Model rotation curves of disk galaxies oriented at an arbitrary angle to the plane of the sky

We consider the effects of projection, absorption, and velocity dispersion on the shape of the rotation curve for a galaxy as a function of its disk inclination to the plane of the sky. We conclude that for galaxies with a fairly massive compact bulge these effects lead to a marked discrepancy between the rotation curve and the circular velocity curve even if their disks are viewed far from edge-on, especially for the rotation curves constructed from observations of the stellar component.     

Rotation curves for 135 edge-on galaxies

We summarize the results of our survey of rotation curves for edge-on galaxies. The observations were carried out with the 6-m Special Astrophysical Observatory telescope. Over the four years of our observations, we obtained spectra for 306 galaxies from the FGC catalog (Karachentsev et al. 1993). Rotation curves and radial velocities are given for 135 galaxies. The median radial velocity of the galaxies studied is 7800 km s^?1. Together with the observations performed by other authors with different instruments, this survey allowed us to produce a homogeneous sample of edge-on galaxies from the RFGC catalog (Karachentsev et al. 1999) uniformly distributed over the entire sky and to analyze the velocity field of galaxies on scales up to 100 Mpc.     

On the understanding of the observed flat or slowly rising rotation curves in large disk galaxies

Recent observations of the rotation curves of large disk galaxies of all Hubble-types have shown that they possess flat or slowly rising rotation curves up to large distances from the centre. It has been suggested here that such rotation curves are understood under normal fluid dynamical considerations provided that viscous (and/or magnetic) transfer of mass and angular momentum from inner to outer regions of these galaxies is efficient. Flow of gas from halo to the disk in regions close to the axis of rotation is also suggested. The existence of rising rotation curves in some galaxies with varying gradients and flat rotation curves in others suggest that probably these galaxies are not coeval. The formers are probably of more recent origin.     

GHASP: an Hα kinematic survey of spiral and irregular galaxies – IV. 44 new velocity fields. Extension, shape and asymmetry of Hα rotation curves

We present Fabry–Perot observations obtained in the frame of the GHASP survey (Gassendi HAlpha survey of SPirals). We have derived the Hα map, the velocity field and the rotation curve for a new set of 44 galaxies. The data presented in this paper are combined with the data published in the three previous papers providing a total number of 85 of the 96 galaxies observed up to now. This sample of kinematical data has been divided into two groups: isolated (ISO) and softly interacting (SOFT) galaxies. In this paper, the extension of the Hα discs, the shape of the rotation curves, the kinematical asymmetry and the Tully–Fisher relation have been investigated for both ISO and SOFT galaxies. The Hα extension is roughly proportional to R₂₅ for ISO as well as for SOFT galaxies. The smallest extensions of the ionized disc are found for ISO galaxies. The inner slope of the rotation curves is found to be correlated with the central concentration of light more clearly than with the type or the kinematical asymmetry, for ISO as well as for SOFT galaxies. The outer slope of the rotation curves increases with the type and with the kinematical asymmetry for ISO galaxies but shows no special trend for SOFT galaxies. No decreasing rotation curve is found for SOFT galaxies. The asymmetry of the rotation curves is correlated with the morphological type, the luminosity, the  ( B − V )  colour and the maximal rotational velocity of galaxies. Our results show that the brightest, the most massive and the reddest galaxies, which are fast rotators, are the least asymmetric, meaning that they are the most efficient with which to average the mass distribution on the whole disc. Asymmetry in the rotation curves seems to be linked with local star formation, betraying disturbances of the gravitational potential. The Tully–Fisher relation has a smaller slope for ISO than for SOFT galaxies.     

Ionized gas rotation curves in nearby dwarf galaxies

We present the results of study of the ionized gas velocity fields in 28 nearby (systemic velocity below 1000 km s^?1) dwarf galaxies. The observations were made at the 6-m BTA telescope of the SAO RAS with the scanning Fabry-Perot interferometer in the Hα emission line. We were able to measure regular circular rotation parameters in 25 galaxies. As a rule, rotation velocities measured in HII are in a good agreement with the data on the HI kinematics at the same radii. Three galaxies reveal position angles of the kinematic axis in the HII velocity fields that strongly (tens of degrees) differ from the measurements in neutral hydrogen at large distances from the center or from the orientation of the major axis of optical isophotes. The planes of the gaseous and stellar disks in these galaxies most likely do not coincide. Namely, in DDO99 the gaseous disk is warped beyond the optical radius, and in UGC3672 and UGC8508 the inclination of orbits of gas clouds varies in the inner regions of galaxies. It is possible that the entire ionized gas in UGC8508 rotates in the plane polar to the stellar disk.     

