More on ULIRGs

My presentation on my research is coming up, and there were some questions after my first post, so I thought I'd elaborate.



Remember this graph?

It's called the SED, or Spectral Emission Decomposition. It breaks up the total radiation emitted from a galaxy into its constituent sources. The solid yellow line above all the others is the total emission spectrum, graphed in flux vs wavelength. (Note the wavelength range: near to far infrared)


The other lines represent emissions from different sources. The yellow dashed line in the lower left corresponds to light from stars. You can't see it much on this graph, but some have a purple line to represent emissions from Polycyclic Aromatic Hydrocarbons (PAH). These are often a good indicator of widespread star formation.


The rest represent dust at different temperatures, and the one my project chiefly concerned was the dash-and-dot magenta line in the near-infrared, which is hot dust.


The greater the fraction of hot dust emissions out of total galactic (observed) radiation, the more an Active Galactic Nucleus (the central supermassive black hole) is probably contributing to the galaxy's luminosity.


Also notice the data points on the top yellow line. These represent flux measurements taken at specific wavelengths, and they constrain the fit, making the results more accurate (we hope). My main contribution to the project involved adding data points at 3.6 and 4.5 microns. Because it turns out that having constraining data points in that region of the spectrum, where hot dust occurs, can have a dramatic effect.

This is a fit of the same object, but without the points at 3.6 and 4.5 microns. Notice that the hot dust peak is much lower. This helps demonstrate the significance of collecting those data points.


Adding the new points doesn't always increase the amount of hot dust, though. It could lower it, or the fraction could stay about the same. But you won't know if your fit at that region is really accurate until you have some actual data backing it up.


But anyway, I did this process for around 40 objects, including 6 known QSOs (Quasi-stellar objects, likely quasars). Maybe after my presentation, I'll post something about my results.