Daily Image
24-08-2009
Modeling the Neutral Hydrogen of UGC 09519
| Submitter: | Phil Cigan |
| Description: | Early-type galaxies are generally considered to be 'boring' when compared to their brethren with spiral arms, active nuclei, and nearby companions. That is to say, for a small isolated S0 galaxy like UGC 09519, we would expect its evolution to be fairly uneventful with simple geometry and little star formation. What we see, however, is something much more complex. UGC 09519 has a very extended ring of neutral hydrogen that is warped and tilted with respect to the HI in the inner galaxy. Furthermore, we detect molecular gas and young stars in the center, so stars are forming. Before we can answer questions about the galaxy's formation, we need to verify what the gas is doing. So now we ask: how is the gas arranged in this system and how is the outer HI linked to the gas in the inner disk? I worked with Paolo Serra to construct models of the HI and CO in this galaxy using TiRiFiC, a program developed by Gyula Jozsa. TiRiFiC performs fits directly to data cubes, and excels at producing models of warped and tilted disks. Several different scenarios were tried, and all of the physically reasonable models were generally consistent. The final model we chose consists of two rings where the geometry of the inner ring is constrained to be a flat disk while the outer gas can vary freely in position angle and inclination as it keeps a flat rotation curve. The above movie shows the actual HI emission with contours in red overplotted with yellow contours of the final model. The fit is really quite nice, with only few discrepancies. We attribute these to asymmetries in the system, since the code assumes circular orbits and circular symmetry in the gas. While the project is not yet complete, we can say some things in conclusion. Most importantly, The model does appear to support the idea that the outer ring is at least somewhat separated from the inner disk. The angles between the two reqions are quite different, though the rotational velocities at the common edges more or less agree. Now that we have a model of the gas in UGC 09519, we are closer to understanding how this peculiar system formed. |
| Copyright: | Phil Cigan / ASTRON |
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