A sample of 6C radio sources designed to find objects at redshift z>4– III. Imaging and the radio galaxy K–z relation     

Matt J. Jarvis  Steve Rawlings  Steve Eales  Katherine M. Blundell  rew J. Bunker  Steve Croft  Ross J. McLure  Chris J. Willott 《Monthly notices of the Royal Astronomical Society》2001,326(4):1585-1600

In this paper, the third and final of a series, we present complete K -band imaging and some complementary I -band imaging of the filtered 6C* sample. We find no systematic differences between the K – z relation of 6C* radio galaxies and those from complete samples, so the near-infrared properties of luminous radio galaxies are not obviously biased by the additional 6C* radio selection criteria (steep spectral index and small angular size). The 6C* K – z data significantly improve delineation of the K – z relation for radio galaxies at high redshift ( z >2) . Accounting for non-stellar contamination, and for correlations between radio luminosity and stellar mass, we find little support for previous claims that the underlying scatter in the stellar luminosity of radio galaxies increases significantly at z >2 . In a particular spatially flat universe with a cosmological constant (Ω_M=0.3 and Ω_Λ=0.7) , the most luminous radio sources appear to be associated with galaxies with a luminosity distribution with a high mean (≈5  L *), and a low dispersion ( σ ∼0.5 mag) which formed their stars at epochs corresponding to z ≳2.5 . This result is in line with recent submillimetre studies of high-redshift radio galaxies and the inferred ages of extremely red objects from faint radio samples.  相似文献   

Photometric properties of Titan''s surface from Cassini VIMS: Relevance to titan''s hemispherical albedo dichotomy and surface stability     

R.M. Nelson  R.H. Brown  B.W. Hapke  W.D. Smythe  L. Kamp  M.D. Boryta  F. Leader  K.H. Baines  G. Bellucci  J.-P. Bibring  B.J. Buratti  F. Capaccioni  P. Cerroni  R.N. Clark  M. Combes  A. Coradini  D.P. Cruikshank  P. Drossart  V. Formisano  R. Jaumann  Y. Langevin  D.L. Matson  T.B. McCord  V. Mennella  P.D. Nicholson  B. Sicardy  C. Sotin 《Planetary and Space Science》2006,54(15):1540-1551

The Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini Saturn Orbiter returned spectral imaging data as the spacecraft undertook six close encounters with Titan beginning 7 July, 2004. Three of these flybys each produced overlapping coverage of two distinct regions of Titan's surface. Twenty-four points were selected on approximately opposite hemispheres to serve as photometric controls. Six points were selected in each of four reflectance classes. On one hemisphere each control point was observed at three distinct phase angles. From the derived phase coefficients, preliminary normal reflectances were derived for each reflectance class. The normal reflectance of Titan's surface units at 2.0178 μm ranged from 0.079 to 0.185 for the most absorbing to the most reflective units assuming no contribution from absorbing haze. When a modest haze contribution of τ=0.1 is considered these numbers increase to 0.089–0.215. We find that the lowest three reflectance classes have comparable normal reflectance on either hemisphere. However, for the highest brightness class the normal reflectance is higher on the hemisphere encompassing longitude 14–65° compared to the same high brightness class for the hemisphere encompassing 122–156° longitude. We conclude that an albedo dichotomy observed in continental sized units on Titan is due not only to one unit having more areal coverage of reflective material than the other but the material on the brighter unit is intrinsically more reflective than the most reflective material on the other unit. This suggests that surface renewal processes are more widespread on Titan's more reflective units than on its less reflective units.

We note that one of our photometric control points has increased in reflectance by 12% relative to the surrounding terrain from July of 2004 to April and May of 2005. Possible causes of this effect include atmospheric processes such as ground fog or orographic clouds; the suggestion of active volcanism cannot be ruled out.

Several interesting circular features which resembled impact craters were identified on Titan's surface at the time of the initial Titan flyby in July of 2004. We traced photometric profiles through two of these candidate craters and attempted to fit these profiles to the photometric properties expected from model depressions. We find that the best-fit attempt to model these features as craters requires that they be unrealistically deep, approximately 70 km deep. We conclude that despite their appearance, these circular features are not craters, however, the possibility that they are palimpsests cannot be ruled out.

We used two methods to test for the presence of vast expanses of liquids on Titan's surface that had been suggested to resemble oceans. Specular reflection of sunlight would be indicative of widespread liquids on the surface; we found no evidence of this. A large liquid body should also show uniformity in photometric profile; we found the profiles to be highly variable. The lack of specular reflection and the high photometric variability in the profiles across candidate oceans is inconsistent with the presence of vast expanses of flat-lying liquids on Titan's surface. While liquid accumulation may be present as small, sub-pixel-sized bodies, or in areas of the surface which still remain to be observed by VIMS, the presence of large ocean-sized accumulations of liquids can be ruled out.

