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851.
852.
Marcella Massardi Ronald D. Ekers Tara Murphy Roberto Ricci Elaine M. Sadler Sarah Burke Gianfranco De Zotti Philip G. Edwards Paul J. Hancock Carole A. Jackson Michael J. Kesteven Elizabeth Mahony Christopher J. Phillips Lister Staveley-Smith Ravi Subrahmanyan Mark A. Walker Warwick E. Wilson 《Monthly notices of the Royal Astronomical Society》2008,384(2):775-802
The Australia Telescope 20-GHz (AT20G) Survey is a blind survey of the whole southern sky at 20 GHz (with follow-up observations at 4.8 and 8.6 GHz) carried out with the Australia Telescope Compact Array from 2004 to 2007.
The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic ) radio sources south of δ=−15° with Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz.
In this paper we present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index α, assuming S ∝να , decreases from α8.6 4.8 = 0.11 between 4.8 and 8.6 GHz to α20 8.6 =−0.16 between 8.6 and 20 GHz), even if the sample is dominated by flat spectra sources (85 per cent of the sample has α20 8.6 > −0.5) . The almost simultaneous spectra in total intensity and polarization allowed us a comparison of the polarized and total intensity spectra: polarized fraction slightly increases with frequency, but the shapes of the spectra have little correlation. Optical identifications provided an estimation of redshift for 186 sources with a median value of 1.20 and 0.13, respectively, for QSO and galaxies. 相似文献
The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic ) radio sources south of δ=−15° with Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz.
In this paper we present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index α, assuming S ∝ν
853.
854.
J. A. Green J. L. Caswell G. A. Fuller S. L. Breen K. Brooks M. G. Burton A. Chrysostomou J. Cox P. J. Diamond S. P. Ellingsen M. D. Gray M. G. Hoare M. R. W. Masheder N. McClure-Griffiths M. Pestalozzi C. Phillips L. Quinn M. A. Thompson M. Voronkov A. Walsh D. Ward-Thompson D. Wong-McSweeney J. A. Yates R. J. Cohen † 《Monthly notices of the Royal Astronomical Society》2008,385(2):948-956
855.
S. Dye S. A. Eales I. Aretxaga S. Serjeant J. S. Dunlop T. S. R. Babbedge S. C. Chapman M. Cirasuolo D. L. Clements K. E. K. Coppin L. Dunne E. Egami D. Farrah R. J. Ivison E. van Kampen A. Pope R. Priddey G. H. Rieke A. M. Schael D. Scott C. Simpson T. Takagi T. Takata M. Vaccari 《Monthly notices of the Royal Astronomical Society》2008,386(2):1107-1130
We present estimates of the photometric redshifts, stellar masses and star formation histories of sources in the Submillimetre Common-User Bolometer Array (SCUBA) HAlf Degree Extragalactic Survey (SHADES). This paper describes the 60 SCUBA sources detected in the Lockman Hole covering an area of ∼320 arcmin2 . Using photometry spanning the B band to 8 μm, we find that the average SCUBA source forms a significant fraction of its stars in an early period of star formation and that most of the remainder forms in a shorter more intense burst around the redshift it is observed. This trend does not vary significantly with source redshift. However, the sources show a clear increase in stellar mass with redshift, consistent with downsizing. In terms of spectral energy distribution types, only two out of the 51 sources we have obtained photometric redshifts for are best fitted by a quasar-like spectrum, with approximately 80 per cent of the sources being best fitted with late-type spectra (Sc, Im and starburst). By including photometry at 850 μm, we conclude that the average SCUBA source is forming stars at a rate somewhere between 6 and 30 times the rate implied from the rest-frame optical in a dust obscured burst and that this burst creates 15–65 per cent of the total stellar mass. Using a simplistic calculation, we estimate from the average star formation history that between one in five and one in 15 bright ( L * + 2 < L optical < L * − 1 mag) galaxies in the field over the interval 0 < z < 3 will at some point in their lifetime experience a similar energetic dusty burst of star formation. Finally, we compute the evolution of the star formation rate density and find it peaks around z ∼ 2 . 相似文献
856.
