A SLUGGS and Gemini/GMOS combined study of the elliptical galaxy M60: wide-field photometry and kinematics of the globular cluster system

We present new wide-field photometry and spectroscopy of the globular clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo cluster. Imaging of NGC 4649 was assembled from a recently obtained Hubble Space Telescope/Advanced Camera for Surveys mosaic, and new Subaru/Suprime-Cam and archival Canada–France–Hawaii Telescope/MegaCam data. About 1200 sources were followed up spectroscopically using combined observations from three multi-object spectrographs: Keck/Deep Imaging Multi-Object Spectrograph, Gemini/Gemini Multi-Object Spectrograph and Multiple Mirror Telescope/Hectospec. We confirm 431 unique GCs belonging to NGC 4649, a factor of 3.5 larger than previous data sets and with a factor of 3 improvement in velocity precision. We confirm significant GC colour bimodality and find that the red GCs are more centrally concentrated, while the blue GCs are more spatially extended. We infer negative GC colour gradients in the innermost 20 kpc and flat gradients out to large radii. Rotation is detected along the galaxy major axis for all tracers: blue GCs, red GCs, galaxy stars and planetary nebulae. We compare the observed properties of NGC 4649 with galaxy formation models. We find that formation via a major merger between two gas-poor galaxies, followed by satellite accretion, can consistently reproduce the observations of NGC 4649 at different radii. We find no strong evidence to support an interaction between NGC 4649 and the neighbouring spiral galaxy NGC 4647. We identify interesting GC kinematic features in our data, such as counter-rotating subgroups and bumpy kinematic profiles, which encode more clues about the formation history of NGC 4649

Globular cluster luminosity function as distance indicator

Globular clusters are among the first objects used to establish the distance scale of the Universe. In the 1970-ies it has been recognized that the differential magnitude distribution of old globular clusters is very similar in different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the so-called Globular Cluster Luminosity Function has been then established as a secondary distance indicator. The intrinsic accuracy of the method has been estimated to be of the order of ~0.2 mag, competitive with other distance determination methods. Lately the study of the Globular Cluster Systems has been used more as a tool for galaxy formation and evolution, and less so for distance determinations. Nevertheless, the collection of homogeneous and large datasets with the ACS on board HST presented new insights on the usefulness of the Globular Cluster Luminosity Function as distance indicator. I discuss here recent results based on observational and theoretical studies, which show that this distance indicator depends on complex physics of the cluster formation and dynamical evolution, and thus can have dependencies on Hubble type, environment and dynamical history of the host galaxy. While the corrections are often relatively small, they can amount to important systematic differences that make the Globular Cluster Luminosity Function a less accurate distance indicator with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review paper based on the invited talk at the conference "The Fundamental Cosmic Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13 pages, 8 figures

Star clusters near and far; tracing star formation across cosmic time

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00690-x.Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e.\ detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations.Peer reviewedFinal Accepted Versio

Sediment and nutrient exports for the Burdekin River catchment, north Queensland: a comparison of monitoring and modelling data

