CDFS天区中喑蓝星系的测光红移研究

从COMBO-17数字巡天数据里,选择了CDFS(Chandra Deep Field South)天区中1231个测光红移在0.1～0.3之间的暗蓝星系作为样本,研究了这些星系分别在只有光学波段和光学加近红外波段数据情况下做测光红移得到的红移分布,以及这些星系在静止参考系下的能谱分布(Spectral Energy Distributions,SEDs)特征.结果表明有183个星系在利用光学加近红外波段数据做测光红移时得到的红移大于1.2,它们的误差为0.046,提高测光的信噪比也有利于区分这类被光学波段误认为低红移的星系.这些暗蓝星系中高红移星系的观测近红外流量相对于光学流量有上升的趋势,而低红移星系的观测近红外流量相对于光学流量有下降的趋势.     

A Study on the Photometric Redshifts of Faint Blue Galaxies in CDFS

From the COMBO-17 digital sky survey data, 1,231 faint blue galaxies with photometric redshifts of 0.1 < z < 0.3 in the sky region CDFS (Chandra Deep Field South) are selected as the sample. We have studied the distributions of the photometric redshifts of these sample galaxies, in the conditions that the photometric redshifts are obtained respectively by using only optical data and by using both optical and near-infrared data. The results indicate that there are 183 galaxies whose photometric redshifts derived from both optical and infrared data are greater than 1.2, that the rms error of the derived photometric redshifts is 0.046, and that to increase the photometric SNR is also helpful for discriminating those misjudged low-redshift galaxies by using only the optical data. We have studied as well the typical spectral energy distributions (SEDs) of these galaxies in the reference system at rest. It is found that for the high-redshift galaxies the observed near-infrared flux tends to be greater than the optical flux, while for the low-redshift galaxies the observed near-infrared flux tends to be less than the optical flux.     

Cooling Radius vs. Absorption Size of Galaxies

The discussion of the relationship between cooling radius in two-phaseadiabatic halo models and observationally established maximal radiusof absorption in luminous galaxies at low redshift is presented. It isof paramount importance that any viable model of the halo is able toreproduce empirical value of the absorption cross-section of normalgalaxies and its scaling with luminosity. Several ways for bringingthe theoretical and observational values into agreement are outlined.It is of great methodological importance to fully assess the difficultiesany model is likely to encounter when testing predicted extent ofabsorption and column density distribution against recently obtainedlow-redshift Ly absorption data.     

Quantized Redshifts of Galaxies: Stimulated Raman Scattering in Cold Intergalactic Rydberg Matter

That the redshifts for galaxies in the local supercluster are quantizedwas recently confirmedby Guthrie and Napier(A&Amp;Amp;A310 (1996) 353). These redshifts are here proposed to be due to stimulatedStokes Raman processes in intergalactic matter in the form of Rydberg Matter (RM). Rydberg Matteris an electronically excited material, as demonstrated by its use as laser medium in a thermally excitedultra-broadband tunable IR laser (Chem. Phys. Lett. 376 (2003) 812). Its existence in interstellar andintergalactic space is demonstrated by several observational results, notably the unidentified IR bands,that agree well with the emission from Rydberg Matter. A stimulated Raman process will allow theH I 21 cm radiation to proceed without deflection, in agreement with observation. Such redshiftswill be additive during the passage through space. The process in Rydberg Matter here proposed togive rise to the Stokes Raman process is excitation of electronic translational modes in the planarclusters forming the matter. The specific cluster sizes found in laboratory experiments give rise toa few differently sized redshift quanta, which is in good agreement with the observed quanta. Anexcitation level (principal quantum number) of Rydberg Matter in intergalactic space between 175and 200 gives the correct size of the redshift quanta.     

The Colour–Magnitude Relation and the Formation of Early-Type Galaxies

The colour-magnitude relation provides important information on the formation and evolution of cluster galaxies. By looking into the evolution of the relation as a function of redshift and using the small colour scatter around the relation in Coma, we put constraints on the star formation history and the galaxy merging history of cluster early-type galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Number Density of Sunyaev-Zeldovich Clusters of Galaxies

We study the conversion of a neutron star to a strange star as a possible energy source for gamma-ray bursts. We use different recent models for the equation of state of neutron star matter and strange quark matter. We show that the total amount of energy liberated in the conversion is in the range of &parl0;1-4&parr0;x1053 ergs (1 order of magnitude larger than previous estimates) and is in agreement with the energy required to power gamma-ray burst sources at cosmological distances.     

