Centrality dependence of the N($\Omega$)/N($\phi$) ratios and $\phi$ anisotropic flow

Due to its long lifetime and relatively small hadronic interaction cross-section, the $\phi$-meson is a clean probe for studying the properties of the hot and dense medium created in high-energy nuclear collisions. We present the first results of the centrality dependence of the N($\Omega$)/N($\phi$) ratios and $\phi$ anisotropic flow ($v_{2}$) from $\sqrt{s_{NN}}=$ 200 GeV Au+Au collisions measured by STAR at RHIC. In more central collisions, the eccentricity-scaled anisotropic flow ($v_{2}/\epsilon$) is large, indicating a stronger collective expansion at the early partonic stage. For $p_{T}>$2 GeV/$c$, the $v_{2}$ values are consistent with the $v_{2}$ values of other mesons, and expectations from parton recombination models. In addition, the N($\Omega$)/N($\phi$) ratio is found to increase linearly as a function of $p_{T}$, a characteristic of coalescence of thermal quarks for both $\phi$ and $\Omega$. In the most central collisions, the linear increase reaches up to $p_{T}\sim$4 GeV/$c$ implying that most of the multistrange hadrons are formed directly from thermalized $s$-quarks in Au+Au collisions at RHIC.