On the dust content of galaxy clusters

We present a study to estimate the dust content in galaxy clusters by using one the most complete existing catalogues of galaxy clusters based on SDSS data and following two methods: the first one compares the colours of samples of galaxies in the background of clusters with those of galaxies in the field. Using this method, we have explored clustercentric distances up to 6 Mpc. The galaxies used in this first method were selected from the SDSS-DR9, among those having reliable photometry and accurate estimation of photometric redshifts. The results are largely independent of the galactic cut applied. At |b|>20 deg., the sample contains 56,985 clusters in the redshift range 0.05<z<0.68 (the mean redshift is 0.30) and ~5.3x10^6 galaxies. The second method computes the contribution of dust in clusters of galaxies to the far infrared sky. That is estimated indirectly by measuring the effect of clusters in the E(B-V) extinction map. Using the first method, we did not find any dependence with clustercentric distance in the colours of background galaxies. This allows us to constrain the mass of dust in the intracluster media, M_dust<8.4x10^9 M_sun (95% C.L.) within a cluster radius of 3 Mpc. With the second method, which averages the extinction of all clusters, we find a surface integral of the excess of colour g-i of 3.4+/-0.1 millimag Mpc^2. This is equivalent to ~60 times the far infrared luminosity of a Milky Way-like galaxy. By assumming similar properties for the dust, we can estimate a total dust mass per cluster of ~2x10^9 M_sun, which is compatible with the hypothesis that the dust is within the spiral galaxies of a cluster. Separating the clusters in 5x5 bins in redshift and richness, we confirm previous findings of a clear increase in luminosity with a redshift that agrees with the trend expected from current models.