The Low Metallicity ISM of Dwarf Galaxies

The properties of the low metallicity environments of dwarf galaxies are studied through dust observations in conjunction with the FIR fine-structure cooling lines. There is a striking enhancement of the I[CII]/I(CO) in dwarf galaxies that is explained by the decreased attenuation of the UV light in molecular clouds. An important consequence is that a significant mass of the molecular gas mass inventory can be missed through CO observations alone. Modeling the infrared spectral energy distribution into submillimeter wavelengths in dwarf galaxies reveals the presence of very cold (∼ 8K) dust,which accounts for a large fraction of the dust mass, until now missed by models using IRAS observations alone. In spite of the striking defficiency of the mid-infrared aromatic band carriers, cooling in the photodissociation regions, via [CII] line emission is a very efficient process. This revised version was published online in September 2006 with corrections to the Cover Date.     

The Colour–Magnitude Relation of Early-Type Galaxies in the Hubble Deep Field North

We present the rest-frame colour–magnitude diagram for 35 early-type galaxies in the Hubble Deep Field with median redshift 0.9.Although with considerable scatter, a red sequence well described by the passive evolution of an intrinsically old stellar population is observed. Comparison with the passively evolved colour–magnitude relation of the rich Coma Cluster (z = 0.023) indicates that at least ∼1/2 of the early-type galaxies in the field at this redshift are as old as those in rich clusters. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Evolution of Star-Forming Galaxies: The SFR Density of the Universe

The evolution of the Star Formation Rate (SFR) density of the Universe as a function of look-back time is a fundamental parameter in order to understand the formation and evolution of galaxies. The current picture, only outlined in the last years, is that the global SFR density has dropped by about an order of magnitude from a redshift of z∼1.5 to the current value at z=0. Because these SFR density studies are now extended to the whole range in redshift, it becomes mandatory to combine data from different SFR tracers. At low redshifts, optical emission lines are the most widely used. Using Hα as current-SFR tracer, the Universidad Complutense de Madrid (UCM) Survey provided the first estimation of the global SFR density in the Local Universe. The Hα flux in emission is directly related to the number of ionizing photons and, modulo IMF, to the total mass of stars formed. Metallic lines like [OII]λ3727 and [OIII]λ5007 are affected by metallicity and excitation. Beyond redshifts z∼0.4, Hα is not observable in the optical and [OII]λ3727 or UV luminosities have to be used. The UCM galaxy sample has been used to obtain a calibration between [OII]λ3727 luminosity and SFR specially suitable for the different types of star-forming galaxies found by deep spectroscopic surveys in redshifts up to z∼1.5. These calibrations, when applied to recent deep redshift surveys confirm the drop of the SFR density of the Universe since z∼1 previously infered in the UV. However, the fundamental parameter that determines galactic evolution is mass, not luminosity. The mass function for local star-forming galaxies is critical for any future comparison with other galaxy populations of different evolutionary status. Hα velocity-widths for UCM galaxies indicate that besides a small fraction of 10¹⁰-10¹¹ M_⊙ starburst nuclei spirals, the majority have dynamical masses in the ∼10⁹ M_⊙ range. A comparison with published data for faint blue galaxies suggests that star-forming galaxies at z∼1 would have SFR per unit mass and burst strengths similar to those at z=0, but being intrinsically more massive. This revised version was published online in July 2006 with corrections to the Cover Date.     

Density and Radial Velocity Strucutre of the Hydra I Cluster of Galaxies

The investigation of the distributions of number densities, radial velocities and morphological types in the Hydra I cluster led us to the conclusion that this cluster possesses dominant substructures. This result is in agreement with former conclusions of different authors that substructures are a typical phenomenon for a high percentage of all clusters of galaxies. The galaxies inside the radius 60 from the cluster centre giv ea mean cluster redshift 3332±102 km/s and a velocity dispersion 679 ± 87 km/s.     

A Study of 2MASS Low Surface Brightness Galaxies

A study is being made of a sample of about 4,000 Low Surface Brightness (LSB) galaxies detected in the 2MASS all-sky near-infrared survey. These objects have similar central K-band surface brighnesses as optically selected LSBs. About 1,000 of them were observed in HI, and one third of these were detected. BVRI CCD photometry was obtained of 65 objects. These multi-wavelength data provide us with important information on a large, homogenous sample of LSB galaxies (e.g., colors, gas content). They will be used to construct models of the star formation histories and evolution of LSBs, and for a study of their Tully-Fisher (TF) relation, particularly to search for deviations from the ‘classical’ TF relation. This revised version was published online in September 2006 with corrections to the Cover Date.     

