Mapping the Ionized Component of High-Velocity Cloud Complex A

Allison Duncan
Rose-Hulman Institute of Technology

Astrophysics REU - Summer 2005
University of Wisconsin-Madison
Advisor: Matt Haffner

Ionized Component of Complex A

The results of my research this summer include the first map of the ionized component of Complex A. The image shown below is a smoothed map of the integrated H-alpha intensity over the velocity range -220 km/s to -110 km/s LSR.

H-alpha emission integrated over -220 km/s to -110 km/s LSR

Another goal of my research this summer was to compare the H-alpha and HI emission. The map above can be compared with the HI emission map shown on my introduction page to determine the spatial correlation between the two components. The parameters from the automated fitting can also be used to compare the velocity and intensity correlation. These comparisons appear in the following sections.

Comparison Maps

The following plots compare the spatial and intensity correlation of the H-alpha and HI emission. They were created from the subtracted H-alpha and original HI data, integrated over -220 to -110 km/s LSR. One component is mapped and overlayed with contours of the other component.

H-alpha map and HI contours

HI map and H-alpha contours

The correlation is somewhat difficult to see in the left plot due to the faintness of the H-alpha emission and signal to noise ratio of the data. Though the H-alpha emission is faint, it does appear to have spatial correlation with the HI emission. There are two notable areas where I detected H-alpha but there was very little HI emission, in the upper and lower left corners.

Comparison Plots

To compare the mean, area, and width of the H-alpha and HI components, the following plots were produced from the automated H-alpha and HI fit parameters. Only pointings for which both HI and H-alpha produced good fits (based on the criteria) are included.

	The means are appear correlated, although there are more points above the line of unity than below.
The areas of the components (intensity and column density) do not appear correlated. This implies that the intensity of the H-alpha component is not dependent on the amount of HI present, which does not rule out the possibility that skin ionization of the HVC is taking place.
	The widths have a large amount of scatter but are roughly balanced about the line of unity.

Conclusions

My work this summer has resulted in the first map of the ionized component of high-velocity cloud Complex A. I also made some comparisons between the H-alpha and HI emission in the region. Since the ionization of HVCs is not well understood, it is difficult to make conclusions about the exact nature of my results. However, by comparing my results with findings from other HVC and IVC complexes, and through further research, we hope to learn more about the ionization process and the dynamics of the warm ionized medium.