Vol 15, No 6

The inner ~ 40 pc radial distribution of the star formation rate for a nearby Seyfert 2 galaxy M51

Li-Ling Fang, Xiao-Lei Jiang, Zhi-Cheng He, Wei-Hao Bian


Abstract We investigate the spatially resolved specific star formation rate (SSFR) in the inner ~40 pc for a nearby Seyfert 2 galaxy, M51 (NGC 5194) by analyzing spectra obtained with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS). We present 24 radial spectra measured along the STIS long slit in M51, extending ~ 1′′ from the nucleus (i.e., –41.5 pc to 39.4 pc). By simple stellar population synthesis, the stellar contributions in these radial optical spectra are modeled. It is found that the mean flux fraction of young stellar populations (younger than 24.5 Myr) is about 9%. Excluding some regions with zero young flux fraction near the center (from –6 pc to 2 pc), the mean mass fraction is about 0.09%. The young stellar populations are not required in the center inner ~8 pc in M51, suggesting a possible SSFR suppression in the circumnuclear region (~10 pc) from the feedback of active galactic nuclei (AGNs). The radial distribution of SSFR in M51 is not symmetrical with respect to the long slit in STIS. This unsymmetrical SSFR distribution is possibly due to the unsymmetrical AGN feedback in M51, which is related to its jet.


Keywords galaxies: active — galaxies: Seyfert — galaxies: starburst

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