共查询到20条相似文献，搜索用时 0 毫秒
1.
Jesper Sommer-Larsen Martin Götz Laura Portinari 《Astrophysics and Space Science》2002,281(1-2):519-524
We have performed TreeSPH simulations of galaxy formation in a standard ΛCDM cosmology, including effects of star formation,
energetic stellar feedback processes and a meta-galactic UV field, and obtain a mix of disk, lenticular and elliptical galaxies.
The disk galaxies are deficient in angular momentum by only about a factor of two compared to observed disk galaxies. The
stellar disks have approximately exponential surface density profiles, and those of the bulges range from exponential to r
1/4, as observed. The bulge-to-disk ratios of the disk galaxies are consistent with observations and likewise are their integrated
B-V colours, which have been calculated using stellar population synthesis techniques. Furthermore, we can match the observed
I-band Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk galaxies is (M/L
I) ≃ 0.6–0.7. The ellipticals and lenticulars have approximately r
1/4 stellar surface density profiles, are dominated by non-disklike kinematics and flattened due to non-isotropic stellar velocity
distributions, again consistent with observations.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
2.
We are conducting a systematic study of a carefully selected sampleof nearby E/S0 galaxies and Sa bulges using the unique
panoramic integral-fieldspectrograph SAURON, mounted at the WHT. The goal of the SAURON projectis to fully map the gaseous/stellar
kinematics and the stellar populations of a representative sample of 80 early-type galaxies up to 1 Re,probing different environments
(clusters, field). These data, used in combination with existing ground-based and HST observations, and fed to the theoretical
machinery we have developed, will allow to determine theintrinsic dynamical structure of the galaxies. We will also measure
the masses of central black holes, relate the internal dynamics to the ageand metallicity of the stellar populations, and
establish the historyof metal enrichment as a function of Hubble type and environment. Some brief results on two targets observed
during the SAURON campaign will serve as an illustration of the unique and high quality data we are currently gathering.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
3.
O. A. Merkulova L. V. Shalyapina V. A. Yakovleva G. M. Karataeva 《Astronomy Letters》2008,34(8):542-550
We present the results of our study of the stellar kinematics in the elliptical galaxy UGC 5119, which has previously been suspected to be a polar-ring galaxy. We have detected a rapidly rotating disk in the central region (r ≤ 3.2 kpc) of the galaxy’s main body and found a radial velocity gradient along its minor axis (in the putative ring). We conclude that UGC 5119 is a medium-luminosity elliptical galaxy with a rapidly rotating disk component and a stellar (probably polar) ring. We have calculated the Lick indices of the Hβ, Mggb, Fe 5270, and Fe 5335 absorption lines and compared them with evolutionary synthesis models. Differences in the [Mg/Fe] ratios, metallicities, and ages of the stars have been found: the young stellar population with a solar [Mg/Fe] ratio and a high metallicity dominates in the circumnuclear region (r ≤ 1 kpc), while the old one with a low metal abundance dominates in the ring. 相似文献
4.
Abell 85 is a cD galaxy cluster in the southern hemisphere and has a redshift of 0.055. Based on the spectra of 242 member galaxies provided by the Sloan spectral survey data, using the stellar population constituents and star formation history of these member galaxies obtained from the population synthesis software STARLIGHT, we study the regularities of the variations of star formation properties of galaxies (such as the ages, metal abundances and star formation rates of the characteristic stellar populations) with the local surface density of galaxies. As revealed by the results, the galaxies situated in the highdensity environments of the central region of the cluster possess higher population ages and metal abundances, and their rates of star formation are rather low, the recent activities of star formation are obviously suppressed. Besides, the correlations of the galaxy metal abundance and speci?c star formation rate with the stellar mass are asserted. 相似文献
5.
DDO 68 (UGC 5340) is the second most metal-poor star-forming galaxy (12 + log(O/H) = 7.14). Its peculiar optical morphology
and its HI distribution and kinematics are indicative of a merger origin. We use the u, g, r, and i photometry based on the SDSS images of DDO 68 to estimate its stellar population ages. The Hα images of DDO 68 were used to select several representative regions without nebular emission. The derived colors were analyzed
by comparison with the PEGASE2 evolutionary tracks for various star formation (SF) scenarios, including the two extreme cases:
(i) an instantaneous starburst and (ii) continuous SF with a constant rate. The (u − g) and (g − r) colors for all of the selected regions are consistent with the scenario of several “instantaneous” SF episodes with ages
between ∼0.05 and ∼1 Gyr. The total mass of the visible stars in DDO 68 was estimated by comparing the colors and fluxes of
the observed stellar subsystems with PEGASE2 models to be ∼2.4 × 107
M
⊙. This accounts for ∼6% of the total baryonic mass of the galaxy. All of the available data are consistent with the fact that
DDO 68 is a very rare candidate for young galaxies. The bulk of its stars were formed during the recent (with the first encounter
∼1 Gyr ago) merger of two very gas-rich disks. DDO 68 is closest in its properties to cosmologically young low-mass galaxies.
