Scd Galaxies Research Articles

Dark matter effects explanation with the torsion in the Minkowski space

Investigating rotation curves and the Tully–Fisher ratio within galaxies represents a central theme of extensive research and scientific interest. Despite several theoretical models, a comprehensive explanation of the observed correlation between galaxy types and their rotation curves remains elusive. This study endeavors to bridge this knowledge gap by delving into the discernible connection between the presence of dark matter and galaxy classification. By meticulously examining the gravitational field’s dependency on its source’s point symmetry, we introduce a novel theoretical framework that offers a coherent rationale for these empirical findings. Our proposed model explains the appearance of dark matter as a direct consequence of the reduction of point symmetry in gravitational systems. Neither arbitrary systems with a high mass density nor a perfectly spherically symmetric mass distribution give the observable effects of dark matter. Special attention was paid to the axial symmetry scenario as a reasonable approach for modeling the mass distribution in most galaxies. We thoroughly analyzed, showing strong agreement with experimental observations for dwarf, Sb, and Scd galaxies. Thus, our study provides a compelling theoretical foundation for elucidating the intricate interplay between galaxy types, rotation curves, and the presence of dark matter, shedding new light on the dynamics of the cosmos.

Classification and evolution of galaxies according to the dynamical state of host clusters and galaxy luminosities

ABSTRACT We analyse the dependence of galaxy evolution on cluster dynamical state and galaxy luminosity for a sample of 146 galaxy clusters from the Yang SDSS catalogue. Clusters were split according to their velocity distribution in Gaussians (G) and Non-Gaussians (NG), and further divided by luminosity regime. We performed a classification in the plane of mean stellar age versus specific star formation rate, providing three classes: star-forming (SF), passive (PAS) and intermediate (GV – green valley). We show that galaxies evolve in the same way in G and NG systems, but also suggest that their formation histories lead to different mixtures of galactic types and infall patterns. Separating the GV into star-forming and passive components, we find more bright galaxies in the passive mode of NG systems than in that of G systems. We also find more intermediate faint galaxies in the star-forming component of NG systems than in that of G systems. Our results suggest that GV is the stage where the transition from types Sab and Scd to S0 must be taking place, but the conversion between morphological types is independent of the dynamical stage of the clusters. Analysing the velocity dispersion profiles, we find that objects recently infalling onto clusters have a different composition between G and NG systems. While all galaxy types infall on to G systems, Sab and Scd dominate the infall on to NG systems. Finally, we find that faint Scd galaxies in the outskirts of NG systems present higher asymmetries relative to the mean asymmetry of field galaxies, suggesting that there are environmental effects acting on these objects.

Alignment of galaxies relative to their local environment in SDSS-DR8

We study the alignment of galaxies relative to their local environment in SDSS-DR8 and, using these data, we discuss evolution scenarios for different types of galaxies. We defined a vector field of the direction of anisotropy of the local environment of galaxies. We summed the unit direction vectors of all close neighbours of a given galaxy in a particular way to estimate this field. We found the alignment angles between the spin axes of disc galaxies, or the minor axes of elliptical galaxies, and the direction of anisotropy. The distributions of cosines of these angles are compared to the random distributions to analyse the alignment of galaxies. Sab galaxies show perpendicular alignment relative to the direction of anisotropy in a sparse environment, for single galaxies and galaxies of low luminosity. Most of the parallel alignment of Scd galaxies comes from dense regions, from 2...3 member groups and from galaxies with low luminosity. The perpendicular alignment of S0 galaxies does not depend strongly on environmental density nor luminosity; it is detected for single and 2...3 member group galaxies, and for main galaxies of 4...10 member groups. The perpendicular alignment of elliptical galaxies is clearly detected for single galaxies and for members of < 11 member groups; the alignment increases with environmental density and luminosity. We confirm the existence of fossil tidally induced alignment of Sab galaxies at low z. The alignment of Scd galaxies can be explained via the infall of matter to filaments. S0 galaxies may have encountered relatively massive mergers along the direction of anisotropy. Major mergers along this direction can explain the alignment of elliptical galaxies. Less massive, but repeated mergers are possibly responsible for the formation of elliptical galaxies in sparser areas and for less luminous elliptical galaxies.

