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1.
Lucio Mayer Fabio Governato Monica Colpi Ben Moore Thomas R. Quinn Carlton M. Baugh 《Astrophysics and Space Science》2001,276(2-4):375-382
We study the evolution of galaxy satellites with high resolutionN-body simulations. Satellites are modelled as replicas of typical low and high surface brightness galaxies (LSBs and HSBs).
Encounters on high eccentricity orbits (as typical in hierarchical models of galaxy formation) strip LSBs of most of their
stars and tend to decrease their surface brightness. In contrast, bar instability in HSBs leads to substantial loss of angular
momentum of the stellar component and to an increase in central surface brightness. In both cases the remnant resembles a
spheroidal galaxy with an exponential surface brightness profile. A simple modelling of colour evolution and interaction-driven
star formation gives M/L ratios for the remnants that are roughly consistent with observations. These results suggest an evolutionary scenario for
the dwarf galaxies in our Local Group, faint dSphs being the descendants of LSBs and brighter dSphs/dEs being the final state
of HSB satellites.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
3.
J.P. Gardner 《Astrophysics and Space Science》1999,267(1-4):343-351
We present deep galaxy number counts and colours of K—band selected galaxy surveys. We argue that primeval galaxies are present within the survey data, but have remained unidentified.
There are few objects with the colours of an L
* elliptical galaxy at a redshift of z ≈ 1, in contradiction to standard luminosity evolution models. We present K—band photometry of the objects in a spectroscopic redshift survey selected at 21 < B < 22.5. The absolute K magnitudes of the galaxies are consistent with the no-evolution or pure luminosity evolution models. The excess faint blue
galaxies seen in the B—band number counts at intermediate magnitudes are a result of a low normalization, and do not dominate the population until
B ≈ 25. Extreme merging or excess dwarf models are not needed at z < 1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
We review selected measurements of the galaxy luminosity function including the field, the local group, the local sphere,
nearby clusters (Virgo, Coma and Fornax) and clusters in general. We conclude that, excluding the super-luminous cD and D
galaxies, the overall cluster luminosity function is fully consistent with the field luminosity function over the magnitude
range in common (–22 ≤ M
B
–5log
h
0.68
≤ –17). We find that only in the core regions of clusters (r ≤ 300 kpc) does the overall form of the luminosity function show significant variation. However when the luminosity function
is subdivided by spectral type some further variations are seen. We argue that these results imply: substantial late infall,
efficient star-formation suppression, and the confinement of mass-changing evolutionary processes to the core regions only.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
B. Vollmer V. Cayatte C. Balkowski A. Boselli W.J. Duschl 《Astrophysics and Space Science》2001,276(2-4):459-465
We present new HI and CO data including velocity information of NGC 4548, an anaemic galaxy in the Virgo Cluster. The distribution
of the atomic gas shows a ring-like structure. The HI rotation curve is deduced and can be extrapolated inwards with the help
of the CO data. The derived molecular fraction decreases continuously up to a radius of about 40″ showing a rather sharp transition
between the molecular and the atomic disc. A three-dimensional visualization of the data cube permits us to detect a perturbation
of the velocity field in the northern part of the galaxy. In a first approach we reconstruct the possible sites of HI emission
with the help of a simple kinematical model in three dimensions. The reconstructed model shows a ridge which is believed to
be due to ram-pressure stripping. In addition, we show first results of a dynamical model to simulate the interaction between
the intra-cluster medium and the galaxy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Gerhard Hensler Daniel Tschöke Dominik Bomans Alessandro Boselli 《Astrophysics and Space Science》2003,284(2):467-470
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. 相似文献
7.
8.
We determine the mass profile of a synthetic cluster built from the combination of 59 nearby clusters observed in the ESO
Nearby Abell Cluster Survey (ENACS). We use ellipticals and S0s as tracers of the cluster potential, and solve the Jeans equation
assuming isotropic orbits. Such an assumption is justified by the analysis of the shape of the velocity distribution of ellipticals
and S0s. We find that the cluster mass profile is consistent with the Navarro, Frenk and White(NFW) model. We use this cluster
mass profile to search for equilibrium solutions for the other cluster galaxy populations: very bright ellipticals (M
R
≤–22+5 log h),early-type spirals (Sa-Sb), and late-type spirals and irregulars (Sbc-Ir), together with emission-line galaxies. We find
equilibrium solutions for both the early- and the late-spirals, but not for the very bright ellipticals. The dynamics of very
bright ellipticals is probably affected by dissipative processes which invalidate the use of the collisionless Jeans equation.
