Giant Arcs Research Articles

The probability of arc lensing by clusters of galaxies

view Abstract Citations (15) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Probability of Arc Lensing by Clusters of Galaxies Nemiroff, Robert J. ; Dekel, Avishai Abstract We examine the probability that clusters of galaxies act as gravitational lenses and create extended detectable arcs, or unusually elongated images, from distant sources. It is assumed that the clusters are isothermal spheres, and the sources are galaxies modeled as exponential disks. We consider detection thresholds in image shape (axial ratio, A, and angular extent θ), and in brightness (apparent surface brightness, s, or apparent magnitude, m). For galaxies of a given size, these thresholds define an axisymmetric source volume behind the cluster extending to a maximum redshift z_m_, within which a galaxy must fall to be lensed by the cluster into an arc. The number of detectable sources is then determined by integration over the number density of visible galaxies in this volume. We find that for a cluster like Abell 370 (σ ~ 1500 km s^-1^ and z_l_ ~ 0.37), the probability of observing giant arcs like those already found (A >= 15, θ >= 90^deg^) is about 1 in 200 for z_m_ = 0.72, and approaches 1 in 10 if the cluster is inspected down to a B_j_ surface brightness of 26.5 mag arcsec^-2^. Many more clusters should show distorted galaxy images which are unusually elongated perpendicular to the radius vector to the cluster center. For example, if nearby clusters of σ >= 1000 are inspected to a limiting B_j_ magnitude of 26.5, roughly 1 in 3 (1 in 16) should show a distorted galaxy with axial ratio >= 5 (>=10). Publication: The Astrophysical Journal Pub Date: September 1989 DOI: 10.1086/167776 Bibcode: 1989ApJ...344...51N Keywords: Computational Astrophysics; Galactic Clusters; Gravitational Lenses; Brightness Distribution; Red Shift; Velocity Distribution; Astrophysics; GALAXIES: CLUSTERING; GRAVITATIONAL LENSES full text sources ADS | data products SIMBAD (1) NED (1)

Large-scale magnetic-field structure in the spiral galaxy M83

THE large-scale structure of magnetic fields in spiral galaxies, as deduced from the linear polarization of scattered starlight1 and from the intensity and linear polarization of continuum synchrotron radio emission2, tends to follow the visible spiral arm structure. Both axisymmetric (in the galaxies IC342 and M31; refs 3 and 4) and bisymmetric (in M81; ref. 5) patterns are seen, the latter showing a field reversal between the arms. We have measured the linear polarization at a spatial resolution of ∼2 kpc in VLA (Very Large Array) observations of 20-cm continuum radio emission from the bright, nearly face-on, spiral galaxy M83 (NGC5236). The strongest linearly polarized emission is from two giant arcs, ∼30 kpc long, situated roughly opposite each other in the dark outer regions of the galaxy, ∼12 kpc from the centre. These regions do not coincide with any prominent spiral arm tracers, and from a comparison with earlier results at 6-cm wavelength, we conclude that the low polarization in the centre of the galaxy indicates disorder in the interstellar magnetic field, probably connected with star formation activity observed there.

Diagnostics of compact clusters of galaxies by giant luminous arcs

view Abstract Citations (41) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Diagnostics of Compact Clusters of Galaxies by Giant Luminous Arcs Kovner, Israel Abstract Images of high-redshift galaxies distorted by gravitational fields of foreground clusters can sometimes form arcs, continuous or broken. The gross features of these arcs, namely the degrees of circularity and uniformity, the angular extents, and the widths, can be used to constrain the shapes of cluster gravitational wells. In the case in which an arc and a counterarc are seen, their angular extents can indicate whether the potential can possibly be approximated by a small quadrupole lens. If so, the ellipticity of the lens can be constrained, and it may be possible to discriminate between the large arcs which are single images and those which are triplets. The arcs in clusters A963 and 2244-02 can be reproduced by small quadrupole lenses, given the photographs published so far, whereas the recent B-R picture of cluster A370 seems to favor a more complex lens potential. It is possible to constrain a combination of the source galaxy shape and orientation and of the ellipticity of the mass distribution in the core of cluster A963. Unless the source galaxy is elongated with axis ratio less than 1:5 and is suitably oriented, the ellipticity of the major mass constituent is smaller than the reported ellipticity of the central cD galaxy. In the 2244-02 case, the small quadrupole model has mass centered off the center of light of the core. Other models for this case are found in a Monte Carlo search scheme restricted to some resemblance between the mass and light distribution, and a condition that there are no extra images except those hidden by the cluster galaxies. There are models in which the dense group of galaxies near the arc (group A) traces a deep potential well, either the only such well or one of the two deep wells in the cluster. There are also models in which group A traces a moderate or small addition to a dominant potential well centered away from the arc center. Some of the latter models imply that one of the small galaxies near the second dense group of galaxies (group B) is an extra image of the source of the arc. All the suitable models found have extra images hidden by cluster galaxies. Publication: The Astrophysical Journal Pub Date: February 1989 DOI: 10.1086/167133 Bibcode: 1989ApJ...337..621K Keywords: Galactic Clusters; Gravitational Lenses; Astronomical Models; Computational Astrophysics; Mass Distribution; Monte Carlo Method; Astrophysics; GALAXIES: CLUSTERING; GRAVITATIONAL LENSES full text sources ADS | data products SIMBAD (3) NED (2)

Supernovae in luminous arcs

The giant luminous arcs seem to be images of galaxies distorted by foreground clusters acting as gravitational lenses, with galaxies close to the cusps of gravitational lens caustic. The part of a galaxy located inside a cusp has three images of itself within an arc. The arcs are very blue, so the galaxies may be in a stage of active star formation with supernovae exploding every few years. If a supernova goes off inside a cusp it will be observed thrice, at three positions. The apparent magnitudes of the supernovae images may be M(R) roughly 20-23. The arrival time differences between the images can be as short as a few weeks or even days, whereas for ordinary lenses on a cluster scale the differences can be decades to centuries. Simple relations between the ratios of the arrival time differences, magnifications, and image separations are predicted.

