Spin parameter and scale-free density perturbations in hierarchical clustering

The present attempt aims to predict the dependence of the spin parameter, , the angular momentum,J, and the typical radius,a _vir, on the mass,M, which have been found inN-body simulations of expanding density perturbations in hierarchical clustering, when virialization is attained. We show that M ⁰ for systems with same adimensional density distribution and velocity distribution, and in particular for scale-free density perturbations in hierarchical clustering. In the special case of ellipsoidal perturbations, it is also found:J M ^7/4,a _vir M ^1/2. All these results turn out to be in close agreement withN-body simulations, despite the simple model adopted. Expanding and virialized perturbations are modelled, respectively, by homogeneous and heterogeneous, similar ellipsoids which allow flat rotation curves far from the centre. Both energy and angular momentum maintain from a given time on, lying between the beginning of strong decoupling from the Hubble flow and the occurrence of maximum volume. Then the whole set of virialized ellipsoidal configurations with same energy and angular momentum are derived, and the dependence of the spin parameter on the anisotropy parameter, _pec is investigated. Turning our attention to the formation of galaxies, we derive the total mass as a function of the collapse factor, using the empirical anticorrelation between dark to visible mass ratio within the optical radius of disk galaxies and their luminous masses. Observational data related to a sample of elliptical galaxies provide evidence that the contraction in these bodies occurred in proportion to the square root of the ratio of total to luminous mass. On the contrary, it is deduced that dissipation of angular momentum in elliptical galaxies occurred more or less at the same rate. If both shape and anisotropy parameter are preserved during the collapse, typical axis rations ₂₁ = 0.98, ₃₁ = 0.69, are found to correspond to a moderate anisotropy, _pec 0.27, with a small dependence on the spin parameter in the range allowed.     

On the properties of elliptical and spiral galaxies in a CDM scenario

This paper aims to investigate what kind of density perturbations did lead to elliptical galaxies and what kind to spiral galaxies, in the context of a CDM scenario. Previous work by HP (Heavens and Peacock, 1988) is reviewed and extended; more particularly: (i) a theoreticalJM relation is derived for virialized configurations, with a slope increasing with the mass, in the range 5/3<<2, and compared with its counterpart deduced by HP for expanding configurations; (ii) an non-dimensional angular momentum =J/(G ² M ⁵ t _ff )^1/3; witht _ff free-fall time at turnaround, is calculated explicitly and compared with the usual spin parameter =J(–E) ^1/2/(GM ^5/2), in the special case of polytropic spheres and for different peak heights; (iii) a model is built up where the ellipsoidal density perturbations described by HP are approximated as spherical density perturbations with the same mass and the same rate of acquisition of angular momentum, and the contribution of the latter to the expansion is also taken into account. The calculations are limited to the special case of Einstein-de Sitter universes (of dust only), in the whole range of HP distributions of angular momenta. If a massM=10¹² m is typical for galaxies, the results are consistent with both an inferred difference roughly in a factor of six times between angular momenta of ellipticals and spirals, and a continuous transition from the former to the latter, for each peak height. It is argued that star formation together with angular momentum, instead of peak height alone, makes the fate of a given proto-object; more specifically, if star formation is high enough and/or angular momentum is low enough, the system will be frozen as an elliptical galaxy; if, on the other hand, the rate of star formation is low enough, and/or angular momentum is high enough, the system will be frozen as a spiral galaxy. In addition, the results lead to an obvious trend: more ellipticals are associated with higher peak heights and more spirals with lower peak heights.     

Flat Galaxies of the RFGC Catalog Detected in the HIPASS Survey

Data from the H I Parkes All-Sky Survey (HIPASS) of the southern sky in the neutral hydrogen line are used to determine the radial velocities and widths of the H I line for flat spiral galaxies of the Revised Flat-Galaxy Catalog (RFGC) seen edge-on. The sample of 103 flat galaxies detected in HIPASS is characterized by a median radial velocity of +2037 km/sec and a median width of the H I line at the level of 50% of maximum of 242 km/sec. For RFGC galaxies the 50% detection level in HIPASS corresponds to an apparent magnitude B _t = 14 ^m .5 or an angular diameter a = 2.9. The relative number of detected galaxies increases from 2% for the morphological types Sbc and Sc to 41% for the type Sm. The median value of the ratio of hydrogen mass to total mass for RFGC galaxies is 0.079. With allowance for the average internal extinction for edge-on galaxies, <B _t< = 0 ^m .75, the median ratio of hydrogen mass to luminosity, M _{H I}/L _B = 0.74 M /L , is typical for late-type spirals. Because of its small depth, HIPASS reveals only a few RFGC galaxies with previously unknown velocities and line widths.     

