Populations of Bright X-ray Sources in the Starburst Galaxies NGC 4038/4039

Assuming a naive star formation history, we construct synthetic X-ray source pop- ulations, using a population synthesis code, for comparison with the observed X-ray lumi- nosity function (XLF) of the interacting galaxies NGC 4038/4039. We have included high- and intermediate-mass X-ray binaries, young rotation-powered pulsars and fallback disk-fed black holes in modeling the bright X-ray sources detected. We find that the majority of the X-ray sources are likely to be intermediate-mass X-ray binaries, but for typical binary evolu- tion parameters, the predicted XLF seems to be steeper than observed. We note that the shape of the XLFs depends critically on the existence of XLF break for young populations, and suggest super-Eddington accretion luminosities or the existence of intermediate-mass black holes to account for the high luminosity end and the slope of the XLF in NGC 4038/4039.     

A Statistical Analysis of Point-like Sources in the Chandra Galactic Center Survey

The Chandra Galactic Center Survey detected ～ 800 X-ray point-like sources in the 2°× 0.8° sky region around the Galactic Center. We study the spatial and luminosity distributions of these sources according to their spectral properties. Fourteen bright sources detected are used to fit jointly an absorbed power-law model, from which the power-law photon index is determined to be ～2.5. Assuming that all other sources have the same power-law form, the relation between hardness ratio and HI column density NH is used to estimate the NH values for all sources. Monte Carlo simulations show that these sources are more likely concentrated in the Galactic center region, rather than distributed throughout the Galactic disk. We also find that the luminosities of the sources are positively correlated with their HI column densities, i.e., a more luminous source has a higher HI column density. From this relation, we suggest that the X-ray luminosity comes from the interaction between an isolated old neutron star and interstellar medium (mainly dense molecular clouds). Using the standard Bondi accretion theory and the statistical information of molecular clouds in the Galactic center, we confirm this positive correlation and calculate the luminosity range in this scenario,which is consistent with the observation (1032 - 1035 erg s-1).     

Chandra Observation of Point Sources in the X-Ray Elliptical Galaxy NGC 1407

With the Chandra pointing observation of about 50 ks, we have detected41 point sources in the X-ray relatively faint elliptical galaxy NGC 1407, most ofwhich appear to be low mass X-ray binaries. In luminosity flux units, these resolvedpoint sources contribute about 17.8% of the total emission of the galaxy in 0.3-10 keV. Of the remaining diffuse emission, about 53.4% (or 43.9% of total) may arisefrom unresolved point sources. We find six ultraluminous X-ray sources with lumi-nosities above 10~(39) erg s~(-1). This number is less than has been found in NGC 720,but more than in NGC 4697 and NGC 1553, so suggesting a possible correlationbetween the number of ULXs and the total X-ray luminosity of early-type galaxies.A central point-like source is detected whose luminosity (2.36±0.14×10~(39)erg s~(-1))is the highest among all resolved sources. However, because of its relatively lowhardness ratio, we speculate that it is not likely to be a low luminosity AGN.     

Stellar and HI Mass Functions Predicted by a Simple Preheating Galaxy Formation Model

According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.     

Disk Thicknesses and Some Parameters of 108 Non-Edge-On Spiral Galaxies

We present disk thicknesses, some other parameters and their statistics of 108 non-edge-on spiral galaxies. The method for determining the disk thickness is based on solving Poisson's equation for a disturbance of matter density in three-dimensional spiral galaxies. From the spiral arms found we could obtain the pitch angles, the inclination of the galactic disk, and the position of the innermost point (the forbidden region with radius r 0 to the galactic center) of the spiral arm, and finally the thickness.     

