12/09: 2nd Year Project: Aleks Popstefanija

LGRT 1033

Open to everyone

Title: The Gas Physics of Interacting Galaxies: Feedback and Ram Pressure in NGC4631 and NGC4319

Abstract: We present a panchromatic study of two spiral galaxies (NGC4631 and NGC4319) that are involved in galaxy-galaxy interactions and provide unique constraints on the roles played by gas and dust in merger-driven galaxy evolution. NGC4631, the 'Whale Galaxy', is an edge-on spiral undergoing a merger and starburst. Above the midplane in the hot, x-ray emitting halo, O VI emission indicates that there is a kiloparsec-scale outflow originating from the disk. The ratio of far-ultraviolet to 24um emission shows dramatic changes along and perpendicular to the midplane of NGC4631; we suggest that multiple 'chimneys' are present in the disk, including a nuclear outflow that has evacuated the center and is the likely source of the hot gas seen in X-rays.  To investigate the origin of the O VI emission, we compare the O VI brightness at several positions above the midplane to the star formation properties of the underlying disk. NGC4319 is a face-on spiral with prominent tidal features that is also going through a merger. We find a large spatial offset between the 21cm and 24um emission, indicative of removal of the atomic gas from the galaxy due to ram-pressure stripping by intragroup gas. This is corroborated by an extraordinarily high molecular gas fraction in the disk (albeit with low overall column density), which is measured through detection of molecular hydrogen absorption lines along the line of sight to a background quasar. However, FCRAO 14m observations indicate that the molecular gas emission is probably centered on the 24um emission. We use the CO,  21cm, and 24um emission to study how the regions of molecular gas and star formation can be physically separated from the H I gas reservoir in galaxy interactions. We discuss the importance of molecular gas in these processes and how observations of CO rotational emission can provide the missing link for understanding the physics of interacting systems like NGC4319.