scholarly journals Analysis of the Alignment of Non-Random Patterns of Spin Directions in Populations of Spiral Galaxies

Particles ◽  
2021 ◽  
Vol 4 (1) ◽  
pp. 11-28
Author(s):  
Lior Shamir
Keyword(s):  
Random Distribution ◽  
Spiral Galaxies ◽  
Dipole Axis ◽  
False Detection ◽  
Annotation Process ◽  
Axis Alignment ◽  
Celestial Pole ◽  
The Galaxy ◽  
Random Patterns ◽  
Very High

Observations of non-random distribution of galaxies with opposite spin directions have recently attracted considerable attention. Here, a method for identifying cosine-dependence in a dataset of galaxies annotated by their spin directions is described in the light of different aspects that can impact the statistical analysis of the data. These aspects include the presence of duplicate objects in a dataset, errors in the galaxy annotation process, and non-random distribution of the asymmetry that does not necessarily form a dipole or quadrupole axes. The results show that duplicate objects in the dataset can artificially increase the likelihood of cosine dependence detected in the data, but a very high number of duplicate objects is required to lead to a false detection of an axis. Inaccuracy in galaxy annotations has relatively minor impact on the identification of cosine dependence when the error is randomly distributed between clockwise and counterclockwise galaxies. However, when the error is not random, even a small bias of 1% leads to a statistically significant cosine dependence that peaks at the celestial pole. Experiments with artificial datasets in which the distribution was not random showed strong cosine dependence even when the data did not form a full dipole axis alignment. The analysis when using the unmodified data shows asymmetry profile similar to the profile shown in multiple previous studies using several different telescopes.

scholarly journals Galaxy spin direction distribution in HST and SDSS show similar large-scale asymmetry

2020 ◽  
Vol 37 ◽  
Author(s):  
Lior Shamir
Keyword(s):  
Large Scale ◽  
Spiral Galaxies ◽  
Hubble Space Telescope ◽  
Gravitational Interaction ◽  
Large Data ◽  
Sloan Digital Sky Survey ◽  
Data Sets ◽  
Dipole Axis ◽  
Data Set ◽  
The Asymmetry

Abstract Several recent observations using large data sets of galaxies showed non-random distribution of the spin directions of spiral galaxies, even when the galaxies are too far from each other to have gravitational interaction. Here, a data set of $\sim8.7\cdot10^3$ spiral galaxies imaged by Hubble Space Telescope (HST) is used to test and profile a possible asymmetry between galaxy spin directions. The asymmetry between galaxies with opposite spin directions is compared to the asymmetry of galaxies from the Sloan Digital Sky Survey. The two data sets contain different galaxies at different redshift ranges, and each data set was annotated using a different annotation method. The results show that both data sets show a similar asymmetry in the COSMOS field, which is covered by both telescopes. Fitting the asymmetry of the galaxies to cosine dependence shows a dipole axis with probabilities of $\sim2.8\sigma$ and $\sim7.38\sigma$ in HST and SDSS, respectively. The most likely dipole axis identified in the HST galaxies is at $(\alpha=78^{\rm o},\delta=47^{\rm o})$ and is well within the $1\sigma$ error range compared to the location of the most likely dipole axis in the SDSS galaxies with $z>0.15$ , identified at $(\alpha=71^{\rm o},\delta=61^{\rm o})$ .

scholarly journals Megamasers as probes of galaxy mass spectrum evolution

1991 ◽  
Vol 147 ◽  
pp. 440-440
Author(s):  
V.K. Khersonskii ◽  
N.V. Voshchinnikov
Keyword(s):  
Mass Spectrum ◽  
Spectral Line ◽  
Emission Line ◽  
Frequency Shift ◽  
Empirical Relation ◽  
Far Infrared ◽  
Merging Galaxies ◽  
Maser Emission ◽  
The Galaxy ◽  
Very High

OH megamasers having very high luminosities in the spectral line can be effectively used for the probing of the evolutionary properties of the galaxies in the earliest cosmological epochs. The frequency shift of the emission line uniqually determines the redshift z, which tells about the epoch of emission. One of the important cosmological problems is the investigation of the galaxy mass spectrum in the expanding Universe. There is the empirical relation between the OH and far-infrared luminosities of galaxies. Therefore, if in the earliest cosmological epochs, there were galaxies with sufficient powerful infrared excesses and containing molecular material, they can be detected using the observations of their OH maser emission. The interacting and merging galaxies can be considered as the best candidates for such objects.

scholarly journals The impact of bars and interactions on optically selected AGNs in spiral galaxies

