共查询到20条相似文献，搜索用时 31 毫秒
1.
Duncan A. Forbes Antonis E. Georgakakis Jean P. Brodie 《Monthly notices of the Royal Astronomical Society》2001,325(4):1431-1440
The presence of two globular cluster subpopulations in early-type galaxies is now the norm rather than the exception. Here we present two more examples for which the host galaxy appears to have undergone a recent merger. Using multi-colour Keck imaging of NGC 1052 and 7332 we find evidence for a bimodal globular cluster colour distribution in both galaxies, with roughly equal numbers of blue and red globular clusters. The blue ones have similar colours to those in the Milky Way halo and are thus probably very old and metal-poor. If the red globular cluster subpopulations are at least of solar metallicity, then stellar population models indicate young ages. We discuss the origin of globular clusters within the framework of formation models. We conclude that recent merger events in these two galaxies have had little effect on their overall globular cluster systems. We also derive globular cluster density profiles, global specific frequencies and, in the case of NGC 1052, radial colour gradients and azimuthal distribution. In general these globular cluster properties are normal for early-type galaxies. 相似文献
2.
Duncan A. Forbes Carl J. Grillmair Williger Elson & Jean P. Brodie 《Monthly notices of the Royal Astronomical Society》1998,293(3):325-336
The Fornax cluster galaxies NGC 1399 and NGC 1404 are ideal for studying the effects of a cluster environment on globular cluster systems. Here we present new optical imaging of these two galaxies from both the Hubble Space Telescope 's Wide Field and Planetary Camera 2 and the Cerro Tololo Inter-American Observatory 1.5-m telescope. The combination of both data sets provides a unique insight on the spatial and colour distribution of globular clusters. From B − I colours, we find that both galaxies have a broad globular cluster metallicity distribution that is inconsistent with a single population. Two Gaussians provide a reasonable representation of the metallicity distribution in each galaxy. The metal-rich subpopulation is more centrally concentrated than the metal-poor one. We show that the radial metallicity gradient can be explained by the changing relative mix of the two globular cluster subpopulations. We derive globular cluster surface density profiles, and find that they are flatter (i.e., more extended) than the underlying starlight. The total number of globular clusters and specific frequency are calculated to be N =5700±500, SN =11.5±1.0 for NGC 1399, and N =725±145, SN =2.0±0.5 for NGC 1404. Our results are compared with the expectations of globular cluster formation scenarios. 相似文献
3.
J. Gerssen 《Astronomische Nachrichten》2004,325(2):84-87
The high central stellar densities in globular clusters provide a unique environment to study the fundamental dynamical process of two‐body relaxation. This process is the main driver of the dynamical evolution in the center of a globular cluster and has a profound effect on the structure of the cluster and on its stellar environment. We have obtained stellar absorption line spectra with STIS to measure the radial velocities of individual stars in the crowded center of the globular cluster M15. These data increase the number of stars with known radial velocities within the central arcsec by a factor of about three and significantly improve the constraints on the mass distribution in M15. The data provide the most detailed look of the central structure of any globular cluster and show that there is a compact dark central mass component. Similar studies using ground based facilities can be efficiently performed by employing Integral Field Units. We have started a project to better constrain the central mass density in the globular cluster M3 using the GMOS‐IFU on Gemini North. The data will also allow us to better understand the central rotation which is neither explained nor predicted by any globular cluster model. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
We have obtained spectra for 103 published globular cluster candidates in the Sculptor group galaxies NGC 253 and 55. On the basis of radial velocities and digitized plate images, 14 globular clusters are identified in NGC 253 and one probable globular cluster is identified in NGC 55. The majority of the objects in the sample appear to be background galaxies. We have obtained and analysed COSMOS plate scans of NGC 253 and 55 and use these along with the spectroscopically identified clusters to define new samples of globular cluster candidates in the two galaxies which should have reduced contamination. 相似文献
5.
