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Davis M.,University of California at Berkeley | Masters K.L.,University of Portsmouth | Springob C.,Anglo Australian Observatory | Huchra J.P.,Harvard - Smithsonian Center for Astrophysics | Lemson G.,Max Planck Institute for Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2011

We perform a reconstruction of the cosmological large-scale flows in the nearby Universe using two complementary observational sets. The first, the SFI++ sample of Tully-Fisher (TF) measurements of galaxies, provides a direct probe of the flows. The second, the whole sky distribution of galaxies in the 2MASS (Two Micron All Sky Survey) redshift survey (2MRS), yields a prediction of the flows given the cosmological density parameter, Ω, and a biasing relation between mass and galaxies. We aim at an unbiased comparison between the peculiar velocity fields extracted from the two data sets and its implication on the cosmological parameters and the biasing relation. We expand the fields in a set of orthonormal basis functions, each representing a plausible realization of a cosmological velocity field smoothed in such a way as to give a nearly constant error on the derived SFI++ velocities. The statistical analysis is done on the coefficients of the modal expansion of the fields by means of the basis functions. Our analysis completely avoids the strong error covariance in the smoothed TF velocities by the use of orthonormal basis functions and employs elaborate mock data sets to extensively calibrate the errors in 2MRS predicted velocities. We relate the 2MRS galaxy distribution to the mass density field by a linear bias factor, b, and include a luminosity-dependent, ∝L α, galaxy weighting. We assess the agreement between the fields as a function of α and β=f(Ω)/b, where f is the growth factor of linear perturbations. The agreement is excellent with a reasonable χ 2 per degree of freedom. For α= 0, we derive 0.28 < β < 0.37 and 0.24 < β < 0.43, respectively, at the 68.3 per cent and 95.4 per cent confidence levels (CLs). For β= 0.33, we get α < 0.25 and α < 0.5, respectively, at the 68.3 per cent and 95.4 per cent CLs. We set a constraint on the fluctuation normalization, finding σ 8= 0.66 ± 0.10, which is only 1.5σ deviant from Wilkinson Microwave Anisotropy Probe (WMAP) results. It is remarkable that σ 8 determined from this local cosmological test is close to the value derived from the cosmic microwave background, an indication of the precision of the standard model. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Anderson J.P.,University of Chile | Covarrubias R.A.,Anglo Australian Observatory | James P.A.,Liverpool John Moores University | Hamuy M.,University of Chile | Habergham S.M.,Liverpool John Moores University
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present constraints on the progenitor metallicities of core-collapse supernovae. To date, nearly all metallicity constraints have been inferred from indirect methods such as metallicity gradients in host galaxies, luminosities of host galaxies or derived global galaxy metallicities. Here, progenitor metallicities are derived from optical spectra taken at the sites of nearby supernovae, from the ratio of strong emission lines found in their host HII regions.We present results from the spectra of 74 host HII regions and discuss the implications that these have on the nature of core-collapse supernova progenitors. Overall, while we find that the mean metallicity of Type Ibc environments is higher than that of Type II events, this difference is smaller than observed in previous studies. There is only a 0.06 dex difference in the mean metallicity values, at a statistical significance of ~1.5σ, while using a Kolmogorov-Smirnov test we find that the two metallicity distributions are marginally consistent with being drawn from the same parent population (probability >10 per cent). This argues that progenitor metallicity is not a dominant parameter in deciding supernovae type, with progenitor mass and/or binarity playing a much more significant role. The mean derived oxygen metallicities [12+log(O/H)] for the different supernova types, on the Pettini & Pagel scale, are 8.580 (standard error on the mean of 0.027) for the 46 Type II supernovae (dominated by Type II plateau), 8.616 (0.040) for 10 Type Ib and 8.626 (0.039) for 14 Type Ic. Overall, the Type Ibc supernovae have a mean metallicity of 8.635 (0.026, 27 supernovae). Hence, we find a slight suggestion of a metallicity sequence, in terms of increasing progenitor metallicity going from Type II through Ib and finally Ic supernovae arising from the highest metallicity progenitors. Finally we discuss these results in the context of all current literature progenitor metallicity measurements, and discuss biases and selection effects that may affect the current sample compared to overall supernova and galaxy samples. © 2010 The Authors. Journal compilation. © 2010 RAS.