This article was submitted by the authors in English. 相似文献
6.
Markus Samland 《Astrophysics and Space Science》2002,281(1-2):305-308
The formation of a disk galaxy within a slowly growing dark halo is simulated with a new chemo-dynamical model. The model
describes the evolution of the stellar populations, the multi-phase ISM and all important interaction. I find, that the galaxy
forms radially from inside-out and vertically from top-to-bottom. The derived stellar age distributions show that the inner
halo is the oldest component, followed by the outer halo, the triaxial bulge, the halo-disk transition region and the disk.
Despite the still idealized model, the final galaxy resembles present-day disk galaxies in many aspects. In particular, the
stellar metallicity distribution in the halo of the model resembles the one of M31. The bulge in the model shows, at least
two stellar subpopulations, an early collapse population and a population that formed later out of accreted disk mass. In
the stellar metallicity distribution of the disk, I find a pronounced ‘G-dwarf problem’ which is the result of a pre-enrichment
of the disk ISM with metal-rich gas from the bulge.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
7.
对于星系际弥散恒星的研究是分别从观测、数值模拟和半解析模型这三个方面进行的.现在已经在邻近星系团及中低红移处观测到弥散恒星,甚至在Virgo及Coma星系团中观测到了单个的弥散恒星.观测数据的积累使得人们能够从统计上了解星系际弥散恒星的性质.研究表明星系际弥散恒星围绕着星系团势阱中心呈椭球状对称分布,其在星系团恒星总质... 相似文献
8.
I. V. Chilingarian O. K. Sil’chenko V. L. Afanasiev Ph. Prugniel 《Astronomy Letters》2007,33(5):292-298
We report the discovery of young embedded structures in three diffuse elliptical galaxies (dE) in the Virgo cluster: IC 783,
IC 3468, and IC 3509. We performed 3D spectroscopic observations of these galaxies with the MPFS spectrograph at the 6-m Special
Astrophysical Observatory telescope and obtained spatially resolved distributions of kinematic and stellar population parameters
by fitting high-resolution PEGASE. HR synthetic single stellar populations (SSP) in pixel space. In all three galaxies, the
luminosity-weighted age of the nuclei (∼4 Gyr) is considerably younger than that of the population in the outer regions of
the galaxies. We discuss two possibilities for the formation of such structures—a dissipative merger event and a different
ram pressure stripping efficiency during two consecutive crossings of the Virgo cluster centre.
The article was translated by the authors. 相似文献
9.
10.
The purpose of our work is to strongly constrain the mass to light ratio in the disk of the flocculent isolated Sc type spiral
NGC 4414 using a combined high resolution interferometric CO(1-0) and HI rotation curve, and deep HST B-V-I images of the
galaxy. To identify the mass contributions of the visible – stellar and gaseous – components, we observed the rotation curve
with high resolution in the optical disk. The M/L ratios we derive are low, about 1.5 in I band and 0.5 in K' band. The B
and V band M/L ratios vary greatly due to absorption by dust, reaching 4 in the molecular ring and decreasing to about 1.6
–1.8 at larger radii. This unequivocally shows that models, like most maximum disk models, assuming constant M/L ratios in
an optical waveband, simply are not appropriate. We illustrate this by making mock maximum disk models with a constant V band
M/L ratio. The key is having the central light distribution unobscured such that it can be used to trace the mass. The K'
band M/L ratio is virtually constant over the disk, suggesting that the intrinsic (unobscured) stellar M/L ratio is roughly
constant. We use our knowledge of the visible mass distribution to test disk and halo dark matter models. Fitting an NFW (Navarro
et al., 1996) halo to the rotation curve suggests that NGC 4414 is in a low mass concentrated halo typical of small galaxies
and early halo formation times.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
We have investigated the gas and stellar kinematics and the stellar population properties at the center of the early-type galaxy NGC 4245 with a large-scale bar by the method of two-dimensional spectroscopy. The galaxy has been found to possess a pronounced chemically decoupled compact stellar nucleus, which is at least a factor of 2.5 richer in metals than the stellar population of the bulge, and a ring of young stars with a radius of 300 pc. Star formation goes on in the ring even now; its location corresponds to the inner Lindblad resonance of the large-scale bar. According to Hubble Space Telescope data, the mean stellar age in the chemically decoupled nucleus is significantly younger than that within 0″.25 of the center. It may be concluded that we take the former ultracompact star formation ring with a radius of no more than 100 pc located at the inner Lindblad resonance of the now disappeared nuclear bar as the chemically decoupled nucleus. On the whole, the picture of star formation at the center of this gas-poor galaxy is consistent with theoretical predictions of the consequences of the secular evolution of a stellar-gaseous disk under the action of a bar or bars. 相似文献
12.
