共查询到20条相似文献,搜索用时 0 毫秒
1.
Chenggang Shu Zhijian Luo Mao-an Han Abraham C.-L. Chian Wen-Ping Chen Zhen-yu Wu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Taking a wide range of the initial conditions, including spatial density distribution and mass function etc, the dynamical evolution of globular clusters in the Milky Way is investigated in detail by means of Monte Carlo simulations. Four dynamic mechanisms are considered: stellar evaporation, stellar evolution, tidal shocks due to both the disk and bulge, and dynamical friction. It is found that stellar evaporation dominates the evolution of low-mass clusters and all four are important for massive ones. For both the power-law and lognormal initial clusters mass functions, we can find the best-fit models which can match the present-day observations with their main features of the mass function almost unchanged after evolution of several Gyr. This implies that it is not possible to determine the initial mass function only based on the observed ones today. Moreover, the dispersion of the modelled mass functions mainly depends on the potential wells of host galaxies with the almost constant peaks, which is consistent with current observations. 相似文献
2.
Jonathan E. Grindlay 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2923-2929
We review new Chandra and HST observations of the core collapsed cluster NGC 6397 as a guide to understanding the compact binary (CB) populations in core collapse globulars. New cataclysmic variables (CVs) and main sequence chromospherically active binaries (ABs) have been identified, enabling a larger sample for comparison of the Lx, Fx/FV and X-ray vs. optical color distributions. Comparison of the numbers of CBs with Lx 1031 erg s−1 in 4 core collapse vs. 12 King model clusters reveals that the specific frequency SX (number of CBs per unit cluster mass) is enhanced in core collapse clusters, even when normalized for their stellar encounter rate. Although core collapse is halted by the dynamical heating due to stellar (and binary) interaction with CBs in the core, we conclude that production of the hardest CBs – especially CVs – is enhanced during core collapse. NGC 6397 has its most luminous CVs nearest the cluster center, with two newly discovered very low luminosity (old, quiescent) CVs far from the core. The active binaries as well as neutron star systems (MSP and qLMXB) surround the central core. The overall CB population appears to be asymmetric about the cluster center, as in several other core collapse clusters observed with Chandra, suggesting still poorly understood scattering processes. 相似文献
3.
N.A. Webb D. Barret B. Gendre 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2930-2933
Using the new generation of X-ray observatories, we are now beginning to identify populations of close binaries in globular clusters, previously elusive in the optical domain because of the high stellar density. These binaries are thought to be, at least in part, responsible for delaying the inevitable core collapse of globular clusters and their identification is therefore essential in understanding the evolution of globular clusters, as well as being valuable in the study of the binaries themselves. Here, we present observations made with XMM-Newton of six globular clusters, in which we have identified neutron star low mass X-ray binaries and their descendants (millisecond pulsars), cataclysmic variables and other types of binaries. We discuss not only the characteristics of these binaries, but also their formation and evolution in globular clusters and their use in tracing the dynamical history of these clusters. 相似文献
4.
P.E.J. Nulsen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
Rapidly cooling gas is commonly found near the centres of clusters of galaxies. The structure of the resulting gas flows is reviewed. Total gas cooling rates of several hundred M yr−1 have been observed in a number of cases. Thermal instability and the ultimate fate of the cooled gas are discussed. The cooled gas could easily have formed a massive central galaxy. 相似文献
5.
N. Visvanathan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
Multiaperture photometry in V (5500Å), r (6738Å) and IV (10500Å) of 52 spirals in nearby clusters Virgo, Fornax and Grus and farther clusters Cancer, Zw 74-23 and Peg I in the redshift range up to 6000 Km s−1 was combined with HI width to derive three independant distances for each galaxy in these clusters.The plot between the mean distance of each cluster and its redshift, indicates the Hubble ratios of distant clusters Cancer, Zw 74-23 and Peg I are about 77 Km s−1 Mpc−1. Further, the Hubble ratios of distant clusters vary only from 76.3 to 78.9 Km s−1 Mpc−1 while those of nearby clusters Virgo, Fornax and Grus vary through a large range of 58.5 to 83.5 Km s−1 Mpc−1. We interpret these data by postulating a systematic motion toward Virgo for the Local Group.The best value for the global Hubble constant from farther and nearby clusters is derived as 74.3± 4 Km s−1 Mpc−1 and an average value of 289±60 Km s−1 for the infall velocity of the Local Group toward Virgo is also derived. 相似文献
6.