Reid W.A.,Macquarie University | Parker Q.A.,Macquarie University | Parker Q.A.,Anglo Australian Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2010

Our previous identification and spectroscopic confirmation of 431 faint, new planetary nebulae (PNe) in the central 25 deg2 region of the Large Magellanic Cloud (LMC) permit us to now examine the shape of the LMC planetary nebula luminosity function (PNLF) through an unprecedented 10 mag range. The majority of our newly discovered and previously known PNe were observed using the 2dF, multi-object fibre spectroscopy system on the 3.9-m Anglo-Australian Telescope and the FLAMES multi-object spectrograph on the 8-m Very Large Telescope. We present reliable [O iii] 5007 Å and Hβ flux estimates based on calibrations to well-established PN fluxes from previous surveys and spectroscopic standard stars. The bright cut-off (M*) of the PNLF is found by fitting a cumulative function to the bright end of the PNLF over a 3.4 mag range. This cut-off is used to estimate a new distance modulus of 18.46 to the LMC, in close agreement with previous PNLF studies and the best estimates by other indicators. The bright-end cut-off is robust to small samples of bright PNe since significantly increased PN samples do not change this fiducial. We then fit a truncated exponential curve directly to the bright end of the function over a 6 mag range and test the curve's ability to indicate the position of M*. Because of the significant increase in the number of LMC PNe, the shape of the PNLF is now examined in greater detail than has previously been possible. Newly discovered features include a small increase in the number of PNe over the brightest 4 mag followed by a steep rise over 2 mag, a peak at 6 mag below the bright cut-off and an almost linear drop-off to the faint end. Dips at the bright end of the PNLF are examined in relation to the overall shape of the PNLF and the exponential increase in the number of PNe. Through cumulative functions, the new LMC PNLF is compared to those from the Small Magellanic Cloud and a new deep local Galactic sample revealing the effects of incompleteness. The new [O iii] 5007 Å LMC PNLF is then compared to our new Hβ LMC PNLF using calibrated and measured fluxes for the same objects, revealing the effects of metallicity on the [O iii] 5007 Å line. © 2010 The Authors. Journal compilation © 2010 RAS.


Reid W.A.,Macquarie University | Parker Q.A.,Macquarie University | Parker Q.A.,Anglo Australian Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2013

We have extended our planetary nebulae (PNe) survey to the outer ~64 deg2 of the Large Magellanic Cloud (LMC) using maps from the Magellanic Cloud Emission Line Survey (MCELS) and the UK Schmidt Telescope (UKST) Hα survey. Although the MCELS survey has poorer ~5 arcsec resolution than both the UKST Hα survey and the original Hα median stacked map in the LMC's central 25 deg2, it has the advantage of additional narrow-band filters at Hα, [OIII] and [S II] providing improved diagnostic capabilities. Using these data to uncover new emission line candidates we have so far spectroscopically confirmed an extra 61 LMC PNe which we present here for the first time.We have also independently recovered and spectroscopically confirmed 107 of the 109 (98 per cent) PNe that were previously known to exist in the outer LMC. The majority of our newly discovered and previously known PNe were confirmed using the AAOmega, multi-object fibre spectroscopy system on the 3.9-m Anglo-Australian Telescope (AAT) and the 6dF multi-object spectrograph on the UKST. These newly identified PNe were cross-checked against extant multi-wavelength imaging surveys in the near- and mid-infrared in particular and against the latest emission-line ratio diagnostic plots for improved confidence in PNe identification. © 2013 The AuthorsPublished by Oxford University Press on behalf of the Royal Astronomical Society.


Frew D.J.,Macquarie University | Frew D.J.,Perth Observatory | Parker Q.A.,Macquarie University | Parker Q.A.,Anglo Australian Observatory
Publications of the Astronomical Society of Australia | Year: 2010

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. © Astronomical Society of Australia 2010.


Jeffers S.V.,University Utrecht | Donati J.-F.,LATT | Alecian E.,University of Paris Descartes | Marsden S.C.,Anglo Australian Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2011

The magnetic field topology and differential rotation are fundamental signatures of the dynamo processes that generate the magnetic activity observed in the Sun and solar-type stars. To investigate how these dynamo processes evolve in stars with shallow convective zones, we present high-resolution spectropolarimetric observations of the young GO dwarf HD171488 over three epochs. Using the Zeeman-Doppler tomographic imaging technique, we have reconstructed surface brightness images that are dominated by polar and high-latitude starspots and a magnetic field topology that shows large-scale radial and azimuthal magnetic field components. Over the time-span of our observations, we do not observe a reversal of the magnetic field polarity as has been observed in other solar-type stars with shallow convective zones. The phase coverage of our data was sufficient to determine the differential rotation for two epochs where in conjunction with previous work, we conclude that there is no evidence for the temporal evolution of differential rotation. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.