The Cassini orbital tour offers the opportunity for VIMS to image the same parts of Titan's surface repeatedly at many different illumination and observation geometries. This creates the possibility of understanding the properties of Titan's atmosphere and haze by iteratively adapting models to create a best fit to the surface reflectance properties.  相似文献   

Numerical requirements for simulations of self-gravitating and non-self-gravitating discs     

Andrew F. Nelson †‡ 《Monthly notices of the Royal Astronomical Society》2006,373(3):1039-1073

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Deep optical imaging of the field of PC 1643+4631A&B – I. Spatial distributions and the counts of faint galaxies     

Toby Haynes  Garret Cotter †  Joanne C. Baker  Steve Eales  Michael E. Jones  Steve Rawlings  Richard Saunders 《Monthly notices of the Royal Astronomical Society》2002,334(2):262-282

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A sample of 6C radio sources designed to find objects at redshift z > 4 – II. Spectrophotometry and emission-line properties     

Matt J. Jarvis  Steve Rawlings  Mark Lacy  Katherine M. Blundell  rew J. Bunker  Steve Eales  Richard Saunders  Hyron Spinrad  Daniel Stern  Chris J. Willott 《Monthly notices of the Royal Astronomical Society》2001,326(4):1563-1584

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Temporal Variations in the Second-Degree Stokes Tesseral Geopotential Coefficients from Topex/Poseidon Altimetry   总被引：1，自引：0，他引：1  

Burša  Milan  Kenyon  Steve  Kouba  Jan  Ŝíma  Zdislav  Vatrt  Viliam  Vítek  Vojtêch  Vojtíŝková  Marie 《Earth, Moon, and Planets》2003,93(1):37-64

The TOPEX/POSEIDON (T/P) altimetry data set covering the periodof January 1, 1993 to January 3, 2001 was used to derive monthlyseries of the second-degree tesseral geopotential coefficients.To account for the sea water temperature variations, rathersimple models have been devised and discussed, describinglocalized as well as areal variations of sea water temperatureand heights. The second-degree tesseral coefficients have alsobeen shown to be proportional to the pressureportions of the oceanic equatorial effective excitation functions,used in Ocean Angular Momentum (OAM) data. OAM datatogether with Atmospheric Angular Momentum (AAM) data canbe used to study observed polar motion (PM) series.The excess PM rates, derived from the T/P effective excitationfunctions, were compared to the corresponding observed PM rates,derived from the International Earth Rotation Service (IERS)Bulletin A and corrected with AAM also obtainedfrom IERS. The noise of the T/P derived PM rate series was foundto be significantly larger than the corresponding Bulletin A/AAMPM rate residuals as well as the PM rates derived from anindependent OAM series that was also available for the1993–2000 period.  相似文献   

Galaxy groups in the 2dF Galaxy Redshift Survey: large-scale structure with groups     

Ariel Zandivarez  Manuel E. Merchán  Nelson D. Padilla 《Monthly notices of the Royal Astronomical Society》2003,344(1):247-256

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The interaction of a giant planet with a disc with MHD turbulence – I. The initial turbulent disc models     

John C. B. Papaloizou  Richard P. Nelson 《Monthly notices of the Royal Astronomical Society》2003,339(4):983-992

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Determination of the linear mass power spectrum from the mass function of galaxy clusters     

Ariel G. Sánchez  Nelson D. Padilla  Diego G. Lambas † 《Monthly notices of the Royal Astronomical Society》2002,337(1):161-171

We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation  σ( M )  using the expression for the mass function in the Press & Schechter, Sheth, Mo & Tormen and Jenkins et al. formalisms. We apply different techniques to recover the adimensional power spectrum  Δ²( k )  from  σ( M )  namely the   k _eff  approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the τCDM and ΛCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (FKP) method. We find that the mass function based method presented here can provide a very accurate estimate of the linear power spectrum, particularly for low values of k . This estimate is comparable to, or even better behaved than, the FKP solution.
The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution.  相似文献   

The 2dF Galaxy Redshift Survey: the number and luminosity density of galaxies     

Nicholas Cross  Simon P. Driver  Warrick Couch  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Gavin Dalton  Kathryn Deeley  Roberto De Propris  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Darren Madgwick  Stephen Moody  Peder Norberg  John A. Peacock  Bruce A. Peterson  Ian Price  Mark Seaborne  Will Sutherland  Helen Tadros  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,324(4):825-841

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