scholarly journals Dissipation and the Formation of Galaxies

1987 ◽  
Vol 127 ◽  
pp. 353-366
Author(s):  
R.G. Carlberg
Keyword(s):  
Angular Momentum ◽  
Galaxy Formation ◽  
Elliptical Galaxies ◽  
Stellar Disk ◽  
Disk Galaxies ◽  
The Core ◽  
Hubble Sequence ◽  
The Galaxy ◽  
Isothermal Gas ◽  
Gas Cloud

The evidence for dissipation in elliptical galaxies indicates neither the epoch of formation nor the rate of radiation. The hypotheses for the formation of ellipticals include mergers of pre-existing, mostly stellar, disk galaxies; accumulation of gassy fragments that subsequently turn into stars; and the dynamical collapse of a distinct protogalactic gas cloud with simultaneous star formation. Mergers of purely stellar disks seem unlikely, because the phase space density of disks is everywhere far below that of the cores of normal ellipticals. Allowing a few percent of the mass of the galaxy to dissipate into the core and turn into stars could remove this difficulty. In the Hubble sequence of galaxies, ellipticals are characterized by their low angular momentum content. As a start to understanding the general problem for galaxy formation and angular momentum acquisition in the presence of dissipation, a cosmological N-body experiment containing both a dominant collisionless component and an isothermal gas is described. The collisionless component clusters in the usual hierarchical manner appropriate to the spectrum of fluctuations. In contrast, the gas fragments only when the Jeans mass drops below the turnaround mass. The fragments subsequently shrink, becoming distinct entities with relatively low chances of being quickly incorporated in a larger unit. Gravitational torques transfer angular momentum outward in the dissipating gas, placing most of the gas angular momentum at large radii in the protogalaxy. The distant, high angular momentum gas has a relatively long infall time onto the galaxy. The gas may continue to rain down for some time if the galaxy remains undisturbed, or, the growth of clustering may strip the gas off, leaving a low angular momentum system.

scholarly journals ФРАГМЕНТИ З ЖИТТЯ ГАЛАКТИК

2020 ◽  
pp. 230-256
Author(s):  
А. Н. Нарожный
Keyword(s):  
Formation Rate ◽  
Low Frequency ◽  
Central Zone ◽  
Elliptical Galaxies ◽  
Big Bang ◽  
Disk Galaxies ◽  
Radiation Emission ◽  
The Core ◽  
The Galaxy ◽  
Frequency Radiation

Separate fragments from the life of galaxies are considered. The motive uniting them is the component of dark matter. Using the hypothesis stated earlier about its origin and properties, the distribution of this component in galaxies and the influence it exerts on some galactic processes are analyzed. A comparison of the distribution of the dark component in elliptical and disk galaxies shows a higher concentration in elliptical galaxies. This conclusion follows from the relatively mature age of the stars in these galaxies and their chaotic motion. For this reason, in elliptical galaxies, the effect of radiation emission of a dark component outside the central zone decreases, which allows its particles to gather near the galactic core. For a quasar to appear in the center of a galaxy, some preparation is required. It represents both the accumulation of baryonic matter in the central body of the galaxy and near it, and the replenishment of the corresponding reserve of electromagnetic energy supplied by the dark component. In elliptical galaxies, the preparation for the quasar phase is faster compared to disk galaxies. In recent galaxies, the higher-frequency radiation of young stars has a greater resistance to the movement of dark component particles from the halo to the core. For the same reason, in disk galaxies, the particle formation rate of the dark component from intrinsic low-frequency radiation will be lower. It is concluded that after a series of cycles of utilization of galactic waste, accompanied by hydrogen regeneration, the life reserve of the galaxy decreases, and it gradually passes into the stage of slow extinction. But even in this state, a quasar appears in the core of the galaxy. Therefore, the situation is quite real when the underlying galaxy of a quasar can be invisible precisely because of faded stars, and not just because of the excessive brightness of the quasar itself. In addition, an almost extinct galaxy can capture a small young galaxy. The resources of a captured galaxy can contribute to the appearance of a quasar, giving the impression of its origin in a young and small galaxy. This explains the appearance of supermassive central objects in the forming galaxies, which cannot be explained in the Big Bang hypothesis. A possible mechanism of radio bursts is shown. They occur in galactic nuclei and are determined by the dark component of matter.

scholarly journals Assembling Spiral Galaxies

1996 ◽  
Vol 171 ◽  
pp. 11-18
Author(s):  
R.C. Kennicutt
Keyword(s):  
Galaxy Formation ◽  
Spiral Galaxies ◽  
Dynamical Evolution ◽  
Star Formation History ◽  
Physical Mechanisms ◽  
Hubble Sequence ◽  
Galaxy Formation And Evolution ◽  
The Galaxy ◽  
History Of ◽  
Formation And Evolution

