共查询到20条相似文献，搜索用时 656 毫秒
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The local face-on disk galaxies are selected as galaxy sample from the main galaxy sample of the Seventh Data Release of Sloan Digital Sky Survey (SDSS DR7). The correlations between the colors and sizes of disk galaxies with equivalent total stellar masses are statistically investigated and their realities are tested. It is found that for the disk galaxies with equivalent masses, the correlation between u-r color and size is very weak. However, there are anticorrelations between g-r, r-i, r-z colors and sizes, i.e., the larger are the sizes of galaxies, the bluer are their colors. This result means that the mass distribution of disk galaxies has a significant influence on their star formation history. The galaxies with more extended mass distributions evolve more slowly. 相似文献
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R.I. Davies A. Burston M.J. Ward 《Monthly notices of the Royal Astronomical Society》2002,329(2):367-376
We present 0.5-arcsec-resolution near-infrared images of six ultraluminous infrared galaxies with known redshifts. Six of the eight bright nuclei are resolved on kiloparsec scales, suggesting that there is significant circumnuclear star formation or close progenitor nuclei. At this spatial resolution, the nuclei have very red colours that cannot in general be reproduced by reddening stellar light, but require an additional component of hot dust emission. In five of the six primary nuclei more than 20 per cent of the K -band continuum originates in hot dust, but the temperature cannot be determined by JHK broad-band colours alone. Comparison with the spectral shapes, however, does allow the temperature to be constrained, and we find in every case that it is at the upper end of the permissible range, ≳1000 K. This does not necessarily imply that there is an active galactic nucleus present, since there is evidence that stellar processes can also generate dust this hot via stochastic heating of small grains. The quantities of hot dust we have found here can make up to 0.5-mag difference to the K -band magnitude even at , with implications for observations and population synthesis models of higher-redshift objects. Observations in the L or M bands, where hot dust is most important at , could help to discriminate between models of dusty starbursts and ellipticals. 相似文献
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Eric F. Bell Roelof S. de Jong † 《Monthly notices of the Royal Astronomical Society》2000,312(3):497-520
We have used a large sample of low-inclination spiral galaxies with radially resolved optical and near-infrared photometry to investigate trends in star formation history with radius as a function of galaxy structural parameters. A maximum-likelihood method was used to match all the available photometry of our sample to the colours predicted by stellar population synthesis models. The use of simplistic star formation histories, uncertainties in the stellar population models and considering the importance of dust all compromise the absolute ages and metallicities derived in this work; however, our conclusions are robust in a relative sense. We find that most spiral galaxies have stellar population gradients, in the sense that their inner regions are older and more metal rich than their outer regions. Our main conclusion is that the surface density of a galaxy drives its star formation history, perhaps through a local density dependence in the star formation law. The mass of a galaxy is a less important parameter; the age of a galaxy is relatively unaffected by its mass; however, the metallicity of galaxies depends on both surface density and mass. This suggests that galaxy‐mass-dependent feedback is an important process in the chemical evolution of galaxies. In addition, there is significant cosmic scatter suggesting that mass and density may not be the only parameters affecting the star formation history of a galaxy. 相似文献
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Abundance diagnosis of E+A (post-starburst) galaxies 总被引：1，自引：0，他引：1
Tomotsugu Goto 《Monthly notices of the Royal Astronomical Society》2007,377(3):1222-1228
