On the Ongoing Multiple Blowout in NGC 604

Several facts regarding the structure of NGC 604 are examined here. The three main cavities produced by the mechanical energy from massive stars, which in NGC 604 are spread over a volume of 10<SUP>6</SUP> pc<SUP>3</SUP>, are shown here to be undergoing blowout into the halo of M33. High-resolution long-slit spectroscopy is used to track the impact from massive stars, while Hubble Space Telescope archive data are used to display the asymmetry of the nebula. NGC 604 is found to be a collection of photoionized filaments and sections of shells that are in direct contact with the thermalized matter ejected by the massive stars. The multiple blowout events presently drain the energy injected by massive stars, and thus the densest photoionized gas is found almost at rest and is expected to suffer a slow evolution.