Cosmic distributions of stellar tidal disruptions by massive black holes
  at galactic centers
  Stars can be consumed (either tidally disrupted or swallowed whole) by
massive black holes (MBHs) at galactic centers when they move into the vicinity
of the MBHs. In this study, we investigate the rates of stellar consumption by
central MBHs and their cosmic distributions, including the effects of triaxial
galaxy shapes in enhancing the reservoir of low-angular-momentum stars and
incorporating realistic galaxy distributions. We find that the enhancement in
the stellar consumption rates due to triaxial galaxy shapes can be significant,
by a factor of ~3 for MBH mass $M_{\rm BH}\sim10^5$-$10^6$Msun and up to more
than one order of magnitude for $M_{\rm BH}\gtrsim10^8$Msun. Only for $M_{\rm
BH}\lesssim10^7$Msun are the stellar consumption rates significantly higher in
galaxies with steeper inner surface brightness profiles. The average (per
galaxy) stellar consumption rates correlate with central MBH masses positively
for $M_{\rm BH}\gtrsim10^7$Msun and negatively for $M_{\rm
BH}\lesssim10^7$Msun. The volumetric stellar tidal disruption rates are
~$3\times10^{-5}$/yr/Mpc$^3$ for MBHs in the mass range of $10^5$-$10^8$Msun at
z=0; and the volumetric stellar consumption rates by MBHs with higher masses
are ~$10^{-6}$/yr/Mpc$^3$, which can be the stellar tidal disruption rate if
the high-mass BHs are extremely spinning Kerr BHs or the rate of being
swallowed if those BHs are Schwarzschild ones. The volumetric stellar
consumption rates decrease with increasing redshift, and the decrease is
relatively mild for $M_{\rm BH}\sim10^5$-$10^7$Msun and stronger for higher
$M_{\rm BH}$. Most of the stellar tidal disruption events (TDEs) at z=0 occur
in galaxies with mass $M_{\rm gal}\lesssim10^{11}$Msun, and about 1%-2% of the
TDEs can occur in high-mass galaxies with $M_{\rm gal}\gtrsim10^{11}$Msun.