We propose a number of prospective observational programs for the ultraviolet space observatory WSO-UV, which seem to be of great importance to modern galactic astronomy. The programs include the search for binary Cepheids; the search and detailed photometric study and the analysis of radial distribution of UV-bright stars in globular clusters (“blue stragglers”, blue horizontal-branch stars, RR Lyrae variables, white dwarfs, and stars with UV excesses); the investigation of stellar content and kinematics of young open clusters and associations; the study of spectral energy distribution in hot stars, including calculation of the extinction curves in the UV, optical and NIR; and accurate definition of the relations between the UV-colors and effective temperature. The high angular resolution of the observatory allows accurate astrometric measurements of stellar proper motions and their kinematic analysis. 相似文献
13.
Rosa M. González Delgado 《Astrophysics and Space Science》2009,324(2-4):231-239
Stellar population models are a very useful tool to derive the stellar cluster age and luminosity mass from its integrated light. Evolutionary synthesis models depend on the stellar evolutionary tracks and the stellar libraries used to predict the spectral energy distribution of the stellar populations. In this review, I briefly comment on the new models that have incorporated the new evolutionary tracks with rotation and new computations for the evolutionary tracks of the TP-AGB. A more extended summary is also given of the current status of the most recent high-resolution stellar libraries at optical wavelengths and their implementation in evolutionary synthesis models. A comparison of the results obtained fitting the optical spectra of LMC and SMC stellar clusters with different high spectral resolution evolutionary synthesis models is also presented. 相似文献
14.
Long filamentary structures composed of chains of denser clumps fan out from the high mass star-forming KL core region in OMC-1. We present a high resolution VLA NH3 study of the structure, kinematics, and temperature of the region over a large, multi-field scale. The region appears to contain multiple superimposed cloud components. Clumps along the filaments may be the result of instabilities and fragmentation; some show fast velocity gradients. Sheaths around the clumps along the filaments are heated. This is possibly the result of external radiation or of interaction with high velocity outflows from young stellar objects in OMC-1. 相似文献
15.
In this lecture, we review the properties of protoplanetary disks as derived from high angular resolution observations at millimeter wavelengths. We discuss how the combination of several different high angular resolution techniques allow us to probe different regions of the disk around young stellar objects and to derive the properties of the dust when combined with sophisticated disk models. The picture that emerges is that the dust in circumstellar disks surrounding pre-main sequence stars is in many cases significantly evolved compared to the dust in molecular clouds and the interstellar medium. It is however still difficult to derive a consistent picture and timeline for dust evolution in disks as the observations are still limited to small samples of objects.We also review the evidence for and properties of disks around high-mass young stellar objects and the implications on their formation mechanisms. The study of massive YSOs is complicated by their short lifetimes and larger average distances. In most cases high angular resolution data at millimeter wavelengths are the only method to probe the structure of disks in these objects.We provide a summary of the characteristics of available high angular resolution millimeter and submillimeter observatories. We also describe the characteristics of the ALMA observatory being constructed in the Chilean Andes. ALMA is going to be the world leading observatory at millimeter wavelengths in the coming decades, the project is now in its main construction phase with early science activities envisaged for 2010 and full science operations for 2012. 相似文献
16.
The velocity dispersion of stars in the solar neighbourhood thin disc increases with time after star formation. Nordström et al. performed the most recent observations to constrain the age–velocity dispersion relation. They fitted the age–velocity dispersion relations of each Galactic cardinal direction space velocity component, U (towards the Galactic Centre), V (in the direction of Galactic rotation) and W (towards the North Galactic Pole), with power laws and interpreted these as evidence for continuous heating of the disc in all directions throughout its lifetime. We revisit these relations with their data and use the results of Famaey et al. to show that structure in the local velocity distribution function distorts the in-plane ( U and V ) velocity distributions away from Gaussian so that a dispersion is not an adequate parametrization of their functions. The age–σ W relation can however be constrained because the sample is well phase-mixed vertically. We do not find any local signature of the stellar warp in the Galactic disc. Vertical disc heating does not saturate at an early stage. Our new result is that a power law is not required by the data: disc heating models that saturate after ∼4.5 Gyr are equally consistent with observations. 相似文献
17.
