Distribution Of Axial Ratios Research Articles

Morphology and domain pattern of L1 ordered FePt films

Magnetic force microscope (MFM) was used to characterize the L10 ordered FePt(001) films sputter deposited directly on MgO(001) substrates at an elevated temperature. With the change of nominal thickness (tN), the morphology varied from isolated particles to continuous films. The coercivity showed a marked change at the percolation boundary of tN≅45 nm, where the film morphology changed from a discontinuous to a continuous state. Below tN=45 nm, the coercivity did not change apparently, though the number of single-domain particles increased gradually with decreasing tN. At tN=20 nm, a critical (maximum) size of single domain particles, d=180 nm, was obtained from a size distribution, which was taken from the atomic force microscope/MFM measurement. The value calculated for this critical size was found to be d=155 nm in the assumption that the particles had ellipsoidal shape. The slight difference between experimental and theoretical values is likely to be attributed to an axis ratio (c/a) distribution of particles.

Optical and Near‐Infrared Imaging of the IRAS 1 Jy Sample of Ultraluminous Infrared Galaxies. I. The Atlas

The present paper discusses the results from an analysis of the images presented in Paper I (astro-ph/0207373) supplemented with new spectroscopic data obtained at Keck. All but one object in the 1-Jy sample show signs of a strong tidal interaction/merger. Multiple mergers involving more than two galaxies are seen in no more than 5 of the 118 ( 0.2) and the more luminous systems (> 10^{12.5} L_sun) all show a strong tendency to be advanced mergers with a single nucleus. An analysis of the surface brightness profiles of the host galaxies in single-nucleus sources reveals that about 73% of the R and K' surface brightness profiles are fit adequately by an elliptical-like R^{1/4}-law. These elliptical-like 1-Jy systems have luminosities, half-light radii, and R-band axial ratio distribution that are similar to those of normal (inactive) intermediate-luminosity ellipticals and follow with some scatter the same mu_e - r_e relation. These elliptical-like hosts are most common among merger remnants with Seyfert 1 nuclei (83%), Seyfert 2 optical characteristics (69%) or mid-infrared (ISO) AGN signatures (80%). In general, the results from the present study are consistent with the merger-driven evolutionary sequence ``cool ULIGs --> warm ULIGs --> quasars,'' although there are many exceptions. (abridged)

Finite strain estimation using the mean radial length of elliptical objects with bootstrap confidence intervals

A new method for calculating finite sectional strain from distributions of elliptical objects is presented. The only assumptions required are that before deformation (1) long axis orientations are uniformly distributed and (2) the distribution of axial ratios is independent of orientation. Importantly, an estimate of the orientation of the long axis of the strain ellipse is not required before the method can be applied. The method is based on the conceptually simple fact that the mean radial length of a set of uniformly oriented ellipses in the unstrained state equates to that of a circle, so that after strain, the mean radial length evaluates to the strain ellipse. Errors associated with the method are calculated from the bootstrap, and a simulation study verifies both the applicability of the new method for finite strain estimation and the accuracy of errors calculated with the bootstrap. The method is applied to a large set of sandstone quartz clast data from the Irish Variscides, whilst cross-checking of results with those from established methods also validates the approach taken.

The Shapes of Galaxies in the Sloan Digital Sky Survey

We estimate the distribution of apparent axis ratios q for galaxies in the Sloan Digital Sky Survey Early Data Release. We divide the galaxies by profile type (de Vaucouleurs vs. exponential) as well as by color (u* - r* ≤ 2.22 vs. u* - r* > 2.22). The axis ratios found by fitting models to the surface photometry are generally smaller than those found by taking the second moments of the surface brightness distribution. Using the axis ratios found from fitting models, we find that galaxies with de Vaucouleurs profiles have axis ratio distributions that are inconsistent, at the 99% confidence level, with their being a population of randomly oriented oblate spheroids. Red de Vaucouleurs galaxies are slightly rounder, on average, than blue de Vaucouleurs galaxies. By contrast, red galaxies with exponential profiles appear very much flatter, on average, than blue galaxies with exponential profiles. The red exponential galaxies are primarily disk galaxies seen nearly edge-on, with reddening due to the presence of dust, rather than to an intrinsically red stellar population.

