Optical Spectroscopy of Halpha Filaments in Cool Core Clusters:
  Kinematics, Reddening, and Sources of Ionization
  We have obtained deep, high spatial and spectral resolution, long-slit
spectra of the Halpha nebulae in the cool cores of 9 galaxy clusters. This
sample provides a wealth of information on the ionization state, kinematics,
and reddening of the warm gas in the cool cores of galaxy clusters. We find
evidence for only small amounts of reddening in the extended, line-emitting
filaments, with the majority of filaments having E(B-V) < 0.2. The combination
of [O III]/Hb, [N II]/Ha, [S II]/Ha, and [O I]/Ha allow us to rule out
collisional ionization by cosmic rays, thermal conduction, and photoionization
by ICM X-rays and AGN as strong contributors to the ionization of the warm gas
in both nuclei and filaments. The data are adequately described by a composite
model of slow shocks and star formation. This model is further supported by an
observed correlation between the linewidths and low ionization line ratios
which becomes stronger in systems with more modest star formation activity
based on far ultraviolet observations. We find that the more extended, narrow
filaments tend to have shallower velocity gradients and narrower linewidths
than the compact filamentary complexes. We confirm that the widths of the
emission lines decrease with radius, from FWHM \sim 600 km/s in the nuclei to
FWHM ~ 100 km/s in the most extended filaments. We suggest that this radial
dependence of the velocity width may in fact be linked to ICM turbulence and,
thus, may provide a glimpse into the amount of turbulence in cool cores. In the
central regions (r < 10 kpc) of several systems the warm gas shows kinematic
signatures consistent with rotation. We find that the kinematics of the most
extended filaments in this sample are broadly consistent with both infall and
outflow, and recommend further studies linking the warm gas kinematics to both
radio and X-ray maps in order to further understand the observed kinematics.
