The gaseous Halo of the Virgo Cluster Galaxy 45

Observations of the Virgo Cluster galaxy NGC 4569 in soft X-rays and in Hα reveal both an asymmetrically distributed hot gaseous halo and a giant filament of diffuse emission, respectively, extending from the same side of the disk, the latter one to at least 8.8 kpc. A deep longslit spectrum along the filament shows velocities systematically different from the systemic velocity of NGC 4569. With the inclination of the disk one can determine the Hα spur as a giant outflow in NGC 4569. This revised version was published online in August 2006 with corrections to the Cover Date.     

Radio Identifications of Markarian Galaxies and the Correlation between Radio and Far-Infrared Properties

By checking DSS optical images and NVSS radio images, 782 Markarian galaxies were identified to be NVSS radio sources. A comparison of the radio luminosity at 1.4 GHz and the far-infrared (FIR) luminosity for 468 "normal" galaxies shows a tight correlation. Most of the Seyfert galaxies and quasars follow the radio-FIR relation deduced from the "normal" galaxy sample, but with a somewhat larger scatter. A total 167 Markarian galaxies, comprising 100 "normal" galaxies, 66 Seyfert galaxies and one quasar, have either excess radio emission or much lower FIR spectral index α(25μm,60μm). These galaxies may be classified as "AGN-powered". For "normal" galaxies, the average q value (defined as the log ratio between FIR and radio luminosities) is 2.3. There seems a trend for q to slightly decrease with increasing radio luminosity. This may imply that the ongoing active star formation in galaxies with higher radio luminosities is more efficient in heating the cosmic-ray electrons.     

Galaxy Mergers and the Creation of Cluster S0 Galaxies

When and how red S0 galaxies were formed is a longstanding and noteworthy problem. Recent morphological and photometric studies of S0sin distant clusters of galaxies have revealed a smaller S0 population fraction and the existence of S0s with bluer colours, which suggests that some physical processes drive continuous creation of S0s with younger stellar populations in higher-redshift clusters. We propose here that the major mechanism for S0 creation is galaxy merging between two spirals of unequal masses. Our numerical simulations demonstrate that galaxy merging exhausts a large amount of the interstellar medium of two gas-rich spirals owing to the moderately enhanced star formation, and subsequently transforms the two into a single gas-poor S0 galaxy with structure and kinematics strikingly similar to those observed. This secondary S0 formation via unequal-mass merging thus provides an evolutionary link between a larger number of blue spirals observed in intermediate-redshift clusters and the red S0s prevalent in present-day ones. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Population of KPC-Scale Flat-Spectrum Radio Sources

In this paper we present a subsample of 55 flat-spectrum radio sources dominated by (∼ 100 mas) kpc-scale structure, selected from a parent sample of 1665 VLA sources. Most are core-jets and 23 are CSO/MSO candidates. Properties of the subsample are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the stratification of elements in the atmospheres of Globular Cluster and Halo B-stars

A theoretical check is performed to determine for the horizontal-branch stars the zone (in the H-R diagram) in which the surface convection is acting. A possible experimental test of the efficiency of the depletion mechanism is also proposed.At present at Osservatorio Astronomico, Bologna.Since RR Lyrae stars have surely extended convective envelopes we expected that at least a part of the blue H.B. stars would have surface convection.     

Comparisons of Jet Properties between GeV Radio Galaxies and Blazars

We compile a sample of spectral energy distributions(SEDs) of 12 GeV radio galaxies(RGs),including eight FR Ⅰ RGs and four FR Ⅱ RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification, as expected in the unification model, is found for the derived jet parameters between FR Ⅰ RGs and BL Lacertae objects(BL Lacs) and between FR Ⅱ RGs and flat spectrum radio quasars(FSRQs). However, on average FR Ⅰ RGs have a larger γb(break Lorentz factor of electrons) and lower B(magnetic field strength) than FR Ⅱ RGs, analogous to the differences between BL Lacs and FSRQs. The derived Doppler factors(δ) of RGs are on average smaller than those of blazars, which is consistent with the unification model such that RGs are the misaligned parent populations of blazars with smaller δ. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carried by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs.However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for GeV RGs and blazars in both the observer and co-moving frames, indicating that the "sequence" behavior among blazars, together with the GeV RGs, may be intrinsically dominated by jet power.     