Sharp R.G.,Anglo Australian Observatory | Bland-Hawthorn J.,University of Sydney | Bland-Hawthorn J.,University of Oxford
Astrophysical Journal | Year: 2010

In recent years, we have come to recognize the widespread importance of large-scale winds in the life cycle of galaxies. The onset and evolution of a galactic wind is a highly complex process which must be understood if we are to understand how energy and metals are recycled throughout the galaxy and beyond. Here we present three-dimensional spectroscopic observations of a sample of 10 nearby galaxies with the AAOmega-SPIRAL integral-field spectrograph on the 3.9 m Anglo-Australian Telescope, the largest survey of its kind to date. The double-beam spectrograph provides spatial maps in a range of spectral diagnostics: [O III]5007, Hβ, Mgb, Na D, [O I]6300, Hα, [N II]6583, [S II]6717, 6731. We demonstrate that these flows can often separate into highly ordered structures through the use of ionization diagnostics and kinematics. All of the objects in our survey show extensive wind-driven filamentation along the minor axis, in addition to large-scale disk rotation. Our sample can be divided into either starburst galaxies or active galactic nuclei (AGNs), although some objects appear to be a combination of these. The total ionizing photon budget available to both classes of galaxies is sufficient to ionize all of the wind-blown filamentation out to large radius. We find, however, that while AGN photoionization always dominates in the wind filaments, this is not the case in starburst galaxies where shock ionization dominates. This clearly indicates that after the onset of star formation, there is a substantial delay (≳10 Myr) before a starburst wind develops. We show why this behavior is expected by deriving "ionization" and dynamical timescales for both AGNs and starbursts. We establish a sequence of events that lead to the onset of a galactic wind. The clear signature provided by the ionization timescale is arguably the strongest evidence yet that the starburst phenomenon is an impulsive event. A well-defined ionization timescale is not expected in galaxies with a protracted history of circumnuclear star formation. Our three-dimensional data provide important templates for comparisons with high-redshift galaxies. © 2010. The American Astronomical Society.


Sharp R.,Anglo Australian Observatory | Parkinson H.,University of Edinburgh
Monthly Notices of the Royal Astronomical Society | Year: 2010

We report on the limitations of sky-subtraction accuracy for long-duration fibre-optic multiobject spectroscopy of faint astronomical sources during long-duration exposures. We show that while standard sky subtraction techniques yield accuracies consistent with the Poisson noise limit for exposures of 1 h duration, there are large-scale systematic defects that inhibit the sensitivity gains expected on the summation of longer duration exposures. For the AAOmega system at the Anglo-Australian Telescope, we identify a limiting systematic sky-subtraction accuracy, which is reached after integration times of 4-10 h. We show that these systematic defects can be avoided through the use of the fibre nod-and-shuffle (N+S) observing mode, but with a potential cost in observing efficiency. Finally, we demonstrate that these disadvantages can be overcome through the application of a Principal Components Analysis (PCA) sky-subtraction routine. Such an approach minimize systematic residuals across long-duration exposures, allowing deep integrations.We apply the PCA approach to over 200 h of on-sky observations and conclude that for the AAOmega system, the residual error in long-duration observations falls at a rate proportional to τ-0.32 in contrast to the τ-0.5 rate expected from theoretical considerations. With this modest rate of decline, the PCA approach represents a more efficient mode of observation than the N+S technique for observations in the sky limited regime with durations of 10-100 h (even before accounting for the additional signal-to-noise ratio and targeting efficiency losses often associated with the N+S technique).This conclusion has important implications for the observing strategies of the next generation of fibre-optics redshift surveys with existing facilities as well as design implications for fibre-optic systems destined for new facilities. It argues against the use of the inherently inefficient N+S technique for faint object fibre-optic survey spectroscopy. © 2010 The Authors. Journal compilation © 2010 RAS.


Sharp R.,Anglo Australian Observatory | Birchall M.N.,Anglo Australian Observatory
Publications of the Astronomical Society of Australia | Year: 2010

We report an optimal extraction methodology, for the reduction of multi-object fibre spectroscopy data, operating in the regime of tightly packed (and hence significantly overlapping) fibre profiles. The routine minimises crosstalk between adjacent fibres and statistically weights the extraction to reduce noise. As an example of the process we use simulations of the numerous modes of operation of the AAOmega fibre spectrograph and observational data from the SPIRAL Integral Field Unit at the Anglo-Australian Telescope. © 2010 Astronomical Society of Australia.


Shortridge K.,Anglo Australian Observatory | Vuong M.,Anglo Australian Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Traditionally, AAO tasks controlling hardware were able to operate in a simulation mode, simply ignoring the actual hardware and responding as if the hardware were working properly. However, this did not allow a rigorous testing of the low-level details of the hardware control software. For recent projects, particularly the replacement of the control system for the 3.9m AAT, we have introduced detailed software simulators that mimic the hardware and its interactions down to the individual bit level in the interfaces. By having one single simulator task representing the whole of the hardware, we get a realistic simulation of the whole system. Communications with the simulator task are introduced just above the driver calls that would normally communicate with the real hardware, allowing all of the hardware control software to be tested. Simulation can be partial, only simulating those bits of the hardware not yet available This allows incremental software releases that demonstrate full functioning of complete aspects of the system before any hardware is available, and supports a rigorous 'value-added' approach for tracking the software development process. This was particularly successful for the telescope control system, and has been used since for other projects including the new HERMES spectrograph. © 2010 SPIE.

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