We report the discovery of a new, complex, gravitationally lensed arc system in the X-ray luminous cluster of galaxies MS 0440+0204 at z = 0.190. This cluster has Lx = 4.0 × 10⁴⁴ ergs s⁻¹ and is one of a sample of 38 high X-ray luminosity (Lx > 2 × 10⁴⁴ ergs s⁻¹), intermediate-redshift (z > 0.15) clusters we are systematically searching for evidence of gravitational lensing. The clusters were selected from the Einstein Observatory Extended Medium Sensitivity Survey (EM SS) and form a statistically complete, X-ray luminosity limited sample. We present CCD images of MS 0440+0204 that show at least 15 blue circular structures surrounding a multiple nucleus cD galaxy in the core of a compact, poor cluster. The largest giant luminous arc has a length 1> 10" and remains unresolved in 0."5 seeing. The three brightest arcs all of which may be bright enough for spectroscopy and many of the fainter arcs trace out a 22" radius circular critical line corresponding to 90h⁻¹₅₀ kpc radius at the cluster redshift (q₀ = ½). The thin arcs provide strong evidence for a compact lensing mass distribution. The optical morphology of the cluster is remarkable. The core contains six bright galaxies and numerous fainter galaxies embedded in a low surface brightness halo. It appears that we are seeing a poor cluster in the short-lived period when many of the cluster galaxies are merging to form the giant, central cD galaxy. In addition, Donahue, Stocke, & Gioia have observed extended Hα emission coincident with the core of the cluster, suggesting the presence of a large cooling flow an interpretation supported by the presence of radio emission associated with the cD galaxy. We measure a total optical luminosity of 9.4 × 10¹¹ Lsun and compute a lower limit to the total mass enclosed by the arcs of 1.0 × 10¹⁴ Msun (assuming a source redshift of zs ≃ 0.4), corresponding to a central mass-to-light ratio of 110 Msun/Lsun. This cluster is an ideal target for future X-ray observations with Astro-D (Asuka) and ROSAT, and optical spectroscopy with large telescopes. Furthermore, the bright (R = 15.9) foreground star located within a few arcseconds of the cluster center will allow us to obtain very high resolution, ground-based images with a low-order, natural guide star, adaptive optics system.
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Luppino et al. (1993) studied this question.