A theory of galactic mass and rotation curves

The goal of this paper is to account for the complete observed rotation curves of disk galaxies without dark matter. To attain that goal, use is made of a conservation law from stability theory of linear waves, leading to a vector-based theory of gravitation. In the theory, galactic centers are sites of strong gravitational fields. The new theory predicts extra matter at the center of disk galaxies, which is well-known to be consistent with intergalactic dynamics. For given disk radiusr ₀ and edge tangential speedv, the greater the deviation of a rotation curve from linear (solid disk rotation), the greater the mass of the galaxy as a multiple of Newtonian massr ₀v²/G, up to a factor of about 1000. In an approximate calculation it turns out that disk density (r) (in kg m^–2) is proportional to 1/r for typical rotation curves. Rotation is characterized by two constants which in turn are determined by the edge speed and mass distribution. Not just any curve shape can be so obtained; in fact, the theoretically possible curves correspond to observed curves.     

Kinematics and stellar disk modeling of lenticular galaxies

We present the results of spectroscopic observations of three S0-Sa galaxies: NGC 338, NGC 3245, and NGC 5440 at the SAO RAS 6-m BTA telescope. The radial distributions of the line-ofsight velocities and radial velocity dispersions of stars and ionized gas were obtained, and rotation curves of galaxies were computed. We construct the numerical dynamic N-body galaxy models with N ?? 10⁶ points. The models include three components: a ??live?? bulge, a collisionless disk, dynamically evolving to the marginally stable state, and a pseudo-isothermal dark halo. The estimates of radial velocities and velocity dispersions of stars obtained from observations are compared with model estimates, projected onto the line of sight. We show that the disks of NGC 5440 and the outer regions of NGC 338 are dynamically overheated. Taking into account the previously obtained observations, we conclude that the dynamic heating of the disk is present in a large number of early-type disk galaxies, and it seems to ensue from the external effects. The estimates of the disk mass and relative mass of the dark halo are given, as well as the disk mass-to-luminosity ratio for seven galaxies, observed at the BTA.     

A fluid dynamical flow model for the central peak in the rotation curve of disk galaxies

The rotation curve of the central region in some disk galaxies shows a linear rise, terminating at a peak (primary peak) which is then followed by a deep minimum. The curve then again rises to another peak at more or less half-way across the galactic radius. This latter peak is considered as the peak of the rotation curve in all large-scale analysis of galactic structure. The primary peak is usually ignored for the purpose. In this work an attempt has been made to look at the primary peak as the manifestation of the post-explosion flow pattern of gas in the deep central region of galaxies. Solving hydrodynamical equations of motion, a flow model has been derived which imitates very closely the actually observed linear rotational velocity, followed by the falling branch of the curve to minimum. The theoretical flow model has been compared with observed results for nine galaxies. The agreement obtained is extremely encouraging. The distance of the primary peak from the galactic centre has been shown to be correlated with the angular velocity in the linear part of the rotation curve. Here also, agreement is very good between theoretical and observed results. It is concluded that the distance of the primary peak from the centre not only speaks of the time that has elapsed since the explosion occurred in the nucleus, it also speaks of the potential capability of the nucleus of the galaxy for repeating explosions through some efficient process of mass replenishment at the core.     

The kinematic effects on the rotation curve of a galaxy

In this paper, it is pointed out that if the spiral galaxy revolves about some common centre as a whole, the rotation curve will be changed by the kinematic effects. The common centre could be the centre of supercluster or the centre of dark matter and luminous matter.The kinematic effects on rotation curve are calculated. The additional velocity caused by revolving about the common centre is obtained. In case the direction of revolution is opposite (or consistent) to the direction of rotation, then in the outer region of nucleus, a flat rotation curve could be changed to a constant negative (or postive) gradient. The 44 rotation curves of Sb and Sc galaxies are expressed by means of linear least-squares fit, from which the period of revolving and the ratio of tidal force to self-gravitating force are calculated for every galaxy in extreme cases. The periods for most galaxies are in the reasonable region about 10⁹ years. The tidal force is always less than gravitating force, so the system could be maintained in such a revolving cases. At last, rotation curves in all directions of disk are suggested to pick out the kinematic effects from pure rotation.Work supported by the National Science Foundation of China, under Grant No. 1860610.     

