Thermal Stability of Cold Clouds in Galaxy Halos

We consider the thermal properties of cold, dense clouds of molecular hydrogen and atomic helium. For cloud masses below 10-1.7 M middle dot in circle, the internal pressure is sufficient to permit the existence of particles of solid or liquid hydrogen at temperatures above the cosmic microwave background temperature. Optically thin thermal continuum emission by these particles can balance cosmic-ray heating of the cloud, leading to equilibria that are thermally stable even though the heating rate is independent of cloud temperature. For the Galaxy, the known heating rate in the disk sets a minimum mass of order 10-6 M middle dot in circle necessary for survival. Clouds of this type may in principle comprise most of the dark matter in the Galactic halo. However, we caution that the equilibria do not exist at redshifts z greater, similar1 when the temperature of the microwave background was substantially larger than its current value; therefore, the formation and the survival of such clouds to the present epoch remain open questions.     

Giant Radio Halos in Galaxy Clusters as Probes of Particle Acceleration in Turbulent Regions

Giant radio halos in galaxy clusters probe mechanisms of particle acceleration connected with cluster merger events. Shocks and turbulence are driven in the inter-galactic medium (IGM) during clusters mergers and may have a deep impact on the non-thermal properties of galaxy clusters. Models of turbulent (re)acceleration of relativistic particles allow good correspondence with present observations, from radio halos to γ-ray upper limits, although several aspects of this complex scenario still remain poorly understood.     

Clustering of Lyman-Alpha Emitters galaxies

Galaxy clustering properties have been studied for decades to constrain cosmological parameters and have today, with large datasets of high-redshift sources piling up, become a powerful tool to discriminate and characterize primeval galaxies. In the last years, several Lyman-Alpha Emitter (LAE) galaxy samples have been gathered, which are big, uniform and compact enough to allow clustering analysis. Here we present a summary of the discussion session on the clustering properties of LAEs at the “Understanding Lyman-Alpha Emitters” conference.     

The 2dF-SDSS LRG and QSO Survey: the spectroscopic QSO catalogue

We present the final spectroscopic QSO catalogue from the 2dF-SDSS LRG (luminous red galaxy) and QSO (2SLAQ) survey. This is a deep,  18 < g < 21.85  (extinction corrected), sample aimed at probing in detail the faint end of the broad line active galactic nuclei luminosity distribution at   z ≲ 2.6  . The candidate QSOs were selected from SDSS photometry and observed spectroscopically with the 2dF spectrograph on the Anglo-Australian Telescope. This sample covers an area of 191.9 deg² and contains new spectra of 16 326 objects, of which 8764 are QSOs and 7623 are newly discovered [the remainder were previously identified by the 2dF QSO Redshift Survey (2QZ) and SDSS]. The full QSO sample (including objects previously observed in the SDSS and 2QZ surveys) contains 12 702 QSOs. The new 2SLAQ spectroscopic data set also contains 2343 Galactic stars, including 362 white dwarfs, and 2924 narrow emission-line galaxies with a median redshift of   z = 0.22  .
We present detailed completeness estimates for the survey, based on modelling of QSO colours, including host-galaxy contributions. This calculation shows that at   g ≃ 21.85  QSO colours are significantly affected by the presence of a host galaxy up to redshift   z ∼ 1  in the SDSS ugriz bands. In particular, we see a significant reddening of the objects in   g − i   towards the fainter g -band magnitudes. This reddening is consistent with the QSO host galaxies being dominated by a stellar population of age at least 2–3 Gyr.
The full catalogue, including completeness estimates, is available on-line at http://www.2slaq.info/ .     

The Shadow of Comet Hale–Bopp in Lyman-Alpha

For a few months around perihelion, thecentral part of the Hale–Bopp hydrogencloud has been optically thick to thesolar Lyα radiation, and hassignificantly reduced the solar flux availablefor the resonance glow of interstellarhydrogen beyond the comet. This shadowing effecton the interstellar gas is the first everobserved comet shadow. It is modeled andcompared with SWAN observations. Shadowmodelling will help to constrain the cometwater production and radiative transfer effectsin the interstellar ionisation cavity.     

