Filamentary Features Research Articles

II. LARGE-SCALE DISTRIBUTION OF GALAXIES: FILAMENTARY STRUCTURE AND VISUAL BIAS

ABSTRACT We show that our eye is good at detecting global coherence and at the same time easily fooled into seeing large-scale filamentary features where none exist. For this reason an objective method of identification that also assesses statistical significance is necessary to confirm or reject the presence of filaments in the distribution of galaxies. We have found that a construction called the minimal spanning tree (MST), together with a data-permuting technique, works very well. We demonstrate the validity of this procedure on Glass patterns, a case where we know that our eyes are being fooled. It shows that we should not neglect visual cues but question their subjective interpretation. The MST procedure applied to the CfA redshift data finds statistical evidence for the presence of filamentary features.

Giant Luminous Arcs in Clusters of Galaxies

During a program of study of surface brightness of elliptical galaxies in large redshift clusters in 1976 by a video camera at the KPNO 4-meter telescope, we in colaboration with Alan Sandage discovered filamentary and arc-like features in three clusters of galaxies. More recently, the same clusters (Abell 370, Abell 2218, and Cl2244-02) were observed by three different CCD's at the same telescope. These new observations confirm ouir old observations, and being of higher quality, show that the features in two of the clusters (Abell 370 and Cl 2244) form well defined continuous arcs with the following properties: 1)Large nearly circular features (length and radius of curvature ∼100 Kpc) with the center of curvature located near the center of gravity of the cluster.2)Large optical luminosity (≃1011L⊙).3)Bluer than the elliptical galaxies with unexpectedly high ultraviolet emission for Abell 370 giving rise to an unusual spectrum (see figure 1).4)Nearly uniform width along the arc with almost abrupt termination points, indicating a one dimensional structure rather than projection of a portion of a spherical shell.5)the arcs are nearly resolved perpendicular to their length with widths of ≤ 1″ (≤ 6 Kpc). i)In case of Abell 370 the surface brightness is very uniform but the width varies with wavelength, becoming wider toward blue and ultraviolet.ii)In case of CI 2244 there is considerable variation of surface brightness along the arc. We have no information on the variation of the width with wavelength.6)Our data does not show any other unusual features associated with the clusters as a whole or with the giant cD galaxies. These clusters may, however, be unusual in that they seem to have two distinct centers of gravity, this is especially true for Abell 370 which has two almost identical giant cD galaxies instead of the usual clusters dominated by one centrally located cD galaxy.7)Polarization observations show that the arcs are not highly polarized (polarization < 20%).8)From a short exposure spectral observation of C12244 we can only deduce absence of very strong emission lines.

Distribution and kinematics of neutral hydrogen in the barred spiral galaxy NGC 3359

view Abstract Citations (44) References (70) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Distribution and Kinematics of Neutral Hydrogen in the Barred Spiral Galaxy NGC 3359 Ball, R. Abstract The H I content of the bright barred spiral galaxy NGC 3359 has been mapped with the VLA at a resolution of 18 arcsec (0.95 kpc) and 25 km/s. The neutral hydrogen is distributed in a grand-design, two-armed spiral pattern which dominates the large-scale structure. This H I spiral coincides very closely with the optical arms and the loci of H II regions, but extends to larger radii and is essentially bisymmetric, unlike the impression given by the rather patchy optical structure. On scales comparable to the synthesized beam, the gas is strongly clumped. Most of the total H I mass of 5 x 10 to the 9th solar mass is confined to a regularly bounded disk of radius 13.1 kpc, with some filamentary features extending to more than twice that distance from the nucleus. The velocity field of NGC 3359 exhibits large symmetric noncircular motions superposed on its rotation. The maxima of these disturbances are spatially coincident with the H I spiral arms, indicating that a density wave of large amplitude governs the global circulation of the gas in the disk of this galaxy. Streaming motions of at least 45 km/s are observed. The rotation curve rises to a maximum of 153 km/s at 11.2 kpc and then declines very slowly out to the last measured point at 21.6 kpc. The total mass within that radius is inferred to be 1.2 x 10 to the 11th solar mass. The observed kinematics suggest that the plane of the galaxy is not substantially warped at any radius. An extremely small and faint satellite galaxy has been discovered in this synthesis. Its global properties may be similar to those of the intergalactic H II regions, except that it is not observed in a phase of active star formation. Publication: The Astrophysical Journal Pub Date: August 1986 DOI: 10.1086/164435 Bibcode: 1986ApJ...307..453B Keywords: Gas Dynamics; Nebulae; Radio Galaxies; Spiral Galaxies; Astronomical Maps; Centimeter Waves; Galactic Structure; H Ii Regions; Interstellar Matter; Neutral Gases; Spatial Distribution; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3359; GALAXIES: INTERNAL MOTIONS; GALAXIES: STRUCTURE; INTERSTELLAR: MATTER; RADIO SOURCES: GALAXIES; RADIO SOURCES: 21 CM RADIATION full text sources ADS | data products SIMBAD (5) NED (3)