Searching for GeV gamma-ray emission from the bulge of M31

The three major large-scale, diffuse γ-ray structures of the Milky Way are the Galactic disk,a bulge-like GeV excess towards the Galactic center, and the Fermi bubble. Whether such structures can also be present in other normal galaxies remains an open question. M31, as the nearest massive normal galaxy, holds promise for spatially-resolving the γ-ray emission. Based on more than 8 years of Fermi-LAT observations, we use(1) disk,(2) bulge, and(3) disk-plus-bulge templates to model the spatial distribution of the γ-ray emission from M31. Among these, the disk-plus-bulge template delivers the best-fit, in which the bulge component has a TS value 25.7 and a photon-index of 2.57 ± 0.17, providing strong evidence for a centrally-concentrated γ-ray emission from M31, that is analogous to the Galactic center excess. The total0.2–300 GeV γ-ray luminosity from this bulge component is(1.16 ± 0.14) × 1038 erg s-1, which would require ～ 1.5 × 105 millisecond pulsars, if they were the dominant source. We also search for a Fermi bubble-like structure in M31 using the full dataset(pass8), but no significant evidence has been found.In addition, a likelihood analysis using only photons with the most accurate reconstructed direction(i.e.,PSF3-only data) reveals a 4.8 σ point-like source located at ～10 kpc to the northwest of the M31 disk, with a luminosity of(0.97 ± 0.27) × 1038 erg s-1 and a pho@ton-$i·nd3 ex of 2.31 ± 0.18. Lacking a counterpart on the southeast side of the disk, the relation between this point-like source and a bubble-like structure remains elusive.     

Velocity Space of Galactic O-B Stars

Based on the Hipparcos proper motions and available radial velocity data of O-B stars, we have re-examined the local kinematical structure of the young disk population of-1500 O-B stars not including the Gould-belt stars. A systematic warping motion of the stars about the direction to the Galactic center has been reconfirmed. A negative K-term implying a systematic contraction of stars in the solar vicinity has been detected. Two different distance scales are used in order to find out their impact on the kinematical parameters, and we conclude that the adopted distance scale plays an important role in characterizing the kinematical parameters at the present level of the measurement uncertainty.     

Kinematics and stellar population properties of the Andromeda galaxy by using the spectroscopic observations of the Guoshoujing Telescope

The Andromeda galaxy was observed by the Guoshoujing Telescope (formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope — LAMOST),during the 2009 commissioning phase.Due to the absence of standard stars for flux calibration,we use the photometric data of 15 intermediate bands in the Beijing-Arizona-Taipei-Connecticut (BATC) survey to calibrate the spectra.In total,59 spectra located in the bulge and disk of the galaxy are obtained.Kinematic and stellar population properties of the stell...     

The Inclination, Pitch Angle and Forbidden Radius of Spiral Arms of PGC 35105

We have studied some properties including surface brightness in the u, g, r, i, and z bands of the nearly face-on galaxy PGC 35105. By subtracting a model surface brightness distribution from the observed image we obtain the residual image that shows only the spiral arms freed from the contamination by the bulge. From this we measured the the inclination, pitch angle, and forbidden radius (identified with the innermost point of the arm) for each of the two arms; and that for each of the five observing bands. We found these three parameters are largely independent of the observing band.     

Do protostellar fountains shape the regional core mass function?

The emerging massive binary system associated with AFGL 961 signifies the latest generation of massive star and cluster formation in the Rosette Molecular Complex. We present the detection of a compact cluster of dusty cores toward the AFGL 961 region based on continuum imaging at 1.3 mm by the Submillimeter Array. The binary components of AFGL 961 are associated with the most intensive millimeter emission cores or envelopes, confirming that they are indeed in an early stage of evolution. The other massive cores, however, are found to congregate in the close vicinity of the central high-mass protostellar binary. They have no apparent infrared counterparts and are, in particular, well aligned transverse to the bipolar molecular outflows originating from AFGL 961. This provides evidence for a likely triggered origin of the massive cores. All 40 individual cores with masses ranging between 0.6 and 15 M⊙ were detected above a 3 σ level of 3.6 mJy beam-1 (or0.4 M⊙ ), based on which we derive a total core mass of 107 M⊙ in the AFGL 961 region. As compared to the stellar initial mass function, a shallow slope of 1.8 is, however, derived from the best fit to the mass spectrum of the millimeter cores with a prestellar and/or protostellar origin. The flatter core mass distribution in the AFGL 961 region is attributed here to dynamic perturbations from the massive molecular outflows that originated from the massive protostellar binary, which may have altered the otherwise more quiescent conditions of core or star formation, enhanced the formation of more massive cores and, as a result, influenced the core mass distribution in its close vicinity.     

