Line-of-sight velocity and metallicity measurements of the Palomar 5
  tidal stream
  We present Subaru/FOCAS and Keck/DEIMOS medium-resolution spectroscopy of a
tidally disrupting Milky Way (MW) globular cluster Palomar 5 and its tidal
stream. The observed fields are located to cover an angular extent of $\sim
17$\arcdeg along the stream, providing an opportunity to investigate a trend in
line-of-sight velocities ($V_{\rm los}$) along the stream, which is essential
to constrain its orbit and underlying gravitational potential of the Milky
Way's dark matter halo. A spectral fitting technique is applied to the observed
spectra to obtain stellar parameters and metallicities ([Fe/H]) of the target
stars. The 19 stars most likely belonging to the central Pal 5 cluster have a
mean $V_{\rm los}$ of $-58.1\pm 0.7$ km s$^{-1}$ and metallicity
[Fe/H]$=-1.35\pm 0.06$ dex, both of which are in good agreement with those
derived in previous high-resolution spectroscopic studies. Assuming that the
stream stars have the same [Fe/H] as the progenitor cluster, the derived [Fe/H]
and $V_{\rm los}$ values are used to estimate the possible $V_{\rm los}$ range
of the member stars at each location along the stream. Because of the heavy
contamination of the field MW stars, estimated $V_{\rm los}$ range depends on
prior assumptions about the stream's $V_{\rm los}$, which highlights the
importance of more definitely identifying the member stars using proper motion
and chemical abundances to obtain an unbiased information of $V_{\rm los}$ in
the outer part of the Pal 5 stream. The models for the gravitational potential
of the MW's dark matter halo that are compatible with the estimated $V_{\rm
los}$ range are discussed.