On the Correlation between Radio Properties and Black Hole Mass of Quasars

The question whether the radio properties of quasars are related to the mass of the central black hole or the accretion rate is important for our understanding of the formation of relativistic jets, but no consensus has been reached from statistical analyses. Using two large quasar samples, one radio-selected, one optical-selected, we re-exarnined these relations and find that previous differences between radio- and optical- selected samples can be ascribed, at least partly, to the effect of the narrow line component. All previous claimed correlations are much weaker, if exist at all.     

Abell星系团A514的射电研究

用4km Ooty综合孔径射电望远镜,来研究Abell星系团A514在326.5MHz上的射电结构。该文给出了A514星系团中四个射电星系(射电源)的射电图,并作了初步分析,得出射电星系的某些结构特性及其物理参数。     

射电选和X射线选BL Lacertae天体的射电性质

收集了射电选和X射线选BL Lac天体的射电数据(包括核和延展光度), 并计算了它们的核主导系数R.研究显示: 射电选BL Lac(RBLs)天体的总射电光度是X射线选BL Lac(XBLs)天体的2个量级.详细分析得到这种差别主要是来自于核光度的差别因为延展光度差别只有1个量级.研究RBLs和XBLs的核(延展元)光度与核主导系数之间的关系, 发现延展元光度与核主导系数负相关, 而核(总)光度几乎与核主导系数没有相关.     

The Connection between Spheroidal Galaxies and QSOs

In view of the extensive evidence of tight inter-relationships between spheroidal galaxies (and galactic bulges) with massive black holes hosted at their centers, a consistent model must deal jointly with the evolution of the two components. We describe one such model, which successfully accounts for the local luminosity function of spheroidal galaxies, for their photometric and chemical properties, for deep galaxy counts in different wavebands, including those in the (sub)-mm region which proved to be critical for current semi-analytic models stemming from the standard hierarchical clustering picture, for clustering properties of SCUBA galaxies, of EROs, and of LBGs, as well as for the local mass function of massive black holes and for quasar evolution. Predictions that can be tested by surveys carried out by SIRTF are presented. This revised version was published online in September 2006 with corrections to the Cover Date.     

The Structure of the Galactic Halo

We used the star counts in 21 BATC fields obtained with the National Astronomical Observatories (NAOC) 60/90 cm Schmidt Telescope to study the structure of the Galactic halo.Adopting a de Vaucouleurs γ/4 law halo,we found that the halo is somewhat flatter (c/a～0.4) towards the Galactic center than in the anticentre and antirotation direction (c/a ＞ 0.4).We also notice that the axial ratios are smaller (flatter) towards the low latitude fields than the high latitude fields,except for a few fields.We provide robust limits on the large-scale flattening of the halo.Our analysis shows that the axial ratio of the halo may vary with distance and the observation direction.At large Galactocentric radii,the halo may not have a smooth density distribution,but rather,it may be largely composed of overlapping streams or substructures,which provides a support for the hybrid formation model.     

The Connection of Solar Wind Parameters with Radio and UV Emission from Coronal Holes

This paper presents the results of a comparison between observations of coronal holes in UV (SOHO EIT) and radio emission (17, 5.7 GHz, 327 and 150.9 MHz, from NoRH, SSRT and Nançay radioheliographs), and solar wind parameters, from ACE spacecraft data over the period 12 March?–?31 May 2007. The increase in the solar wind velocity up to ～?600 km?s^?1 was found to correlate with a decrease in the UV flux in the central parts of the solar disk. A connection between the parameters of the radio emission from three different layers of the solar atmosphere and the solar wind velocity near the Earth’s orbit was discovered. Such a connection is suggestive of a common mechanism of solar wind acceleration from chromospheric heights to the upper corona.     

The Substellar Population in the Young σ Orionis Cluster, Spatial Distribution

We review different surveys, in the optical and infrared, conducted in the very young (age 1–8 Myr), nearby (d ～ 350 pc) σ Orionis cluster aimed to characterize the substellar population. We describe spectral characteristics of very low mass stars, brown dwarfs and planetary mass objects in the cluster with spectral types from K7 to T6. We study the spatial distribution of the substellar population detected in a IZJ survey covering an area of 1.12 deg.² We find that the radial distribution of substellar objects can be well fitted by an exponential law (ρ = ρ_o e ^?r/ro ), with a central density (ρ _o ) of 0.26 ± 0.03 objects/arcmin² and a characteristic radius (r _o) of 8.8 arcmin ± 0.6 (equivalent to 0.90 ± 0.06 pc at the distance of the cluster). We discuss the presence of possible inhomogeneities in this distribution due to the existence of subclustering. We also compare the spatial distribution of the substellar population with previously known stars in the cluster. We report the initial mass spectrum in the substellar domain.     

