise spectroscopy of 72 globular clusters using Gemini-S/GMOS to obtain the ages, metallicities, and the level of alpha enrichment of the metal-poor and metal-rich globular cluster subpopulations. Second, we have explored the rotational signature and velocity dispersion of the galaxy's halo using over 560 globular clusters with radial velocity measurements. We have also compared the dependence of these properties on galactocentric distance and globular cluster age and metallicity. Using globular clusters as tracer objects, we have analyzed the mass, and mass-to-light ratio of NGC 5128. Last, we have measured the structural parameters, such as half-light radii, of over 570 globular clusters from a superb 1.2-square-degree Magellan/IMACS image. We will present the findings of these studies and discuss the connection to the formation and evolution of NGC 5128.

A concise summary of the recent international workshop held in honour of the career of Agnès Acker is presented together with a brief exposition of her productive career in the study of Planetary Nebulae, the expelled, ionised outer shrouds of dying stars.

To investigate the ultraviolet (UV) activity of the bright, non-eclipsing, double-lined spectroscopic binary system UX Ari, IUE spectra (194 images) were taken from the IUE archive. The spectra, obtained during the period 1978–1996, show emission lines originating in the chromosphere and transition region. The long-wavelength low dispersion spectra were examined for ultraviolet excess by comparing the UV continuum level of UX Ari with the levels of k Cet and η Cep in the spectral range 2100–3200 Å. The individual Mgiih and k emission-line fluxes of component stars show that the contributions to the activity of the system for G5 V and K0 IV are about 20% and 80%, respectively. Apart from the flare event observed on 1979 Jan 1, there are some flux enhancements in the years 1987, 1991 and 1994 which may suggest existence of a periodicity of about 7–9 years. Examination of the ultraviolet excess in the system showed that there is some UV excess in UX Ari, which varies from 1% up to 24% with the exception of two images which showed no UV excess. The results revealed that there was an agreement on the source of emission regions which could be attributed to magnetic activity. The contribution of G5 V and K0 IV components to the Mgii activity of the system suggests a need to take into consideration the spot distribution not only on the surface of the K0 IV but also on the surface of the G5 V component of UX Ari.

Planetary nebulae (PN) are powerful tracers of both stellar and Galactic evolution. The capacity of PN to perform these studies is critically dependent on the size of the population, a major problem with a remarkable advance thanks to Quentin Parker and his team, who from 1997 to 2008 discovered an unprecedented sample of ∼1250 PN with the deep, high resolution AAO/UKST SuperCosmos Halpha Survey (SHS) of the Southern Galactic Plane (Parker et al. 2005), doubling the sample collected over the previous century, and leading to ∼2700 for the number of known PN today. A highly productive collaboration between Quentin and I has been established since 2001. Our complementary levels of expertise and facilities constitute the Macquarie/AAO/Strasbourg H-α Planetary Nebulae Project.

The new MASH PN were added to the Centre de Données de Strasbourg as a new PN database continuously updated, and detailed in Parker et al. (2006) and Miszalski et al. (2008). In the framework of a cotutelle agreement between the Strasbourg and Macquarie universities, two PhD projects based on MASH PN have been conducted under the supervision of Quentin and myself, both projects focusing on the mysterious crowded region of the Galactic Bulge. Alan Peyaud proposed new constraints on late stages of stellar evolution and on the dynamics of the Galactic Bulge (defence 21 December 2005, Strasbourg). Brent Miszalski discovered ∼360 new PN (MASH-II) completing the largest and most representative sample of PN towards the Galactic bulge (defence 15 August 2009).

