THE TRANSPARENCY OF GALAXY CLUSTERS

If galaxy clusters contain intracluster dust, the spectra of galaxies lying behind clusters should show attenuation by dust absorption. We compare the optical (3500-7200 angstrom) spectra of 60,267 luminous, early-type galaxies selected from the Sloan Digital Sky Survey to search for the signatures of intracluster dust in z similar to 0.05 clusters. We select massive, quiescent (i.e., non-star-forming) galaxies using an EW(H alpha) <= 2 angstrom cut and consider galaxies in three bins of velocity dispersion ranging from 150 to 300 km s(-1). The uniformity of early-type galaxy spectra in the optical allows us to construct inverse-variance-weighted composite spectra with high signal-to-noise ratios (ranging from 10(2) to 10(3)). We compare the composite spectra of galaxies that lie behind and adjacent to galaxy clusters and find no convincing evidence of dust attenuation on scales of similar to 0.15-2 Mpc; we derive a generic limit of E(B - V) < 3 x 10(-3) mag on scales of similar to 1-2 Mpc at the 99% confidence level, using conservative jackknife error bars, corresponding to a dust mass less than or similar to 10(8) M-circle dot. On scales smaller than 1 Mpc, this limit is slightly weaker, E(B - V) < 8 x 10(-3) mag.