2018 ◽  
Vol 618 ◽  
pp. A149 ◽  
Author(s):  
Sol Alonso ◽  
Georgina Coldwell ◽  
Fernanda Duplancic ◽  
Valeria Mesa ◽  
Diego G. Lambas
Keyword(s):  
Spiral Galaxies ◽  
Control Sample ◽  
Sloan Digital Sky Survey ◽  
Blue Color ◽  
Nuclear Activity ◽  
Internal Process ◽  
Two Samples ◽  
Accretion Rates ◽  
The Galaxy ◽  
The Impact

Aims. With the aim of performing a suitable comparison of the internal process of galactic bars with respect to the external effect of interactions on driving gas toward the inner most region of the galaxies, we explored and compared the efficiency of both mechanisms on central nuclear activity in optically selected active galactic nuclei (AGNs) in spiral galaxies. Methods. We selected homogeneous samples of barred AGNs and active objects residing in pair systems, derived from the Sloan Digital Sky Survey (SDSS). In order to carry out a reliable comparison of both samples (AGNs in barred hosts in isolation and in galaxy pairs), we selected spiral AGN galaxies with similar distributions of redshift, magnitude, stellar mass, color and stellar age population from both catalogs. With the goal of providing an appropriate quantification of the influence of strong bars and interactions on nuclear activity, we also constructed a suitable control sample of unbarred spiral AGNs without a companion and with similar host properties to the other two samples. Results. We found that barred optically selected AGNs show an excess of nuclear activity (as derived from the Lum[OIII]) and accretion rate onto a central black hole (ℛ) with respect to AGNs in pairs. In addition, both samples show an excess of high values of Lum[OIII] and ℛ with respect to unbarred AGNs in the control sample. We also found that the fractions of AGNs with powerful nuclear activity and high accretion rates increase toward more massive hosts with bluer colors and younger stellar populations. Moreover, AGNs with bars exhibit a higher fraction of galaxies with powerful Lum[OIII] and efficient ℛ with respect to AGN galaxies inhabiting pair systems, in bins of different galaxy properties. Regarding AGNs belonging to pair systems, we found that the central nuclear activity is remarkably dependent on the galaxy pair companion features. The Lum[OIII] for AGNs in pairs is clearly enhanced when the galaxy companion exhibits a bright and more massive host with high metallicity, blue color, efficient star formation activity and young stellar population. The results of this work reveal an important capacity of both mechanisms, bars and interactions, to transport material towards the galaxy central regions. In this context, it should also be noted that the internal process of the bar is more efficient at improving the central nuclear activity in AGN objects than that corresponding to the external mechanism of the galaxy–galaxy interactions.

scholarly journals A Very High Energy γ-Ray Survey toward the Cygnus Region of the Galaxy

2018 ◽  
Vol 861 (2) ◽  
pp. 134 ◽  
Author(s):  
A. U. Abeysekara ◽  
A. Archer ◽  
T. Aune ◽  
W. Benbow ◽  
R. Bird ◽  
...  
Keyword(s):  
High Energy ◽  
The Galaxy ◽  
Very High Energy ◽  
Γ Ray ◽  
Very High

scholarly journals Periodic Orbits and Warps

1983 ◽  
Vol 100 ◽  
pp. 189-190
Author(s):  
W. A. Mulder
Keyword(s):  
Density Distribution ◽  
Periodic Orbits ◽  
Spiral Galaxies ◽  
Closed Orbits ◽  
The Galaxy

Orbit calculations were done in a rotating triaxial system with a density distribution in accordance with recent observations of spiral galaxies. A search was made for simple closed orbits which are tilted with respect to the plane of the galaxy. A family of stable prograde tilted orbits was found which can explain warps as stationary phenomena.

scholarly journals The Massive Dark Corona Of Our Galaxy

1996 ◽  
Vol 173 ◽  
pp. 175-176
Author(s):  
K.C. Freeman
Keyword(s):  
Rotation Curve ◽  
Spiral Galaxies ◽  
Galactic Center ◽  
Galactic Disk ◽  
Galactic Rotation ◽  
Rotation Curves ◽  
Stellar Component ◽  
The Galaxy ◽  
Galactic Rotation Curve

From their rotation curves, most spiral galaxies appear to have massive dark coronas. The inferred masses of these dark coronas are typically 5 to 10 times the mass of the underlying stellar component. I will review the evidence that our Galaxy also has a dark corona. Our position in the galactic disk makes it difficult to measure the galactic rotation curve beyond about 20 kpc from the galactic center. However it does allow several other indicators of the total galactic mass out to very large distances. It seems clear that the Galaxy does indeed have a massive dark corona. The data indicate that the enclosed mass within radius R increases like M(R) ≈ R(kpc) × 1010M⊙, out to a radius of more than 100 kpc. The total galactic mass is at least 12 × 1011M⊙.

