The WARPS survey – IV. The X-ray luminosity–temperature relation of high-redshift galaxy clusters

We present a measurement of the cluster X-ray luminosity–temperature ( L – T ) relation out to high redshift ( z ∼0.8). Combined ROSAT PSPC spectra of 91 galaxy clusters detected in the Wide Angle ROSAT Pointed Survey (WARPS) are simultaneously fitted in redshift and luminosity bins. The resulting temperature and luminosity measurements of these bins, which occupy a region of the high-redshift L – T relation not previously sampled, are compared with existing measurements at low redshift in order to constrain the evolution of the L – T relation. We find the best fit to low-redshift ( z <0.2) cluster data, at T >1 keV, to be L ∝ T ^3.15±0.06. Our data are consistent with no evolution in the normalization of the L – T relation up to z ∼0.8. Combining our results with ASCA measurements taken from the literature, we find η =0.19±0.38 (for Ω₀=1, with 1 σ errors) where L _Bol∝(1+ z ) ^η T ^3.15, or η =0.60±0.38 for Ω₀=0.3. This lack of evolution is considered in terms of the entropy-driven evolution of clusters. Further implications for cosmological constraints are also discussed.     

Compton dragged gamma-ray bursts: the spectrum

Recently several studies have jointly analysed data from different cosmological probes with the motivation of estimating cosmological parameters. Here we generalize this procedure to allow freedom in the relative weights of various probes. This is done by including in the joint χ ² function a set of 'hyper-parameters', which are dealt with using Bayesian considerations. The resulting algorithm, which assumes uniform priors on the log of the hyper-parameters, is very simple: instead of minimizing     (where     is per data set j ) we propose to minimize     (where N _j is the number of data points per data set j ). We illustrate the method by estimating the Hubble constant H ₀ from different sets of recent cosmic microwave background (CMB) experiments (including Saskatoon, Python V, MSAM1, TOCO and Boomerang ). The approach can be generalized for combinations of cosmic probes, and for other priors on the hyper-parameters.     

The diversity of SCUBA-selected galaxies

We present extensive observations of a sample of distant, submillimetre (submm) galaxies detected in the field of the massive cluster lens Abell 1835, using the Submm Common-User Bolometer Array (SCUBA). Taken in conjunction with earlier observations of other submm-selected sources, we now have detailed, multiwavelength observations of seven examples of the submm population, having exploited the combination of achromatic amplification by cluster lenses and lavish archival data sets. These sources, all clearly at z ≳1, illustrate the wide range in the radio and optical properties of distant submm-selected galaxies. We include detailed observations of the first candidate 'pure' starburst submm galaxy at high redshift, a z =2.56 interacting galaxy which shows no obvious sign of hosting an AGN. The remaining sources have varying degrees of inferred AGN activity (three out of seven of the most luminous show some evidence of the presence of an AGN), although even when an AGN is obviously present it is still not apparent whether reprocessed radiation from this source dominates the submm emission. In contrast with the variation in the spectral properties, we see relatively homogeneous morphologies for the population, with a large fraction of merging or interacting systems. Our study shows that virtually identical spectral energy distributions are seen for galaxies that exhibit strikingly different optical/UV spectral-line characteristics. We conclude that standard optical/UV spectral classifications are misleading when applied to distant, highly obscured galaxies, and that we must seek other means of determining the various contributions to the overall energy budget of submm galaxies and hence to the far-infrared extragalactic background.     

Eddies along front of warm winter current off the north coast of Spain and at Jovellanos Seamount

I~IOXSatellite infrared measurements are now accepted as an effeCtive way of mapping sea surfacetemperature (SST) distributions on global and regional scales. While regional SST maps are widely uest as background data for oceanographic experiments, they tend to be considered by oceanographers as at best qualitative tools. There is SCOPe for developing the use of satellite SST imagesac extensively for the study of mesoscale d~ical processes, as this paper seeks to demonstrate. As Part O…     

Intrinsic correlation of galaxy shapes: implications for weak lensing measurements