BiL(E) and the Hubble sequence: A new theory of galaxies

We show that magnetic fields can be important in the formation and evolution of galaxies and that they might be indeed the missing parameters to explain the Hubble sequence. We use the self-consistent theory of spiral magneto-hydrodynamic flow developed by Henriksen and co-workers over the last few years. Section 2 is a short outline of this theory, where we introduce and justify the simplifying assumptions and list the relevant physical relations.Section 3 deals mainly with the formation of galactic nuclei and proto-galaxies. We envisage the following scenario: The first objects to form after recombination in a canonical hot big-bang universe with turbulence and magnetic fields have masses of order 10⁹ M . In a violent burst of activity—possible mechanisms are discussed—they ionize the surrounding medium, raising the Jeans mass to a galactic scale, and becoming the condensation seeds of galaxies. The subsequent evolution of these nuclei, including recurrent activity, is discussed in some detail.The remaining sections—in principle independent from Section 3—deal with galactic morphology as the result of the collapse of a hot, spherical, rotating proto-galaxy endowed with a regular magnetic field. The main parameter determining the morphological type is the anglei between the magnetic field and the angular momentum. Smalli give rise to Sc galaxies, largei to ellipticals (Section 4), and intermediate values to the rest of the Hubble sequence. Subtypes are produced by variation of the strength of the magnetic field in comparison to the angular momentum. Thus relatively strong fields will produce triaxial ellipticals, barred spirals and irregulars.Some of the observationally testable predictions of our theory concern: the energetics, duration and frequency of nuclear activity, the absence of dwarf spiral galaxies, rigidly rotating nuclear regions in galaxies, the mass and structure of galactic halos, leading and trailing spiral arms and their pitch angle, the bulge-to-disc ratio, the frequency distribution of morphological types, and the warping of galactic discs. Moreover some seemingly pathological galaxies like NGC 2685 and 4314 find a simple explanation.On leave of absence from Astronomisches Institut der Ruhr-Universität Bochum, F.R.G.     

Evolution of a cloudy protogalaxy interacting with an early galactic wind and galaxy formation

We argue that a combined evidence from galactic and extragalactic studies suggests that a major star formation in giant galaxies is preceded by an evolutionary phase at which a strong galactic wind driven by the initial burst of star formation enriches the gaseous protogalaxy with metals and heats it up, so that the latter turns over from contraction to expansion. The result is the ejection of enriched material from the outer part of the protogalaxy into the intergalactic space, while the inner part, after a delay of about one to a few Gyr, finally contracts and cools down to form the galactic major stellar component (the hot model of galaxy formation). The paper presents a specific mechanism to produce a hot protogalaxy according to which an early galactic wind is imparting energy and momentum into a collapsing protogalaxy whose mass is contained mainly in clouds and only a small portion is in the intercloud gas that provides pressure confinement for the clouds. The model is then capable of accounting for the nearly equal mass and iron abundance in cluster giant galaxies and the intracluster gas provided the observationally plausible input parameters for giant galaxies and early galactic winds are adopted. It also predicts the formation of long-lived X-ray coronae with characteristics similar to those observed around giant ellipticals.The model specifies a characteristic length-scale that can be very naturally interpreted as a size for a stellar system to come; a very encouraging result is that it perfectly fits in with a typical size of giant ellipticals.     

Unseen matter and angular momentum in the Milky Way and other galaxies: Simple two-component models

