The graph of the function $f ( x ) = \sin \left( \omega x + \frac { \pi } { 3 } \right) ( \omega > 0 )$ is shifted left by $\frac { \pi } { 2 }$ units. If the minimum value of the resulting curve is $-1$ and the distance between two consecutive minimum points is $\pi$, then the minimum value of $\omega$ is
A. $\frac { 1 } { 6 }$
B. $\frac { 1 } { 4 }$
C. $\frac { 1 } { 3 }$
D. $\frac { 1 } { 2 }$