Weak gravitational lensing is now established as a powerful method to measure mass fluctuations in the universe. It relies on the measurement of small coherent distortions of the images of background galaxies. Even low-level correlations in the intrinsic shapes of galaxies could however produce a significant spurious lensing signal. These correlations are also interesting in their own right, since their detection would constrain models of galaxy formation. Using     haloes found in N -body simulations, we compute the correlation functions of the intrinsic ellipticity of spiral galaxies assuming that the disc is perpendicular to the angular momentum of the dark matter halo. We also consider a simple model for elliptical galaxies, in which the shape of the dark matter halo is assumed to be the same as that of the light. For deep lensing surveys with median redshifts ∼1, we find that intrinsic correlations of ∼10⁻⁴ on angular scales     are generally below the expected lensing signal, and contribute only a small fraction of the excess signals reported on these scales. On larger scales we find limits to the intrinsic correlation function at a level ∼10⁻⁵, which gives a (model-dependent) range of separations for which the intrinsic signal is about an order of magnitude below the ellipticity correlation function expected from weak lensing. Intrinsic correlations are thus negligible on these scales for dedicated weak lensing surveys. For wider but shallower surveys such as SuperCOSMOS, APM and SDSS, we cannot exclude the possibility that intrinsic correlations could dominate the lensing signal. We discuss how such surveys could be used to calibrate the importance of this effect, as well as study spin–spin correlations of spiral galaxies.     

A new quadruple gravitational lens system: CLASS B0128+437

High-resolution MERLIN observations of a newly discovered four-image gravitational lens system, B0128+437, are presented. The system was found after a careful re-analysis of the entire CLASS data set. The MERLIN observations resolve four components in a characteristic quadruple-image configuration; the maximum image separation is 542 mas and the total flux density is 48 mJy at 5 GHz. A best-fitting lens model with a singular isothermal ellipsoid results in large errors in the image positions. A significantly improved fit is obtained after the addition of a shear component, suggesting that the lensing system is more complex and may consist of multiple deflectors. The integrated radio spectrum of the background source indicates that it is a gigahertz peaked spectrum source. It may therefore be possible to resolve structure within the radio images with deep VLBI observations and thus to constrain the lensing mass distribution better.     

脉冲星PSR B0329+54的多波段观测

给出1999年3月12日至6月8日,使用国家天文观测中心乌鲁木齐南山站25m射电望远镜在0．327GHZ,1．5GHZ,2．3GHZ,4．8GHZ和8．4GHZ频段,对脉冲星PSRB0329＋54进行的多波段观测结果．PSRB0329＋54的辐射呈幂律谱,并出现频谱转折现象,低频段谱指数为1．59,高频段为2．45,平均谱指数为1．72．五个频段上的平均脉冲轮廓的角宽度和二个弱成分峰值间的角宽度都随频率的增加而减小．     

脉冲星Geminga MeV 脉冲辐射证据

利用直接解调方法分析COMPTELVPI数据,得到了脉冲星Geminga10-30MeV脉冲辐射存在的证据：全位相及分位相成像均得到了Geminga．分位相成像结果显示,光变曲线的峰值位于pulse1附近,而其它位相区域只能给出上限．由于成像分析不存在选择效应,该成像结果表明,Geminga在MeV能区仍存在脉冲辐射．虽然Geminga的弱MeV辐射使得很难就VP1数据作时间分析,但仍得到了一些周期信号的迹象,并且与成像结果不相矛盾．进一步考察EGRET观测Geminga在30MeV以上的强度比Pulse2／Pulse1,发现在VP1观测的较低能区,Pulse1有渐强于Pulse2的趋势,这和我们在MeV能区的成像及时间分析结果相一致．成像得到的流强表明,Geminga的能谱至少在10MeV以上不应出现偏折．     

Starburst galaxies and structure in the submillimetre background towards the Hubble Deep Field

We use an 850-μm SCUBA map of the Hubble Deep Field (HDF) to study the dust properties of optically-selected starburst galaxies at high redshift. The optical/infrared (IR) data in the HDF allow a photometric redshift to be estimated for each galaxy, together with an estimate of the visible star-formation rate. The 850-μm flux density of each source provides the complementary information: the amount of hidden, dust-enshrouded star formation activity. Although the 850-μm map does not allow detection of the majority of individual sources, we show that the galaxies with the highest UV star-formation rates are detected statistically, with a flux density of about S ₈₅₀=0.2 mJy for an apparent UV star-formation rate of 1  h ⁻² M_⊙ yr⁻¹. This level of submillimetre output indicates that the total star-forming activity is on average a factor of approximately 6 times larger than the rate inferred from the UV output of these galaxies. The general population of optical starbursts is then predicted to contribute at least 25 per cent of the 850-μm background. We carry out a power-spectrum analysis of the map, which yields some evidence for angular clustering of the background source population, but at a level lower than that seen in Lyman-break galaxies. Together with other lines of argument, particularly from the NICMOS HDF data, this suggests that the 850-μm background originates over an extremely wide range of redshifts – perhaps 1≲ z ≲6.