Simple two-component (dark+bright) models are built up for the Milky Way, where both the density distribution and the rotation curve are deduced from known observations. The derived dark to bright mass ratio turns out to be in the range 10, in close agreement with the results of more refined approaches, with a weak dependence on the geometry of the model. The related angular momentum appears to be well in agreement with theoretical predictions, if proto-galaxies gain angular momentum via either gravitational interactions or peculiar velocities of their own sub-units, according to a logarithmic distribution of the squared fractional angular momenta close to a Maxwellian one. The rougher assumption that the whole system is represented by a rigidly rotating polytrope leads to dark components rounder than _D 0.7 if proto-galaxies gain angular momentum via gravitational interactions, and to much more flattened dark components if proto-galaxies gain angular momentum via peculiar velocities of their own sub-units and few (4) sub-units are present at the beginning. To fit the observed positions of several galaxies on the (Oê _B q _B ) plane-ê _B representing the ellipticity andq _B close to the ratio of maximum rotational to central peculiar velocity, averaged for all the inclinations to the line of sight — galaxies are modelled by two-component (dark+bright) rigidly rotating, concentric, co-polar, homogeneous spheroids and the Galaxy is assumed to be a typical system. An acceptable fit is produced only under the assumption that protogalaxies gain their angular momentum in late stages of evolution, i.e., after having decoupled from the Hubble flow.     

Investigation of Barred Galaxies. VII. Comparative Statistics of SB and SA Galaxies. Near and Mid-IR Regions

The near and mid-IR properties of barred and unbarred spiral galaxies are discussed on the basis of complete samples that were compiled earlier. The two types of spirals are shown not to differ from one another in emission power in the near and mid-IR ranges. Multiple regression and principal component analysis have been applied to investigate near and mid-IR properties of SB and SA galaxies, particularly their relation to X-ray and radio continuum emissions. There are definite differences between SB and SA spirals in the near and mid-IR. In the case of SB galaxies, the compactness of 10 m emission is closely related to the J - H color index, and the redder J - H color corresponds to relatively more extended emission at 10 m. It is assumed that these are caused by the bar itself, which stimulates enhanced star formation in a barred galaxy with respect to unbarred spiral.     

One example of mass exchange in case AB in system 5m ⊙+4m ⊙

Evolution of a binary system with masses of 5m and 4m , respectively, and with orbital period of 1.41 days is studied by means of non-stationary model calculations under assumptions of conservation of total mass and total orbital angular momentum of the system. As a result of mass exchange between the components we obtain a binary with masses of 8.46 and 0.54m . Physical parameters of the final product indicate possible connection with shell stars.It is also pointed out that the new secondary component can become rotationally unstable soon after the end of mass exchange.     

The universal rotation curve of spiral galaxies – II. The dark matter distribution out to the virial radius

In the current ΛCDM cosmological scenario, N -body simulations provide us with a universal mass profile, and consequently a universal equilibrium circular velocity of the virialized objects, as galaxies. In this paper we obtain, by combining kinematical data of their inner regions with global observational properties, the universal rotation curve of disc galaxies and the corresponding mass distribution out to their virial radius. This curve extends the results of Paper I, concerning the inner luminous regions of Sb–Im spirals, out to the edge of the galaxy haloes.     

Inertia tensor and tidal transfer of angular momentum for special ellipsoidal mass distributions

This paper deals with ellipsoidal mass distributions made by concentric, coaxial, and similar shells, whose density is specified for two special situations both including the whole range between the limiting cases of homogeneous systems, on one side, and Roche generalized systems, on the other side. The components of the related inertia tensor are calculated and the dependence of the spin growth on the density distribution is shown, concerning tidal transfer of angular momentum to both virialized proto-galaxies and encountering galaxies.     

Numerical modeling of galaxy evolution

A very significant problem in the modeling of disk-galaxy formation in the cold dark matter (CDM) cosmology is the so-called `angular momentum problem'. This problem arises when we numerically model the collapse of baryons within a dark halo in the CDM model. The formed baryonic disk has much less angular momentum than observed disk galaxies due to the considerable loss of angular momentum during the progressive merger of small clumps. As a result of efficient radiative cooling, the gas component collapses too deeply within the dark halo. When two such systems are merging, the angular momentum of the material near the center is effectively transported outwards by the tidal force. This is a physical reason for this problem, however, there may be a numerical origin due to the nature of the Smoothed Particle Hydrodynamics (SPH) method widely used in galaxy formation models. To address the numerical origin of the `angular momentum problem' with a much higher-resolution SPH model, we are developing our Parallel Tree-SPH code. After evolving four initial models with different mass and force resolution, we compare the angular momentum content of SPH particles. We find that both mass and force resolutions clearly affect the evolution of radiative cosmological SPH models. In most previous radiative cosmological SPH models, a mass ratio between SPH and dark matter particles is .However, we find that this mass ratio is a crucial parameter when we consider the angular momentum content of SPH particles and it is better to make the mass ratio ∼ 1.0 in such models. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the direction of rotation of the spirals in galaxies