Nearby spiral galaxies offer vital clues to some of the most fundamental questions about galaxy formation and evolution: What is the star formation history of the universe, past and future? When did disks form, during the final stages of a single primeval collapse, or as a continuous or episodic process? What is the evolutionary nature of the Hubble sequence, and what are the physical mechanisms that dictate the present-day Hubble type of a galaxy? Was Hubble type imprinted at birth, or can it be deterined or at least modified by infall, mergers, or secular dynamical evolution within the galaxy? These issues are not specific to spirals, of course, and much of this conference will address just these questions in a broader context. However present-day spirals offer unique advantages for studying these problems; they exhibit a broad range of dynamical and evolutionary properties, and the dynamical fragility of disks makes them excellent seismometers of galaxy interaction and merger rates at recent epochs.

scholarly journals Formation and Evolution of Disk Galaxies

1999 ◽  
Vol 183 ◽  
pp. 153-153
Author(s):  
C. Firmani ◽  
V. Avila-Reese
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Power Spectrum ◽  
Mass Velocity ◽  
Dark Matter Halo ◽  
Stellar Disk ◽  
Physical Factors ◽  
Disk Galaxies ◽  
Velocity Relation ◽  
Formation And Evolution

We have developed a semianalitical approach to study galaxy formation and evolution in the cosmological context. Disk galaxies (dark matter halo+luminous disk) are considered to be formed through an extended process of gravitational collapse, whose character is determined by the statistical properties of the density fluctuation field assumed here to be Gaussian. Gas disks in centrifugal equilibrium within the collapsing dark halos are built up (detailed angular momentum conservation is assumed), and their galactic evolution is calculated with a model which consider all the gravitational interactions, the hydrodynamics of the ISM, and the SF process. A bulge as product of stellar disk gravitational instabilities is constructed. To study general behaviors a Gaussian σ8 = 1 SCDM model is used. For a given mass one obtains a range of dark matter configurations. The average case is in excellent agreement with results of cosmological N-body simulations. The slope of the mass-velocity relation agrees with the slope of the H- and I-band Tully-Fisher relations, but the velocities are too high. This problem dissapears if the power spectrum is renormalized to σ8 = 0.57, suggesting that the TF relation is result of the natural extension to galactic scales of the galaxy distribution power spectrum, and that on the basis of its origin are the cosmological initial conditions. The scatter on the mass-velocity relation is realistic. The models predict disk exponential surface brightness (SB) profiles, nearly flat rotation curves, and negative radial gradients in the B-V color. The obtained, gas fractions, B-V colors, central SBs μB0, bulge-to-disk (b/d) ratios, and rotation velocities (for σ8 = 0.57) are in agreement with observations, and their correlations are similar to those which define the Hubble sequence, including the LSB galaxies. These properties and correlations are the product of the combination of three fundamental physical factors: the mass, the mass aggregation history (MAH), and the initial angular momentum. The intensive properties are almost invariant to the mass, the MAH determines the B-V color, and the spin parameter λ mainly influences on μB0, and b/d ratio.

scholarly journals Correlations between r1/4-Law Parameters for Bulges and Elliptical Galaxies

1987 ◽  
Vol 127 ◽  
pp. 379-380 ◽  
Author(s):  
Masaru Hamabe ◽  
John Kormendy
Keyword(s):  
Galaxy Formation ◽  
Surface Brightness ◽  
Scaling Law ◽  
Elliptical Galaxies ◽  
High Accuracy ◽  
Effective Radius ◽  
Strongly Coupled ◽  
The Galaxy ◽  
Galaxy Sample ◽  
Two Parameter

The correlation between the effective radius re and surface brightness μe for elliptical galaxies is a fundamental scaling law that theories of galaxy formation must explain. When re and μe are derived by fitting two-parameter fitting functions such as the de Vaucouleurs r1/4 law to brightness profiles, the errors in the parameters are strongly coupled. The purpose of this paper is to rederive the μe(log re) relations for ellipticals and bulges, taking account of the coupling in the errors and using only high-accuracy CCD data. Our preliminary conclusions are: (1) The coupled errors are too small to affect significantly the correlation derived for elliptical galaxies. (2) The correlation for bulges is not very different from that for ellipticals, but the galaxy sample is small and the errors in the parameters are large due to the inherent uncertainty in bulge-disk decomposition.

scholarly journals The Local Density and Morphology Dependence of the Galaxy Luminosity Function

1987 ◽  
Vol 127 ◽  
pp. 457-457
Author(s):  
Jacek Choloniewski ◽  
Miroslaw Panek
Keyword(s):  
Galaxy Formation ◽  
Luminosity Function ◽  
Local Density ◽  
Elliptical Galaxies ◽  
Low Density ◽  
Early Type ◽  
The Galaxy ◽  
The Moment ◽  
Galaxy Luminosity Function ◽  
Selection Of