A study of the intrinsic flatness of disk galaxies

The intrinsic flatness of disk galaxies is very important when calculating their angle of inclinations. Our statistical analysis of 14,988 disk galaxies taken from the Lyon-Meudon Extragalactic Database shows that the intrinsic flatness is closely related to the morphological type. In general, the intrinsic axis ratio q 0 is larger for lenticulars and irregulars than for spirals, and among the sprials, is larger for the early types than for the late types. The Scd galaxies are found to have the smallest q 0.

UBVRI PHOTOMETRY OF SPIRAL GALAXIES IN THE VIRGO AND FORNAX CLUSTERS

ABSTRACT In this study multi-aperture photo electric photometry in the five passbands UBVRI for 171 and 46 galaxies in the Virgo and Fornax clusters, respectively, are presented. New radial velocities and H I profiles for 17 galaxies in Fornax have been obtained. Total magnitudes and colours are derived for around 800 individual measurements using standard growth curves in B, U-B and B-V. Total colours V-R and R-I are derived from a set of synthetic colour growth curves. The resulting total B magnitudes have an internal error of 0.09 mag, the U-B colours have an internal error of 0.03 mag, and in B-V V-R and R-I the error is 0.02 mag. The derived magnitudes of a nearly complete sample (~90%) of all Virgo and Fornax spirals with i >/= 45 degrees (as listed in the Virgo and Fornax cluster catalogues) lend themselves for a detailed study of the luminosity-line width relation (Tully-Fisher relation) in UBVRI. In particular the effects of different parameter sets (line widths, axial ratios, morphological types) and corrections on the luminosity-lkine width relation are investigated. Furthermore, the dependence on morphological galaxy type is examined, new internal absorption corrections are derived and the accuracy of the luminosity-line width method in different passbands is studied. The data are used to determine a distance of the spiral galaxies of the Fornax cluster relative to the Virgo spirals. The results are as follows: The slope of the luminosity-line width relation in B is -6.50 ± 0.36 and depends on the line width correction. Differences of up to 0.2 mag in the intercept of each cluster are found when using different input parameter; changes due to different corrections apply to both clusters simultaneously, and have little effect on the relative distance. Subsamples as to inclination or galaxy type affect the relative distance only marginally, while a restriction in apparent magnitude results in a change of the slope and the intercept of each cluster and of the relative distance. A limitation in line width affects Fornax more than Virgo, because the scatter in the luminosity-line width relation of the Fornax cluster changes strongly with line widths (or magnitude). The luminosity-line width relation s in other passbands show the same scatter for Virgo (about 0.64 mag); in Fornax the scatter varies with wavelength and is largest in the I-band. The slope is dependent on wavelength and approaches an asymptotic value of about -8.5 at long wavelengths. The mean relative distance modulus over all passbands is mF - mV = -0.40 ± 0.10 mag. The variation of the inclination dependent part of the internal absorption with wavelength is investigated. The colours show a dependence on axial ratio only for Sb to Scd galaxies. The resulting internal absorption with respect to the RC3 B-band absorption for these galaxy types is 116% in the U-band, 82% in V, 74% in R and 63% in I. Furthermore, a new absorption law of AB = 1.7 log R was found for Sb to Scd galaxies (as compared with the RC3 law of AB = 1.47 log R), though the present sample is too small for the result to be reliable. The potential of a luminosity-colour relation is inspected. However, error and scatter are much higher than in the luminosity-line width relation. The resulting relative distance of Fornax and Virgo is consistent within the errors with the distance found using the luminosity-line width relation. The spiral galaxies of the Fornax cluster are found to be closer than the Virgo spirals by 0.40 mag. The resulting peculiar velocity of Fornax relative to Virgo lies between 150 km s-1 and 300 km s-1, depending on the virgocentric infall model, and points away from the Local Group. The division of Virgo into subclusters and the effect of H I stripping are discussed.