The detection of trailing arms in twenty spiral galaxies, completed by the 60s, allowed one to suggest the overwhelming prevalence of this sense of rotation. Pasha and Dambis (1982) have recently determined the direction of rotation in a further 54 galaxies and found two leading spirals, NGC 4490 and NGC 5395. The current sample of galaxies with an established sense of rotation contains 79 trailing and two leading systems. The two spirals found to be leading belong to M51 type galaxies.In this paper we present a more detailed investigation of the system NGC 4490/85 which confirms that the arms in NGC 4490 are leading. Statistics are invoked to estimate a probable percentageX _p and an upper limitX _up of galaxies with leading arms. It gives, for 79 trailing and two leading spirals, the valuesX _p 3.5% andX _up 8.2%.     

A model of the formation of spiral galaxies

It has been verified that the analytical results derived in a previous article for elliptical galaxies may also be used to describe spiral galaxies. Exploration of the model for small values of the principal parameter yields surface mass density distributions as functions of radius which, while always displaying the exponential disk, describe both of the subcategories of spiral galaxies. Within the constraints of the model, the two main questions concerning spirals posed some years ago by Freeman appear to be successfully addressed.An intrinsic model mechanism has been identified that could account for the extended state of elliptical galaxies, as opposed to the flat disks of spirals. In general, the model correctly describes the relative sizes of the various types of galaxies.     

The angular momentum-vs-mass relation for spectroscopic binaries

The spectroscopic binaries, considered as a single data point, fall roughly on the universal power-law of index 1.8 for angular momentum vs total mass, as defined by planets, spiral galaxies, and numerous other objects. But the individual systems in theSeventh Catalogue of the Orbital Elements of Spectroscopic Binary Systems define a curve of rather shallower slope, 1.63±0.07, over more than two orders of magnitude in mass and four in angular momentum. Various subsets (long and short periods; single and double line systems; known and unknown orbital orientations) all yield slopes from 1.48 to 1.77. These values, as well as the slightly larger one found for eclipsing systems by Sisteró and Marton, are very much what one would expect, given the form of Kepler's Third Law and the Stellar mass-radius relation.If only these well-known pieces of physics are at work, then the still-wider visual binaries should yield a slope near 5/3. Catalogues currently in press will permit easy testing of this prediction. It seems unlikely that deep clues to the origin of either binary systems or angular momentum are to be found from considerations of this nature.     

An integrable case of a rotational motion analogous to that of Lagrange and Poisson for a gyrostat in a Newtonian force field

The scope of the present paper is to provide analytic solutions to the problem of the attitude evolution of a symmetric gyrostat about a fixed point in a central Newtonian force field when the potential function isV ⁽²⁾.We assume that the center of mass and the gyrostatic moment are on the axis of symmetry and that the initial conditions are the following: (t ₀)=₀, (t ₀)=₀, (t ₀)=(t ₀)=₀, ₁(t ₀)=0, ₂(t ₀)=0 and ₃(t ₀)= ₃ ⁰ .The problem is integrated when the third component of the total angular momentum is different from zero (B ₁ 0). There now appear equilibrium solutions that did not exist in the caseB ₁=0, which can be determined in function of the value ofl ₃ ^r (the third component of the gyrostatic momentum).The possible types of solutions (elliptic, trigonometric, stationary) depend upon the nature of the roots of the functiong(u). The solutions for Euler angles are given in terms of functions of the timet. If we cancel the third component of the gyrostatic momentum (l ₃ ^r =0), the obtained solutions are valid for rigid bodies.     

V-R diagram for spiral galaxies. New insights into the hubble sequence

We examine the relation between the global parameters of spiral galaxies and their morphological type. We have represented the rotational velocityV at a radius of 25 mag arc sec^–2 against this radiusR for a sample of 56 galaxies. Different types of galaxies appear separated on this diagram. We have plotted above theV-R diagram isolines of total mass, angular momentum and mean surface density for isolated galaxies with circular motion in centrifugal equilibrium showing: (1) That the parameter that represents the morphological type is the mean surface density or its observational parameterV ²/R. (2) From aV-R diagram we can easily see what kinds of correlations we expect to find between the global properties of galaxies and their morphological type. (3) For every morphological type of galaxies there is a critical mass above which there is a change in its dynamical behaviour. Finally, consideringV ²/R as representative of the morphological type, we can deduce theoretically the empirical Tully-Fisher relation and the dependence of the slope and the zero point on the morphological type. The separation in logV that we expect to find for different types of galaxies for a constant luminosity is the same order as the experimental errors in the determination of logV. This explains the tight power-law relationship observed between this and the luminosity.     

