HST NICMOS and WFPC2 observations of molecular hydrogen and dust in the central galaxies in cluster cooling flows

Abstract

We present preliminary results of HST imaging observations of three central galaxies in X-ray luminous clusters of galaxies with putative major cooling flows in their cores: NGC 1275 in the Perseus cluster, Abell 2597, and PKS 0745-19. Narrow-band NICMOS imaging at 2 microns reveals extended, warm ( T∼2000–3000 K) molecular hydrogen structures in the cores of Abell 2597 and PKS 0745-19 that appear to be co-spatial with the ionized hydrogen revealed in H α+[N II] images obtained with WFPC2. The H 2/H α emission line ratio is unexpectedly high in Abell 2597 and PKS 0745-191: too high to be explained by shocks with v>50 km s −1 or by power-law photo-ionization. Photo-ionization by the surrounding X-ray gas is unlikely in Abell 2597. Fluorescent heating by hot stars is plausible in both Abell 2597 and PKS 0745-191. No extended H 2 emission was discovered in NGC 1275. The H 2/H α ratio allowed by our detection limits are consistent with shocks or nuclear photo-ionization in NGC 1275. A paper by Donahue et al. is in preparation.