Several empirical models have been developed to estimate sediment and nutrient inputs into the Great Barrier Reef lagoon, although limited monitoring data are available for their validation. The lack of monitoring data for GBR catchments limits the refinement of these models, and\ud particularly their assumptions of tropical landscape processes. Such limitations reduce the confidence of these models for application within the Reef Water Quality Protection Plan process, such as the setting of end-of-river load targets, and scenario load forecasting based on improved catchment condition from the adoption of best\ud management practices. The benefits of a coupled monitoring and modelling approach have been demonstrated in a number of other north Queensland catchments, such as the Tully/Murray\ud Water Quality Improvement Plan (WQIP) (Armour et al., 2007). Improved modelling estimates have been produced for these\ud catchments due to their smaller size, resultant less\ud variability and the use of higher resolution input data. The considerable size of the Burdekin makes similar efforts difficult; however, this is a first attempt at comparing available monitoring data with modelling efforts for this catchment. We present flow weighted sediment and nitrogen\ud loads averaged over three wet seasons of monitoring data (2002/03, 2004/05 and 2005/06) from the major sub-catchments and river mouth of the Burdekin River to compare with recent\ud SedNet and ANNEX model load estimates by CSIRO. CSIRO incorporated a number of refinements to the models based on issues identified during previous modelling runs. These\ud refinements include improvements to the hillslope erosion component through better input data resolution (estimates of actual ground cover and improved spatial resolution of slope) and improved gully and river bank erosion components through the incorporation of field measurements from the Burdekin catchment. In most cases, monitored and modelled\ud comparisons of TSS loads were reasonable, although poorer comparisons occurred for some sites, explainable by limited monitoring data or coarse resolution “blanket” model assumptions, such as riparian vegetation and dam trapping\ud capacity. The dam trapping algorithm applied to the Burdekin Falls Dam (BFD) by the SedNet model appears to be overestimating the suspended sediment and particulate nutrient trapping capacity of this dam. A modified algorithm that accounts for the dry tropical hydrology (i.e. highly episodic flows with shorter residence times than assumed by SedNet) will allow for better load estimates at the mouth of the Burdekin River. Particulate nutrient comparisons were less satisfactory, with the model seemingly overestimating monitored PN exports; the ANNEX model estimates are based on the Australian Soil Resource Information System database of nutrient concentrations in soils. This database may need refinement for these highly weathered, nutrient-poor landscapes. Reasonable comparisons were found between the modelled and monitored loads of dissolved organic nitrogen, however, comparisons were only fair for dissolved inorganic nitrogen. Further investigation of the role of inorganic nitrogen in this tropical system is warranted, and particularly, the contributions from natural sources, such as rainfall or bedrock, compared to those from land uses including fertilisers and cow excreta. Additional monitoring data at different spatial and temporal scales are required to further test the accuracy of these models, particularly for the southern region of the Burdekin catchment, where\ud below-average flow events have occurred within the timeframe of the monitoring project. This will allow further confidence in using modelled outputs to identify catchment point sources and consequent delivery to downstream environments, and for the setting of water quality targets

A review of load tools available for calculating pollutant exports to the Great Barrier Reef lagoon: a case study of varying catchment areas

Several load methods and software programs have been developed to calculate sediment, nutrient and other pollutant exports from waterways of the Great Barrier Reef (GBR) catchments. These different methods can produce large discrepancies in the calculation of catchment loads. Such\ud discrepancies reduce the confidence of these methods for application within the Reef Water Quality Protection Plan process, such as the setting of end-of-river load targets as well as the comparison to modelled outputs, namely the\ud SedNet and ANNEX models (e.g. Brodie et al. 2003). We present a case study based on intensive monitoring data collected over a range of spatial (paddock, a Dry Tropics sub-catchment and a large Dry Tropics end-of-river catchment) and temporal (hourly - yearly) scales. We simulate changes in load calculations of total suspended solids based on the selected removal of monitoring data from\ud intervals throughout the flow hydrograph. We attempt to quantify errors in load calculations based on the different load tools, as well as investigate optimal load methods and ideal sampling frequencies over these different catchment areas. Three software programs were used to calculate loads including WQ Loads Tool, Brolga and GUMLEAF. We found that all three software programs provided suitable methods to\ud calculate loads for the catchments of the GBR where continuous flow and concentration data were available. The linear interpolation (and associated inter sample mean) methods were optimal in the Brolga and Loads Tool program\ud while the flow regime estimators provided ideal load estimates in the GUMLEAF program. Our findings suggest that six samples evenly-spaced over the flow hydrograph (e.g. 2-3 samples on rise, 1 on peak and 2-3 on the falling limb) will provide reliable load estimations (within 10% of our best\ud estimate) at the paddock scale provided that the optimal methods are used. We recommend that at least daily (but up to 4-5 samples per day in catchments with very high TSS concentrations on the rising limb such as the Bowen sub-catchment) sampling is suitable for load estimations at the sub-catchment scale. One sample collected every two days is an adequate sampling frequency for load calculations of larger catchments of the GBR such as the Burdekin River. We note that researchers need to account for the uncertainty in\ud all load estimates before the significance of longterm\ud trends can be analysed