scholarly journals On role of Triple Systems in the Dynamics of the Galaxy: Stars with High Velocities

1995 ◽  
Vol 164 ◽  
pp. 369-369
Author(s):  
J. Anosova ◽  
J. Colin ◽  
L. Kiseleva
Keyword(s):  
Galactic Halo ◽  
Galactic Plane ◽  
Stellar Systems ◽  
Galactic Disc ◽  
Triple Systems ◽  
The Galaxy ◽  
Escape Process ◽  
Very High

There are a number of stars with very high pecular velocities in the Galactic halo within the region of about 1.5 kpc from the Galactic plane. At least some of these stars could be the result of an escape process in multiple stellar systems located in the Galactic disc.

scholarly journals Relation Between Star Formation and Angular Momentum in Spiral Galaxies

1983 ◽  
Vol 100 ◽  
pp. 135-136
Author(s):  
L. Carrasco ◽  
A. Serrano
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Radial Distribution ◽  
Spiral Galaxies ◽  
Formation Rate ◽  
Inverse Function ◽  
Solar Neighborhood ◽  
Spin Angular Momentum ◽  
Stellar Formation ◽  
The Galaxy

We derive the radial distribution of the specific angular momentum j=J/M, for the gas in M31, M51 and the galaxy, objects for which well observed unsmoothed rotation curves are available in the literature. We find the specific angular momentum to be anti-correlated with the present stellar formation rate, i.e. minima of spin angular momentum correspond to the loci of spiral arms. We find that the stellar formation rate is an inverse function of j. We derive new values of Oort's A constant for the arm and interarm regions in the solar neighborhood.

scholarly journals High Velocity Gas in the Halos of Spiral Galaxies

2004 ◽  
Vol 217 ◽  
pp. 136-141 ◽  
Author(s):  
Filippo Fraternali ◽  
Tom Oosterloo ◽  
Rense Boomsma ◽  
Rob Swaters ◽  
Renzo Sancisi
Keyword(s):  
High Velocity ◽  
Spiral Galaxies ◽  
High Sensitivity ◽  
Neutral Gas ◽  
Ngc 6946 ◽  
Inclination Angles ◽  
High Velocity Clouds ◽  
Halo Gas ◽  
Very High ◽  
Thick Layers

Recent, high sensitivity, HI observations of nearby spiral galaxies show that their thin ‘cold’ disks are surrounded by thick layers (halos) of neutral gas with anomalous kinematics. We present results for three galaxies viewed at different inclination angles: NGC 891 (edge-on), NGC 2403 (i=60°), and NGC 6946 (almost face-on). These studies show the presence of halo gas up to distances of 10-15 kpc from the plane. Such gas has a mean rotation 25-50 km s−1 lower than that of the gas in the plane, and some complexes are detected at very high velocities, up to 200-300 km s−1. The nature and origin of this halo gas are poorly understood. It can either be the result of a galactic fountain or of accretion from the intergalactic medium. It is probably analogous to some of the High Velocity Clouds (HVCs) of the Milky Way.

scholarly journals An Hα Survey of the Galactic Plane

1998 ◽  
Vol 179 ◽  
pp. 179-181
Author(s):  
Q.A. Parker ◽  
S. Phillipps
Keyword(s):  
Galactic Plane ◽  
Narrow Band ◽  
Interference Filter ◽  
Low Noise ◽  
Magellanic Clouds ◽  
Coverage Depth ◽  
Ionized Gas ◽  
Fine Grain ◽  
The Galaxy ◽  
Very High

We describe a major new Anglo-Australian proposal for a U.K. Schmidt Telescope (UKST) Hα survey of the Southern Galactic plane, Magellanic clouds and selected regions. The agreed survey will use a new 12 × 12 inch monolithic Hα interference filter of very high specification in combination with Tech Pan film. Tech Pan offers significant advantages for this work due to an inherent sensitivity at Hα and its extremely fine grain, high resolution, exceptional DQE, excellent imaging and low noise (e.g., Parker et al. 1994). The combination of Tech Pan and a narrow band Hα filter will provide a survey of unprecendented area coverage, depth and resolution, superior to any previous optical survey of ionized gas in the galaxy. It should to lead to exciting new discoveries and avenues of research.

Sign in / Sign up

Export Citation Format

Share Document