What question did this study set out to answer?

This research aims to understand the formation and characteristics of optical rings around galaxies in rich clusters through gravitational lensing.

July 1, 1991The Astrophysical Journal13 citationsOpen Access

Formation and distortion of optical rings around rich cluster galaxies

CKC. S. Kochanek RBR. D. Blandford

Key Points

This research aims to understand the formation and characteristics of optical rings around galaxies in rich clusters through gravitational lensing.
Analyzed the impact of gravitational lensing on optical rings formation
Derived mathematical relationships such as ring radius and mass density ratios
Examined probabilities of ring occurrence based on galaxy mass and background density
Found that rings form in regions with specific surface density limits κ_min_~0.4 and κ_max_~<1
Determined that half-illuminated rings occur twice as often as completely illuminated ones
Calculated the probability of finding a half ring to be approximately 0.02 times the square of the source radius over surface density of background galaxies

Abstract

view Abstract Citations (11) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Formation and Distortion of Optical Rings around Rich Cluster Galaxies Kochanek, Christopher S. ; Blandford, Roger D. Abstract Luminous optical rings may be formed around individual galaxies in rich clusters by gravitational deflection of light from a background galaxy. Observation of these rings can provide a direct measurement of the local surface density in the cluster if the cluster redshift, the source redshift, and the lens galaxy velocity dispersion are measured. If the major and minor axes of the ring are r_+_ and R_-_, then the harmonic mean ring radius defined by R = 2_+r-_/ (r_+_ + r_-_) = bg_/ (1 - κ) where bg_ is the critical radius of the unperturbed galaxy, and κ = SIGMA/SIGMAc_ is the ratio of the smoothly distributed local surface mass density of the cluster to the critical surface density for gravitational lensing. The ellipticity of the ring measures the local shear in the combined potential of the cluster and the galaxy. Rings will only be found in regions with κₘin_ <κ<κₘax_ where the limit κₘin_~0. 4 depends on the sensitivity of the observations, and the limit 0. 5~<κₘax_~< 1 depends on the cluster density profile. Cross sections for the formation of complete and incomplete rings are given. The formation of a closed ring implies that the source is comparable in size to or larger than the tangential caustic associated with the lens galaxy. Half-illuminated rings should be at least twice as common as completely illuminated rings. The probability per lens galaxy of finding a half ring is ~0. 02 (q/1") ²^ (nₛ_/10 arcmin^- 2^), where q is the source radius and nₛ_ is the surface density of background galaxies. A modification of this optical arrangement may account for the twinned arc in A2218. Publication: The Astrophysical Journal Pub Date: July 1991 DOI: 10. 1086/170211 Bibcode: 1991ApJ. . . 375. . 492K Keywords: Galactic Clusters; Gravitational Lenses; Mass Distribution; Dark Matter; Galactic Mass; Red Shift; Astrophysics; GALAXIES: CLUSTERING; GRAVITATIONAL LENSES full text sources ADS | data products SIMBAD (3) NED (1)

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