The Intrinsic Shapes of Molecular Cloud Fragments over a Range of Length Scales

We decipher intrinsic three-dimensional shape distributions of molecular clouds, cloud cores, Bok globules, and condensations using recently compiled catalogs of observed axis ratios for these objects mapped in carbon monoxide, in ammonia, through optical selection, or in continuum dust emission. We apply statistical techniques to compare assumed intrinsic axis ratio distributions with observed projected axis ratio distributions. Intrinsically triaxial shapes produce projected distributions that agree with observations. Molecular clouds mapped in 12CO are intrinsically triaxial but more nearly prolate than oblate, while the smaller cloud cores, Bok globules, and condensations are also intrinsically triaxial but more nearly oblate than prolate.

Why Is the Fraction of Four‐Image Radio Lens Systems So High?

We investigate the frequency of two- and four-image gravitational lens systems in the Jodrell-VLA Astrometric Survey (JVAS) and Cosmic Lens All-Sky Survey (CLASS), and the possible implications for dark matter halo properties. A simple lensing statistics model, which describes lens galaxies as singular isothermal ellipsoids with a projected axis ratio distribution derived from the surface brightness ellipticities of early-type galaxies in the Coma cluster, is ruled out at the 98% level since it predicts too few four-image lenses (quads). We consider a range of factors that may be increasing the frequency of radio quads, including external shear fields, mass distributions flatter than the light, shallow lensing mass profiles, finite core radii, satellite galaxies, and alterations to the luminosity function for faint flat-spectrum radio sources. We find that none of these mechanisms provide a compelling solution to the quad problem on their own while remaining consistent with other observational constraints.

Sensitivity of 5-cm Wavelength Polarimetric Radar Variables to Raindrop Axial Ratio and Drop Size Distribution

Abstract The sensitivity of polarimetric variables at a 5-cm wavelength to raindrop size and axial ratio is examined using T-matrix modeling of the scattering process for gamma raindrop size distributions fitted to tropical rainfall collected at Darwin, Australia. These simulations demonstrate that, while specific differential phase (KDP)–based estimates of rainfall, attenuation (AH), and differential attenuation are less affected by drop size distribution (DSD) variations, large drop occurrence can have significant impacts. Attenuation is sensitive to the occurrence of large drops, which can produce anomalously high values associated with resonance effect scattering. The polarimetric variables are sensitive to the relation between the equivolume diameter and axial ratio. Variations in the assumed form of the raindrop axial ratio can result in significant biases in rainfall and attenuation. Combined rainfall estimators, which include differential reflectivity (ZDR), such as R(KDP, ZDR) and R(AH, ZDR) are ...

Galaxy clusters: oblate or prolate?

ABSTRA C T It is now well known that a combined analysis of the Sunyaev‐Zel’dovich (SZ) effect and the X-ray emission observations can be used to determine the angular diameter distance to galaxy clusters, from which the Hubble constant is derived. Given that the SZ/X-ray Hubble constant is determined through a geometrical description of clusters, the accuracy to which such distance measurements can be made depends on how well one can describe intrinsic cluster shapes. Using the observed X-ray isophotal axial ratio distribution for a sample of galaxy clusters, we discuss intrinsic cluster shapes and, in particular, if clusters can be described by axisymmetric models, such as oblate and prolate ellipsoids. These models are currently favoured when determining the SZ/X-ray Hubble constant. We show that the current observational data on the asphericity of galaxy clusters suggest that clusters are more consistent with a prolate than with an oblate distribution. We address the possibility that clusters are intrinsically triaxial by viewing triaxial ellipsoids at random angles with the intrinsic axial ratios following an isotropic Gaussian distribution. We discuss implications of our results on current attempts at measuring the Hubble constant using galaxy clusters and suggest that an unbiased estimate of the Hubble constant, not fundamentally limited by projection effects, would eventually be possible with the SZ/X-ray method.

The microlensing rate and mass function versus dynamics of the Galactic bar

With the steady increase of the sample size of observed microlenses towards the central regions of the Galaxy, the main source of the uncertainty in the lens mass will shift from the simple Poisson noise to the intrinsic non-uniqueness of our dynamical models of the inner Galaxy, particularly the Galactic bar. We use a set of simple self-consistent bar models to investigate how the microlensing event rate varies as a function of axis ratio, bar angle and velocity distribution. The non-uniqueness of the velocity distribution of the bar model adds a significant uncertainty (by about a factor of 1.5) to any prediction of the lens mass. Kinematic data and self-consistent models are critical to lift the non-uniqueness. We discuss the implications of these results for the interpretation of microlensing observations of the Galactic bulge. In particular we show that Freeman bar models scaled to the mass of the Galactic bulge/bar imply a typical lens mass of around 0.8 M⊙, a factor of 3–5 times larger than the value from other models.

