The inner $\sim$ 40 pc Radial Distribution of the Star formation Rate for a nearby Seyfert 2 galaxy M51

TL;DR

This study maps the spatial distribution of star formation rates within the central 40 parsecs of galaxy M51, revealing potential suppression near the nucleus likely caused by AGN feedback, and highlights asymmetries possibly due to jet activity.

Contribution

First spatially resolved analysis of star formation rate distribution within 40 pc of M51's nucleus using HST spectra, revealing suppression and asymmetry linked to AGN feedback.

Findings

Young stellar populations are absent within ~8 pc of the nucleus.

The SSFR distribution is asymmetrical, likely due to AGN jet feedback.

Star formation is suppressed in the circumnuclear region.

Abstract

We investigate spatially resolved specific star formation rate (SSFR) in the inner $\sim$ 40 pc for a nearby Seyfert 2 galaxy, M51 (NGC 5194) by analyzing spectra obtained with the \emph{Hubble Space Telescope (HST)} Space Telescope Imaging Spectrograph (STIS). We present 24 radial spectra measured along the STIS long slit in M51, extending $\sim 1\arcsec$ from the nucleus (i.e., -41.5 pc to 39.4 pc). By the simple stellar population synthesis, the stellar contributions in these radial optical spectra are modeled. Excluding some regions with zero young flux fraction near the center (from -6 pc to 2 pc), we find that the mean flux fraction of young stellar populations (younger than 24.5 Myr) is about 9 \%, the mean mass fraction is about 0.09\%. The young stellar populations are not required in the center inner $\sim$ 8 pc in M51, suggesting a possible SSFR suppression in the circumnuclear region ($\sim$ 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.