The structure of the Cygnus A radio galaxy

view Abstract Citations (50) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Structure of the Cygnus A Radio Galaxy Pierce, M. J. ; Stockton, A. Abstract Interference-filtered CCD optical images were obtained of Cygnus A at a wavelength of 6100 A using a FWHM 100 A bandpass and at 6495 A with a FWHM of 170 A. The data yielded a radial surface brightness profile of the region, emission line and absorption spectra, velocity field, and ratios of H-alpha flux/continuum flux near H-beta. The analytic procedures applied to the data are described. Interactions among stars, dust, emitting gas and a featureless continuum were in evidence. The continuum and emission-line radiation exhibited different distributions, with the latter displaying clumped and filamentary features. The featureless continuum radiation arose from an extended region; the generating source was not resolved. Publication: The Astrophysical Journal Pub Date: June 1986 DOI: 10.1086/164240 Bibcode: 1986ApJ...305..204P Keywords: Astronomical Spectroscopy; Galactic Structure; Radio Galaxies; Continuous Spectra; Emission Spectra; Galactic Nuclei; H Alpha Line; Interstellar Extinction; Interstellar Gas; Astrophysics; GALAXIES: INDIVIDUAL NAME: CYGNUS A; GALAXIES: STRUCTURE; RADIO SOURCES: GALAXIES full text sources ADS | data products SIMBAD (1) NED (1)

Filamentary galaxy clustering - A mapping algorithm

The Shane-Wirtanen galaxy count catalog gives the strong visual impression of large-scale linear or filamentary features in the galaxy distribution. Computer simulations of hierarchical galaxy clustering constructed to have two-, three-, and four-point autocorrelation functions like those observed do not have such an appearance. A simple and well-defined algorithm which maps and quantifies filamentary structure is developed. It appears to be successful in identifying those (and only those) filaments which the eye picks out in the Shane-Wirtanen catalog and thus provides an objective tool for studying these structures. A catalog and map of the most prominent Shane-Wirtanen filaments is given. Application of the algorithm to a computer simulation of hierarchical galaxy clustering reveals a set of visually less conspicuous filaments with statistical properties strikingly similar to those of the Shane-Wirtanen filaments in many respects. Long (> or approx. =10/sup 0/) filaments do occur significantly more frequently in the data than in the simulations and the real filaments do occur at slightly higher relative contrast than the simulation filaments. These facts may explain their greater visual impact. It is not yet clear whether the Shane-Wirtanen filaments can be understood in terms of simple hierarchical galaxy clustering models.

Molecular Clouds in Orion and Monoceros

A 1.2-meter millimeter-wave telescope has been used to survey CO in the constellations of Orion and Monoceros. Many new molecular clouds have been found. The distribution of molecular material shows two striking characteristics: 1) Most of the molecular clouds in this region appear to be connected by continuous extensions and filaments. To judge from continuity in radial velocity, most of these connections appear to be real, and are not merely the result of projection along the line of sight. 2) There are at least two slender filamentary features longer than 10° in angular extent. These filaments may connect the molecular clouds lying well out of the Galactic plane to clouds lying in the plane. Their shape and orientation suggest that magnetic fields may play a role in their evolution. The observed velocity gradients may be explained by accelerated gas flow along the filament.

