On the Recent History of Star Formation in the Blue Compact Dwarf Galaxy VII Zw 403

Here we attempt to infer the recent history of star formation in the BCD galaxy VII Zw 403, based on an analysis that accounts for the dynamics of the remnant generated either by an instantaneous burst or by a continuous star formation event. The models are restricted by the size of the diffuse X-ray–emitting region, the Hα luminosity from the star-forming region, and the superbubble diffuse X-ray luminosity. We have reobserved VII Zw 403 with a better sensitivity corresponding to the threshold Hα flux 8.15 × 10-17 ergs cm-2 s-1. The total Hα 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 Hα emission. This result has a profound impact on the predicted properties of the starburst-blown superbubble. Numerical calculations based on the Hubble Space Telescope Hα 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 × 105 M⊙ and a star-forming event with a constant star formation rate SFR = 4 × 10-3 M⊙ yr-1, which lasts for 35 Myr. The numerical calculations based on the energy input rate derived from our observations predict a short episode of star formation lasting less than 10 Myr with a total star cluster mass of ∼(1–3) × 106 M⊙. However, the five main star-forming knots are sufficiently distant to form a coherent shell in a short timescale and still keep their energies blocked within local, spatially separated bubbles. The X-ray luminosities of these are here shown to be consistent with the ROSAT PSPC diffuse X-ray emission.