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 onset of warps in Spitzer observations of edge-on spiral galaxies

We analyse warps in the nearby edge-on spiral galaxies observed in the Spitzer /Infrared Array Camera (IRAC) 4.5-μm band. In our sample of 24 galaxies, we find evidence of warp in 14 galaxies. We estimate the observed onset radii for the warps in a subsample of 10 galaxies. The dark matter distribution in each of these galaxies are calculated using the mass distribution derived from the observed light distribution and the observed rotation curves. The theoretical predictions of the onset radii for the warps are then derived by applying a self-consistent linear response theory to the obtained mass models for six galaxies with rotation curves in the literature. By comparing the observed onset radii to the theoretical ones, we find that discs with constant thickness can not explain the observations; moderately flaring discs are needed. The required flaring is consistent with the observations. Our analysis shows that the onset of warp is not symmetric in our sample of galaxies. We define a new quantity called the onset-asymmetry index and study its dependence on galaxy properties. The onset asymmetries in warps tend to be larger in galaxies with smaller disc scalelengths. We also define and quantify the global asymmetry in the stellar light distribution, that we call the edge-on asymmetry in edge-on galaxies. It is shown that in most cases the onset asymmetry in warp is actually anticorrelated with the measured edge-on asymmetry in our sample of edge-on galaxies and this could plausibly indicate that the surrounding dark matter distribution is asymmetric.     

Study of the structure and kinematics of the NGC 7465/64/63 triplet galaxies

We analyze new observational data obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the multimode SCORPIO instrument and the Multi-Pupil Fiber Spectrograph for the group of galaxies NGC 7465/64/63. For one of the group members (NGC 7465), the presence of a polar ring has been suspected. We have constructed the large-scale brightness distributions, the ionized-gas velocity and velocity dispersion fields for all three galaxies as well as the line-of-sight velocity curves based on emission and absorption lines and the stellar velocity field in the central region for NGC 7465. As a result of our analysis of the data obtained, we have discovered an inner stellar disk (r ?? 0.5 kpc) and a warped gaseous disk in NGC 7465, in addition to the main stellar disk. Based on a joint study of our photometric and spectroscopic data, we have established that NGC 7464 is an irregular IrrI-type galaxy whose structural and kinematic peculiarities most likely resulted from its gravitational interaction with NGC 7465. The velocity field of the ionized gas in NGC 7463 turns out to be typical of barred spiral galaxies, and the warp of the outer parts of its disk could arise from a close encounter with one of the galaxies of the environment.     

Rotation curve of galaxies by the force induced by mass of moving particles

Many attempts have been made to explain the flat rotation curve of spiral galaxies regardless of distance from the center, in disagreement with the Newtonian prediction that this speed should diminish as the inverse square of distance. One explanation for this discrepancy is that the galaxy is embedded in dark matter, which interacts with baryonic matter only gravitationally. Many studies have focused on finding the distribution of this dark matter that fits well with observed data, but it is by definition undetectable by current technology, and must therefore remain hypothetical. Instead of dark matter, we propose a novel force, named mirinae force, generated by the mass of relatively-moving particles, and demonstrate that this force explains the rotation curve and evolution of a galaxy in which some of the inner mass of the supermassive black hole at the galactic center is assumed to be revolving at a relativistic speed. The calculation yielded important results that support the existence of mirinae force and validate the proposed model: First, the mirinae force explains why most of the matter is in the galactic disk and in circular motion which is similar to that of particles in a cyclotron. Second, the mirinae force explains well both the flat rotation curve and the varied slope of the rotation curve observed in spiral galaxies. Third, at the flat velocity of 220 km/s, the inner mass of the Milky Way calculated by using the proposed model is 6.0×10¹¹ M _⊙, which is very close to 5.5×10¹¹ M _⊙ (r<50 kpc, including Leo I) estimated by using the latest kinematic information.     