In this review I summarise recent advances in our understanding of the importance of starburst events to the evolutionary histories of nearby galaxies. Ongoing bursts are easily diagnosed in emission-line surveys, but assessing the timing and intensity of fossil bursts requires more effort, usually demanding color–magnitude diagrams or spectroscopy of individual stars. For ages older than ∼1 Gyr, this type of observation is currently limited to the Local Group and its immediate surroundings. However, if the Local Volume is representative of the Universe as a whole, then studies of the age and metallicity distributions of star clusters and resolved stellar populations should give statistical clues as to the frequency and importance of bursts to the histories of galaxies in general. Based on starburst statistics in the literature and synthetic colour-magnitude diagram studies of Local Group galaxies, I attempt to distinguish between systemic starbursts that strongly impact galaxy evolution and stochastic bursts that can appear impressive but are ultimately of little significance on gigayear timescales. As a specific case, it appears as though IC 10, the only starburst galaxy in the Local Group, falls into the latter category and is not fundamentally different from other nearby dwarf irregular galaxies.

Due to its proximity, the neutral hydrogen belonging to Cen A can be observed at high resolution with good sensitivity. This allows us to study the morphology and kinematics in detail, in order to understand the evolution of this radio-loud source (e.g. merger history, AGN activity). At the same time, it is important to compare results to other sources of the same class (i.e. early-type galaxies in general and radio galaxies in particular) to see how Cen A fits into the global picture of early-type/radio galaxy evolution. The amount of Hi, the morphology of a warped disk with Hi clouds surrounding the disk and the regular kinematics of the inner part of the Hi disk are not unusual for early-type galaxies. The growing evidence that mergers are not necessarily responsible for AGN activity fits with the observational result that the recent merger event in Cen A is not directly connected to the current phase of activity. Based on these results, we conclude that Cen A has typical neutral hydrogen properties for an early-type and radio galaxy and it can therefore — from the perspective of Hi — be seen as a typical example of its class.

It is well known that interstellar travel is bounded by the finite speed of light, but on very large scales any rocketeer would also need to consider the influence of cosmological expansion on their journey. This paper examines accelerated journeys within the framework of Friedmann–Lemaître–Robertson–Walker universes, illustrating how the duration of a fixed acceleration sharply divides exploration over interstellar and intergalactic distances. Furthermore, we show how the universal expansion increases the difficulty of intergalactic navigation, with small uncertainties in cosmological parameters resulting in significantly large deviations. This paper also shows that, contrary to simplistic ideas, the motion of any rocketeer is indistinguishable from Newtonian gravity if the acceleration is kept small.

Metals are found in all baryonic phases and environments, and our knowledge of their distribution ‘in and around galaxies’ has significantly improved over the past few years. Theoretical work has shown that the fraction of metals in different baryonic components can vary significantly when different feedback schemes are adopted. Therefore, studies of element abundances provide important information about all gas-dynamical processes which determine the cosmic evolution of baryons. I give here a brief review of recent observational progress, describe the implications of recent theoretical studies, and discuss briefly future prospects.

We compile position and inclination angles for tilted ring fits to the warped dusty and gaseous disk of Cen A, spanning a radius of 1.8 to 6500 pc, from recent observations. For radii exterior to 1 kpc, tilted-ring orientations lie on an arc, on a plot of polar-inclination versus position-angle, suggesting that precession following a merger can account for the ring morphology. Three kinks in the ring orientations are seen on the polar plot, the one at radius of about 1.3 kpc we suspect corresponds to the location where self-gravity in the disk affects the ring precession rate. Another at a radius of about 600 pc may be associated with a gap in the gas distribution. A third kink is seen at a radius of 100 pc. A constant inclination tilted disk precessing about the jet axis may describe the disk between 100 and 20 pc but not interior to this. A model with disk orientation matching the molecular circumnuclear disk at 100 pc that decays at smaller radii to an inner flat disk perpendicular to the jet may account for disk orientations within 100 pc. Neither model would account for the cusps or changes in disk orientation at 100 or 600 pc.

A concise and critical review of Balmer-dominated shocks (BDSs) is presented, summarizing the state of theory and observations, including models with/without shock precursors and their synergy with atomic physics. Observations of BDSs in supernova remnants are reviewed on an object-by-object basis. The relevance of BDSs towards understanding the acceleration of cosmic rays in shocks is emphasized. Probable and possible detections of BDSs in astrophysical objects other than supernova remnants, including pulsar wind nebulae and high-redshift galaxies, are described. The case for the continued future of studying BDSs in astrophysics is made, including their relevance towards understanding electron–ion temperature equilibration in collisionless shocks.