日冕物质抛射的观测性质

综述日冕物质抛射的观测和持性，简短的前言之后，给出ＣＭＥ的发现经过及统计特性，着重介绍ＣＭＥ与其他种类太阳活动的相关。然后介绍ＣＭＥ的一般特性，包括可能与ＣＭＥ相关的一些物理过程的观测特性。初步结论是：ＣＭＥ是一种演变中的磁结构现象。     

日冕物质抛射研究进展

作为一种大尺度的太阳高能活动现象，日冕物质抛射（ＣＭＥ）的发现令人瞩目，其强烈的行星际和地球物理效应更引起了天文、空间和地球物理学家的共同关注。在本文中介绍了自ＣＭＥ发现以来的２２年中观测和研究所取得的进展，以及它给太阳物理学带来的影响，并分析了研究工作所面临的困难和障碍，展望了ＣＭＥ研究的前景。     

X-ray active galactic nuclei in the core of the Perseus cluster

We present a study of the X-ray emission from the nuclei of galaxies observed in the core of the Perseus cluster in a deep exposure with Chandra . Point sources are found coincident with the nuclei of 13 early-type galaxies, as well as the central galaxy NGC 1275. This corresponds to all galaxies brighter than M _B > −18 in the Chandra field. All of these sources have a steep power-law spectral component and four have an additional thermal component. The unabsorbed power-law luminosities in the 0.5–7.0 keV band range from 8 × 10³⁸ to 5 × 10⁴⁰ erg s⁻¹. We find no simple correlations between the K -band luminosity, or the FUV and NUV AB magnitudes of these galaxies and their X-ray properties. We have estimated the black hole masses of the nuclei using the K -band   M _BH– L _{K bol}  relation and again find no correlation between black hole mass and the X-ray luminosity. Bondi accretion on to the black holes in the galaxies with minihaloes should make them much more luminous than observed.     

Radio properties of the Shapley Concentration – III. Merging clusters in the A3558 complex

We present the results of a 22-cm radio survey carried out with the Australia Telescope Compact Array (ATCA) covering the A3558 complex, a chain formed by the merging ACO clusters A3556–A3558–A3562 and the two groups SC 1327−312 and SC 1323−313, located in the central region of the Shapley Concentration. The purpose of our survey is to study the effects of cluster mergers on the statistical properties of radio galaxies and to investigate the connection between mergers and the presence of radio haloes and relic sources.
We found that the radio source counts in the A3558 complex are consistent with the background source counts. The much higher optical density compared with the background is not reflected as a higher density of radio sources. Furthermore, we found that no correlation exists between the local density and the radio source power, and that steep-spectrum radio galaxies are not segregated in denser optical regions.
The radio luminosity function for elliptical and S0 galaxies is significantly lower than for cluster early-type galaxies and for those not selected to be in clusters at radio powers log  P _1.4≳22.5, implying that the probability of a galaxy becoming a radio source above this power limit is lower in the Shapley Concentration compared with any other environment. Possible explanations will be presented.
The detection of a head–tail source in the centre of A3562, coupled with careful inspection of the 20-cm NRAO VLA Sky Survey (NVSS) and of 36-cm MOST observations, allowed us to spot two extended sources in the region between A3562 and SC 1329−313, i.e. a candidate radio halo at the centre of A3562 and low brightness extended emission around a 14.96-mag Shapley galaxy. The relation between these two extended galaxies and the ongoing group merger in this region of the Shapley Concentration are discussed.     

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.     

Chandra constraints on the thermal conduction in the intracluster plasma of A2142

In this Letter, we use the recent Chandra observation of Abell 2142 reported by Markevitch et al. to put constraints on thermal conduction in the intracluster plasma. We show that the observed sharp temperature gradient requires that classical conductivity has to be reduced at least by a factor of between 250 and 2500. The result provides a direct constraint on an important physical process relevant to the gas in the cores of clusters of galaxies.