P.B. Marty S. Bardeau O. Czoske H. Ebeling J.P. Kneib R. Sadat I. Smail 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2509-2515
We present an analysis of seven clusters observed by XMM-Newton as part of our survey of 17 most X-ray luminous clusters of galaxies at z 0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using the public software FTOOLS and XMMSAS we have set up an automated pipeline to reduce the EPIC MOS and pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM-Newton deep spectro-imaging of these clusters allowed us to fit a standard β-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations. 相似文献
7.
Nicholas E. White 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2632-2636
The X-ray evolution of the luminosity of normal galaxies is primarily driven by the evolution of their X-ray binary populations. The imprints left by a cosmological evolution of the star formation rate (SFR) will cause the average X-ray luminosity of galaxies to appear higher in the redshift range 1–3. As reported by White and Ghosh [ApJ, 504 (1998) L31] the profile of X-ray luminosity with redshift can both serve as a diagnostic probe of the SFR profile and constrain evolutionary models for X-ray binaries. In order to observe the high redshift (z>3) universe in the X-ray band, it is necessary to avoid confusion from foreground field galaxies. We report on the predictions of these models of the X-ray flux expected from galaxies and the implications for the telescope parameters of future deep universe X-ray observatories. 相似文献
8.
H. Katayama K. Hayashida 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2519-2524
We investigate the dark matter distributions in the central region of two clusters of galaxies (A1835 and MKW3S) using Chandra data. N-body simulations in the standard cold dark matter (CDM) model predict the dark matter distribution shows a cuspy dark matter profile: ρ(r) ∝ r, with in the range 1–2, while observations of dwarf and low surface brightness galaxies seem to favor the presence of a relatively flat core: 0 < < 1. To investigate the dark matter distributions in the central region of clusters of galaxies, we analyze the Chandra data of A1835 and MKW3S with a deprojection method. We derive the mass profiles without the assumption of analytical models. We examine the inner slope of derived mass profiles assuming the dark matter profile is described with a power-law expression. The values of the slope are 0.95 ± 0.10 for A1835 and 1.33 ± 0.12 for MKW3S within the radius of 200 kpc. These are consistent with the result of the CDM simulations. However, within the radius of 100 kpc, the value of is less than unity for A1835 (0.47 ± 0.31). Our result implies that the central dark matter profile of some clusters cannot be described by CDM halos. 相似文献
9.
M. Guainazzi I. Barbarisi S. Bianchi P. Osuna J. Salgado 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):1998-2001
High-energy, high-resolution in the spatial and energy domains is crucial to derive the geometrical distribution and the physical properties of gas and dust surrounding Active Galactic Nuclei (AGN). These are, in turn, basic ingredients of any serious attempt to build an AGN structure model. We present in this paper CIELO-AGN, the first catalogue of ionized emission lines detected in the soft X-ray spectra of a sample of 69 nearby obscured AGN. This catalogue has been implemented according to an IVOA data model, and can be accessed through VO-compatible applications. 相似文献
10.
S.G. Anokhin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We present here new XMM-Newton observations of 3 relatively cool clusters at z ≈ 0.4, complemented by archival observations of 3 other clusters at similar redshift. We derived the M–T and R–T relations from the hydrostatic equation using an isothermal temperature distribution. 相似文献
11.
M. Kalinkov K. Stavrev I. Kuneva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
An attempt is made to compare optical properties of Abell clusters with X-ray sources. 相似文献
12.
