Near-infrared properties of i-drop galaxies in the Hubble Ultra Deep Field     

Elizabeth R. Stanway  Richard G. McMahon  Andrew J. Bunker 《Monthly notices of the Royal Astronomical Society》2005,359(3):1184-1192

We analyse near-infrared Hubble Space Telescope ( HST )/Near-Infrared Camera and Multi-Object Spectrometer F 110 W ( J ) and F 160 W ( H ) band photometry of a sample of 27 i '-drop candidate   z ≃ 6  galaxies in the central region of the HST /Advanced Camera for Surveys Ultra Deep Field . The infrared colours of the 20 objects not affected by near neighbours are consistent with a high-redshift interpretation. This suggests that the low-redshift contamination of this i '-drop sample is smaller than that observed at brighter magnitudes, where values of 10–40 per cent have been reported. The J – H colours are consistent with a slope flat in   f_ν ( f_λ ∝λ⁻²)  , as would be expected for an unreddened starburst. However, there is evidence for a marginally bluer spectral slope  ( f_λ ∝λ^−2.2)  , which is perhaps indicative of an extremely young starburst (∼10 Myr old) or a top heavy initial mass function and little dust. The low levels of contamination, median photometric redshift of   z ∼ 6.0  and blue spectral slope, inferred using the near-infrared data, support the validity of the assumptions in our earlier work in estimating the star formation rates, and that the majority of the i -drop candidates galaxies lie at   z ∼ 6  .  相似文献   

Supersonic turbulence, filamentary accretion and the rapid assembly of massive stars and discs     

Robi Banerjee  Ralph E. Pudritz  Dave W. Anderson 《Monthly notices of the Royal Astronomical Society》2006,373(3):1091-1106

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Anisotropy in the distribution of satellites around primary galaxies in the 2dF Galaxy Redshift Survey: the Holmberg effect   总被引：1，自引：0，他引：1  

Laura Sales  Diego G. Lambas†‡ 《Monthly notices of the Royal Astronomical Society》2004,348(4):1236-1240

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Dynamical Evolution of Barred Galaxies     

E. Athanassoula 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):9-31

Angular momentum redistribution within barred galaxies drives their dynamical evolution. Angular momentum is emitted mainly by near-resonant material in the bar region and absorbed by resonant material mainly in the outer disc and in the halo. This exchange determines the strength of the bar, the decrease of its pattern speed, as well as its morphology. If the galaxy has also a gaseous component and/or a companion or satellite, then these also take part in the angular momentum exchange. During the evolution a bar structure forms in the inner parts of the halo as well. This bar is shorter and fatter than the disc bar and stays so all through the simulation, although its length grows considerably with time. Viewed edge-on, the bar in the disc component acquires a boxy or peanut shape. I describe the families of periodic orbits that explain such structures and review the observations showing that boxy/peanut ‘bulges’ are in fact just bars seen edge-on.  相似文献   

The baseline intracluster entropy profile from gravitational structure formation     

G. Mark Voit  Scott T. Kay  Greg L. Bryan 《Monthly notices of the Royal Astronomical Society》2005,364(3):909-916

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Evolution of the velocity field in model potentials     

V. V. Orlov 《Astronomy Letters》2005,31(7):494-499

We consider the evolution of the structure of the velocity field formed by the loops of the trajectory in a generalized Hénon-Heiles model potential. Box-shaped orbits alternating with periodic trajectories are shown to dominate at low values of the energy integral. Signatures of shell-and tube-shaped structures appear as the energy increases. Tube-shaped orbits are associated with stable periodic trajectories with small resonance ratios. Zones of stochastic orbits appear at values of the energy integral close to its critical value, which corresponds to the opening of the zero-velocity contour.  相似文献   

Hilda asteroids among Jupiter family comets     

Romina P. Di Sisto  Adrián Brunini  Lorena D. Dirani  Rosa B. Orellana 《Icarus》2005,174(1):81-89

Hilda asteroids and comets are similar from the compositional point of view. The D-taxonomic class prevailing among Hildas has all the characteristics found in cometary spectra. Jupiter Family Comets (JFCs) coming from the trans-neptunian region are under the gravitational control of Jupiter, making them a dynamically unstable population with a mean dynamical lifetime of 10⁴ to ¹⁰⁵ years. In contrast, Hilda asteroids residing in the 3:2 mean motion resonance with Jupiter are a very stable population. But once they escape from the resonance, they are dynamically controlled by Jupiter, and in this sense their behavior resembles that of JFC. We performed a numerical simulation to analyze the dynamical evolution that Hildas follow after escaping from the resonance, and their contribution to the JFC population. We found that 8% of the particles leaving the resonance end up impacting Jupiter. 98.7% of the escaped Hildas live at least 1000 years as a JFC, with a mean lifetime of 1.4×¹⁰⁶ years. In particular, escaped Hildas stay mainly in the region of perihelion distances greater than 2.5 AU. On the other hand, the number of escaped Hildas reaching the inner Solar System (q<2.5 AU) is negligible. So, there are almost no Hilda asteroids among the NEO population. We also analyzed the possibility that the Shoemaker-Levy 9 were an escaped Hilda asteroid. In this case, it would be possible to give stronger constraints to its pre-capture orbital elements.  相似文献   

Rotational evolution of protoneutron stars with hyperons: spin up or not?     

Y.-F. Yuan  Jeremy S. Heyl † 《Monthly notices of the Royal Astronomical Society》2005,360(4):1493-1505

We study the evolution of a rigidly rotating protoneutron star (PNS) with hyperons and nucleons or solely nucleons in its core due to the escape of trapped neutrinos. As the neutrinos escape, the core nucleonic neutron star (NS) expands and the stellar rotation slows. After the neutrinos escape, the range of the spin periods is narrower than the initial one, but the distribution is still nearly uniform. A PNS with hyperons, at the late stage of its evolution, keeps shrinking and spinning up until all the trapped neutrinos escape. Consequently, the distribution of the stellar initial spin periods is skewed towards shorter periods. If the hyperonic star is metastable, its rotational frequency accelerates distinguishedly before it collapses to a black hole.  相似文献   

Morphological studies of the Spitzer Wide-Area Infrared Extragalactic survey galaxy population in the UGC 10214 Hubble Space Telescope/Advanced Camera for Surveys field     

E. Hatziminaoglou  P. Cassata  G. Rodighiero  I. Pérez-Fournon  A. Franceschini  A. Hernán-Caballero  F. M. Montenegro-Montes  A. Afonso-Luis  T. Jarrett  G. Stacey  C. Lonsdale  F. Fang  S. Oliver  M. Rowan-Robinson  D. Shupe  H. E. Smith  J. Surace  C. K. Xu  E. A. González-Solares 《Monthly notices of the Royal Astronomical Society》2005,364(1):47-58

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The ages and metallicities of galaxies in the local universe     

Anna Gallazzi  Stéphane Charlot  Jarle Brinchmann  Simon D. M. White  Christy A. Tremonti 《Monthly notices of the Royal Astronomical Society》2005,362(1):41-58

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