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We study the chemical and spectrophotometric evolution of galactic discs with detailed models calibrated on the Milky Way and using simple scaling relations, based on currently popular semi-analytic models of galaxy formation. We compare our results with a large body of observational data on present-day galactic discs, including disc sizes and central surface brightness, Tully–Fisher relations in various wavelength bands, colour–colour and colour–magnitude relations, gas fractions versus magnitudes and colours and abundances versus local and integrated properties, as well as spectra for different galactic rotational velocities. Despite the extremely simple nature of our models, we find satisfactory agreement with all those observables, provided that the time-scale for star formation in low-mass discs is longer than for more massive ones. This assumption is apparently in contradiction with the standard picture of hierarchical cosmology. We find, however, that it is extremely successful in reproducing major features of present-day discs, like the change in the slope of the Tully–Fisher relation with wavelength, the fact that more massive galaxies are on average 'redder' than low-mass ones (a generic problem of standard hierarchical models) and the metallicity–luminosity relation for spirals. It is concluded that, on a purely empirical basis, this new picture is at least as successful as the standard one. Observations at high redshifts could help to distinguish between the two possibilities. 相似文献
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A.J. Burston M.J. Ward R.I. Davies 《Monthly notices of the Royal Astronomical Society》2001,326(1):403-415
We present near-infrared observations of a sample of mainly interacting ultraluminous infrared galaxies, comprising H - and K -band spectra. Our main aims are to investigate the power source of these extremely luminous objects and the various excitation mechanisms of the strong molecular hydrogen emission often seen in such objects. Broadened emission lines were only detected in one object, IRAS 23498, consistent with the previous results for this galaxy. The [Si vi ] emission line was detected in IRAS 17179 and 20210, both classified as Sy2s. Two of the samples were unclassified, IRAS 00150 and 23420, which exhibit neither [Si vi ] emission nor broadened H i emission. However this does not rule out the presence of an obscured AGN. Analysis of the molecular hydrogen emission showed that the major excitation mechanism for most objects was thermal. Modelling of the more luminous objects indicates that for IRAS 20210 10 per cent, and for both IRAS 23365 and IRAS 23420 30 per cent, of the 1–0 S(1) line emission has a non-thermal origin. 相似文献
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Tian-Zhi Zhang Xue-Bing WuDepartment of Astronomy School of Physics Peking University Beijing 《中国天文和天体物理学报》2002,2(6)
The sizes of the Broad Line Region (BLR) of some Seyfert 1 galax-ies and nearby quasars can be determined by the reverberation mapping method.Combining with the observed FWHM of Hβ emission line and assuming that themotion of BLR clouds is virialized, the black hole masses of these objects have beenestimated. However, this method strongly depends on the poorly-understood geom-etry and inclination of the BLR. On the other hand, a tight correlation between theblack hole mass and the bulge velocity dispersion was recently found for both activeand nearby inactive galaxies. This may provide another method, independent of theBLR geometry, for estimating the black hole mass. Using this method for estimatingthe black hole mass and combining with the measured BLR size and FWHM of Hβemission line, we derived the BLR inclination angles for 20 Seyfert I galaxies underthe assumption that the BLR is disk-like. The derived inclination angles agree wellwith those derived previously by fitting the UV continuum and Hβ emission lineprofiles. Adopting a relation between the FWHMs of [OⅢ]λ5007 forbidden line andthe stellar velocity dispersion, we also estimated the BLR inclinations for 50 nar-row line Seyfert 1 galaxies (NLSls). We found that the inclinations of broad LineSeyfert 1 galaxies (BLS1s) are systematically greater than those of NLS1s, whichseldom exceed 30. This may be an important factor that leads to the differencesbetween NLS1s and BLS1s if the BLR of NLS1s is really disk-like. 相似文献
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We present here the first study of the X-ray properties of an evolutionary sample of merging galaxies. Both ROSAT PSPC and HRI data are presented for a sample of eight interacting galaxy systems, each believed to involve a similar encounter between two spiral discs of approximately equal size. The mergers span a large range in age, from completely detached to fully merged systems.
A great deal of interesting X-ray structure is seen, and the X-ray properties of each individual system are discussed in detail. Along the merging sequence, several trends are evident: in the case of several of the infrared bright systems, the diffuse emission is very extended, and appears to arise from material ejected from the galaxies. The onset of this process seems to occur very soon after the galaxies first encounter one another, and these ejections soon evolve into distorted flows. More massive extensions (perhaps involving up to 1010 M⊙ of hot gas) are seen at the 'ultraluminous' peak of the interaction, as the galactic nuclei coalesce.