Glenn van de Ven † Rachel Mandelbaum † Charles R. Keeton 《Monthly notices of the Royal Astronomical Society》2009,398(2):607-634
Studies of strong gravitational lensing in current and upcoming wide and deep photometric surveys, and of stellar kinematics from (integral-field) spectroscopy at increasing redshifts, promise to provide valuable constraints on galaxy density profiles and shapes. However, both methods are affected by various selection and modelling biases, which we aim to investigate in a consistent way. In this first paper in a series, we develop a flexible but efficient pipeline to simulate lensing by realistic galaxy models. These galaxy models have separate stellar and dark matter components, each with a range of density profiles and shapes representative of early-type, central galaxies without significant contributions from other nearby galaxies. We use Fourier methods to calculate the lensing properties of galaxies with arbitrary surface density distributions, and Monte Carlo methods to compute lensing statistics such as point-source lensing cross-sections. Incorporating a variety of magnification bias modes lets us examine different survey limitations in image resolution and flux. We rigorously test the numerical methods for systematic errors and sensitivity to basic assumptions. We also determine the minimum number of viewing angles that must be sampled in order to recover accurate orientation-averaged lensing quantities. We find that for a range of non-isothermal stellar and dark matter density profiles typical of elliptical galaxies, the combined density profile and corresponding lensing properties are surprisingly close to isothermal around the Einstein radius. The converse implication is that constraints from strong lensing and/or stellar kinematics, which are indeed consistent with isothermal models near the Einstein radius, cannot trivially be extrapolated to smaller and larger radii. 相似文献
18.
对银河系内卫星星系进行全面的"人口普查"具有重要的意义。目前已经发现了二十几个卫星星系,其光度范围分布很广,最暗的矮星系比球状星体还暗。叙述了卫星星系的光度分布、空间分布和动力学性质。总结了观测和理论研究进展,并讨论了星流和伽玛射线在研究银河系结构和暗物质性质方面的贡献。表明了卫星星系的统计分布能用来很好地限制冷暗物质理论和星系形成的相关物理过程,同时指出当前研究的局限性和可能的发展方向。 相似文献
19.
In the last few years, galaxies at redshifts up to z ∼ 1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10 m-class telescopes. With kinematic
and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation
(TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests
of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially
resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at
redshifts 0.1 < z < 1.0. We find evidence for a B-band luminosity increase of up to 2 mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity
as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of
previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical
simulations based on the hierarchical merging scenario.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
C. Pichon A. Siebert O. Bienaymé 《Monthly notices of the Royal Astronomical Society》2002,329(1):181-194
A method for inverting the statistical star counts equation, including proper motions, is presented; in order to break the degeneracy in that equation, it uses the supplementary constraints required by dynamical consistency. The inversion gives access to both the kinematics and the luminosity function of each population in three régimes: the singular ellipsoid, the constant ratio Schwarzschild ellipsoid plane-parallel models and the epicyclic model. This more realistic model is tailored to account for the local neighbourhood density and velocity distribution.
The first model is fully investigated, both analytically and by means of a non-parametric inversion technique, while the second model is shown to be formally its equivalent. The effect of noise and incompleteness in apparent magnitude is investigated. The third model is investigated by a non-parametric inversion technique where positivity of the underlying luminosity function is explicitly accounted for.
It is argued that its future application to data such as the Tycho catalogue (and in the upcoming satellite GAIA ) could lead – provided that the vertical potential and or the asymmetric drift or w⊙ are known – to a non-parametric determination of the local neighbourhood luminosity function without any reference to stellar evolution tracks. It should also yield the proportion of stars for each kinematic component and a kinematic diagnostic to split the thin disc from the thick disc or the halo. 相似文献
The first model is fully investigated, both analytically and by means of a non-parametric inversion technique, while the second model is shown to be formally its equivalent. The effect of noise and incompleteness in apparent magnitude is investigated. The third model is investigated by a non-parametric inversion technique where positivity of the underlying luminosity function is explicitly accounted for.
It is argued that its future application to data such as the Tycho catalogue (and in the upcoming satellite GAIA ) could lead – provided that the vertical potential and or the asymmetric drift or w