FIR Emission From Rich Clusters
Session 89 -- Clusters of Galaxies - Galaxy Evolution
Oral presentation, Wednesday, 11, 1995, 10:00am - 11:30am

## [89.03D] FIR Emission From Rich Clusters

Caroline Cox (University of Michigan)

Previous searches for far infrared (FIR) emission from dominant cluster galaxies using small, X-ray selected samples have found 20\% to 50\% of clusters to have significant FIR emission. In a new study, I have analyzed the 60$\mu m$ and 100$\mu m$ emission properties of cD galaxies in a complete sample of 163 Abell Clusters. For comparison, a control sample of 207 blank fields was analyzed to determine the distribution of spurious detections, which is greater than expected from Gaussian statistics. The contribution of Galactic cirrus at 60 $\mu m$ and 100 $\mu m$ to non-Gaussian noise is clearly demonstrated by the correspondence of a 98\% confidence level to a signal to noise of 4 or 4.5 rather than to a signal to noise of 2 as expected from Gaussian statistics.

After correcting for contaminated fields and spurious signals, I find that about 10\% of cD galaxies in rich clusters are sources of FIR emission. Typical detected cDs have FIR luminosities of about 3 $\times$ 10$^{44}$ erg sec$^{-1}$, which is comparable to the blue luminosities from these objects and an order of magnitude greater than the X-ray luminosities produced in the cores of clusters. Dust masses derived from the 60$\mu m$ and 100 $\mu m$ fluxes are $\sim$ $10^{7}$ M $_\odot$. Because only about 10\% of the clusters have high FIR luminosities, such strong emission is probably a transient state for an individual cluster.

It has been suggested that this FIR emission is due to dust heated by electron collisions from the hot gas that dominates the intra-cluster medium. Study of the optical and X-ray properties of these clusters allows us to test models for the heating process of the dust, the origin of the dust, and its importance as a mechanism for cooling the hot gas. The central electron density and the temperature distribution for the hot gas are determined from analysis of ROSAT PSPC observations of four of these clusters. My program of $UBVI$ imaging is designed to identify dust lanes and morphology that might indicate that stripping of gas and dust from a galaxy has been or is occuring in these clusters.