Priyamvada Natarajan Philip J. Armitage 《Monthly notices of the Royal Astronomical Society》1999,309(4):961-968
The radial distribution of globular clusters in galaxies is always less peaked to the centre than that of the halo stars. Extending previous work to a sample of Hubble Space Telescope globular cluster systems in ellipticals, we evaluate the number of clusters potentially lost to the galactic centre as the integrals of the difference between the observed globular cluster system distribution and the underlying halo light profile. In the sample of galaxies examined it is found that the initial populations of globular clusters may have been ∼30 per cent to 50 per cent richer than now. If these 'missing' globular clusters have decayed and have been partly destroyed in the very central galactic zones, they have carried there a significant quantity of mass that, plausibly, contributed to the formation and feeding of a massive object therein. It is relevant to note that the observed correlation between the core radius of the globular cluster system and the parent galaxy luminosity can be interpreted as a result of evolution. 相似文献
6.
Pauline Barmby Kathryn M. Perrett Terry J. Bridges 《Monthly notices of the Royal Astronomical Society》2002,329(2):461-464
The M31 globular cluster candidate has long been known to be an extremely red, non-stellar object. The first published spectrum of this object is used to confirm that it is a globular cluster belonging to M31, with rather typical values of and . Using the spectroscopic metallicity to predict the intrinsic colours, we derive a reddening value of , in good agreement with the value obtained using reddening-free parameters. The extinction-corrected magnitude of is (absolute magnitude , which makes it the most luminous globular cluster in M31. We examine van den Bergh's argument regarding the brightest and most-reddened globular cluster in M31; we find that the brightest clusters are more heavily reddened than average, but this can be explained by selection effects rather than a different R V in M31. 相似文献
7.
M. A. Beasley R. M. Sharples T. J. Bridges D. A. Hanes S. E. Zepf K. M. Ashman D. Geisler 《Monthly notices of the Royal Astronomical Society》2000,318(4):1249-1263
We have derived ages and metallicities from co-added spectra of 131 globular clusters associated with the giant elliptical galaxy NGC 4472. Based upon a calibration with Galactic globular clusters, we find that our sample of globular clusters in NGC 4472 span a metallicity range of approximately −1.6≤[Fe/H]≤0 dex. There is evidence of a radial metallicity gradient in the globular cluster system which is steeper than that seen in the underlying starlight. Determination of the absolute ages of the globular clusters is uncertain, but formally, the metal-poor population of globular clusters has an age of 14.5±4 Gyr and the metal-rich population is 13.8±6 Gyr old. Monte Carlo simulations indicate that the globular cluster populations present in these data are older than 6 Gyr at the 95 per cent confidence level. We find that within the uncertainties, the globular clusters are old and coeval, implying that the bimodality seen in the broadband colours primarily reflects metallicity and not age differences. 相似文献
8.
R. Capuzzo-Dolcetta I. Donnarumma 《Monthly notices of the Royal Astronomical Society》2001,328(2):645-652
We studied and compared the radial profiles of globular clusters and of the stellar bulge component in three galaxies of the Fornax cluster observed with the WFPC2 of the Hubble Space Telescope ( HST ). The stars are more concentrated toward the galactic centres than globular clusters, in agreement with what has already been observed in many other galaxies: if the observed difference is the result of evolution of the globular cluster systems starting from initial profiles similar to those of the halo–bulge stellar components, a relevant fraction of their initial mass (74, 47 and 52 per cent for NGC 1379, 1399 and 1404, respectively) should have disappeared in the inner regions. This mass has probably contributed to the nuclear field population, local dynamics and high-energy phenomena in the primeval life of the galaxy. An indication in favour of the evolutionary interpretation of the difference between the globular cluster system and stellar bulge radial profiles is given by the positive correlation we found between the value of the mass lost from the globular cluster system and the central galactic black hole mass in the set of seven galaxies for which these data are available. 相似文献
9.
R. Capuzzo-Dolcetta A. Vicari 《Monthly notices of the Royal Astronomical Society》2005,356(3):899-912
The present work extends and deepens previous examinations of the evolution of globular cluster orbits in elliptical galaxies, by means of numerical integrations of a wide set of orbits in five self-consistent triaxial galactic models characterized by a central core and different axial ratios. These models are valid and complete in the representation of regular orbits in elliptical galaxies. Dynamical friction is definitely shown to be an efficient cause of evolution for the globular cluster systems in elliptical galaxies of any mass or axial ratio. Moreover, our statistically significant sample of computed orbits confirms that the globular cluster orbital decay times are, at least for clusters moving on box orbits, much shorter than the age of the galaxies. Consequently, the mass carried into the innermost galactic region in the form of decayed globular clusters may have contributed significantly to feeding and accreting a compact object therein. 相似文献
10.
