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Zhi-Jian Luo Cheng-Gang Shu 《中国天文和天体物理学报》2007,7(4):590-594
According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function. 相似文献
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E. Athanassoula Rachael Lynn Beaton 《Monthly notices of the Royal Astronomical Society》2006,370(3):1499-1512
The inclination of M31 is too close to edge-on for a bar component to be easily recognized and is not sufficiently edge-on for a boxy/peanut bulge to protrude clearly out of the equatorial plane. Nevertheless, a sufficient number of clues allow us to argue that this galaxy is barred. We use fully self-consistent N -body simulations of barred galaxies and compare them with both photometric and kinematic observational data for M31. In particular, we rely on the near-infrared photometry presented in a companion paper. We compare isodensity contours to isophotal contours and the light profile along cuts parallel to the galaxy major axis and offset towards the north, or the south, to mass profiles along similar cuts on the model. All these comparisons, as well as position–velocity diagrams for the gaseous component, give us strong arguments that M31 is barred. We compare four fiducial N -body models to the data and thus set constraints on the parameters of the M31 bar, as its strength, length and orientation. Our 'best' models, although not meant to be exact models of M31, reproduce in a very satisfactory way the main relevant observations. We present arguments that M31 has both a classical and a boxy/peanut bulge. Its pseudo-ring-like structure at roughly 50 arcmin is near the outer Lindblad resonance of the bar and could thus be an outer ring, as often observed in barred galaxies. The shape of the isophotes also argues that the vertically thin part of the M31 bar extends considerably further out than its boxy bulge, that is, that the boxy bulge is only part of the bar, thus confirming predictions from orbital structure studies and from previous N -body simulations. It seems very likely that the backbone of M31's boxy bulge is families of periodic orbits, members of the x1 -tree and bifurcating from the x1 family at its higher order vertical resonances, such as the x1v3 or x1v4 families. 相似文献
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E. Athanassoula 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):9-31
Angular momentum redistribution within barred galaxies drives their dynamical evolution. Angular momentum is emitted mainly
by near-resonant material in the bar region and absorbed by resonant material mainly in the outer disc and in the halo. This
exchange determines the strength of the bar, the decrease of its pattern speed, as well as its morphology. If the galaxy has
also a gaseous component and/or a companion or satellite, then these also take part in the angular momentum exchange. During
the evolution a bar structure forms in the inner parts of the halo as well. This bar is shorter and fatter than the disc bar
and stays so all through the simulation, although its length grows considerably with time. Viewed edge-on, the bar in the
disc component acquires a boxy or peanut shape. I describe the families of periodic orbits that explain such structures and
review the observations showing that boxy/peanut ‘bulges’ are in fact just bars seen edge-on. 相似文献
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Alister W. Graham 《Monthly notices of the Royal Astronomical Society》2007,379(2):711-722
The differing M bh – L relations presented in McLure & Dunlop, Marconi & Hunt and Erwin et al. have been investigated. A number of issues have been identified and addressed in each of these studies, including but not limited to the removal of a dependency on the Hubble constant, a correction for dust attenuation in the bulges of disc galaxies, the identification of lenticular galaxies previously treated as elliptical galaxies and the application of the same ( Y ∣ X ) regression analysis. These adjustments result in relations which now predict similar black hole masses. The optimal K -band relation is log( M bh /M⊙ ) =−0.37(±0.04)( M K + 24) + 8.29(±0.08) , with a total (not intrinsic) scatter in log M bh equal to 0.33 dex. This level of scatter is similar to the value of 0.34 dex from the relation of Tremaine et al. and compares favourably with the value of 0.31 dex from the M bh – n relation of Graham & Driver. Using different photometric data, consistent relations in the B and R band are also provided, although we do note that the small ( N = 13) R -band sample used by Erwin et al. is found here to have a slope of −0.30 ± 0.06. Performing a symmetrical regression on the larger K -band sample gives a slope of ∼−0.40, implying M bh ∝ L 1.00 . Implications for galaxy–black hole co-evolution, in terms of dry mergers, are briefly discussed, as are the predictions for intermediate mass black holes. Finally, as noted by others, a potential bias in the galaxy sample used to define the M bh – L relations is shown and a corrective formula provided. 相似文献
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