The shapes of Shakhbazian compact groups of galaxies

AbstractWe have completed an investigation (preliminary results for which were reported in Oleak et al. 1995) into the shapes of Shakhbazian compact groups of galaxies. Ellipticites for 299 groups in the Shakhbazian survey have been examined using the technique proposed by Rood (1979) for deriving the average “flatness” of a large sample of objects. The distribution of the apparent axial ratios (g = b/a) for the groups is found to be broad with a mean of< b/a > ∽ 0.5. This distribution is compared with randomly generated spherical and elliptical model systems. The results confirm the findings of our earlier study: the frequency distribution of axial ratios for Shakhbazian groups is represented soley by a population of prolate spheroids with low intrinsic axial ratios, < q > = 0.3, σ = ∽0.17 (assuming random true orientations in 3D space). This now provides further strong evidence that the Shakhbazian groups are more highly flattened than either rich clusters or elliptical galaxies, and represent the most elongated systems yet found. The result also provides confirmation of the reality of the groups, since in the case of systems of chance line‐of‐sight superpositions of galaxies we would expect to see much higher axial ratios.

The Axis Ratio Distribution of Local and Distant Galaxies

Surface photometry from 16 HST/WFPC2 fields in the I(F814W) filter is used to derive the distribution of apparent axis ratios for galaxies in progressively fainter magnitude intervals for I<25. We assess the systematic and accidental errors in ellipticity measurements as a function of image resolution and signal-to-noise ratio, and statistically correct for the effect of cosmological surface brightness dimming on our isophotal measurements. The axis ratio distribution for the local galaxy population was computed using logR measurements for 1569 RC3 galaxies with Bt<13 mag. Nonparametric tests are used to show that our distant samples, in the redshift range 0.1<z<1.5, are not statistically different from the local sample. We present image montages of galaxies selected randomly from different axis ratio and apparent magnitude ranges and discuss the evolutionary consequences of the lack of a strong difference between the ellipticity distributions in near and far data sets.

Obscuration in the Host Galaxies of Soft X‐Ray–selected Seyfert Nuclei

We define a new sample of 96 low-redshift (z < 0.1), soft X-ray-selected Seyfert galaxies from the catalog of the Einstein Slew Survey. We probe the geometry and column depth of obscuring material in the host-galaxy disks using galactic axial ratios determined mainly from the Digitized Sky Survey. The distribution of host-galaxy axial ratios clearly shows a bias against edge-on spirals, which confirms the existence of a geometrically thick layer of obscuring material in the host-galaxy planes. Soft X-ray selection recovers some of the edge-on objects missed in UV and visible surveys but still results in 30% incompleteness for type 1 nuclei. We speculate that thick rings of obscuring material such as the ones we infer for these Seyfert galaxies might be commonly present in early-type spirals, sitting at the inner Lindblad resonances of the nonaxisymmetric potentials of the host galaxies.

Laboratory measurements of mineral dust scattering phase function and linear polarization

With the goal of improving our understanding of how small mineral dust particles scatter light at visible and near‐infrared wavelengths, we measured the scattering phase function and linear polarization of small mineral dust particles over the scattering angle range 15°–170° at three wavelengths (0.47, 0.652, and 0.937 μm). Particle samples were obtained from Duke Scientific Corp., and include aluminum oxide, silicon carbide, aluminum silicate, antimony oxide, calcium carbonate, and cerium oxide. Particle equivalent‐sphere radii range from a few tenths of a micron to about 10 μm. The particles were injected into a laboratory chamber, where they scattered light as they fell through the air. They were collected on a scanning electron micrograph (SEM) substrate. Particle shapes and sizes were then measured from the SEM images. We compare measured phase functions with those calculated for spheroids with a distribution of axial ratios and sizes, random orientation, and refractive index 1.53+0.008i [Mishchenko et al., this issue]. Two of the samples (one of which has a refractive index close to that used in theoretical computations) produced scattering phase functions that were quite similar to those for spheroids. Two samples produced phase functions whose variation between 15° and 170° was much less than that for the spheroids or for the other samples. We suspect this difference may be due to the very high refractive index of those particles, although differences in particle microstructure may also be important. Two samples produced positive linear polarization which had a single broad maximum near 100° scattering angle, and a magnitude greater than 40% at some wavelengths. Two samples had generally positive linear polarization but a more complicated structure, and two samples produced mostly negative polarization whose amplitude was small. We do not have numerical results for the appropriate refractive index and size parameter with which to compare the polarization measurements. We hope the questions raised by this work will stimulate additional effort to develop and test numerical codes for scattering by nonspherical particles.

