Cl 1358+62: Characterizing the Physical Properties of Cluster Galaxies atz= 0.33

Abstract

We examine the physical properties of 173 cluster members in CL 1358+62 (z = 0.3283) from HST WFPC2 imaging taken in the F606W (∼rest-frame B) and F814W (∼rest-frame V ) filters over a 2.2×2.2 Mpc 2 field (H 0 = 100 km s −1 Mpc −1 , Ω M = 0.3, Ω Λ = 0.7). Structural parameters are measured for each galaxy by fitting a PSF-convolved, two component model to their 2D surface brightness distribution. We examine bulge+disk models using three different bulge profiles (de Vaucouleurs, Sérsic, and exponential), and rigorously test the robustness of our results by analyzing several thousand artificial galaxies in the same manner as the cluster data. The measured physical properties from the best-fit profile of the cluster galaxies are combined with ground-based spectroscopy to test for correlations between morphological characteristics, current star formation, total galaxy colors, and cluster substructure. We find that: (1) Bulge-to-total ratio [(B/T ) deV ] and Hubble type (−5 ≤ T ≤ 8) are strongly correlated (99% confidence), but the scatter is large and early-type spirals are not reliably distinguished from ellipticals and S0's based on (B/T ) deV . (2) From comparison of their physical properties, the low luminosity (−17.3 ≥ M B z − 5 log h ≥ −19.3) ellipticals in our sample are likely to be face-on S0 galaxies. (3) High galaxy asymmetry and strong [OII]λ3727 emission are strongly correlated for disk-dominated members [(B/T ) deV < 0.4].(4) There exists a small population (∼ 5%) of bulge-dominated members whose significant [OII]λ3727 emission (< −5Å) suggest they harbor active galactic nuclei. (5) At these redshifts, determining the correct Sérsic index n can be highly unreliable.

Evolution of the early-type galaxy fraction in clusters since z = 0.8

“…After several iterations, we settled on B/T ≥ 0.35 and S 2 ≤ 0.075 as our definition of an early-type galaxy. These limits are very similar to those used in previous studies (Im et al 2002;McIntosh et al 2002;Tran et al 2003). With these criteria, our quantitative selection can be translated into visual classification terms as…”

“…Local late-type galaxies with n = 1 bulges have B/T ≤ 0.1 (de Jong 1996). Since such bulges contain only 10% of the total galaxy light, low signalto-noise measurements of late-type high-redshift galaxies make it very difficult, if not impossible, to determine the Sérsic index of distant bulges even with the spatial resolution of the Hubble Space Telescope as demonstrated by an extensive set of tests on HST images of the high-redshift cluster CL1358+62 (Tran et al 2003). On the other hand, n is more important for bulgedominated galaxies, and n = 4 is the expected value based on local early-type galaxies.…”

“…As shown by previous works (Im et al 2002;McIntosh et al 2002;Tran et al 2003;Blakeslee et al 2006), quantitative and visual morphologies can be best linked together by focussing on three structural parameters: bulge fraction B/T , image smoothness S and bulge ellipticity e. The image smoothness, S , is defined as:…”

“…Recent works on stellar mass-selected cluster galaxy samples van der Wel et al 2007) paint a different picture. The fractions of E+S0 galaxies in clusters, groups and the field do not appear to have changed significantly from z ∼ 0.8 to z ∼ 0.03 for galaxies with masses greater than 4 × 10 10 M .…”

Dark matter deprivation in the field elliptical galaxy NGC 7507

“…It is, however, notoriously difficult to distinguish face-on S0 galaxies from elliptical galaxies (e.g. Tran et al 2003;Bamford et al 2009;Weinmann et al 2009). Rapid rotation may also be the result of a major merger.…”