Probing the Balance of AGN and Star-Forming Activity in the Local
  Universe with ChaMP
  The combination of the SDSS and the Chandra Multiwavelength Project (ChaMP)
currently offers the largest and most homogeneously selected sample of nearby
galaxies for investigating the relation between X-ray nuclear emission, nebular
line-emission, black hole masses, and properties of the associated stellar
populations. We present here novel constraints that both X-ray luminosity Lx
and X-ray spectral energy distribution bring to the galaxy evolutionary
sequence H II -> Seyfert/Transition Object -> LINER -> Passive suggested by
optical data. In particular, we show that both Lx and Gamma, the slope of the
power-law that best fits the 0.5 - 8 keV spectra, are consistent with a clear
decline in the accretion power along the sequence, corresponding to a softening
of their spectra. This implies that, at z ~ 0, or at low luminosity AGN levels,
there is an anti-correlation between Gamma and L/Ledd, opposite to the trend
exhibited by high z AGN (quasars). The turning point in the Gamma -L/Ledd LLAGN
+ quasars relation occurs near Gamma ~ 1.5 and L/Ledd ~ 0.01. Interestingly,
this is identical to what stellar mass X-ray binaries exhibit, indicating that
we have probably found the first empirical evidence for an intrinsic switch in
the accretion mode, from advection-dominated flows to standard (disk/corona)
accretion modes in supermassive black hole accretors, similar to what has been
seen and proposed to happen in stellar mass black hole systems. The
anti-correlation we find between Gamma and L/Ledd may instead indicate that
stronger accretion correlates with greater absorption. Therefore the trend for
softer spectra toward more luminous, high redshift, and strongly accreting
AGN/quasars could simply be the result of strong selection biases reflected in
the dearth of type 2 quasar detections.
