scholarly journals The frequency of ring galaxies and the probability of their formation by collisions

1978 ◽  
Vol 79 ◽  
pp. 117-120 ◽  
Author(s):  
V. Dostal ◽  
V. Metlov
Keyword(s):  
Spiral Galaxy ◽  
Relative Velocity ◽  
Unit Volume ◽  
Spiral Galaxies ◽  
Absolute Magnitude ◽  
Stellar Systems ◽  
Clusters Of Galaxies ◽  
Central Collisions ◽  
Ring Galaxies ◽  
Minimum Separation

A survey of ring galaxies which were discovered in 1960 by B. Vorontsov-Velyaminov has been carried out using the Morphological Catalogue of Galaxies. Clusters of galaxies were also included. Such galaxies without spiral arms constitute 0.7% of all galaxies down to 15m.0, and are 100 times less frequent than spiral galaxies. This percentage is the same for clusters, but there are fields where ring galaxies are 3–5 times more frequent than the average. the probability of nearly central chance collisions of galaxies as proposed by some theories has been calculated. It was assumed that a ring galaxy is formed from the encounter of a spiral galaxy with another galaxy if its mass or luminosity is not less than 1% of that of the principal galaxy. the minimum separation of their centres was taken to be less than 2.7 kpc, but the angles between the vectors of the relative velocity and the planes of galaxies were not restricted. the lifetime of the rings once they are formed was assumed to be 109 years and the distribution of the galactic velocities was calculated according to a Maxwellian distribution. the number of galaxies of given absolute magnitude per unit volume was taken from Holmberg (Stars and Stellar Systems, 9, 123). the curvature of the trajectories was taken into account. So conditions were chosen to be most favourable for nearly central collisions.

Subluminal Mass

2020 ◽  
pp. 239-278
Author(s):  
P. J. E. Peebles
Keyword(s):  
Spiral Galaxy ◽  
Spiral Galaxies ◽  
Clusters Of Galaxies ◽  
Spiral Arms ◽  
The Galaxy ◽  
History Of ◽  
Large Clusters ◽  
Mass Component ◽  
Significant Mass

This chapter studies the presence of “subliminal matter.” The presence of significant mass in subluminal matter was first suggested in the 1930s by the surprisingly large velocities of galaxies in clusters of galaxies. The chapter traces the history of discovery of astronomical evidence of subluminal matter in large clusters of galaxies, in groups of a few or just two galaxies that are close enough that they seem likely to be gravitationally bound, and in individual spiral galaxies. There must be enough mass in spirals to account for the circular velocities of disk stars, and the mass rotationally supported in the disk must be large enough that gravity can form spiral arms, but this mass component cannot be so large that the spiral arms grow to destroy the observed nearly circular motions in the disk. These conditions require that most of the mass in a spiral galaxy is in a stable subluminal massive halo draped around the outskirts of the luminous parts of the galaxy.

Desiderata in connection by the calibration of the MK-system

1966 ◽  
Vol 24 ◽  
pp. 348-349
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Absolute Magnitude ◽  
Review Article ◽  
Stellar Systems ◽  
Astronomical Data ◽  
Intrinsic Colour

This is only an informal remark about some difficulties I am worrying about.I have tried to recalibrate the MK system in terms of intrinsic colour (B–V)0and absolute magnitudeMv. The procedures used have been described in a review article by Voigt (Mitt. Astr. Ges.1963, p. 25–35), and the results for stars of the luminosity classes Ia-O,I and II have been given also in Blaauw's article on the calibration of luminosity criteria in vol. III (Basic Astronomical Data, p. 401) ofStars and Stellar Systems.

Ultralong-period Cepheids: a possible primary distance indicator?

2012 ◽  
Vol 8 (S289) ◽  
pp. 282-286 ◽  
Author(s):  
G. Fiorentino ◽  
F. Annibali ◽  
G. Clementini ◽  
R. Contreras Ramos ◽  
M. Marconi ◽  
...  
Keyword(s):  
Spiral Galaxies ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Variable Stars ◽  
Evolutionary Status ◽  
Stellar Systems ◽  
Classical Cepheids ◽  
Type Ia ◽  
Distance Indicator ◽  
Crucial Test

AbstractWe present a project that aims to provide a complete theoretical and observational framework for an as yet unexplored class of variable stars, the ultralong-period Cepheids (P longer than 80–100 days). Given their very high luminosities (MV up to −7 mag), with the Hubble Space Telescope we will be able to observe them easily in stellar systems located at large distances (~ 100 Mpc). This limit will be further increased, out to the Hubble flow (~ 350 Mpc), using future ground-based facilities such as the European Extremely Large Telescope. The nature of their pulsation is as yet unclear, as is their evolutionary status, which seems different from the central helium-burning phase generally associated with classical Cepheids. These objects have been found to cover a very large metallicity range, from [Fe/H] ~ −2 dex to solar values, and they are located in heterogeneous stellar systems, from dwarf to spiral galaxies. Once completely characterized, they could provide a crucial test, since they have been found in all Type Ia supernova host spiral galaxies that have been monitored for variability over long periods and that currently offer sound constraints on the estimated value of the Hubble constant.

scholarly journals Rotation of Galaxy Dark Matter Halos

2006 ◽  
Vol 2 (S235) ◽  
pp. 104-104
Author(s):  
Stéphane Herbert-Fort ◽  
Dennis Zaritsky ◽  
Yeun Jin Kim ◽  
Jeremy Bailin ◽  
James E. Taylor
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Numerical Simulations ◽  
Galaxy Formation ◽  
Spiral Galaxy ◽  
Observational Studies ◽  
Spiral Galaxies ◽  
Satellite System ◽  
Dark Matter Halos ◽  
The Mean

