Misaligned Jets

Some time ago, I posted a draft of a paper I had been working on when I left astronomy. There, I said I might post some images some day. I found some really good images of two sources I had been studying: Mrk 501 and 0814+425. I have actually published something on these two sources. I also include a low resolution image of 1633+382.

The primary focus of my dissertation was the study of misaligned jets. At the center of active galactic nuclei (quasars and the like) is believed to be a supermassive black hole that is spinning, causing jets of plasma to be shot out at the poles. When we observe these jets at different size scales, we find they are either straight, i.e. aligned at different scales, or misaligned by 90 degrees. There are very few in the middle, and the question is why. One theory was that the interaction between the fast moving plasma of the jet and the ambient gas created Kelvin-Helmholtz instabilities in the flow, distorting the straight jet into a helix. I studied of a sample of these misaligned jets to try to find evidence of that model.

The primary source I studied was the quasar 3C309.1. That study showed significant interaction between the jet and the ambient gas, resulting in frequent disruptions, and a structure far too complex to be explained by the helix.

But I also others at different frequencies and therefore different resolution scales. Mrk 501 was a popular source at the time for a variety of reasons. The Kelvin-Helmholtz model had been fit to low resolution images of the source. For my thesis, I made a high quality image at higher resolution and found the structure comprised of a series of sharp, highly polarized bends, connected by straight jet. This structure again suggests strong interaction with the ambient material and frequent disruption. Subsequently, I observed the source again at 3.6 cm wavelength (the dissertation observations were at 6 cm). The total intensity and linear polarization were actually published in the paper linked to above, but they are quite good so I'll include bigger versions here.

Total intensity:

Total intensity, with a color scale to show brightness:

Linear polarization:
What's good about these images is that we were able to resolve across the jet, for the first time, and show that the outer edges of the jet are highly polarized with magnetic field parallel to the flow, while the interior of the jet is less highly polarized with a magnetic field orthogonal to the flow. This indicates sheering, and supports the idea of strong interaction with and disruption by the ambient gas.

Another source was 0814+425. This is the total intensity image from my dissertation:

To me, this showed the jet emerging to the east and bending sharply to the south and then twisting around. This was at 18 cm wavelength. The paper linked to above showed the source at 6 cm wavelength. It's a pretty sloppy image, but it shows the jet emerging to the east, bending sharply to the south, then bending sharply again and being diffuse. This image, at 2 cm, shows the structure more plainly:
Unfortunately, I don't have a polarization image.

Another source in my sample was 1633+382. I had to go to a very low frequency--300 MHz--to be able to image the source out through a bend, and at that frequency you can't do polarimetry. But the total intensity image shows the same type of structure:

Another sharp bend, followed by more diffuse emission.

Conclusions drawn from these images are as before, namely that these source are strongly disrupted by interactions with ambient gas. How this would result in a preferential misalignment of 90 degrees, I was not able to explain.