The amplitude of the evolution of the X-ray emission through a merger is markedly different from that of the infrared and radio emission, however. Although the X-ray luminosity rises and falls along the sequence, the factor by which the X-ray luminosity increases, relative to the optical, appears to be only about a tenth of that seen in the far-infrared. This, we believe, may well be linked with the large extensions of hot gas observed.
The late, relaxed remnants appear relatively devoid of gas, and possess an X-ray halo very different from that of typical ellipticals, a problem for the 'merger hypothesis', whereby the merger of two disc galaxies results in an elliptical galaxy. However, these systems are still relatively young in terms of total merger lifetime, and they may still have a few Gyr of evolution to go through before they resemble typical elliptical galaxies. 相似文献
A great deal of interesting X-ray structure is seen, and the X-ray properties of each individual system are discussed in detail. Along the merging sequence, several trends are evident: in the case of several of the infrared bright systems, the diffuse emission is very extended, and appears to arise from material ejected from the galaxies. The onset of this process seems to occur very soon after the galaxies first encounter one another, and these ejections soon evolve into distorted flows. More massive extensions (perhaps involving up to 10
The amplitude of the evolution of the X-ray emission through a merger is markedly different from that of the infrared and radio emission, however. Although the X-ray luminosity rises and falls along the sequence, the factor by which the X-ray luminosity increases, relative to the optical, appears to be only about a tenth of that seen in the far-infrared. This, we believe, may well be linked with the large extensions of hot gas observed.
The late, relaxed remnants appear relatively devoid of gas, and possess an X-ray halo very different from that of typical ellipticals, a problem for the 'merger hypothesis', whereby the merger of two disc galaxies results in an elliptical galaxy. However, these systems are still relatively young in terms of total merger lifetime, and they may still have a few Gyr of evolution to go through before they resemble typical elliptical galaxies. 相似文献
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We present an analysis of the spatial orientations of 1315 galaxies in 10 Abell clusters of BM type II–III (type II–III in the Bautz–Morgan system). It is found that the spin-vector orientations of the galaxies in six clusters (Abell 168, 426, 1035, 1227, 1367 and 1904) tend to lie parallel to the Local Supercluster (LSC) plane. The spin-vector projections of galaxies in six clusters (Abell 168, 1020, 1035, 1227, 1904 and 1920) are found to be oriented perpendicular with respect to the direction of the LSC centre. Three clusters (Abell 1920, 2255 and 2256) show a bimodal orientation: spin vectors tend to be oriented both parallel and perpendicular to the LSC plane. No dependence of radial velocity, distance and cluster magnitude on galaxy orientation is noticed. In a comparison with previous work, we noticed that the anisotropy might increase from early-type (BM type I) to late-type (BM types II–III and III) clusters. We notice a vanishing angular momentum for the less massive galaxy clusters (richness class 0). A significant alignment of the angular momenta of galaxies for massive clusters, e.g. the core of the Shapley Supercluster (richness class 4, M > 1015 M⊙ ), is found. 相似文献
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We explore the implications for the high-redshift universe of 'state-of-the-art' models for the chemical and spectrophotometric evolution of spiral galaxies. The models are based on simple 'scaling relations' for discs, obtained in the framework of cold dark matter models for galaxy formation, and were 'calibrated' so as to reproduce the properties of the Milky Way and of nearby discs (at redshift z ∼0) . In this paper, we compare the predictions of our 'hybrid' approach to galaxy evolution to observations at moderate and high redshift. We find that the models are in fairly good agreement with observations up to z ∼1 , while some problems appear at higher redshift (provided there is no selection bias in the data); these discrepancies may suggest that galaxy mergers (not considered in this work) played a non-negligible role at z >1 . We also predict the existence of a 'universal' correlation between abundance gradients and disc scalelengths, independent of redshift. 相似文献