Integrated photometry of 91 galactic globular clusters was carried out with theUBV and DDO systems. A method to determine reddening is presented. Metal abundances were obtained by means of a calibration ofC(42–45)0 vs [Fe/H]. Thirteen other clusters whose metallicity values were made compatible with those observed here, were added to the sample totalizing a homogenous set of [Fe/H] estimates for 104 globular clusters. This sample is used to analyze the spatial distribution of metallicities. An estimate of the intrinsic metal abundance frequency distribution of the globular cluster system is provided. The chemical properties of the globular cluster system are compared with one-zone-chemical-enrichment models which take into account gas loss from star formation regions. It is concluded that these models cannot describe the complete chemical enrichment of the globular cluster system. 相似文献
11.
评述了球状星团系统研究中的比频、金属度和质量谱三大问题，就目前的认识和存在的问题进行了讨论。指出不同星系球状星团比频之间的差别表明了需要有各种不同的球状星团形成模型；球状星团金属度的分布表明球状星团可能有三个形成时期，分别与三类形成模型效应；尽管对数正态初始质量的数值模拟初步结果与观测结果符合得更好，然而幂函数的初始质量谱在物理上能很好地与球状星团形成联系起来。 相似文献
12.
以球状星团NGC (New General Catalogue) 104、NGC 5139、NGC 6121为实验样区, 选取了视差等10个恒星参数, 通过引入地学中的空间分析理论和相应的分析框架为定量描述球状星团成员星的空间分布特征提出了一种基于地学的研究范式. 通过计算全局和局部莫兰(Moran)指数得到球状星团成员星各恒星参数的空间分布特征. 研究结果表明: 球状星团NGC 104、NGC 5139、NGC 6121成员星的各恒星参数在总体上呈现出空间正相关特性, 表现出空间集聚特征, 但不同恒星参数之间存在差异; 局部空间分布也呈现聚集特征, 而不同的成员星呈现出不同的空间分布特性和趋势. 总体而言, 用地学空间相关分析系统地定量化描述球状星团成员星空间分布特征, 能够为球状星团的研究提供新的思路. 相似文献
13.
球状星团是银河系中最年老的天体之一，是储存着银河系早期演化珍贵信息的“化石”．球状星团的天体测量，主要包括球状星因天区内恒星相对自行的测定，并由这些相对自行数据采用适当方法定出星团的绝对自行，或者直接测定绝对自行．利用这些自行数据，或者进一步与测光和视向速度数据结合，可以开展与球状星团的距离、运动、动力学状况、质量、年龄、演化等等以及银河系的结构和演化等有关的一系列重要的研究．在本文中对本世纪70年代中期以来在球状星团相对自行测定和成员概率估计、内部运动检测、绝对自行测定和空间运动研究这三方面取得的成果和进展以及存在的问题作了评述． 相似文献
14.
15.
Montegriffo Bellazzini Ferraro Martins Sarajedini & Fusi Pecci 《Monthly notices of the Royal Astronomical Society》1998,294(2):315-326
We present deep V - and I -band CCD photometry of the globular cluster Terzan 8, recently found to be a member of the globular cluster system of the Sagittarius dwarf spheroidal galaxy. We accurately estimate the metallicity of Terzan 8, and provide the first direct determination of the colour excess toward this cluster. Our robust age estimate confirms that this cluster is indeed coeval with typical Galactic globulars of comparable metal content, and thus it is probably significantly older than at least two other Sagittarius clusters, Terzan 7 and Arp 2. The implications of this result on the star formation history of the Sagittarius galaxy are briefly discussed. 相似文献
16.
