Formation and distortion of optical rings around rich cluster galaxies

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_-_) = b_g_/(1 - κ) where b_g_ is the critical radius of the unperturbed galaxy, and κ = {SIGMA}/{SIGMA}_c_ 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 κ_min_ <κ<κ_max_ where the limit κ_min_~0.4 depends on the sensitivity of the observations, and the limit 0.5~<κ_max_~< 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^(n_s_/10 arcmin^- 2^), where q is the source radius and n_s_ 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)