Low-mass and High-mass Supermassive Blackholes In Radio-Loud AGNs Are
  Spun-up in Different Evolution Paths
  How Supermassive Blackholes (SMBHs) are spun-up is a key issue of modern
astrophysics. As an extension of the study in Wang et al. (2016), we here
address the issue by comparing the host galaxy properties of nearby ($z<0.05$)
radio-selected Seyfert 2 galaxies. With the two-dimensional bulge+disk
decompositions for the SDSS $r$-band images, we identify a dichotomy on various
host galaxy properties for the radio-powerful SMBHs. By assuming the radio
emission from the jet reflects a high SMBH spin, which stems from the
well-known BZ mechanism of jet production, high-mass SMBHs (i.e.,
$M_{\mathrm{BH}}>10^{7.9}M_\odot$) have a preference for being spun-up in
classical bulges, and low-mass SMBHs (i.e., $M_{\mathrm{BH}}=10^{6-7}M_\odot$)
in pseudo-bulges. This dichotomy suggests and confirms that high-mass and
low-mass SMBHs are spun-up in different ways, i.e., a major "dry" merger and a
secular evolution.