J.S. Kaastra R. Lieu T. Tamura F.B.S. Paerels J.W. den Herder 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2504-2508
We discuss the detection of soft excess X-ray emission in a sample of 19 clusters of galaxies observed by XMM-Newton. In 6/19 clusters evidence for a soft X-ray excess is found. Four of these clusters show soft X-ray and O VII line emission from gas with a temperature of 0.2 keV. The centroid of this oxygen line is consistent with the redshift of the cluster. The intensity and spatial extend of the soft excess agrees with previous PSPC measurements. These observations are interpreted as emission from warm-hot intergalactic medium filaments, with density enhancements near the cluster centers, consistent with theoretical predictions. In the other two soft excess clusters a non-thermal origin is consistent with the data. 相似文献
13.
W.N. Brandt C. Vignali D.P. Schneider D.M. Alexander S.F. Anderson F.E. Bauer X. Fan G.P. Garmire S. Kaspi G.T. Richards 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2478-2485
X-ray studies of high-redshift (z > 4) active galaxies have advanced substantially over the past few years, largely due to results from the new generation of X-ray observatories. As of this writing X-ray emission has been detected from nearly 60 high-redshift active galaxies. This paper reviews the observational results and their implications for models of the first massive black holes, and it discusses future prospects for the field. 相似文献
14.
Chiho Matsumoto John R. Moore Karen M. Leighly Dirk Grupe Beverley J. Wills 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2566-2570
We present preliminary results from analyses of hard X-ray and optical observations of a soft X-ray selected sample. We created a small but complete sample with 20 of the softest and brightest objects with low Galactic absorption from the ROSAT bright soft X-ray selected radio-quiet AGN sample. This sample consists of 10 narrow-line Seyfert 1 galaxies and 10 broad-line Seyfert galaxies. We analyze ASCA data in the 0.6–10 keV band and optical spectra from ground-based telescopes. We investigate the photon indices in the hard X-ray band, soft excesses in the ASCA band, and optical emission line properties. The photon indices in the 2–10 keV band are nominal for both narrow-line Seyfert 1 galaxies and broad-line Seyfert 1 galaxies in each class compared with other heterogeneous samples. All of the narrow-line Seyfert 1 galaxies show soft excesses, but this component seems to be less significant for broad-line Seyfert 1 galaxies. There seems to be a trend of steeper X-ray spectra to be accompanied by narrower Hβ for narrow-line Seyfert 1 galaxies, but this is not extended to the larger velocity width regime of broad-line Seyfert 1 galaxies, and no clear trend is seen among them. 相似文献
15.
K.O. Mason G. Branduardi-Raymont P.M. Ogle M.J. Page E.M. Puchnarewicz N.J. Salvi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2610-2613
Long (>100 ks) observations of the bright Seyfert galaxies Mrk 766 and NGC 4051 have been obtained using XMM-Newton. The RGS 5–38 Å spectra reveal evidence of broad features. These can be modelled with relativistic emission lines coming from the immediate vicinity of a massive rotating black hole. Lines of OVIII, NVII and CVI are required to reproduce the spectrum of Mrk 766, whereas the spectrum of NGC 4051 can be modelled using a single, even broader OVIII line. Both Seyferts also exhibit broad iron line emission in the 2–8 keV range, and the data available thus far suggest that the strength of the low-energy emission lines and the strength of the iron line may be correlated. 相似文献
16.
Michael Loewenstein David S. Davis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):1972-1974
We discuss the elemental composition in the hot ISM of elliptical galaxies derived from new and recent X-ray spectral analysis in the context of new phenomenological models of their chemical evolution. Star formation histories, the IMF, the astrophysics of supernovae, and the nature of galactic winds impact the metal content and relative abundances in the hot ISM. We evaluate how X-ray spectroscopy may be utilized to deconstruct how elliptical galaxies, and the stellar populations that compose them, form and evolve, with an emphasis on present and future high resolution spectroscopic analysis. 相似文献
17.