Possible optical evidence for ram-pressure-sweeping in the Hydra I cluster of galaxies

An asymmetrical distribution of very faint, filamentary features has been detected in blue light extending from the disk of NGC 3312, a peculiar spiral in the Hydra I cluster. Several interpretations for this type of phenomenon are possible (e.g., collisions, internal activity, an M82 type of event), but the location of NGC 3312 near the cluster core suggests the disturbance is related to the cluster environment. Hydra I is an X-ray source and therefore probably contains an intracluster medium. Thus the interesting possibility exists that NGC 3312 is being stripped of its interstellar medium by ram-pressure, and is an optical analog to a radio head-tail source.

Estimation of the size and orientation distribution of filamentary features from measurements on a two‐dimensional section

SUMMARYA procedure is described for determining the joint distribution Lv(r, ø, θ) of the radii (r) and orientation (ø, θ) of a filamentary structure from measurements on a single section. For tubular filaments it is also possible to determine the wall‐thickness distribution. The following assumptions are made: (1) that the filaments have a circular cross‐section; (2) that the length and radius of curvature of the filaments are large compared with their radii.The analysis is also applicable to transmitted images if the thickness of the slice is small compared with the average radius of the filaments.

Formation of holes in the solar corona

SOFT X-ray spectroheliograms obtained from Skylab1 and rocket flights2 show many bright filamentary features which map out the magnetic structure of the solar corona. Additional interesting features are the extensive regions from which the emission is extremely low. These long, but relatively narrow, ‘coronal holes’ can stretch much of the way across the solar disk in a roughly N–S direction. The photosphere and chromosphere beneath are relatively featureless and have low magnetic flux density. The magnetic structure of these lower levels is not untypical of other quiet regions on the Sun where coronal holes have not developed. This suggests that the magnetic configuration associated with the holes might not have emerged from the solar surface with any particularly unusual geometry, but this might have developed later due to some rearrangement within the atmosphere. Changes in field structure within the corona have been regarded for more than a decade as part of the normal process of development during the solar cycle3.

Degradation characteristics of cw optically pumped AlxGa1−xAs heterostructure lasers

The characteristic formation of dark filamentary features during the rapid degradation mode of AlxGa1−xAs double-heterostructure lasers has been observed in material with no contacts, with or without a p-n junction, and in minimal-strain mounting configurations. The degradation was observed in optically pumped cw lasing and nonlasing conditions with active region temperatures near and above room temperature.

A note on chromospheric fine structure at active region polarity boundaries

High resolution Hα filtergrams from Big Bear Solar Observatory reveal that some filamentary features in active regions have fine structure and hence magnetic field transverse to the gross structure and the zero longitudinal field line. These features are distinct from the usual active region filament, in which fine structure, magnetic field and filament are all parallel to the zero longitudinal field line. The latter occur on boundaries between regions of weaker fields while the former occur at boundaries between regions of stronger field.

Superconductivity in Lead-Base Solid Solution Alloys

Magnetization as a function of applied magnetic field has been measured at 4.2°K for binary solid solution alloys of In, Tl, Sn, Hg, Na, and Bi in Pb. For pure Pb, superconductivity is destroyed when the field penetrates abruptly at the thermodynamic critical field HC. With sufficient alloying element in solution, the field, instead, first penetrates at HFP(<HC) and penetrates gradually, full penetration and destruction of superconductivity not being reached until HN (>HC). Increasing solute concentration decreases HFP and increases HN in a manner predicted by the ``negative surface energy'' theories of Abrikosov and others. Annealed specimens approach reversible magnetic behavior and exhibit little trapped flux. Plastic deformation is found to increase HFP, the area under the ascending magnetization curves, the hysteresis, and the trapped flux, but has little effect on HN. The results indicate that the high critical field of these alloys results from the lowered surface energy of a superconducting-normal interface and not from any specific filamentary features of the microstructure. Dislocations do, however, increase the magnetic hysteresis and, it is inferred, the current-carrying capacity of these alloys.