Galaxy Evolution from Deep Field Galaxy Counts

We present deep galaxy number counts and colours of K—band selected galaxy surveys. We argue that primeval galaxies are present within the survey data, but have remained unidentified. There are few objects with the colours of an L ^* elliptical galaxy at a redshift of z ≈ 1, in contradiction to standard luminosity evolution models. We present K—band photometry of the objects in a spectroscopic redshift survey selected at 21 < B < 22.5. The absolute K magnitudes of the galaxies are consistent with the no-evolution or pure luminosity evolution models. The excess faint blue galaxies seen in the B—band number counts at intermediate magnitudes are a result of a low normalization, and do not dominate the population until B ≈ 25. Extreme merging or excess dwarf models are not needed at z < 1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Riemann Ellipsoids with Spherical Halos

Possible ellipsoidal figures of equilibrium are obtained for a rotating, gravitating fluid mass with internal mass flows of constant vorticity, embedded inside a homogeneous gravitating sphere. The classical ellipsoidal figures of equilibrium are generalized and new S-ellipsoids and ellipsoids with oblique rotation are obtained. The stability of embedded S-ellipsoids is investigated and the criterion for their stability is obtained. The existence of an ellipsoid with oblique rotation of type II inside a relatively dense halo becomes impossible.     

Pairwise Velocity Statistics of Dark Halos

We have accurately evaluated the halo pairwise velocity dispersion and the halo mean streaming velocity in the LCDM model (the fiat ω0 = 0.3 model) using a set of high-resolution N-body simulations. Based on the simulation results, we have developed a model for the pairwise velocity dispersion of halos. Our model agrees with the simulation results over all scales we studied. We have also tested the model of Sheth et al. for the mean streaming motion of halos derived from the pair-conservation equation. We found that their model reproduces the simulation data very well on large scale, but under-predicts the streaming motion on scales r < 10 h-1 Mpc. We have introduced an empirical relation to improve their model. These improved models are useful for predicting the redshift correlation functions and the redshift power spectrum of galaxies if the halo occupation number model, e.g. the cluster weighted     

Spectroscopy of 11 QSO candidates

Eleven QSO candidates have been confirmed from the UKST prism plate of the field 0112-35. Their redshifts, finding charts and the spectra are presented. Among these II QSOs, 6 are in 3 pairs with angular separation less than 4 arcmin; one is in a QSO-galaxy pair.     

Galaxy alignments

It is well-known that galaxies tend to form elongated associations stretching many degrees across the sky. It is shown here that especially galaxies of about 3000 to 5000 km s^-1 redshift define narrow filaments of from 10 to 50° in length. The surprising feature is that galaxies of very bright apparent magnitude tend to occur at the centre or ends of these alignments. The 20 brightest galaxies in apparent magnitude north of °= 0° are investigated here and of the 14 which are uncrowded by nearby bright galaxies, a total of 13 have well marked lines and concentrations of fainter, higher redshift galaxies     

Galaxy magnitudes

Systematic corrections to the magnitudes of galaxies in the Zwicky and the Shapley-Ames catalogues have been determined and are tabulated here. The corrections are based on the photographic measures by Holmberg, published photoelectric measures, and 392 photoelectric measures by Kron and Shane. These latter are mostly in the fainter magnitude range. The corrections for Volume I of the Zwicky Catalogue differ substantially from those for Volumes II to VI.     

A clustering analysis of QSO candidates

By means of two-point correlation function, clustering analysis (precolation method) and multiplicity funciton, we analyse the clustering of quasars for two samples of quasar candidates, and find that there is no obvious difference between the results of the observed and Monte-Carlo samples, apart from a weak clustering on the scale of 100 Mpc in the former.     

星系成团与并合研究

宇宙结构的形成和星系演化是当今天体物理学的重大课题.本论文的工作主要包括两部分:星系团的证认和研究;大质量早型星系的并合及引力波辐射.本文第1部分讨论了从SDSS DR6测光数据中证认星系团并研究它们的性质.前人从光学数据中得到的星系团绝大部分红移小于0.3,而且它们的富度估计不够准确.利用星系测光红移,我们在红移0.05相似文献   

Galaxy magnitudes

In this, the first of a short series of papers on the magnitudes of galaxies, the dependence of magnitude on the aperture used in photoelectric measures is discussed. mean results from an empirical study are presented.     

论彗晕的形状

关于彗晕的形状，没有一致的意见和结论．利用何种曲线描述彗晕，对于彗晕模型的建立以及彗晕动力学的理解具有重要的意义．借助于流体力学中一个修正的牛顿公式，指出彗晕的形状接近悬链线．还指出彗晕并不像Eddington所讨论那样，是尘埃颗粒轨道的抛物线包络．     

Modelling the Growth of Dark-Matter Halos

A new model for the cosmological growth of dark matter halos is presented. We compare theoretical predictions with results of N-body simulations. This revised version was published online in July 2006 with corrections to the Cover Date.