AbstractThe degree to which outer dark matter halos of spiral galaxies rotate with the disk is sensitive to their accretion history and may be probed with associated satellite galaxies. We use the Steward Observatory Bok telescope to measure the sense of rotation of nearby isolated spirals and combine these data with those of their associated satellites (drawn from SDSS) to directly test predictions from numerical simulations. We aim to constrain models of galaxy formation by measuring the projected component of the halo angular momentum that is aligned with that of spiral galaxy disks, Jz. We find the mean bulk rotation of the ensemble satellite system to be co-rotating with the disk with a velocity of 22 ± 13 km/s, in general agreement with previous observational studies and suggesting that galaxy disks could be formed by halo baryons collapsing by a factor of ≈10. We also find a prograde satellite fraction of 51% and Jz, of the satellite system to be positively correlated with the disk, albeit at low significance (2655 ± 2232 kpc km/s).

scholarly journals ON THE PROBLEM OF THE SPECIFIC FREQUENCY OF GLOBULAR CLUSTERS

2021 ◽  
pp. 137-142
Author(s):  
Ikram Uralbaevich Tadjibaev
Keyword(s):  
Observational Data ◽  
Globular Clusters ◽  
Spiral Galaxies ◽  
Empirical Relationship ◽  
Flux Ratio ◽  
Quadratic Function ◽  
Absolute Magnitude ◽  
Host Galaxy ◽  
Specific Frequency ◽  
The Absolute

In the article, on the basis of observational data the problems of the specific frequency of globular clusters are studied. Possible relationships between them and the absolute stellar magnitude of their host galaxy are considered, where the observational data published in the literature were presented. It should be noted that before us the relationship between the specific frequency and the absolute magnitude is shown as exponential functions. An empirical relationship between the specific frequency and the absolute value of the host galaxy were obtained and showed that the dependence of the specific frequency on the absolute magnitude is not linear, but has a quadratic function. It is also shown that the specific frequency determines the number of globular clusters in a given galaxy relative to our Galaxy. Also in the article, based on the results of studies of the specific frequency, some discussions are presented related to the origin and evolution of globular clusters. The results obtained show that the ratios of the specific frequency to the luminosity of the host galaxy are different. Variations in the specific frequency of elliptical galaxies are associated with variations in the mass-to-luminous flux ratio. This may be due to the fact that the number of globular clusters in spiral galaxies per unit of luminosity of the halo and not of the entire galaxy. Analysis of the observational data shows that the values of the specific frequency of spiral galaxies are 5–6 times less than that of giant elliptical ones. As a result of the results of studies of the specific frequency of the globular clusters, unsolved problems are listed and possible solutions are shown. It is noted that the problem posed will be solved even more accurately if it is considered by the types of galaxies

scholarly journals Dynamo in Astrophysics

1990 ◽  
Vol 140 ◽  
pp. 83-89
Author(s):  
A.A. Ruzmaikin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Turbulent Flow ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Clusters Of Galaxies ◽  
Magnetic Structures ◽  
Random Magnetic Field ◽  
Astrophysical Objects

The fast dynamo acting in a turbulent flow explains the origin of magnetic fields in astrophysical objects. Stellar cycles and large-scale magnetic fields in spiral galaxies reflect the behaviour of a mean magnetic field. Intermittent magnetic structures in clusters of galaxies are associated with random magnetic field.

scholarly journals Resonant Stellar Orbits in Spiral Galaxies

1975 ◽  
Vol 69 ◽  
pp. 237-244
Author(s):  
P. O. Vandervoort
Keyword(s):  
Excellent Agreement ◽  
Spiral Galaxy ◽  
Harmonic Balance ◽  
Spiral Galaxies ◽  
Numerical Solutions ◽  
Equations Of Motion ◽  
Analytic Solutions ◽  
Stellar Orbits ◽  
Method Of Harmonic Balance ◽  
Resonance Phenomena

This paper reviews a series of investigations of the orbits of stars in the regions of the Lindblad resonances of a spiral galaxy. The analysis is formulated in an epicyclic approximation. Analytic solutions of the epicyclic equations of motion are obtained by the method of harmonic balance of Bogoliubov and Mitropolsky. These solutions represent the resonance phenomena exhibited by the orbits in generally excellent agreement with numerical solutions.

Extended rotation curves of high-luminosity spiral galaxies. III - The spiral galaxy NGC 7217

1978 ◽  
Vol 226 ◽  
pp. 770 ◽  
Author(s):  
C. J. Peterson ◽  
M. S. Roberts ◽  
V. C. Rubin ◽  
W. K., Jr. Ford
Keyword(s):  
Spiral Galaxy ◽  
Spiral Galaxies ◽  
High Luminosity ◽  
Rotation Curves

scholarly journals A Morphological Classification of Clusters of Galaxies from Einstein Images

1982 ◽  
Vol 97 ◽  
pp. 97-106 ◽  
Author(s):  
C. Jones ◽  
W. Forman
Keyword(s):  
Line Emission ◽  
Stellar Systems ◽  
Single Individual ◽  
Clusters Of Galaxies ◽  
Morphological Classification ◽  
Iron Line ◽  
Emission Process ◽  
X Ray ◽  
Extended Sources

The earliest Uhuru observations showed that cluster X-ray sources were not associated with single individual galaxies but were extended sources (Gursky et al. 1971, Kellogg et al. 1972, and Forman et al. 1972). The detection of iron line emission from X-ray spectroscopic observations (Mitchell et al. 1976 and Serlemitsos et al. 1977) showed both that the dominant X-ray emission process was thermal bremsstrahlung and that the gas had been processed through stellar systems before being injected into the intracluster medium.

Sign in / Sign up

Export Citation Format

Share Document