The total number of true, likely and possible planetary nebulae (PN) now known in the Milky Way is nearly 3000, double the number known a decade ago. The new discoveries are a legacy of the recent availability of wide field, narrowband imaging surveys, primarily in the light of H-alpha. In this paper, we summarise the various PN discovery techniques, and give an overview of the many types of objects which mimic PN and which appear as contaminants in both Galactic and extragalactic samples. Much improved discrimination of classical PN from their mimics is now possible based on the wide variety of high-quality multiwavelength data sets that are now available. We offer improved taxonomic and observational definitions for the PN phenomenon based on evaluation of these better diagnostic capabilities. However, we note that evidence is increasing that the PN phenomenon is heterogeneous, and PN are likely to be formed from multiple evolutionary scenarios. In particular, the relationships between some collimated symbiotic outflows and bipolar PN remain uncertain.

The discovery of the radio source Centaurus A and its optical counterpart NGC 5128 were important landmarks in the history of Australian astronomy. NGC 5128 was first observed in August 1826 by James Dunlop during a survey of southern objects at the Parramatta Observatory, west of the settlement at Sydney Cove. The observatory had been founded a few years earlier by Thomas Brisbane, the new governor of the British colony of New South Wales. Just over 120 years later, John Bolton, Gordon Stanley and Bruce Slee discovered the radio source Centaurus A at the Dover Heights field station in Sydney, operated by CSIRO's Radiophysics Laboratory (the forerunner to CSIRO Astronomy and Space Sciences). This paper will describe this early historical work and summarize further studies of Centaurus A by other Radiophysics groups up to 1960.

This study presents a tomographic survey of a subset of the outer halo (10–40 kpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure on spatial scales of >3 degrees is revealed as an excess in the local density of sub-giant stars. With an appropriate assumption of a model stellar isochrone it is possible for us to then derive distances to the sub-giant population. We describe three new candidate halo substructures; the 160- and 180-degree over-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and 1.5 kpc respectively) and an extended feature at 28 kpc that covers at least 162 deg2, the Virgo Equatorial Stream. In addition, we recover the Sagittarius dwarf galaxy (Sgr) leading-arm material and the Virgo Over-Density.

The derived distances, together with the number of sub-giant stars associated with each substructure, enables us to derive the integrated luminosity for the features. The tenuous, low surface brightness of the features strongly suggests an origin from the tidal disruption of an accreted galaxy or galaxies. Given the dominance of the tidal debris of Sgr in this region of the sky we investigate if our observations can be accommodated by tidal disruption models for Sgr. The clear discordance between observations and model predictions for known Sgr features means it is difficult to tell unambiguously if the new substructures are related to Sgr or not. Radial velocities in the stellar over-densities will be critical in establishing their origins.

Extragalactic surveys in the emission line of [O iii] λ5007 have provided us with the absolute line strengths of large, homogeneous sets of planetary nebulae. These data have been used to address a host of problems, from the measurement of the extragalactic distance scale, to the study of stellar populations. I review our current understanding of the [O iii] planetary nebula luminosity function (PNLF), and discuss some of the physical processes that effect its structure. I also describe the features of the Hα PNLF, a function that, upon first glance, looks similar to the [O iii] PNLF, but which includes a very different set of objects. Finally, I discuss recent measurements of α, the number of PNe found in a stellar population, normalized to that population's bolometric luminosity. I show that, contrary to expectations, the values of α found in actively star-forming spirals are essentially the same as those measured in late-type elliptical and lenticular systems. I discuss how this result sheds light on the physics of the planetary nebula phenomenon.

Recent studies of outer spiral disks have given rise to an abundance of new results. We discuss the observational and theoretical advances that have spurred the interest in disk outskirts, as well as where we currently stand in terms of our understanding of outer disk structure, ages, and metallicities.