Near-Infrared Surface-Photometry of Edge-on Scd Galaxies, NGC 3556 and NGC 4244

Near-infrared images in the J and K′ bands of two edge-on late-type galaxies, NGC 3556 and NGC 4244, were obtained with the newly developed common-use instrument for infrared imaging and spectroscopy at the Okayama Astrophysical Observatory (OASIS). These images were analyzed to yield the surface-photometric and model parameters for the global structure of these Scd galaxies. NGC 3556 shows a disk and a bar-like structure, both of which have an approximately exponential surface-brightness distribution. The absorption feature of NGC 3556 is complex, and only the most prominent central dark lane of AJ &amp;lt; 0.5 was taken into the modeling. NGC 4244 comprises a disk and a weak bulge, both having an approximately exponential surface-brightness distribution, suffering under negligible internal absorption by a faint dark lane of AJ &amp;lt; 0.1. Global models of the 3-D emissivity structure and absorption layer have been constructed to reproduce the observed main features. The global models indicate that both galaxies are optically thin in the V band when seen face on (τ0,v &amp;lt; 0.4), with the reservation of a possible presence of locally opaque structures in NGC 3556. Brief discussions are given concerning the insufficiency of simple absorption-layer models and the strong contrast between the two Scd galaxies regarding their interstellar matter and star-forming activities.

Colors and the Byurakan classification of galaxies

It is shown that the galaxies of the Byurakan classes 2 and 5, which belong to the morphological subtypes Sa, Sab, Sb, and Sbc (including the SB galaxies), are on average somewhat bluer than the galaxies of classes 3 and 4 of these same subtypes. Among galaxies of the classes 2, 5, and 2s, objects with excess ultraviolet radiation are found rather more frequently than among galaxies of classes 3 and 4. Whereas Sa, Sab, Sb, and Sbc galaxies of classes 3 and 4 are scarcely different from one another in their mean B -V and U -B, Sc and Scd galaxies of class 4, as also of classes 2 and 5, are on average bluer than class 3. In comparison with the latter, among Sc and Sod ~alaxies of classes 2, 4, and 5, there are rather more objects with negative U -B. These facts, together with the already known indicators of activity in galaxies of the classes 2, 4, 5, and 2s, in their turn point to active processes taking place in galaxies with diffuse, split, semistellar, or starlike nuclei.

Extragalactic CO - Gas distributions which follow the light in IC 342 and NGC 6946

The CO emission in the two Scd galaxies, IC 342 and NGC 6946, has been mapped using the 14 m FCRAO telescope (HPBW = 50''). In each galaxy, the radial distribution of CO out to Rroughly-equal10 kpc exhibits a falloff which follows the exponential luminosity profile from the stellar disk. Neither galaxy shows a breach in the molecular gas like that found in our Galaxy between the nucleus and the molecular cloud annulus. The occurrence of this gap in our own Galaxy, but in neither of the external galaxies, suggests a possible link between the deficiency of gas and the presence of either a nuclear bulge or inner Lindblad resonance (ILR). From its rotation curve, the Milky Way has a large nuclear bulge and also has an ILR expected in the vicinity of the hole in the CO distribution. The CO rotation curves for IC 342 and NGC 6946 agree well with previous HI observations; at the present resolution these galaxies appear to undergo nearly rigid rotation inside R = 5 kpc and therefore have no ILRs and have small nuclear bulges. Further support for the association of the gap with ILR or bulge is provided by brief observations reportedmore » here of NGC 4321, a more distant Sc galaxy with a rotation curve similar to the Milky Way; the CO distribution appears like that in our own Galaxy with coarser resolution.« less

NGC 3344 - UNUSUAL ABUNDANCES FOR AN SBC GALAXY

ABSTRACT Spectrophotometry of H II regions in the Sbc galaxy NGC 3344 reveals that it has a strong radial excitation gradient, with the ratio of the log of forbidden O III to H-beta rising to +0.7 in the outermost arms. Such behavior has heretofore been observed only in Scd galaxies, and it contrasts with observations of a number of galaxies of type Sc or earlier. (The colors and gas fraction of NGC 3344 are typical for its morphological type.) If this galaxy follows the relationship between abundance and excitation that is observed in other galaxies, then it has a strong abundance gradient in which the O/H abundance ratio falls to -0.7 in the outermost arms. Alternatively, the H II regions in NGC 3344 may have normal abundances together with unusually hot ionizing stars or a low dust/gas ratio.

