Spitzer Mid-Infrared Spectra of Selected Galaxy Cluster Cooling Flows

We present sparse spectral maps of eight massive galaxy cluster cooling flows, using the Infrared Spectrograph of the Spitzer Space Telescope. Our targets are located at distances from z = 0.05 to 0.29. The total L_MIR in these objects, integrated from 12 to 25 mum, ranges between 10⁴¹ and 10⁴³ erg s^-1. In the mid-infrared (MIR), two of the targets are point sources, while we have detected extended emission in the other six. The estimated cooling rates from X-ray observations range from 10 to 200 M_Sun/yr. Their MIR spectra exhibit very different morphologies, from classic starbursts to Seyfert nuclei. Vibrationally excited molecular hydrogen is detected in all of our sources, with medium to strong emission lines in most of the spectra. Abell 1068, Abell 1835, and Hydra A display the hallmarks of starburst galaxies: a rising red continuum as well as prominent emission from large aromatic molecules and low-ionization atomic lines, and no high-ionization atomic line emission. Abell 1068 closely resembles a Seyfert 2 galaxy with a nuclear starburst. Three more of the objects, Abell 1795, Abell 478, and Abell 2597, have a common but unusual morphology, characterized by a flat continuum, weak aromatic molecular emission, and strong molecular hydrogen and low-ionization atomic line emission. PKS 0745-19 shares the suite of strong H₂ lines and has a shallow continuum rise toward the red. The MIR spectrum of MS0735.6+7421 is entirely different from the others, dominated by H₂ lines with a continuum rise toward the blue. We will use our results to improve estimates of the star formation rate in the central dominant galaxies and compare this to the gas deposition rate.