Vera C. Rubin

Rotational properties of 21 SC galaxies with a large range of luminosities and radii, from NGC 4605 /R = 4kpc/ to UGC 2885 /R = 122 kpc/

For 21 Sc galaxies whose properties encompass a wide range of radii, masses, and luminosities, we have obtained major axis spectra extending to the faint outer regions, and have deduced rotation curves. The galaxies are of high inclination, so uncertainties in the angle of inclination to the line of sight and in the position angle of the major axis are minimized. Their radii range from 4 to 122 kpc (H = 50km s-1 Mpc-1); in general, the rotation curves extend to 83% or R25i.b. When plotted on a linear scale with no scaling, the rotation curves for the smallest galaxies fall upon the initial parts of the rotation curves for the larger galaxies. All curves show a fairly rapid velocity rise to V ˜ 125 km s-1 at R ˜ 5 kpc, and a slower rise thereafter. Most rotation curves are rising slowly even at the farthest measured point. Neither high nor low luminosity Sc galaxies have falling rotation curves. Sc galaxies of all luminosities must have significant mass located beyond the optical image. A linear relation between log Vmax and log R follows from the shape of the common rotation curve for all Scs, and the tendency of smaller galaxies, at any R, to have lower velocities than the large galaxies at that R. The significantly shallower slope discovered for this relation by Tully and Fisher is attributed to their use of galaxies of various Hubble types and the known correlation of Vmax with Hubble type. The galaxies with very large central velocity gradients tend to be large, of high luminosity, with massive, dense nuclei. Often their nuclear spectra show a strong stellar continuum in the red, with emission lines of [N II] stronger than Halpha. These galaxies also tend to be 13 cm radio continuum sources. Because of the form of the rotation curves, small galaxies undergo many short-period, very differential, rotations. Large galaxies undergo (in their outer parts) few, only slightly differential, rotations. This suggests a relation between morphology, rotational properties, and the van den Bergh luminosity classification, which is discussed. UGC 2885, the largest Sc in the sample, has undergone fewer than 10 rotations in its outer parts since the origin of the universe but has a regular two-armed spiral pattern and no significant velocity asymmetries. This observation puts constraints on models of galaxy formation and evolution.

Rotation Curves of Spiral Galaxies

▪ Abstract Rotation curves of spiral galaxies are the major tool for determining the distribution of mass in spiral galaxies. They provide fundamental information for understanding the dynamics, ev...

Mass Density Profiles of Low Surface Brightness Galaxies

We derive the mass density profiles of dark matter halos that are implied by high spatial resolution rotation curves of low surface brightness galaxies. We find that, at small radii, the mass density distribution is dominated by a nearly constant density core with a core radius of a few kiloparsecs. For , the distribution of inner a r(r) ∼ r slopes a is strongly peaked around . This is significantly shallower than the cuspy halos found a p 0.2 a ≤ 1 in cold dark matter simulations. While the observed distribution of a does have a tail toward such extreme values, the derived value of a is found to depend on the spatial resolution of the rotation curves: is found only a ≈ 1 for the least well resolved galaxies. Even for these galaxies, our data are also consistent with constant-density cores ( ) of modest (∼1 kpc) core radius, which can give the illusion of steep cusps when insufficiently a p 0 resolved. Consequently, there is no clear evidence for a cuspy halo in any of the low surface brightness galaxies observed. Subject headings: dark matter — galaxies: fundamental parameters — galaxies: kinematics and dynamicsWe derive the mass density profiles of dark matter halos that are implied by high spatial resolution rotation curves of low surface brightness galaxies. We find that at small radii, the mass density distribution is dominated by a nearly constant density core with a core radius of a few kpc. For ρ(r) ∼ r, the distribution of inner slopes α is strongly peaked around α = −0.2. This is significantly shallower than the cuspy α ≤ −1 halos found in CDM simulations. While the observed distribution of α does have a tail towards such extreme values, the derived value of α is found to depend on the spatial resolution of the rotation curves: α ≈ −1 is found only for the least well resolved galaxies. Even for these galaxies, our data are also consistent with constant density cores (α = 0) of modest (∼ 1 kpc) core radius, which can give the illusion of steep cusps when insufficiently resolved. Consequently, there is no clear evidence for a cuspy halo in any of the low surface brightness galaxies observed. Subject headings: galaxies: kinematics and dynamics — galaxies: fundamental parameters — dark matter

High-Resolution Rotation Curves of Low Surface Brightness Galaxies. II. Mass Models

We present mass models for a sample of 30 high-resolution rotation curves of low surface brightness galaxies. We fit both pseudoisothermal (core dominated) and cold dark matter (CDM; cusp dominated) halos for a wide variety of assumptions about the stellar mass-to-light ratio. We find that the pseudoisothermal model provides superior fits. CDM fits show systematic deviations from the data and often have a small statistical likelihood of being the appropriate model. The distribution of concentration parameters is too broad, and has too low a mean, to be explained by low-density, flat CDM (ΛCDM). This failing becomes more severe as increasing allowance is made for stellar mass: Navarro, Frenk, & White (NFW) model fits require uncomfortably low mass-to-light ratios. In contrast, the maximum disk procedure does often succeed in predicting the inner shape of the rotation curves, but it requires uncomfortably large stellar mass-to-light ratios. The data do admit reasonable stellar population mass-to-light ratios if halos have cores rather than cusps.

