By using the Hectospec 6.5 m Multiple Mirror Telescope ( MMT ) and the 2.16 m telescope of National Astronomical Observatories , Chinese Academy of Sciences ( NAOC ) , we obtained 188 high signal-to-noise ratio ( S/N ) spectra of H ii regions in the nearby galaxy M101 , which are the largest spectroscopic sample of H ii regions for this galaxy so far .
These spectra cover a wide range of regions on M101 , which enables us to analyze two dimensional distributions of its physical properties .
The physical parameters are derived from emission lines or stellar continuum , including stellar population age , electron temperature , oxygen abundance and etc .
The oxygen abundances are derived using two empirical methods based on O3N2 and R _ { 23 } indicators , as well as the direct T _ { e } method when \hbox { [ O { \sc iii } ] } \lambda 4363 is available .
By applying the harmonic decomposition analysis to the velocity field , we obtained line-of-sight rotation velocity of 71 { km~ { } s } ^ { -1 } and a position angle of 36 degree .
The stellar age profile shows an old stellar population in galaxy center and a relative young stellar population in outer regions , suggesting an old bulge and a young disk .
Oxygen abundance profile exhibits a clear break at \sim 18 kpc , with a gradient of - 0.0364 dex kpc ^ { -1 } in the inner region and - 0.00686 dex kpc ^ { -1 } in the outer region .
Our results agree with the “ inside-out ” disk growth scenario of M101 .