Integral field spectroscopy of H alpha emission in cooling flow cluster cores: disturbing the molecular gas reservoir

We present optical integral field spectroscopy of the H alpha-luminous (> 10(42) erg s(-1)) central cluster galaxies in the cores of the cooling flow clusters A1664, A1835, A2204 and Zw8193. From the [N-II]+H alpha complex in these moderate resolution (70-150 km s(-1)) spectra we derive 2D views of the distribution and kinematics of the emission-line gas, and further diagnostics from the [S-II] and [O-I] lines. The H alpha emission shows a variety of disturbed morphologies, ranging from smooth but distorted to clumpy and filamentary, with velocity gradients and splittings of several hundred km s(-1) on spatial scales of 20 kpc or more. Despite the small sample size, there are some generic features. The most disturbed H alpha emission appears to be associated with secondary galaxies within 10-20 kpc (projected) of the central galaxy and close in velocity to the H alpha. The global H alpha kinematics match those of the CO(1-0) emission in single-dish data. The [N-II]/H alpha, [S-II]/H alpha and [O-I]/H alpha ratios vary little with position, local H alpha surface brightness or between clusters. We propose that the H alpha and CO emission arise in molecular clouds heated by a starburst, and that the latter has been triggered by interaction with a secondary galaxy. Such CO emission is known to trace massive (> 10(10) M-circle dot) compact (< 20 kpc) reservoirs of cool molecular gas, and it is plausible that an infalling galaxy would disturb this gas, distorting the H alpha morphology and initiating widespread star formation. We also examine the role of cloud-cloud collisions in the undisturbed molecular gas reservoir, and suggest that they might be an important source of excitation for the emission-line gas in the cores of lower H alpha luminosity clusters with less intense star formation.