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Bar effects on central star formation and AGN activity

Galactic bars are often suspected to be a channel of gas inflow to the galactic center and trigger central star formation and active galactic nuclei (AGN) activity. However, the current status on this issue based on empirical studies is unsettling, especially on AGN. We investigate this question based on the Sloan Digital Sky Survey (SDSS) Data Release 7. From the nearby (0.01 < z < 0.05) bright (Mr < -19) database, we have constructed a sample of 6,658 relatively face-on late-type galaxies through visual inspection. We found 36% of them to have a bar. Bars are found to be more common in galaxies with earlier morphology. This makes sample selection critical. Parameter-based selections would miss a large fraction of barred galaxies of early morphology. Bar effects on star formation or AGN are difficult to understand properly because multiple factors (bar frequency, stellar mass, black-hole mass, gas contents, etc.) seem to contribute to them in intricate manners. In the hope of breaking these degeneracies, we inspect bar effects for fixed galaxy properties. Bar effects on central star formation seem higher in redder galaxies. Bar effects on AGN on the other hand are higher in bluer and less massive galaxies. These effects seem more pronounced with increasing bar length. We discuss possible implications in terms of gas contents, bar strength, bar evolution, fueling time-scale, and the dynamical role of supermassive black hole.