The equilibrium solution found for the early-spirals implies them to move on nearly-isotropic orbits. Late-spirals are instead
found to be on mildly radial orbits, with the radial anisotropy increasing outwards. We discuss the implications of these
results for the evolutionary histories of the different populations of cluster galaxies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
R. J. van Weeren M. Brüggen H. J. A. Röttgering M. Hoeft 《Journal of Astrophysics and Astronomy》2011,32(4):505-508
Galaxy clusters grow by mergers with other clusters and galaxy groups. These mergers create shocks within the intracluster
medium (ICM). It is proposed that particles can be accelerated to extreme energies within the shocks. In the presence of a
magnetic field these particles should then form large regions emitting synchrotron radiation, creating the so-called radio
relics. An example of a cluster with relics is CIZA J2242.8+5301. Here we present hydrodynamical simulations of idealized
binary cluster collisions with the aim of constraining the merger scenario for this cluster. We conclude that by using the
location, size and width of double radio relics we can set constraints on the mass ratios, impact parameters, time scales,
and viewing geometries of binary cluster merger events. 相似文献
10.
银河系的形成与演化是天体物理学研究的重大前沿课题,银河系的化学演化在其中更具有极其重要的地位。随着观测资料的不断积累和理论工作的不断深入,银河系化学演化的研究取得了一系列进展。在观测方面,从太阳附近区域,整个银盘,银晕和核球等方面简要回顾了银河系化学演化模型主要观测约束的近期结果;在化学演化模型方面,回顾了银河系化学演化研究的发展历程和近期进展,并对未来的研究进行了展望。 相似文献
11.
Abell 85是位于南半天区红移为0.055的cD星系团.基于前人的光谱观测数据和SDSS(Sloan Digital Sky Survey)数据,利用3σ方法筛选出该星系团的370个成员星系,并对其动力学情况进行了分析.从这些成员星系的空间分布和局域视向速度分布中,发现了该星系团含有4个明显的子结构,且正处于两两并合之中.这表明Abell 85处在动力学活跃的状态,远未达到动力学平衡. 相似文献
12.
Abell 85 is a cD cluster of galaxies with the redshift of 0.055 in the southern hemisphere. Based on the spectroscopic data obtained by predecessors and the data of the SDSS (Sloan Digital Sky Survey), 370 member galaxies of the cluster are sieved by means of the 3σ method and their dynamical states are analyzed. From the spatial distribution and the local line-of-sight velocity distribution of these member galaxies it is found that this cluster of galaxies contains 4 clear substructures and they are just in the process of pairwise coalescence. This shows that the cluster Abell 85 is in the actively dynamical state, far from reaching the dynamical equilibrium. 相似文献
13.
B. Guiderdoni 《Astrophysics and Space Science》2002,281(1-2):13-23
We review recent ideas on the evolution of galaxies. Two models are competing to explain the observational features: the monolithic
model in which galaxies assemble at high redshift, and evolve with little influence from the environment, and the hierarchical
model in which small galaxies progressively assemble to form bigger objects. We describe the basic features of the model of
hierarchical formation, and we try to valuate how the observations in the optical and infrared/submillimetre fit in the scenario.
Finally, we show a few results from a hybrid, N-body simulation + semi-analytic model of hierarchical formation that produces
detailed quantitative predictions to be compared to the data.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
14.
Peter Berczik Gerhard Hensler Christian Theis Rainer Spurzem 《Astrophysics and Space Science》2002,281(1-2):297-300
We present our recently developed 3-dimensional chemodynamical code for galaxy evolution. This code follows the evolution
of different galactic components like stars, dark matter and different components of the interstellar medium (ISM), i.e. a
diffuse gaseous phase and the molecular clouds. Stars and dark matter are treated as collisionless N-body systems. The ISM
is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse gas and a sticky particle scheme
for the molecular clouds. Additionally, the galactic components are coupled by several phase transitions like star formation,
stellar death or condensation and evaporation processes within the ISM. As an example we show the dynamical and chemical evolution
of a star forming dwarf galaxy with a total baryonic mass of 2 ċ 109 M⊙. After a moderate collapse phase the stars and the molecular clouds follow an exponential radial distribution, whereas the
diffuse gas shows a central depression as a result of stellar feedback. The metallicities of the galactic components behave
quite differently with respect to their temporal evolution as well as their radial distribution. Especially, the ISM is at
no stage well mixed.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
15.