S. Pellegrini L. Ciotti J.P. Ostriker 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The centers of elliptical galaxies host supermassive black holes that significantly affect the surrounding interstellar medium through feedback resulting from the accretion process. The evolution of this gas and of the nuclear emission during the galaxies’ lifetime has been studied recently with high-resolution hydrodynamical simulations. These included gas cooling and heating specific for an average AGN spectral energy distribution, a radiative efficiency declining at low mass accretion rates, and mechanical coupling between the hot gas and AGN winds. Here, we present a short summary of the observational properties resulting from the simulations, focussing on (1) the nuclear luminosity; (2) the global luminosity and temperature of the hot gas; (3) its temperature profile and X-ray brightness profile. These properties are compared with those of galaxies of the local universe, pointing out the successes of the adopted feedback and the needs for new input in the simulations. 相似文献
18.
T. Yoshioka A. Furuzawa S. Takahashi Y. Tawara S. Sato K. Yamashita Y. Kumai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2525-2529
We investigated properties of four isolated giant elliptical galaxies with extended X-ray halo using ASCA data. The derived size of X-ray halo, X-ray luminosity, and gravitational mass of the dark halo are unusually large those of X-ray halo of a single galaxy, but are typical for X-ray halos of groups and poor clusters of galaxies. The measured temperatures and abundances of the X-ray halo gas in these galaxies are also similar to those of the groups and poor clusters. Based on these results we identified these galaxies as “isolated X-ray overluminous elliptical galaxy” (IOLEG). The radial profiles of dark halo in these objects were derived from X-ray data. It is found that some are similar to those of compact groups while others are the same as those of normal ellipticals. The dark halos of lOLEGs are thus indistinguishable from those of groups (and poor clusters), which appears to be consistent with a widely believed idea that lOLEGs are a product of dynamical evolution of a compact group. However, mass-to-light ratios of IOLEGs (M200/LB 100–1000) are far greater than those of Hickson compact groups M200/LB 40–60). Since it is hard to consider that total optical luminosity of a compact group decreases by an order of magnitude in the course of dynamical evolution, such difference in the observed mass-to-light ratio between IOLEGs and Hickson compact groups strongly suggests that most IOLEGs have not evolved from compact groups which are observed at present. 相似文献
19.
Florence Durret Gastão B. Lima Neto 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We have analyzed XMM-Newton archive data for five clusters of galaxies (redshifts 0.223–0.313) covering a wide range of dynamical states, from relaxed objects to clusters undergoing several mergers. We present here temperature maps of the X-ray gas together with a preliminary interpretation of the formation history of these clusters. 相似文献
20.
Y. Haba Y. Terashima H. Kunieda K. Ohsuga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(1):174-179
We present the results of a systematic study of narrow-line Seyfert 1 galaxies (NLS1s) observed with XMM-Newton. The 2–12 keV X-ray spectra of NLS1s are well represented by a single power law with a photon index Γ ∼ 2. When this hard power law continuum is extrapolated into the low energy band, we found that all objects in our sample show prominent soft excess emission. This excess emission is well parameterized by the thermal emission expected from an optically thick accretion disk, and we found the following three peculiar features: (1) The derived disk temperatures are significantly higher than the expectation from a standard Shakura-Sunyaev accretion disk, if we assume a central mass of a black hole to be 106–8M⊙. (2) The temperatures are distributed within narrow range (ΔkT ∼ 0.08 keV) with an average temperature of 0.18 keV in spite of the range of four orders of magnitude in luminosity (1041–45 erg s−1). (3) We found a peculiar temperature–luminosity relation, where the luminosity seems to be almost saturated in spite of the significant change in temperature, during the observations of the most luminous NLS1 PKS 0558-504. These results strongly suggest that the standard accretion disk picture is no longer appropriate in the nuclei of NLS1s. We discuss a possible origin for the soft excess component, and suggest that a slim disk may be able to explain the observational results, if the photon trapping effect is properly taken into account. 相似文献