A study of CO emission from two Scd galaxies - IC 342 and NGC 6946

view Abstract Citations (79) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A study of CO emission from two Scd galaxies: IC 342 and NGC 6946. Morris, M. ; Lo, K. Y. Abstract In a search for CO emission from an inhomogeneous sample of late-type galaxies, CO emission was detected in two: IC 342 and NGC 6946. Partial mapping of these nearly face-on galaxies shows that the CO emission peaks sharply at the nuclei but is present at a detectable level over most of the disks out to 8-10 kpc. A look at all galaxies studied in CO to date reveals (1) a tendency for galaxies with nuclear minima in their H I surface densities to have nuclear maxima in their H2 surface densities, and (2) no marked tendency, within the present sample, for the presence or abundance of molecular gas in spirals to be correlated with Hubble type. Publication: The Astrophysical Journal Pub Date: August 1978 DOI: 10.1086/156313 Bibcode: 1978ApJ...223..803M Keywords: Carbon Monoxide; Galactic Structure; Interstellar Gas; Molecular Spectra; Abundance; Hydrogen Atoms; Hydrogen Clouds; Line Spectra; Astrophysics; Carbon Monoxide:Galaxies; Galaxies:Interstellar Matter full text sources ADS | data products SIMBAD (23) NED (22)

An H i Study of Scd Galaxies

view Abstract Citations (68) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An H i Study of Scd Galaxies Shostak, G. S. Abstract H iline profiles, together with derived redshifts and integral properties, are presented for 46 Scd galaxies. The profile shapes are quite regular, with a double-peaked structure characteristic of galaxies with flat rotation curves. The ratios Ma 1/MT and MHi/Lpg, which are known to vary with Rubble type, have observed dispersions of I 80 percent within this classification, with intrinsic dispersions being probably less than I 50 percent. This establishes that integral property ratios are substantially homogeneous within the Scd classification. No indication of H I optical-depth effects with inclination is observed. Evidence is presented that distances derived solely from redshifts have an average uncertainty of <0.8 mag in the distance modulus. Subject headings: galaxies, motion in - galaxies, stellar content of - redshifts - 21-cm radiation Publication: The Astrophysical Journal Pub Date: June 1975 DOI: 10.1086/153629 Bibcode: 1975ApJ...198..527S full text sources ADS | data products SIMBAD (66) NED (62)

Gross Properties of Five Scd Galaxies as Determined from 21-CENTIMETER Observations

view Abstract Citations (215) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gross Properties of Five Scd Galaxies as Determined from 21-CENTIMETER Observations Rogstad, D. H. ; Shostak, G. S. Abstract Neutral-hydrogen studies of the five Scd galaxies M33, NGC 2403, IC 342, MIOl, and NGC 6946 have revealed substantial similarities in their hydrogen distributions and rotation curves. We find that 80 percent of the observable II 1 lies within the boundary defined by the Holmberg diameter for each galaxy. The ratio of the H 1 mass to the total mass contained within this same boundary has a mean value of 0.11. The central H 1 surface density is also nearly constant within the Scd classification. We find that all the H 1 global properties and ratios are nearly constant or scale approximately with Holmberg radius or total mass. An observed correlation of maximal rotation velocity with Holmberg radius allows characterization of the total mass with only one parameter. Because of the very flat rotation curves observed for these Scd galaxies, total masses extrapolated to infinite radius are not known. Surface mass-luminosity ratios must reach values of 20 at the HoImberg radius. Publication: The Astrophysical Journal Pub Date: September 1972 DOI: 10.1086/151636 Bibcode: 1972ApJ...176..315R full text sources ADS | data products NED (5)