Shear and Ellipticity in Gravitational Lenses

Galaxies modeled as singular isothermal ellipsoids with an axis ratio distribution similar to the observed axis ratio distribution of E and S0 galaxies are statistically consistent with both the observed numbers of two-image and four-image lenses and the inferred ellipticities of individual lenses. However, no four-image lens is well fit by the model (typical $\chi^2/N_{dof} \sim 20$), the axis ratio of the model can be significantly different from that of the observed lens galaxy, and the major axes of the model and the galaxy may be slightly misaligned. We found that models with a second, independent, external shear axis could fit the data well (typical $\chi^2/N_{dof} \sim 1$), while adding the same number of extra parameters to the radial mass distribution does not produce such a dramatic improvement in the fit. An independent shear axis can be produced by misalignments between the luminous galaxy and its dark matter halo, or by external shear perturbations due to galaxies and clusters correlated with the primary lens or along the line of sight. We estimate that the external shear perturbations have no significant effect on the expected numbers of two-image and four-image lenses, but that they can be important perturbations in individual lens models. However, the amplitudes of the external shears required to produce the good fits are larger than our estimates for typical external shear perturbations (10-15% shear instead of 1-3% shear) suggesting that the origin of the extra angular structure must be intrinsic to the primary lens galaxy in most cases.

The Intrinsic Shapes of Stellar Systems

I compute the estimated distribution function f(q) for the apparent axis ratio q of various types of stellar systems, using a nonparametric kernel method. I then invert f(q) to find the distribution of intrinsic axis ratios, using two different hypotheses: first, that the stellar systems are all oblate, and second, that they are all prolate. The shapes of globular clusters in our own galaxy are consistent, at the 99% confidence level, with both the oblate and prolate hypothesis. The shapes of dwarf galaxies in the Virgo cluster are consistent, at the 99% confidence level, with the prolate hypothesis, but inconsistent with the oblate hypothesis. The shapes of star clusters in the Large Magellanic Cloud, of ordinary elliptical galaxies, of brightest cluster ellipticals, and of galaxy clusters are all inconsistent, at the 99% confidence level, with both the oblate and prolate hypotheses. The globular clusters in our galaxy are older than their half-mass relaxation time, and are most likely rotationally flattened oblate spheroids. The other stellar systems considered are generally younger than their half-mass relaxation time, and thus are triaxial bodies flattened by anisotropy of their velocity dispersion.

The Catalog of Southern Ringed Galaxies: Erratum

view Abstract Citations (8) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Catalog of Southern Ringed Galaxies: Erratum Buta, R. Abstract In the paper "The Catalog of Southern Ringed Galaxies" by R. Buta (ApJS, 96,39 [1995]), the analysis of the completeness of the catalog contains an incorrect statement which, although it has no effect on the analysis or conclusions of the paper, should be noted. In Section 6.1, the differential diameter functions of inner and outer ring, pseudoring, and lens features are fitted by D^-3^ functions, where D is the angular diameter in arcminutes of a feature. Although these functions fit the diameter distributions well down to the adopted diameter limits, they do not represent, as stated in the paper, a uniform density distribution, which would instead give n(D) is proportional to D^-4^. Thus, the catalog is not complete to the angular diameters that were used for limiting the statistics. Figure 1 (See Journal) shows the cumulative diameter distributions for inner and outer features (filled and open circles, respectively). The lines have slopes of -2.93 +/- 0.04 and -2.70 +/- 0.03 for inner and outer features, respectively, and are reasonably close to the expected value of -3 for a uniform distribution. The suggested true completeness limits are 0.5' for inner features and 0.78' for outer features. For comparison, diameter limits of 0.43' for inner features and 0.78' for outer features, corresponding to the medians, were adopted for the analysis in the paper. These are still reasonable choices for the diameter limits because much of the incompleteness near these limits involves high-inclination galaxies which were not part of the statistical analysis. Since the diameter functions applied in the paper were used mainly as a means of allowing for the effect on the errors of the greater proportion of small rings compared to large rings which would contribute to any observed distribution of axis ratios or angles, the misstatement has no effect on the analysis in the paper. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1995 DOI: 10.1086/192176 Bibcode: 1995ApJS...98..739B Keywords: ERRATA; ADDENDA full text sources ADS | Related Materials (1) Original Paper: 1995ApJS...96...39B

The axis ratio distribution of faint galaxies: Evidence for a populatin of dwarfgalaxies at I approximately 20.5

