NGC604 is the largest H ii -region in M33 , second only within the Local Group to 30 Dor , and is important as a laboratory for understanding how massive young stellar clusters interact with the surrounding interstellar medium .
Here , we present deep ( 300ks ) X-ray imagery of NGC604 obtained as part of the Chandra ACIS Survey of M33 ( ChASeM33 ) , which show highly structured X-ray emission covering \sim 70 % of the full H \alpha extent of NGC604 .
The main bubbles and cavities in NGC604 are filled with hot ( kT = 0.5 keV ) X-ray emitting gas and X-ray spectra extracted from these regions indicate that the gas is thermal .
For the western part of NGC604 we derive an X-ray gas mass of \sim 4300 M _ { \odot } and an unabsorbed ( 0.35 – 2.5 keV ) X-ray luminosity of L _ { X } = 9.3 \times 10 ^ { 35 } erg s ^ { -1 } .
These values are consistent with a stellar mass loss bubble entirely powered by about 200 OB-stars .
This result is remarkable because the standard bubble model tends to underpredict the luminosity of X-ray bright bubbles and usually requires additional heating from SNRs .
Given a cluster age of \sim 3 Myr it is likely that the massive stars have not yet evolved into SNe .
We detect two discrete spots of enhanced and harder X-ray emission , which we consider to be fingerprints from a reverse shock produced by a supersonic wind after it collided with the shell wall .
In the eastern part of NGC604 the X-ray gas mass amounts to \sim 1750 M _ { \odot } .
However , mass loss from young stars can not account for the unabsorbed X-ray luminosity of L _ { X } = 4.8 \times 10 ^ { 35 } erg s ^ { -1 } .
Off-center SNRs could produce the additional luminosity .
The bubbles in the east seem to be much older and were most likely formed and powered by young stars and SNe in the past .
A similar dichotomy between east and west is seen in the optical , implying that a massive wall of neutral and ionized gas shields the dynamically quiescent east from the actively star forming west .