857.
Adam A. Miller Jonathan Irwin Suzanne Aigrain Simon Hodgkin Leslie Hebb 《Monthly notices of the Royal Astronomical Society》2008,387(1):349-363
We present the results of a systematic search for transiting planets in a ∼5 Myr open cluster, NGC 2362. We observed ∼1200 candidate cluster members, of which ∼475 are believed to be genuine cluster members, for a total of ∼100 h. We identify 15 light curves with reductions in flux that pass all our detection criteria, and six of the candidates have occultation depths compatible with a planetary companion. The variability in these six light curves would require very large planets to reproduce the observed transit depth. If we assume that none of our candidates are, in fact, planets then we can place upper limits on the fraction of stars with hot Jupiters (HJs) in NGC 2362. We obtain 99 per cent confidence upper limits of 0.22 and 0.70 on the fraction of stars with HJs ( f p ) for 1–3 and 3–10 d orbits, respectively, assuming all HJs have a planetary radius of 1.5 R Jup . These upper limits represent observational constraints on the number of stars with HJs at an age ≲10 Myr, when the vast majority of stars are thought to have lost their protoplanetary discs. Finally, we extend our results to the entire Monitor project, a survey searching young, open clusters for planetary transits, and find that the survey as currently designed should be capable of placing upper limits on f p near the observed values of f p in the solar neighbourhood. 相似文献
858.
Lingyu Wang Michael Rowan-Robinson Issei Yamamura Hiroshi Shibai Rich Savage Seb Oliver Matthew Thomson Nurur Rahman Dave Clements Elysandra Figueredo Tomotsugu Goto Sunao Hasegawa Woong-Seob Jeong Shuji Matsuura Thomas G. Müller Takao Nakagawa Chris P. Pearson Stephen Serjeant Mai Shirahata Glenn J. White 《Monthly notices of the Royal Astronomical Society》2008,387(2):601-615
We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio (S/N) > 5 for a single detector row is 1.1 ± 0.1 Jy which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds. 相似文献
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds. 相似文献
859.
M. E. C. Swanson Max Tegmark rew J. S. Hamilton J. Colin Hill 《Monthly notices of the Royal Astronomical Society》2008,387(4):1391-1402
As galaxy surveys become larger and more complex, keeping track of the completeness, magnitude limit and other survey parameters as a function of direction on the sky becomes an increasingly challenging computational task. For example, typical angular masks of the Sloan Digital Sky Survey contain about N = 300 000 distinct spherical polygons. Managing masks with such large numbers of polygons becomes intractably slow, particularly for tasks that run in time with a naive algorithm, such as finding which polygons overlap each other. Here we present a 'divide-and-conquer' solution to this challenge: we first split the angular mask into pre-defined regions called 'pixels', such that each polygon is in only one pixel, and then perform further computations, such as checking for overlap, on the polygons within each pixel separately. This reduces tasks to , and also reduces the important task of determining in which polygon(s) a point on the sky lies from to , resulting in significant computational speedup. Additionally, we present a method to efficiently convert any angular mask to and from the popular healpix format. This method can be generically applied to convert to and from any desired spherical pixelization. We have implemented these techniques in a new version of the mangle software package, which is freely available at http://space.mit.edu/home/tegmark/mangle/ , along with complete documentation and example applications. These new methods should prove quite useful to the astronomical community, and since mangle is a generic tool for managing angular masks on a sphere, it has the potential to benefit terrestrial mapmaking applications as well. 相似文献
860.
A. L. Tadross 《Monthly notices of the Royal Astronomical Society》2008,389(1):285-291
The main astrophysical parameters of 24 previously unstudied open clusters of Berkeley catalogue are presented here. JHK near-infrared (Two Micron All Sky Survey) photometry and the proper motions astrometry of Naval Observatory Merged Astrometric Dataset (NOMAD) are used. The clusters' centres, angular diameters, ages, distances and colour excesses for these clusters are estimated for the first time. 相似文献