Evaluation of cosmic ray rejection algorithms on single-shot exposures

To maximise data output from single-shot astronomical images, the rejection of cosmic rays is important. We present the results of a benchmark trial comparing various cosmic ray rejection algorithms. The procedures assess relative performances and characteristics of the processes in cosmic ray detection, rates of false detections of true objects and the quality of image cleaning and reconstruction. The cosmic ray rejection algorithms developed by Rhoads (2000), van Dokkum (2001), Pych (2004) and the IRAF task xzap by Dickinson are tested using both simulated and real data. It is found that detection efficiency is independent of the density of cosmic rays in an image, being more strongly affected by the density of real objects in the field. As expected, spurious detections and alterations to real data in the cleaning process are also significantly increased by high object densities. We find the Rhoads' linear filtering method to produce the best performance in detection of cosmic ray events, however, the popular van Dokkum algorithm exhibits the highest overall performance in terms of detection and cleaning.Comment: 12 pages, 4 figures, accepted for publication in PAS

The Wide Field Spectrograph (WiFeS): Performance and Data Reduction

This paper describes the on-telescope performance of the Wide Field Spectrograph (WiFeS). The design characteristics of this instrument, at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) and mounted on the ANU 2.3m telescope at the Siding Spring Observatory has been already described in an earlier paper (Dopita et al. 2007). Here we describe the throughput, resolution and stability of the instrument, and describe some minor issues which have been encountered. We also give a description of the data reduction pipeline, and show some preliminary results.Comment: Accepted for publication in Astrophysics & Space Science, 15pp, 11 figure

Feedback in the cores of clusters Abell 3581, 2A 0335+096, and Sersic 159-03

The cores of massive galaxy clusters, where hot gas is cooling rapidly, appear to undergo cycles of self-regulating energy feedback, in which AGN outbursts in the central galaxies episodically provide sufficient heating to offset much of the gas cooling. We use deep integral-field spectroscopy to study the optical line emission from the extended nebulae of three nearby brightest cluster galaxies and investigate how they are related to the processes of heating and cooling in the cluster cores. Two of these systems, Abell 3581 and Sersic 159-03, appear to be experiencing phases of feedback that are dominated by the activity and output of a central AGN. Abell 3581, shows evidence for significant interaction between the radio outflows and the optical nebula, in addition to accretion flows into the nucleus of the galaxy. X-ray and radio data show that Sersic 159-03 is dominated by the feedback of energy from the central AGN, but the kinematics of the optical nebula are consistent with infall or outflow of material along its bright filaments. The third system, 2A 0335+096, is dominated by mass accretion and cooling, and so we suggest that it is in an accumulation phase of the feedback cycle. The outer nebula forms a disk-like structure, ~14 kpc in radius, that rotates about the central galaxy with a velocity amplitude of ~200 km/s. Overall, our data are consistent with ongoing AGN-driven feedback cycles occurring in these systems.Comment: Preprint: 37 pages with 11 figures and 4 tables, accepted for publication in Ap

The Link Between Extended Line Emission and AGN Feedback in Brightest Cluster Galaxies

This thesis presents a study of the optical emission-line regions of low-redshift brightest cluster galaxies (BCGs) and how these are connected to energy feedback in cluster cores. The cores of massive galaxy clusters appear to undergo cycles of self-regulating energy feedback, in which the output of nuclear activity in BCGs offsets much of the hot cluster gas cooling. Many of the BCGs in these `cool-core' clusters are surrounded by extended filamentary nebulae that produce characteristic low-ionisation emission spectra. The origin and sources of excitation of these structures are not well understood. A sample of BCGs was observed with a new wide-field, optical integral-field spectrograph. These galaxies produce strong line emission with a range of integrated luminosities. Maps of the morphology and velocities of the line-emitting gas are constructed from these data. A deep observation of the nearby galaxy NGC4696, provides a detailed view of the complex emission nebula. In the inner nebula, a bright spiral filament coincides closely with a prominent dust lane. The data reveal velocities in this structure consistent with infalling, orbit-like trajectories encircling the nucleus. A model is presented in which some of the gas in the filaments originated in the accretion of a gas-rich dwarf galaxy. It is suggested that the filaments are excited by ~200km/s ram-pressure-driven shocks as the gas clouds fall through the halo. The shock models described reproduce the optical spectrum of the nebula. Three BCGs with intermediate line luminosities are studied to investigate how the filament structures are related to the processes of feedback in the cluster cores. Two systems, Abell 3581 and Sersic 159-03, appear to be experiencing phases of feedback dominated by AGN heating. The structure and kinematics of the emitting gas in Abell 3581 show evidence for significant interaction between the radio outflows and the optical nebula, and possible accretion flows into the nucleus. X-ray and radio data indicate that Sersic 159-03 is dominated by AGN feedback, but the kinematics of the optical nebula are consistent with infall or outflow along the filaments. The third system, 2A0335+096, is dominated by a cooling and accumulation phase of feedback. The outer nebula forms a disk-like structure, ~14kpc in radius, with a velocity field of rotation about the BCG. Overall, our data are consistent with ongoing AGN-driven feedback in these systems. A comparative study of the line-luminous galaxies in the sample is also presented. The data for several systems show evidence for a correlation between the velocity dispersions and line flux ratios in the nebulae, suggesting a strong contribution from shocks to the excitation. The large-scale excitation properties of the nebulae are assessed using optical diagnostic diagrams and discussed in the context of mixing between shock and stellar photoionisation excitation models. It is suggested that both shock and photoionisation excitation contribute significantly to the properties of the emission in these BCGs, to a degree that varies among the galaxies

Feedback in the cores of clusters A3581, 2A 0335+096, and sersic 159-03

The cores of massive galaxy clusters, where hot gas is cooling rapidly, appear to undergo cycles of self-regulating energy feedback, in which active galactic nucleus (AGN) outbursts in the central galaxies episodically provide sufficient heating to offset much of the gas cooling. We use deep integral-field spectroscopy to study the optical line emission from the extended nebulae of three nearby brightest cluster galaxies and investigate how they are related to the processes of heating and cooling in the cluster cores. Two of these systems, A3581 and Sersic159-03, appear to be experiencing phases of feedback that are dominated by the activity and output of a central AGN. A3581 shows evidence for significant interaction between the radio outflows and the optical nebula, in addition to accretion flows into the nucleus of the galaxy. X-ray and radio data show that Sersic159-03 is dominated by the feedback of energy from the central AGN, but the kinematics of the optical nebula are consistent with infall or outflow of material along its bright filaments. The third system, 2A0335+096, is dominated by mass accretion and cooling, and so we suggest that it is in an accumulation phase of the feedback cycle. The outer nebula forms a disk-like structure, 14kpc in radius, that rotates about the central galaxy with a velocity amplitude of 200kms -1. Overall, our data are consistent with ongoing AGN-driven feedback cycles occurring in these systems

The nuclear ring in the barred spiral galaxy IC 4933

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°

Pacificando o branco

Índios do Norte da Amazônia estão nos descrevendo, nos amansando, tentando nos entender e se entender conosco. Alguns há vários séculos, outros há poucos anos. Como podemos compreender o modo pelo qual somos compreendidos? Durante a última década, a antropologia preocupou-se muito com o problema inverso: como podemos compreender o modo pelo qual compreendemos os outros? E ficou assim entretida demais com seu próprio umbigo. Este livro magistral, esperado há vários anos, é um alívio. Mostra como é fecundo analisar o trabalho simbólico e político de sociedades indígenas, trabalho que resulta em suas “cosmologias do contato” e na forma específica pela qual se apropriam da história e do mundo contemporâneo