Ultra-flat galaxies selected from RFGC catalog. II. Orbital estimates of halo masses

We used the Revised Flat Galaxy Catalog (RFGC) to select 817 ultra-flat (UF) edge-on disk galaxies with blue and red apparent axial ratios of (a/b)_B > 10.0 and (a/b)_R > 8.5. The sample covering the whole sky, except the Milky Way zone, contains 490 UF galaxies with measured radial velocities. Our inspection of the neighboring galaxies around them revealed only 30 companions with radial velocity difference of | ΔV |< 500 kms^?1 inside the projected separation of R_p < 250 kpc. Wherein, the wider area around the UF galaxy within R_p < 750 kpc contains no other neighbors brighter than the UF galaxy itself in the same velocity span. The resulting sample galaxies mostly belong to the morphological types Sc, Scd, Sd. They have a moderate rotation velocity curve amplitude of about 120 km s^?1 and a moderate K-band luminosity of about 10¹⁰L_⊙. The median difference of radial velocities of their companions is 87 km s^?1, yielding the median orbital mass estimate of about 5 × 10¹¹M_⊙. Excluding six probable non-isolated pairs, we obtained a typical halo-mass-to-stellar-mass of UF galaxies of about 30, what is almost the same one as in the principal spiral galaxies, like M31 and M81 in the nearest groups. We also note that ultra-flat galaxies look two times less “dusty” than other spirals of the same luminosity.     

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.     

Relationship between the thickness of stellar disks and the relative mass of a dark galactic halo

We analyze the R-and K _s-band photometric profiles for two independent samples of edge-on galaxies. The thickness of old stellar disks is shown to be related to the relative masses of the spherical and disk components of galaxies. The radial-to-vertical scale length ratio for galactic disks increases (the disks become thinner) with increasing total mass-to-light ratio of the galaxies, which reflects the relative contribution of the dark halo to the total mass, and with decreasing central deprojected disk brightness (density). Our results are in good agreement with numerical models of collisionless disks that evolved to a marginally stable equilibrium state. This suggests that, in most galaxies, the vertical stellar-velocity dispersion, on which the equilibrium-disk thickness depends, is close to a minimum value that ensures disk stability. The thinnest edge-on disks appear to be low-brightness galaxies in which the dark-halo mass far exceeds the stellar-disk mass.     

A note on the mass-loaded MHD flow of the solar wind towards a cometary nucleus

Dependence of the central velocity gradients on Hubble's type is presented for 78 spiral galaxies with existing rotation curves. Also the dependence of the maximum rotational velocities of 27 galaxies on both Hubble's type and the luminosity is studied. The central velocity gradient is shown to be related with Hubble's type. Maximum rotational velocities of 27 galaxies of our sample depend on Hubble's type such that the mean values of maximum rotational velocity decrease from Sa through Sc. It is also determined that there is a dependence of the maximum rotational velocity on the absolute blue magnitude for each intrinsic Hubble type. For each Hubble type, maximum rotational velocity increases with increasing absolute blue magnitudes.     

The formation of superdense gaseous cores in the nuclei of disk galaxies: II

In a previous paper (hereafter referred to as Paper I) we have tried to show that superdense cores in the nuclei of disk galaxies can be formed by accretion of gas ejected by the evolved stars which populate the central bulge of these galaxies. Solving the equations for radial flow of a magnetized gas, we found that the accretion of an explodable mass at the core can be achieved over a time-scale ranging from a few times 10⁷ and a few times 10⁸ yr. It was shown, however, that the accretion process is seriously inhibited if the gas possesses sufficient rotational velocity but lacks any dissipative, mechanism within the system. Since rotational velocity is an observed parameter of the stars which shed the gas to be accreted, one must consider the existence of some dissipative force in it in order that the accretion process may be efficient. In the present paper, therefore, we have solved the problem of the flow of a rotating, viscous (variable), magnetized gas. With plausible assumptions regarding some of the parameters involved, the time-scale for the accretion of an explodable mass (10⁹ M ) at the core again turns out to be ranging between a few times 10⁷ and a few times 10⁸yr. Such time-scale has been proposed by several authors as that for repeated explosions in nuclei of these galaxies. It has also been proposed by many authors that the spiral arms are generated and destroyed in disk galaxies over the same time-scale. Our solution also yields a nearly linear rotational velocity law which is usually observed in the central regions of these galaxies.