Spatial Extent of Diffuse X-Ray Emitting Regions in Major Merging Galaxies

• Main Authors: Wagstaff, Peter, Smith, Dr. Beverly J.
• Published: Digital Commons @ East Tennessee State University 2019
• Subjects: Astronomy; X-ray; Galaxies; Mergers; Chandra; Physics; Radiosources and Infrared and X ray and Gamma Ray
• Online Access: https://dc.etsu.edu/asrf/2019/schedule/165

Galaxies are astronomically large systems that consist of vast amounts of stars, and in between there exists the interstellar medium. This medium consists of clouds of gas which play an important role in a galaxy’s history and formation. With the right conditions a region can experience a period of star formation which we measure with a Star Formation Rate (SFR). The lifecycle of stars can create outbursts of hot gas which collapse back into the galaxy over time to contribute more to the interstellar medium. The gas is hot enough to release X-rays which we can detect with orbiting space observatories such as NASA’s Chandra Telescope. By studying these hot, high energy regions we can relate them to other known properties of galaxies to give us insight on the processes of merging systems. Using archival data from Chandra we measured the spatial extent of the soft diffuse X-ray-emitting hot interstellar gas in a sample of 49 local merging galaxies. The galaxies or galaxy pairs are classified by merger stage based on their morphology. The stages range from post-merger remnants to premerger pairs in which two separate regions could be identified. After processing the data, we made initial estimates of the regions based on their optical extent. X-ray counts were extracted and background counts from the nearby sky were subtracted for calibration. An iterative procedure was used to produce and modify elliptical radial profiles by size and position angle until a good fit was found. The best fit radius was defined as the point where the background subtracted counts decreased to less than twice the uncertainty. With an accurate estimate of the region sizes, we infer a third dimension to find the volumes of the regions. The inferred volumes were used to calculate electron densities and total masses of the hot interstellar gas. Relationships among hot, molecular, and atomic gas were investigated and plotted to determine any trends. Our results show a strong correlation between the volume of hot gas and SFR. Another strong trend was between volume and X-ray luminosity. The SFR is correlated with the ratio of hot to cold gas. Galaxies with higher SFRs have proportionally more hot gas relative to the cold gas. These relationships show that major mergers have regions of starbursts which expel hot gas, and the more numerous the young stars, the larger the volume of hot gas. Future research in this area can reveal more about the process of merging and the evolution of galaxies.