Markus Kissler-Patig Duncan A. Forbes & Dante Minniti 《Monthly notices of the Royal Astronomical Society》1998,298(4):1123-1132
The discovery of protoglobular cluster candidates in many present-day mergers allows us to understand better the possible effects of a merger event on the globular cluster system of a galaxy, and to foresee the properties of the end-product. By comparing these expectations with the properties of globular cluster systems of elliptical galaxies at the present time we can constrain merger models. The observational data indicate that (i) every gaseous merger induces the formation of new star clusters, and (ii) the number of new clusters formed in such a merger increases with the gas content of the progenitor galaxies. Low-luminosity (about M V > −21), discy ellipticals are generally thought to be the result of a gaseous merger. As such, new globular clusters are expected to form but have not been detected to date. We investigate various reasons for the non-detection of subpopulations in low-luminosity ellipticals, i.e. absence of an old population, absence of a new population, destruction of one of the populations and, finally, an age–metallicity conspiracy that allows old and new globular clusters to appear indistinguishable at the present epoch. All of these possibilities lead us to a similar conclusion, namely that low-luminosity ellipticals did not form recently ( z < 1) in a gas-rich merger, and might not have formed in a major merger of stellar systems at all. High-luminosity ellipticals do reveal globular cluster subpopulations. However, it is difficult to account for the two populations in terms of mergers alone and, in particular, we can rule out scenarios in which the second subpopulation is the product of a recent, gas-poor merger. 相似文献
17.
A. Sollima 《Monthly notices of the Royal Astronomical Society》2008,388(1):307-322
I present a simplified analytical model that simulates the evolution of the binary population in a dynamically evolving globular cluster. A number of simulations have been run spanning a wide range in initial cluster and environmental conditions by taking into account the main mechanisms of formation and destruction of binary systems. Following this approach, I investigate the evolution of the fraction, the radial distribution, the distribution of mass ratios and periods of the binary population. According to these simulations, the fraction of surviving binaries appears to be dominated by the processes of binary ionization and evaporation. In particular, the frequency of binary systems changes by a factor of 1–5 depending on the initial conditions and on the assumed initial distribution of periods. The comparison with the existing estimates of binary fractions in Galactic globular clusters suggests that significant variations in the initial binary content could exist among the analysed globular cluster. This model has been also used to explain the observed discrepancy found between the most recent N -body and Monte Carlo simulations in the literature. 相似文献
18.
Thomas J. Maccarone Mathieu Servillat 《Monthly notices of the Royal Astronomical Society》2008,389(1):379-384
We present the results of a deep radio observation of the globular cluster NGC 2808. We show that there are no sources detected within the core of the cluster, placing constraints on both the pulsar population of the cluster and the mass of a possible intermediate-mass black hole in NGC 2808. We compare the results for this cluster with other constraints on intermediate-mass black holes derived from accretion measures. With the exception of G1 in M 31 which has previously shown radio emission, even with considerably more conservative assumptions, only the clusters with the poorest of observational constraints are consistent with falling on the M BH –σ relation. This result is interpreted in terms of the fundamental differences between galaxies and globular clusters. 相似文献
19.
S. Ninkovica 《Astronomische Nachrichten》1985,306(4):237-239
A tidal radius determination for a globular cluster based on its density minimum, which is caused by the galactic tidal forces and derivable from a model of the Galaxy, is proposed. Results obtained on the basis of the Schmidt model for two clusters are in a satisfactory agreement with those obtained earlier by means of other methods. A mass determination for the clusters through the tidal redius, when the latter one is identified with the cluster perigalactic distance, yields unusually large mass values. Probably, the tidal radius should be identified with the instantaneous galactocentric distance. Use of models more recent than the Schmidt one indicates that a globular cluster may contain a significant portion of an invisible interstellar matter. 相似文献
20.
Daniel D. Carpintero Juan C. Muzzio Felipe C. Wachlin 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):159-168
As a first step towards a comprehensive investigation of stellar motions within globular clusters, we present here the results
of a study of stellar orbits in a mildly triaxial globular cluster that follows a circular orbit inside a galaxy. The stellar
orbits were classified using the frequency analysis code of Carpintero and Aguilar and, as a check, the Liapunov characteristic
exponents were also computed in some cases.
The orbit families were obtained using different start spaces. Chaotic orbits turn out to be very common and while, as could
be expected, they are particularly abundant in the outer parts of the cluster, they are still significant in the innermost
regions. Their relevance for the structure of the cluster is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献