On the dust content of galaxy clusters

¹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
e-mail: cgc@ll.iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain

Received: 14 July 2014
Accepted: 5 August 2014

Abstract

Context. Most of the contribution to dust emission in clusters of galaxies comes from late-type galaxies. However, several ejection processes of material from these galaxies could introduce dust in the intracluster media. Even a relatively low abundance of this dust could act as an efficient cooling agent and have a relevant role in the evolution of clusters.

Aims. We present a study to estimate the dust content in galaxy clusters.

Methods. This was done by using one the most complete existing catalogues of galaxy clusters based on Sloan Digital Sky Survey (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; this covers at least 2 × R₂₀₀ for all the clusters in the sample. The galaxies used in this first method were selected from the SDSS-DR9, among those having reliable photometry and accurate estimation of photometric redshifts. Using the colours of background galaxies, we analyzed several regions at galactic latitudes | b | > 20° and >50°. The results are largely independent of the galactic cut applied. At | b | > 20°, the sample contains 56 985 clusters in the redshift range 0.05 <z< 0.68 (the mean redshift is 0.30) and ~5.3 × 10⁶ 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.

Results. Using the first method, we did not find any dependence with clustercentric distance in the colours of background galaxies. As representative of the whole results, the surface integral of the excess of colour g − i in three rings centred in the clusters and with radius 0–1, 0–2, and 0–3 Mpc is −3.7 ± 3.5, + 3.2 ± 6.8, and −4.5 ± 10.1 milimag Mpc², respectively. This allows us to constrain the mass of dust in the intracluster media, M_dust< 8.4 × 10⁹M_⊙ (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 Mpc². From the extinction and redshift of each cluster, we obtain 0.13 Jy and (1.46 ± 0.03) × 10⁴⁵ erg s^-1 for the mean flux and luminosity at 100 μm. This is ~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 ~2 × 10⁹M_⊙, which is compatible with the hypothesis that the dust is within the spiral galaxies of a cluster. Separating the clusters in 5 × 5 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.

Conclusions. The results are compatible with expectations accounting for the contribution of dust in cluster member galaxies and, in particular, a strong increase in luminosity with redshift is demonstrated. The dust in the intracluster media is not detected, but the analyses as a whole show that the amount of this dust is small.