4 Properties of the clusters and arcs

In this section, we summarize the optical, X-ray and radio data for the 38 EMSS clusters, and describe in detail those sources classified as gravitational lens systems. Updated optical coordinates for these clusters can be found in Gioia & Luppino (1994). The general properties of the clusters are presented in Table 1. Columns (1) and (2) list the name and redshift of each EMSS cluster. Columns (3), (4) and (5) contain the X-ray properties of the cluster: the detected flux in the $2.4\thinspace \hbox{$^\prime$}\times 2.4 \thinspace \hbox{$^\prime$}$ IPC cell ($F_{\rm x}^{\rm Det}$) and total flux ($F_{\rm x}^{\rm Tot}$) in erg cm^-2 s^-1, and the corrected cluster X-ray luminosity ($L_{\rm x}$) in the 0.3$\,-\,$3.5 keV band in ergs^-1 respectively. The total flux and X-ray luminosity have been corrected following the prescription outlined by Gioia et al.(1990b) and Henry et al.(1992), which accounts for any extended cluster emission that may have been present outside the IPC detect cell. This correction can be substantial at low redshift (z$\,<\,$0.2) but is small at high redshift.

  

Table 1: Results of observations of the 38 EMSS X-ray-selected distant clusters for gravitational lensing survey

Column (6) lists the H$_\alpha$$\,+\,$[NII] luminosities (in ergs^-1) taken from Donahue et al.(1992) who interpreted this line emission as evidence for a cooling flow. Not all of the clusters in our sample were observed by DSG, so only those clusters with an entry in this column have cooling flow measurements. Column (7) contains the 6cm radio flux measured with the VLA (Gioia et al.1983; Stocke et al.1991; Gioia & Luppino 1994). Columns (8) and (9) indicate the quality of the optical data on each cluster by listing the B and R limiting magnitudes ($1\sigma$) and the seeing. We obtained R images for all 38 of the clusters, but B images for only 22. For many of the clusters, however, we do have V and/or I images, and in several cases, these are quite deep. Finally, in Col. (10), we list the number of arcs () and arclets (l < 8'') seen in each cluster. The ($\dagger$) and ($\ast$) symbols that precede some of the cluster names indicate those clusters that have giant arcs or candidate arcs and appear in Figs. 2 and 6, and in Figs. 7 and 8, respectively. For the purposes of this investigation, we define a giant arc as a large, elongated structure having a length l$\,\gt\,$8'' and an axis ratio l/w>10. We consider both high surface brightness ("luminous'') arcs and fainter, low surface brightness ones as well. Arclets are simply short arcs (l$\,<\,$8'') with axis ratios 3$\,<\,$l/w$\,<\,$10. The clusters in Table 1 have considerable variation in their optical appearance, ranging from poor, compact groups to rich regular and irregular clusters. Cases of multiple nucleus cD galaxies, and clusters with optical substructure exist. Eventually, a quantitative morphological classification (e.g. Bautz-Morgan) would be desirable, but such a classification requires galaxy photometry and often spectroscopy (to verify the cluster membership of the brightest galaxies) and is beyond the scope of this paper. We refer the reader to the R band optical images published in Gioia & Luppino (1994).