On the recent history of star formation in the BCD galaxy VII Zw403

Abstract

The recent history of star formation in the BCD galaxy VII Zw403, is analysed with accounts for the dynamics of the remnant generated either by an instantaneous burst or by a continuous star formation event. We have re-observed VII Zw403 with a better sensitivity corresponding to the threshold H$_{\alpha}$ flux $8.15 \times 10^{-17}$ erg cm$^{-2}$ s$^{-1}$. The total H$_{\alpha}$ luminosity derived from our data is much larger than reported before, and presents a variety of ionized filaments and incomplete shells superimposed on the diffuse H$_{\alpha}$ emission. This result has a profound impact on the predicted properties of the starburst blown superbubble. Numerical calculations based on the previous H$_{\alpha}$ data, predict two different scenarios of star formation able to match simultaneously all observed parameters. These are an instantaneous burst of star formation with a total mass of $5 \times 10^5$ M$_{\odot}$ and a star-forming event with a constant SFR = $4 \times 10^{-3}$ M$_{\odot}$ yr$^{-1}$, which lasts for 35 Myrs. The numerical calculations based on the energy input rate derived from our observations predict a short episode of star formation lasting less than 10 Myrs with a total star cluster mass $\sim (1 - 3) \times 10^6$ M$_{\odot}$.