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Goniopolarimetric Properties and Radio Source Locations

We have performed a statistical analysis of a large number of Type III radio bursts observed by STEREO between May 2007 and February 2013. Only intense, simple, and isolated cases have been included in our data set. We focused on the goniopolarimetric (GP, also referred to as direction-finding) properties at frequencies between 125 kHz and 2 MHz. The apparent source size γ is very extended (≈?60^°) for the lowest analyzed frequencies. Observed apparent source sizes γ expand linearly with a radial distance from the Sun at frequencies below 1 MHz. We show that Type III radio bursts statistically propagate in the ecliptic plane. The calculated positions of radio sources indicate that scattering of the primary beam pattern plays an important role in the propagation of Type III radio bursts in the interplanetary medium.     

The Nature of the Faint Radio Source Population and Star Formation History derived from Sub-MJY Surveys

We present new results on the nature of the faint radio galaxy population obtained from a deep identification study in the Marano Field. This work represents the highest identification fractions attained to date in literature for sub-mJy radio samples. Star-forming galaxies constitute a significant fraction of the optical counterparts of sub-mJy radio sources, although they are not the dominant identification class (as formerly believed). We also present a new determination of the co-moving star formation density from z=0 to z?0.35 using the radio luminosity function of star-forming galaxies. For the local determination, we used a sample of 231 spiral galaxies taken from the B≤12 Revised Shapley-Ames Catalogue, while for the non-local determination, we used a sample of87 star-forming galaxies taken from the Benn et al. (1993) sample. The inferred local star formation rate is about twice as great as the H_α estimate, while the intermediate 0.05<z<0.35 star formation rate is consistent with coeval ultraviolet and H_α estimates. This is due to large-scale structure, rarely accounted for in estimates of the cosmic star formation history; the situation could improve significantly with deep moderate-area radio surveys.     

星系团Abell 2199的恒星形成性质

通过对近邻星系团Abell 2199中290颗成员星系进行形态分类,研究这些星系的恒星形成率及其与形态和相关物理特性之间的关系.该星系团中星系的特征恒星形成率与Ha等值宽度、星系光谱在4000A处的跃变程度以及星系所包含的恒星质量之间有较强的相关性.这些星系的恒星形成活动没有表现出明显的环境效应,表明该星系团仍处在剧烈的动力学演化阶段,远没有达到动力学平衡.     

The (sub)Structure of the Halo

The fossil record of the Milky Way indicates an evolution including periodic accretions of smaller galaxies and clusters, consistent with hierarchical models of galaxy formation. I discuss three observational programs that demonstrate that the phase space distribution of stars, clusters and dwarf galaxies in the Galactic halo contains degrees of substructure left by the débris of tidally disrupted stellar systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

星系团PKS 0745-191中射电气体对X射线气体的加热

对星系团中相对论性粒子的能量演化做了数值计算，在此基础上，联合分析Chandra卫星数据和VLA射电观测结果，计算了星系团PKS0745-191中高能射电气体对X射线气体的加热作用，发现在射电气体幂律谱能量下限为0.001erg时，射电气体对X射线气体的加热不足以补充X射线气体的辐射能损．然后在计算研究了不同能量下限时射电气体对X射线气体的加热作用，并估计了射电气体的能量下限．     

星系团PKS 0745-191中射电气体与X射线气体的相互作用

利用星系团PKS 0745—191中心区域的Chandra数据,研究了在中心星系的西边且沿着射电结构而分布的一团明亮X射线气体的性质,发现这团气体是低温而高密的;另由射电观测计算发现射电气体在中心星系的西边压强梯度要大于东边,这说明那团 X射线冷气体与射电气体之间存在相互作用．该冷气体可能是由射电浮力泡从中心星系带出;或者是外围冷气体受到了射电气体的支撑及扰动而形成．进一步,假设气体处在压强重力平衡状态,计算了中心区域的X射线气体的体积占有率为b=0．69±0．28,并且讨论了射电气体所包含的相对论性粒子的性质以及射电气体膨胀对冷流的影响．