Cen A, at a distance of less than 4 Mpc, is the nearest radio-loud AGN. Its emission is detected from radio to very-high energy gamma-rays. Despite the fact that Cen A is one of the best studied extragalactic objects the origin of its hard X-ray and soft gamma-ray emission (100 keV <E< 50 MeV) is still uncertain. Observations with high spatial resolution in the adjacent soft X-ray and hard gamma-ray regimes suggest that several distinct components such as a Seyfert-like nucleus, relativistic jets, and even luminous X-ray binaries within Cen A may contribute to the total emission in the MeV regime that has been detected with low spatial resolution. As the Spectral Energy Distribution of Cen A has its second maximum around 1 MeV, this energy range plays an important role in modeling the emission of (this) AGN. As there will be no satellite mission in the near future that will cover this energies with higher spatial resolution and better sensitivity, an overview of all existing hard X-ray and soft gamma-ray measurements of Cen A is presented here defining the present knowledge on Cen A in the MeV energy range.

Recent Hα surveys such as SHS and IPHAS have improved the completeness of the Galactic planetary nebula (PN) census. We now know of ∼3000 PNe in the Galaxy, but this is far short of most estimates, typically ~25 000 or more for the total population. The size of the Galactic PN population is required to derive an accurate estimate of the chemical enrichment rates of nitrogen, carbon, and helium. In addition, a high PN count (>20 000) is strong evidence that most main-sequence stars of mass 1–8 M⊙ will go through a PN phase, while a low count (<10 000) argues that special conditions (e.g. close binary interactions) are required to form a PN. We describe a technique for finding hundreds more PNe using the existing data collections of the digital sky surveys, thereby improving the census of Galactic PNe.

We present infrared imaging from IRIS2 on the Anglo–Australian Telescope that shows the barred spiral galaxy IC 4933 has not just an inner ring encircling the bar, but also a star-forming nuclear ring 1.5 kpc in diameter. Imaging in the u′ band with GMOS on Gemini South confirms that this ring is not purely an artifact due to dust. Optical and near-infrared colours alone however cannot break the degeneracy between age, extinction, and burst duration that would allow the star formation history of the ring to be unraveled. Integral field spectroscopy with the GNIRS spectrograph on Gemini South shows the equivalent width of the Paβ line to peak in the north and south quadrants of the ring, indicative of a bipolar azimuthal age gradient around the ring. The youngest star-forming regions do not appear to correspond to where we expect to find the contact points between the offset dust lanes and the nuclear ring unless the nuclear ring is oval in shape, causing the contact points to lead the bar by more than 90°.

The gas added to and removed from galaxies over cosmic time greatly affects their stellar populations and star formation rates. QSO absorption line studies in close QSO/galaxy pairs create a unique opportunity to study the physical conditions and kinematics of this gas. Here we present new Hubble Space Telescope (HST) images of the QSO/galaxy pair, 3C 232/NGC 3067. The quasar spectrum contains a Lyman limit (NHi = 1 × 1020 cm−2) absorption system (LLS) at cz = 1421 km s−1 that is associated with the nearby Sab galaxy NGC 3067. Previous work identifies this absorber as a high-velocity cloud (HVC) in NGC 3067 but the kinematics of the absorbing gas, infalling or outflowing, were uncertain. The HST images presented here establish the orientation of NGC 3067 and so establish that the LLS/HVC is infalling. Using this system as a prototype, we extend these results to higher-z MgII/LLS to suggest that Mgii/LLSs are a sightline sampling of the so-called ‘cold mode accretion’ (CMA) infalling onto luminous galaxies. To match the observed MgII absorber statistics, the CMA must be more highly ionised at higher redshifts. The key observations needed to further the study of low-z LLSs is HST UV spectroscopy, for which a new instrument, the Cosmic Origins Spectrograph, has just been installed greatly enhancing our observational capabilities.