The axis ratio distribution of faint galaxies observed by the Hubble Space Telescope (HST) as part of the Medium Deep Survey (MDS) key project suggests that a very large fraction of the total population at magnitudes I greater than or equal to 20 mag consists of a class of galaxies with luminosity profile, axis ratio distribution, angular size, and color that resemble local dwarfs. We find that galaxies with exponential light profiles and small angular sizes (half-light radius less than 0.6 sec) have an axis ratio distribution that is incompatible with their being intrinsically flattened objects and is instead consistent with local elliptical galaxies. We call these objects 'Small Exponential Ellipticals.' They are most likely dwarf galaxies, and they are numerous enough that, together with irregular galaxies, they can account for most if not all of the excess in the number counts at I approximately 20-21 mag with respect to the standard no-evolution models. This may suggest that the excess number counts are best explained by dwarf-rich models with strong luminosity evolution of the dwarf galaxies. Our data also supports a very mild luminosity evolution of the giant galaxy populations, which contributes little to the excess number counts.

Imaging of 16 distant EMSS clusters with Z greater than or equal to 0.2 and L(subx,44) greater than or equal to 4: New arcs and first consequences

view Abstract Citations (87) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Imaging of 16 Distant EMSS Clusters with Z >= 0.2 and L X,44 >=4: New Arcs and First Consequences Le Fevre, O. ; Hammer, F. ; Angonin, M. C. ; Gioia, I. M. ; Luppino, G. A. Abstract Medium-deep V, R, and I observations of a subsample of 16 clusters of galaxies in the EMSS sample defined from the Einstein satellite data are presented. Three new cases of clusters with giant luminous arcs (length/width> 10, V < 22) have been discovered together with six new arcs (4 < l/w < 10, V < 22), and we propose that these arcs are new examples of gravitational lensing of background galaxies by the rich clusters. Combined with giant luminous arcs already observed in the EMSS sample, there is a total of six giant luminous arcs observed in the sample of 16 clusters. This high rate of success in finding arcs added to their axis ratio distribution is consistent with very small core radii (<100 kpc) for the dark matter distribution in rich clusters, and rules out models in which dark matter follows the X-ray gas. Publication: The Astrophysical Journal Pub Date: February 1994 DOI: 10.1086/187198 Bibcode: 1994ApJ...422L...5L Keywords: Dark Matter; Galactic Clusters; Galactic Evolution; Galactic Mass; Gravitation; Gravitational Lenses; Satellite Perturbation; X Ray Stars; Aspect Ratio; Cluster Analysis; Flux Density; Photometry; Star Clusters; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: CLUSTERS OF; COSMOLOGY: GRAVITATIONAL LENSING; COSMOLOGY: DARK MATTER; GRAVITATION full text sources ADS | data products NED (29) SIMBAD (26)

The shapes of brightest cluster galaxies

view Abstract Citations (24) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Shapes of Brightest Cluster Galaxies Ryden, Barbara S. ; Lauer, Tod R. ; Postman, Marc Abstract The distribution of axis ratios presently computed for a sample of brightest cluster galaxies (BCGs) is found to not vary greatly from a similar distribution for a sample of ordinary ellipticals. A significant difference is noted, however, between the distribution of axis ratios for a sample of BCGs and for a sample of second-brightest cluster ellipticals. It is also noted, in partial support for a hypothesized competition of BCGs for cluster galaxies that would otherwise merge with the second-brightest cluster ellipticals, that the shape of a merger remnant can reflect the relative masses of the progenitor as well as the angular momentum of the merging system. Publication: The Astrophysical Journal Pub Date: June 1993 DOI: 10.1086/172769 Bibcode: 1993ApJ...410..515R Keywords: Elliptical Galaxies; Galactic Clusters; Galactic Structure; Brightness Distribution; Distribution Functions; Shapes; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXIES: INTERACTIONS; GALAXIES: PHOTOMETRY full text sources ADS |

Monodisperse ellipsoidal polystyrene latex particles: Preparation and characterisation

AbstractAn improved version of a novel method first employed by Nagy &amp; Keller for the preparation of monodisperse ellipsoidal polystyrene latex particles is described. The method involves embedding monodisperse spherical polystyrene latex particles as starting material in a deformable polymer matrix such as poly(vinyl alcohol) and deforming these mechanically to various predetermined macroscopic draw ratios to give ellipsoids of various axial ratios. Ellipsoids with lengths ranging from about 350 to 12250nm were prepared. Stable aqueous dispersions of these were recovered and characterised with respect to particle size and axial ratio distributions and surface morphology using electron microscopy. Axial ratios ranging from 2.0 to 5.65 were obtained for the resulting ellipsoids. Various factors influencing the monodispersity of the resulting ellipsoids in the preparation method are discussed.