As the nearest dramatic example of a poststarburst galaxy driving a galactic wind , NGC 1569 is an ideal test environment to understand the impact of “ feedback ” from massive star lives and deaths on the surrounding ISM .
We present HST WFPC2 Based on observations with the NASA/ESA Hubble Space Telescope , obtained at the Space Telescope Science Institute , which is operated by AURA , Inc. , under NASA contract NAS5-26555 . narrowband imagery of NGC 1569 in an attempt to understand the underlying ionizing emission mechanisms on a 3 pc scale and to generate a H ii region size distribution and luminosity function .
We use [ O iii ] /H \beta and [ S ii ] /H \alpha ratio maps to find that non-photoionizing mechanisms ( e.g .
shocks ) are responsible for 10 \pm 3 % of the H \alpha emission , 2.3–3.3 times larger than results from similar galaxies .
Note that our method of determining this result is different than these past results , a point that we discuss further in the article .
The area of the non-photoionized region is 10–23 % of the total .
Our results for NGC 1569 indicate that these non-photoionized areas do not lie in low surface brightness regions exclusively .
A comparison with multiwavelength point source catalogs of NGC 1569 indicates that the dominant non-photoionizing mechanisms are shocks from supernovae or winds from massive stars .
To explain this large percentage of non-photoionized emission , we suggest that NGC 1569 is , indeed , in a post-starburst phase as previous authors have claimed .
We also derived slopes for the H ii region luminosity function ( -1.00 \pm 0.08 ) and size distribution ( -3.02 \pm 0.27 ) .
The luminosity slope , though shallow , is similar to previous work on this galaxy and other irregular galaxies .
The size distribution slope is shallower than previous slopes found for irregular galaxies , but our slope value fits into their confidence intervals and vice versa .
Within 4 pc of the 10-20 Myr old superstar clusters A1 , A2 , and B , no bright HII regions exist to a luminosity limit of 2.95 \times 10 ^ { 36 } erg s ^ { -1 } , suggesting that the winds and shocks have effectively terminated star formation in this small cavity .
In the three annular regions around the SSCs , both the HII region luminosity function and HII region size distribution are consistent with respect to one another and the galaxy as a whole .
The HII region surface densities within the annuli remain the same as the annuli are moved away from the superstar clusters .
These results indicate that “ feedback ” effects in NGC 1569 are confined to the immediate vicinity of the most recent massive star formation event on scales of \sim 1 pc .