Do We Detect the Galactic Feedback Material in X-ray Observations of
  Nearby Galaxies? - A Case Study of NGC 5866
  One of the major sources of X-ray emitting hot gas around galaxies is the
feedback from supernovae (SNe), but most of this metal-enriched feedback
material is often not directly detected in X-ray observations. This missing
galactic feedback problem is extremely prominent in early-type galaxy bulges
where there is little cool gas to make the SNe ejecta radiate at lower
temperature beyond the X-ray domain. We herein present a deep Suzaku
observation of an S0 galaxy NGC5866, which is relatively rich in molecular gas
as an S0 galaxy and shows significant evidence of cool-hot gas interaction. By
jointly analyzing the Suzaku and an archival Chandra data, we measure the Fe/O
abundance ratio to be $7.63_{-5.52}^{+7.28}$ relative to solar values. This
abundance ratio is much higher than those of spiral galaxies, and even among
the highest ones of S0 and elliptical galaxies. NGC5866 also simultaneously has
the highest Fe/O abundance ratio and molecular gas mass among a small sample of
gas-poor early-type galaxies. An estimation of the Fe budget indicates that
NGC5866 could preserve a larger than usual fraction, but far from the total
amount of Fe injected by Type Ia SNe. We also find that the hot gas temperature
increases from inner to outer halos, with the inner halo has a temperature of
~0.25keV, clearly lower than that expected from Type Ia SNe heating. This low
temperature could be most naturally explained by additional cooling processes
related to the cool-hot gas interaction as being indicated by the existence of
many extraplanar dusty filaments. Our results indicate that the large cool gas
content and the presence of cool-hot gas interaction in the inner region of
NGC5866 have significantly reduced the specific energy of the SN ejecta and so
the velocity of galactic outflow. The galaxy could thus preserve a considerable
fraction of metal-enriched feedback material from being blown out.