低面亮度星系的观测特性

光学、近红外、红外、紫外、射电等波段及CO的观测研究表明,低面亮度星系是相对没有充分演化的系统,气体成分比例较高,金属丰度和恒星形成率较低。这样的星系为研究星系的形成和演化提供了新的资料和证据。主要阐述了低面亮度星系的观测特性,包括探测与搜寻、选择效应对观测研究的影响、低面亮度星系的划分、星系的颜色和星族特征、星系的演化和恒星形成、金属丰度、数密度及光度密度;最后,介绍了几个特殊的低面亮度星系。     

Redshifts of the brightest X-ray QSO's

The plot of the X-ray luminosity (in 0.5–4.5 KeV band and for Friedmann universe withq ₀=+1) of the brightest X-ray QSO at each redshift against redshift shows that the X-ray luminosity increases more or less monotonically with redshift uptoz3. This result has been attributed to the selection effect known as the volume effect. When this selection effect is taken into account in the optical, radio and X-ray windows of the electromagnetic spectrum, a sample of the brightest X-ray QSO's is obtained which shows a small dispersion in X-ray luminosity: logL ₁=46.15±0.25. The redshift-X-ray flux density plot for this sample gives slopes of both regression lines which agree, at a confidence level of 95% or greater, with the slopes expected theoretically if the redshifts of the QSO's are cosmological in nature.     

Low Frequency Radio Emission and Star Formation in the Nuclei of Infrared Galaxies

Results of radio observations of luminous and ultraluminous infrared galaxies are discussed. The declining or flattening of the radio spectra of compact and (in some cases) extended sources found using interplanetary scintillation observations at 102 MHz is accounted for by absorption in thermal plasma, in agreement with the observed brightness of optical emission lines. It is argued that a region of violent star formation occupies the area of a molecular disc 1 kpc in size. The discrepancy between the linear sizes of the compact radio sources and the star forming regions is discussed.     

Redshifts and the Hubble diagrams of Quasi-Stellar Objects

In order to investigate the nature of the redshifts of QSOs, Hubble diagrams have been plotted. First, [log (cz),m _v ] pairs have been plotted for a sample of 252 QSOs. This sample has been drawn from the recent catalogue (Burbidgeet al., 1977) of 633 QSOs after excluding those for which either the redshifts are uncertain or theV magnitudes are not known accurately. Before plotting,K-correction has been applied to theV magnitudes. A least-squares linear fit has been obtained for this plot and, as a result, we get a slope of 0.165±0.012 against 0.2 expected theoretically on the basis of the assumption that the QSOs are at cosmological distances implied by their redshifts. The discrepancy in the value of the slope has been attributed partly to the uncertainty in theK-correction and partly to the evolutionary effect. In order to eliminate the uncertainty due to theK-correction, [log (cz), logf(H)] pairs have been plotted for a sample of 52 QSOs and a least-squares linear fit has been obtained which has a slope of –0.497±0.076, in close agreement with the theoretically expected value of –0.5. This lends support to the hypothesis that the redshifts of the QSOs are cosmological in nature. Finally, the evolutionary effect has been examined, and we conclude that the QSOs do evolve in luminosity in course of time.     

Properties of Galaxies in the Second Byurakan Survey. II. Characteristic Features of a Separate Sample of Galaxies

Some features of a sample of galaxies from the Second Byurakan Survey are discussed. Most of them are small galaxies with star formation. It is shown that different types of galaxies are in the Survey, with high, medium, and low levels of excitation and continua ranging from blue to relatively red. Many of the galaxies have absorption lines in their spectra; their continua are formed by stars in later spectral classes.     

An Unusual Group of Low Surface Brightness Galaxies in the Region 1046 + 65

Eine Gruppe von 11 Galaxien mit einer Flächenhelligkeit von etwa 26 mag/□” wurde in Richtung der M81-Gruppe entdeckt. Unter der Annahme gleicher Entfernung wie die M81-Gruppe stimmen ihre linearen Durchmesser (2–3 kpc) und ihre absoluten Helligkeiten (M_B = -11^m bis -12^m mit den Parametern der Zwerggalaxien der Lokalen Gruppe überein. Annahmen über die Stabilität der Zwerggruppe gegenüber M81 erlauben eine Abschätzung ihrer Gesamtmasse zu ℜ ≳ 1 · 10⁸ M ⊙ und ihres Masse-Leuchtkraftverhältnisses ℜ/L ≳ 1.2 (in Sonneneinheiten).     

旋涡星系密度波理论中Poisson积分的简化及应用

本文给出了旋涡星系密度波理论中Poisson积分的一种简化方法。这一简化的最重要应用在于利用它计算旋涡模式时可节省大量计算机时。此外本文还利用这种简化方法对一系列密度——引力势渐近关系进行了系统的数值检验。 用这一简化方法计算核函数比用未简化的核函数形式直接计算节省机时八十四倍。当在数值模式理论研究中大量计算Poisson积分时,应用本文提出的简化将有效地提高计算效率并保证足够高的精度。