Giant Luminous Arcs in Galaxy Clusters

view Abstract Citations (18) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Giant Luminous Arcs in Galaxy Clusters Narasimha, D. ; Chitre, S. M. Abstract The gravitational lensing of an extended source, for example an elliptical galaxy by a transparent lens in the form of a cluster of galaxies, is studied to account for the narrow arclike features observed in the cores of clusters. Publication: The Astrophysical Journal Pub Date: September 1988 DOI: 10.1086/166630 Bibcode: 1988ApJ...332...75N Keywords: GALAXIES: CLUSTERING; GRAVITATIONAL LENSES; NEBULAE: GENERAL full text sources ADS | data products NED (2) SIMBAD (1)

Spectrophotometry and polarimetry of the giant luminous arcs in the clusters 2244–02 and Abell 370

Lynds and Petrosian1 have reported the discovery of very large luminous arcs in two clusters of galaxies, and there have been various conjectures2 about the nature of these unusual features. Some of these are that they are: (1) images of distant objects formed by a gravitational lens generated by the visible clusters of galaxies; (2) regions of star formation stimulated by the passage of a shock front produced by a central (now extinguished) quasistellar object; (3) light echoes of a previously bright object at the centre; or (4) long arcs of stars tidally stripped from galaxies in the clusters. Observational data have been so limited that it has not been possible to establish any clearly favoured interpretation. Here we present new observations which restrict the range of possibilities, by eliminating (2), (3) and (4), even if they do not lead to a unique interpretation.

Is the Giant Luminous Arc in A370 a Gravitational Lensing Effect?

A gravitational lensing model is proposed to explain the giant arc structure we observed in September 1985 in the distant cluster of galaxies Abell 370 (z=0.37.4).

Giant Arcs – Spherical Shells?

A noticeable fact about the giant luminous arcs, which have been detected in a few high-redshift clusters of galaxies (see contributions by Petrosian and by Mellier in this volume), is that they seem to be segments of almost perfectly circular rings – in one case spanning about one third of a circle. If this is a characteristic property of these arcs, they cannot be segments of randomly-oriented three-dimensional rings, which, when viewed from a random direction, should look acircular in most cases. Perhaps the most generic source for a circular ring is a limb-brightened luminous shell – as in planetary nebulae and supernova remnants. Such shells can naturally arise, for example, from explosion-generated shocks which cooled and fragmented into stars. If the sources are shells, and the arcs are either resolved or their thickness is determined by the seeing conditions (and by the CCD pixle size), there is a very general upper-limit on the possible surface-brightness contrast between the arcs and the regions encompassed by them. For the detected arcs, without any special finetuning, this limit is ≃ 3. It might become twice as big if the shell is transparent and the interior is opaque. This limit could exclude the shell model if the preliminary claims for a detected contrast greater than 10 are confirmed. It is interesting to note that the famous ring nebula presents a similar problem. We checked several mechanisms, such as stimulated radiation, which could, in principle, enhance the observed contrast while retaining the spherical symmetry; if such a mechanism is responsible for the enhanced contrast, it should show clear imprints on the spectrum. The figure shows the surface-brightess profile for a shell of thickness d.

The Giant Arcs Are Gravitational Mirages

The Giant Arcs Are Gravitational Mirages

Giant luminous arcs from gravitational lensing

Giant luminous arcs from gravitational lensing

Giant luminous arcs discovered in two clusters of galaxies

Giant luminous arcs discovered in two clusters of galaxies

Paleomagnetism of the Franklin Diabases

Diabase intrusions, which have a probable mean age of 675 m.y., occur in a giant arc across the northern part of the Canadian Shield. They have a paleomagnetic pole position of 167° E, 8° N (α95 = 5°), and at least one reversal. The paleomagnetic results indicate that the northern Canadian Shield was near the equator at the time of intrusion, and this is in agreement with evidence of warm conditions of deposition found in erosional remnants of related late Proterozoic sediments. Some of the diabase, near the shores of Davis Strait, may have been partially remagnetized during the opening of Baffin Bay in the early Tertiary.

Franklin Igneous Events, Tension Faulting, and Possible Hadrynian Opening of Baffin Bay, Canada: ABSTRACT

The Franklin intrusions are an extensive swarm of late Hadrynian (latest Proterozoic) diabase dikes that occur in a giant arc from Great Bear Lake eastward to Melville Peninsula, Baffin Island, and northern Ungava. They are chemically and petrologically classified as tholeiites and are probably co-magmatic. Paleomagnetic pole positions and numerous whole-rock of K-Ar age determinations indicate that the dikes were emplaced at low paleolatitudes 650 m.y. ago. They intrude Hadrynian sedimentary sequences that contain features indicative of deposition under warm climatic conditions. The Baffin dikes are subparallel with the northeast coastline of Baffin Island and a pronounced northwest-trending fault system. Intermittent, mainly normal, movement along these faults persisted from the Helikian to the Quaternary and produced a series of graben structures which may be due to the same regional tension as the dikes. Thus Baffin Bay and Davis Strait may have started to form as early as the late Hadrynian and may contain Paleozoic strata. End_of_Article - Last_Page 2480------------