A review of load tools available for calculating pollutant exports to the Great Barrier Reef lagoon: a case study of varying catchment areas

Several load methods and software programs have been developed to calculate sediment, nutrient and other pollutant exports from waterways of the Great Barrier Reef (GBR) catchments. These different methods can produce large discrepancies in the calculation of catchment loads. Such discrepancies reduce the confidence of these methods for application within the Reef Water Quality Protection Plan process, such as the setting of end-of-river load targets as well as the comparison to modelled outputs, namely the SedNet and ANNEX models (e.g. Brodie et al. 2003). We present a case study based on intensive monitoring data collected over a range of spatial (paddock, a Dry Tropics sub-catchment and a large Dry Tropics end-of-river catchment) and temporal (hourly - yearly) scales. We simulate changes in load calculations of total suspended solids based on the selected removal of monitoring data from intervals throughout the flow hydrograph. We attempt to quantify errors in load calculations based on the different load tools, as well as investigate optimal load methods and ideal sampling frequencies over these different catchment areas. Three software programs were used to calculate loads including WQ Loads Tool, Brolga and GUMLEAF. We found that all three software programs provided suitable methods to calculate loads for the catchments of the GBR where continuous flow and concentration data were available. The linear interpolation (and associated inter sample mean) methods were optimal in the Brolga and Loads Tool program while the flow regime estimators provided ideal load estimates in the GUMLEAF program. Our findings suggest that six samples evenly-spaced over the flow hydrograph (e.g. 2-3 samples on rise, 1 on peak and 2-3 on the falling limb) will provide reliable load estimations (within 10% of our best estimate) at the paddock scale provided that the optimal methods are used. We recommend that at least daily (but up to 4-5 samples per day in catchments with very high TSS concentrations on the rising limb such as the Bowen sub-catchment) sampling is suitable for load estimations at the sub-catchment scale. One sample collected every two days is an adequate sampling frequency for load calculations of larger catchments of the GBR such as the Burdekin River. We note that researchers need to account for the uncertainty in all load estimates before the significance of longterm trends can be analysed

The potential benefits of herbicide regulation: a cautionary note for the Great Barrier Reef catchment area

Industry transitions away from traditional photosystem II inhibiting (PSII) herbicides towards an 'alternative' herbicide suite are now widely advocated as a key component of improved environmental outcomes for Australia's Great Barrier Reef and improved environmental stewardship on the part of the Queensland sugar industry. A systematic desktop risk analysis found that based on current farming practices, traditional PSII herbicides can pose significant environmental risks. Several of the 'alternatives' that can directly fill a specific pre-emergent ('soil residual') weed control function similar to regulated PSII herbicides also, however, presented a similar environmental risk profile, regardless of farming systems and bio-climatic zones being considered. Several alternatives with a pre-emergent residual function as well as alternative post-emergent (contact or 'knockdown') herbicides were, predicted to pose lower environmental risks than the regulated PSII herbicides to most trophic levels, although environmental risks could still be present. While several herbicides may well be viable alternatives in terms of weed control, they can still present equal or possibly higher risks to the environment. Imposing additional regulations (or even de-registrations) on particular herbicides could result in marginal, and possibly perverse environmental impacts in the long term, if usage shifts to alternative herbicides with similar risk profiles. Regardless of any regulatory efforts, improved environmental sustainability outcomes in pesticide practices within the Great Barrier Reef catchment area will hinge primarily on the continuing adoption of integrated, strategic pest management systems and technologies applied to both traditional and 'alternative' herbicides. One of the emerging policy challenges is ensuring the requisite technical and extension support for cane growers to ensure effective adoption of rapidly evolving farming system technologies, in a very dynamic and scrutinised herbicide management environment