  We demonstrate a slow ytterbium atomic beam with a tunable longitudinal
velocity in the range of $20$-$30\ \mathrm{m/s}$, a transverse temperature of
$11\ \mathrm{\mu K}$, and flux of up to $1.2 \times 10^{9}\ \mathrm{atoms/s}$.
Such performance is realized by applying two-dimensional cooling, with an
intercombination transition, to a slow atomic beam generated by a
dipolar-allowed transition. We also discuss the feasibility of narrowing the
transverse momentum width to less than the recoil momentum using the
velocity-selective optical transition of atoms based on a long-lived metastable
state. Such a high-flux atomic beam will be a powerful tool for constructing
compact and continuous Bragg diffraction interferometers with ytterbium atoms.