The gas content in galactic disks: Correlation with kinematics

We consider the relationship between the total HI mass in late-type galaxies and the kinematic properties of their disks. The mass M_HI for galaxies with a wide variety of properties, from dwarf dIrr galaxies with active star formation to giant low-brightness galaxies, is shown to correlate with the product V_cR₀ (V_c is the rotational velocity, and R₀ is the radial photometric disks cale length), which characterizes the specific angular momentum of the disk. This correlation, along with the decrease in the relative mass of the gas in a galaxy with increasing V_c, can be explained in terms of the previous assumption that the gas density in the disks of most galaxies is maintained at a level close to the threshold (marginal) stability of a gaseous layer to local gravitational perturbations. In this case, the regulation mechanism of the star formation rate associated with the growth of local gravitational instability in the gaseous layer must play a crucial role in the evolution of the gas content in the galactic disk.     

Parametric relations of H II galaxies

The integrated H luminosities of giant H II regions and of H II galaxies can be predicted with accuracy comparable to the observational errors from the velocity widths of their emissionline profiles. In addition, giant H II regions also present a relation between linear size and their emission-line width. Based on the similarity of these relations with those expected for virialized systems, Terlevich and Melnick interpreted the observedsupersonic motions as due to the gravitational potential of a complex of gas and stars.We show that H II galaxies also present a relation between linear size and their emission-line width, which supports the gravitating model. We also show that the scatter in the luminosity-line width relation for H II galaxies seems to be correlated with linear size and compare the results with the fundamental plane for elliptical galaxies from Dressleret al. (1987).     

Rotation curves for spiral galaxies in clusters and in the field

Rotation curves of spiral galaxies in clusters are compared with their counterparts in the field using three criteria: (1) inner and outer velocity gradients, (2)M/L gradients, and (3) Burstein's mass type methodology. Both H emission-line rotation curves and more extendedHi rotation curves are used. A good correlation is found between the outer gradient of the rotation curve and the galaxy's distance from the centre of the cluster, in the sense that the inner galaxies tend to have falling rotation curves while the outer galaxies, and field galaxies, tend to have flat or rising rotation curves. A correlation is also found between theM/L gradient across a galaxy and the galaxy's position in the cluster, with the outer galaxies having steeperM/L gradients. Mass types for field spirals are shown to be a function of both Hubble-type and luminosity, contrary to earlier results. The statistical difference between the distribution of mass types in clusters and in the field reported by Bursteinet al. is confirmed. These correlations indicate that the inner cluster environment can strip away some fraction of the mass in the outer halo of a spiral galaxy, or alternatively, may not allow the halo to form.     

The origin of the density distribution of disc galaxies: a new problem for the standard model of disc formation

We present new models for the formation of disc galaxies that improve upon previous models by following the detailed accretion and cooling of the baryonic mass, and by using realistic distributions of specific angular momentum. Under the assumption of detailed angular momentum conservation, the discs that form have density distributions that are more centrally concentrated than an exponential. We examine the influence of star formation, bulge formation, and feedback on the outcome of the surface brightness distributions of the stars. Low angular momentum haloes yield disc galaxies with a significant bulge component and with a stellar disc that is close to exponential, in good agreement with observations. High angular momentum haloes, on the other hand, produce stellar discs that are much more concentrated than an exponential, in clear conflict with observations. At large radii, the models reveal distinct truncation radii in both the stars and the cold gas. The stellar truncation radii result from our implementation of star formation threshold densities, and are in excellent agreement with observations. The truncation radii in the density distribution of the cold gas reflect the maximum specific angular momentum of the gas that has cooled. We find that these truncation radii occur at H  i surface densities of roughly 1 M_⊙ pc⁻², in conflict with observations. We examine various modifications to our models, including feedback, viscosity, and dark matter haloes with constant-density cores, but show that the models consistently fail to produce bulge less discs with exponential surface brightness profiles. This signals a new problem for the standard model of disc formation: if the baryonic component of the protogalaxies out of which disc galaxies form has the same angular momentum distribution as the dark matter, discs are too compact.