We obtained the luminosity function (LF) for samples of galaxies from the CfA North catalogue (Huchra, Davis, Latham and Tonry, 1983). the criteria of selection of samples were the local density (range—more than 2 orders of magnitude) and/or the morphology. No difference in the combined LF for all morphological types is found for subsamples of different density. the LF of elliptical galaxies is found to be less steep at the faint end than the LFs for S and SO galaxies. E galaxies are on the average brighter than the other morphological types. the LFs measured for early–type galaxies (E + S0) in high and low density regions show marginal difference—the low density LF has a steeper faint end slope. (Such a difference is not found for S galaxies). If this feature is maintained for larger samples it may indicate that the LF determined at the moment of galaxy formation is only weakly influenced by the phenomena present in dense regions. This is because these phenomena would rather leave the opposite imprint on the LF—the tidal stripping in dense regions would populate them with faint remnants of disrupted, bright, low angular momentum galaxies. Mergers could not reverse this trend because they act mainly on the bright galaxies.

scholarly journals Simulating Disk Galaxies: First Results of a Systematical Study

2006 ◽  
Vol 2 (S235) ◽  
pp. 114-114 ◽  
Author(s):  
Franziska Köckert ◽  
Matthias Steinmetz
Keyword(s):  
Angular Momentum ◽  
Galaxy Formation ◽  
Initial Conditions ◽  
Disk Galaxies ◽  
Disk Formation ◽  
Numerical Resolution ◽  
First Results ◽  
Low Mass ◽  
Current Paradigm ◽  
Made In

Simulating disk galaxies within the current paradigm of galaxy formation has been a long standing problem. In comparison with observations, the simulated disks were too small and too centrally concentrated, due to a large loss of angular momentum during formation. This is known as the angular momentum catastrophe (Navarro & Benz (1991)). Recently, some progress has been made in reducing this effect by changing the cosmology, including various feedback mechanisms, improving numerical resolution and carefully selecting initial conditions with a quiet merging history after z≈2. Unfortunately, it remains unclear which of these effects, or which combination, has resulted in more realistic disk formation. In order to address this problem, we conduct a systematical study using the N-body code GADGET2 (Springel (2005)). We adopt a flat ΛCDM cosmology with Ωm=0.3, ΩΛ=0.7, Ωbar=0.04 and h=0.65. Using a softening of 0.5 kpc we find disks with a very compact unresolved gas clump in the center and a thin, extended disk (R≈10kpc) of very low mass around it.

scholarly journals Angular Momentum in Elliptical Galaxies

1987 ◽  
Vol 127 ◽  
pp. 521-522
Author(s):  
Rosemary F. G. Wyse ◽  
Susana Lizano
Keyword(s):  
Angular Momentum ◽  
Galaxy Formation ◽  
Elliptical Galaxies

We have used the available published observations of the rotational properties of elliptical galaxies to test theories of galaxy formation which predict an anti-correlation between the angular momentum of a galaxy and its initial overdensity and hence formation epoch. We find that the prediction, at least in its simplest form, is not supported by the data for well studied elliptical galaxies which have a range in rotational support.

scholarly journals Are Elliptical Galaxies Really Metal-Rich?

2002 ◽  
Vol 187 ◽  
pp. 139-146 ◽  
Author(s):  
M. Loewenstein ◽  
R. F. Mushotzky
Keyword(s):  
Spatial Distribution ◽  
Galaxy Formation ◽  
Formation Process ◽  
Total Mass ◽  
Elliptical Galaxies ◽  
Heavy Elements ◽  
Early Epoch ◽  
The Galaxy ◽  
Relative Abundances

In elliptical galaxies, where most of the stars - and therefore most of the heavy elements - were formed at an early epoch, the total mass, spatial distribution, and relative abundances of metals are intimately connected to the galaxy formation process.

scholarly journals The Hydrodynamical Evolution of Gas in Young Elliptical Galaxies

1987 ◽  
Vol 127 ◽  
pp. 437-438
Author(s):  
R. Kunze ◽  
H.H. Loose ◽  
H.W. Yorke
Keyword(s):  
Mass Loss ◽  
Thermal Instability ◽  
Elliptical Galaxy ◽  
Forthcoming Paper ◽  
Elliptical Galaxies ◽  
Stellar Mass ◽  
Early Epoch ◽  
The Galaxy ◽  
Bulk Energy ◽  
Gas Cloud

We calculate the partial inflow of gas fuelled by stellar mass loss at an early epoch (109yr after the birth of the galaxy) during the evolution of an elliptical galaxy assuming a modified King model stellar distribution. The influence of the partial thermalization of stellar mass lost on the amount of gas which can be stored in the nucleus of a typical elliptical during the time of partial inflow is investigated. Masses up to 105M⊙ of cool (≤ 104K) material can be stored in the nucleus of the galaxy before the fast dissipation of the “kinetic bulk energy” of the nuclear gas cloud leads to “thermal” instability and subsequent collapse. A supermassive star can form. A detailed discussion of the model and the results is subject of a forthcoming paper (Kunze et al., 1986).

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