Extended rotation curves of high-luminosity spiral galaxies. IV - Systematic dynamical properties, SA through SC

For a sample of 10 high-luminosity spiral galaxies, Sa through Sc, we have obtained accurate rotation curves which extend to about 80% of the de Vaucouleurs radii.

Rotational properties of 23 Sb galaxies

We have obtained major axis spectra for 23 Sb galaxies in a sample chosen to encompass a wide range of radii, masses, and luminosities. These are generally field galaxies of high inclination, and our spectrograms extend, on the average, to about three quarters of the isophotal radius, R/sub 25/. The Sb rotation curves exhibit many of the systematic trends with luminosity shown by the Scs studied previously. Velocities in small, low-luminosity, low-mass Sb galaxies rise gently to a maximum rotational velocity in a large fraction of their isophotal radius; velocities in large, high-luminosity, high-mass Sb galaxies reach their (higher) rotational velocity in only a small fraction of their isophotal radius. However, rotational velocities span a range of higher values for Sb than for Sc galaxies.

Cospatial counterrotating stellar disks in the Virgo E7/S0 galaxy NGC 4550

Two cospatial stellar disks have been discovered, one orbiting prograde, one orbiting retrograde, in NGC 4550, an E7/SO galaxy in the core of the Virgo Cluster. One of the stellar disks is coincident with a gas disk. Absorption and emission-line velocities for the two counterrotating components have been measured over about one-third of the optical diameter (30″). It is proposed that after the initial stellar disk of NGC 4550 was formed, a substantial amount of counterrotating gas was acquired ≥10 9 yr ago. It then settled to the plane via dissipation; the bulk of the counterrotating stars most likely formed after the gas settled to the plane

Kinematic Disturbances in Optical Rotation Curves among 89 Virgo Disk Galaxies

For 89 galaxies, mostly spirals, in the Virgo Cluster region, we have obtained optical long-slit major-axis spectra of the ionized gas. We find the following: (1) One-half of the Virgo galaxies we observed have regular rotation patterns, while the other half exhibit kinematic disturbances ranging from mild to major. Velocity complexities are generally consistent with those resulting from tidal encounters or accretion events. Since kinematic disturbances are expected to fade within ~109 yr, many Virgo galaxies have experienced several significant kinematic disturbances during their lifetimes. (2) There is no strong correlation of rotation curve complexity with Hubble type, with galaxy luminosity, with local galaxy density, or with H I deficiency. (3) A few Virgo galaxies have ionized gas of limited extent, with velocities exceptionally low for their luminosities. In these galaxies the gas must be not rotationally supported. (4) There is a remarkable difference in the distribution of galaxy systemic velocity for galaxies with regular rotation curves and galaxies with disturbed rotation curves. Galaxies with regular rotation patterns show a flat distribution with velocities ranging from V0 = -300 km s-1 to V0 = +2500 km s-1; galaxies with disturbed kinematics have a Gaussian distribution that peaks at V0 = +1172 ± 100 km s-1, close to the cluster mean velocity. This latter distribution is virtually identical to the distribution of systemic velocity for elliptical galaxies in Virgo. However, disturbed galaxies are less concentrated to the cluster core than are the ellipticals; those near the periphery have velocities closer to the mean cluster velocity. Thus, spirals with disturbed kinematics are preferentially on radial orbits, which bring them to the denser core, where tidal interactions are strong and/or more common. Because they spend much time near apocenter, we observe them near the cluster periphery. Some may be falling into the core for the first time. These observations suggest that for a nonvirialized cluster like Virgo, galaxies may encounter either local (nearby galaxies) or global (cluster-related) interactions. These interactions may alter the morphology of the galaxy and may also play a role in driving the Virgo Cluster toward dynamical equilibrium.

Optical properties and dynamics of galaxies in the Hickson compact groups

Broad-band R images, Hα images, and Hα long-slit spectroscopy for a set of galaxies in 21 Hickson compact groups are presented. Some of the galaxies are tidally interacting and distorted; some appear morphologically normal. Observed velocity patterns range from too peculiar to form rotation curves (one-third of spiral sample), to abnormal (one-third), to normal (one-third); peculiar rotation curves are only loosely coupled with peculiar morphology. For individual galaxies, values of integral M/L B are low, slightly lower than for field spirals of equivalent Hubble type. All of these observations support a model in which the compact group galaxies have only recently accumulated from the lumpy general galaxy distribution, and which tidal interactions are frequent and ongoing.

The rotation of spiral galaxies.

There is accumulating evidence that as much as 90 percent of the mass of the universe is nonluminous and is clumped, halo-like, around individual galaxies. The gravitational force of this dark matter is presumed to be responsible for the high rotational velocities of stars and gas in the disks of spiral galaxie. At present, the form of the dark matter is unknown. Possible candidates span a range in mass of 1070, from non-zero-mass neutrinos to massive black holes.