Zhe Chen Jiang Zhang YanPing Chen WenYuan Cui Bo Zhang 《Astrophysics and Space Science》2006,306(1-2):33-39
The supernova yields of r-process elements are obtained as a function of the mass of their progenitor stars from the abundance patterns of extremely metal-poor stars on the left-side [{Ba/Mg}]--[{Mg/H}] boundary with a procedure proposed by Tsujimoto and Shigeyama. The ejected masses of r-process elements associated with stars of progenitor mass M
ms ≤ 18 M
⊙ are infertile sources and the SNe II with 20 M
⊙ ≤ M
ms ≤ 40 M
⊙ are the dominant source of r-process nucleosynthesis in the Galaxy. The ratio of these stars 20 M
⊙ ≤ M
ms ≤ 40 M
⊙
with compared to the all massive stars is about∼ 18%. In this paper, we present a simple model that describes a star's [r/Fe] in terms of the nucleosynthesis yields of r-process elements and the number of SN II explosions. Combined the r-process yields obtained by our procedure with the scatter model of the Galactic halo, the observed abundance patterns of the metal-poor stars can be well reproduced. 相似文献
16.
We investigate numerically the chemodynamical evolution of major disc–disc galaxy mergers in order to explore the origin of
the mass-dependent chemical, photometric and spectroscopic properties observed in elliptical galaxies. We investigate especially
the dependence of the fundamental properties on merger progenitor disc mass (M
d). Three main results are obtained in this study:– More massive (luminous) ellipticals formed by galaxy mergers between more
massive spirals have higher metallicity (Z) and thus show redder colours; the typical metallicity ranges from ∼ 1.0 solar abundance (Z∼ 0.02) for ellipticals formed by mergers with M
d = 1010
M
⊙to ∼ 2.0 solar (Z∼ 0.04) for those with M
d= 1012
M
⊙.– Both the Mg2 line index in the central part of ellipticals (R ≤ 0.1 R
e) and the radial gradient of Mg2 (δ Mg2 / δ log R) are more likely to be larger for massive ellipticals. δ Mg2 / δ log R correlates reasonably well with the central Mg2 in ellipticals. For most of the present merger models, ellipticals show a positive radial gradient of the Hβ line index. – Both M/L
B and M/L
K (where M, L
B, and L
K are the total stellar mass of galaxy mergers, the B-band and the K-band luminosities, respectively) depend on galactic mass in such a way that more massive ellipticals have larger M/L
B and smaller M/L
K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
18.
M.D. Gregg M.J. Drinkwater M.J. Hilker Steven Phillipps J. Bryn Jones Henry C. Ferguson 《Astrophysics and Space Science》2003,285(1):113-117
We have discovered a new type of galaxy in the Fornax Cluster: `ultra-compact' dwarfs (UCDs). The UCDs are unresolved in ground-based
imaging and have spectra typical of old stellar systems. Although the UCDs resemble overgrown globular clusters, based on
VLT UVES echelle spectroscopy, they appear to be dynamically distinct systems with higher internal velocity dispersions and
M/L ratios for a given luminosity than Milky Way or M31 globulars. Our preferred explanation for their origin is that they
are the remnant nuclei of dwarf elliptical galaxies which have been tidally stripped, or `threshed' by repeated encounters
with the central cluster galaxy, NGC1399. If correct, then tidal stripping of nucleated dwarfs to form UCDs may, over a Hubble
time, be an important source of the plentiful globular cluster population in the halo of NGC1399, and, by implication, other
cD galaxies. In this picture, the dwarf elliptical halo contents, up to 99% of the original dwarf luminosity, contribute a
significant fraction of the populations of intergalactic stars, globulars, and gas in galaxy clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
A composite sample of NIR-selected galaxies having extended multicolor coverage has been used to probe the cosmological evolution
of the blue luminosity function and of the stellar mass function. The bright fraction of the sample has spectroscopic redshifts,
and the remaining fraction well-calibrated photometric redshifts. The resulting blue luminosity function shows an increasing
brightening with redshift respect to the local luminosity function. Hierarchical CDM models predictions are in agreement only
at low and intermediate redshifts but fail to reproduce the observed brightening at high redshifts (z ∼ 2–3). This brightening marks the epoch where starburst activity triggered by galaxy interactions could be an important
physical mechanism for the galaxy evolution. At the same time the NIR galaxy sample has been used to trace the evolution of
the cosmological stellar mass density up to ∼3. A clear decrease of the average mass density is apparent with a fraction ∼15%
of the local value at z ∼ 3. UV bright star-forming galaxies are substancial contributors to the evolution of the stellar mass density. Although
these results are globally consistent with Λ–CDM scenarios, they tend to underestimate the mass density produced by more massive
galaxies present at z > 2. 相似文献
20.
Kenji Bekki 《Astrophysics and Space Science》2001,276(2-4):847-850
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. 相似文献