The Homogeneity of Spheroidal Populations in Distant Clusters

Abstract

The small scatter observed for the (U[V ) colors of spheroidal galaxies in nearby clusters of galaxies provides a powerful constraint on the history of star formation in dense environments. However, with local data alone, it is not possible to separate models where galaxies assembled synchronously over redshifts 0 \ z \ 1 from ones where galaxies formed stochastically at much earlier times. Here we attempt to resolve this ambiguity via high-precision rest-frame UVÈoptical photometry of a large sample of morphologically selected spheroidal galaxies in three z D 0.54 clusters that have been observed with the Hubble Space T elescope (HST ). We demonstrate the robustness of using the HST to conduct the morphological separation of spheroidal and disk galaxies at this redshift and use our new data to repeat the analysis conducted locally at a signiÐcant look-back time. We Ðnd a small scatter (\0.1 mag rms) for galaxies classed as EÏs and E/S0Ïs, both internally within each of the three clusters and externally from cluster to cluster. We do not Ðnd any trend for the scatter to increase with decreasing luminosity down to other than can be accounted for by observational error. Neither is there evidence for a L D L V * ] 3, distinction between the scatter observed for galaxies classiÐed as ellipticals and S0. Our result provides a new constraint on the star formation history of cluster spheroidals prior to z^0.5 conÐrming and considerably strengthening the earlier conclusions. Most of the star formation in the elliptical galaxies in dense clusters was completed before z^3 in conventional cosmologies. Although we cannot rule out the continued production of some ellipticals, our results do indicate an era of initial star formation consistent with the population of star-forming galaxies recently detected beyond z^3.

Clustering of Red Galaxies Near a Radio-Loud Quasar at z = 1.086

“…Detailed studies of elliptical galaxies in nearby and intermediate redshift clusters showed that their photometric properties are homogeneous and evolve only mildly with redshift at z ∼ < 1. This is consistent with the so-called 'passive evolution', namely the change of the photometric properties of elliptical galaxies by the aging of their stars only, with a formation epoch of at least ∼ 10 Gyr ago (Bower, Lucey & Ellis 1992;Aragón-Salamanca et al 1993;Ellis et al 1997;Dickinson 1997b;Stanford, Eisenhardt, & Dickinson 1997). On the other hand, some S0 and spiral galaxies seem to experience faster evolution (e.g., Dressler et al 1994;Dressler and Smail 1997).…”

SNe heating and the chemical evolution of the intra-cluster medium

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Evidence for shock acceleration and intergalactic magnetic fields in a large-scale filament of galaxies ZwCl 2341.1+0000

“…Their ubiquitous colour-magnitude sequence, first noted locally by Baum (Baum 1959), is now well documented in many clusters, ranging from Coma to clusters at redshifts up to z = 1 (Stanford, Eisenhardt, & Dickinson 1998, Ellis et al 1997, Gladders & Yee 2000. The colours of elliptical galaxies become bluer as they become less luminous.…”