It is just the continuing progress and refinement in models of physical phenomena. But it makes things tricky at times. I had done fits for my thesis using a set of models for the emission from the torus surrounding an AGN. The fits were useful and provided reasonable answers. Since then, an updated set of models has been released. Before publishing the results from my thesis as a paper, I compared the old and new models to make sure the results were consistent.
After a few days running fits, I see that the results are broadly in agreement, but different in important ways. For example, with the same set of geometrical parameters, the depth of the silicate absorption at 10microns changes significantly between the old and new models. Fortunately it is likely the models are improving, so the newest ones should be the most physically accurate. However, it means I need to re-fit the data with the new models to derive accurate parameters for the AGN. That is the task ahead.
Most of today has been spent researching and writing a 10 minute talk for my Extragalactic Astronomy class. I picked “Interacting Galaxies” for my talk.. quite a broad subject. After working a bit and doing some research, I settled on the sub-topic of “feeding the nuclear regions”. Basically, how one gets gas from the outer portions of a galaxy, down to a region comparable to the size of the solar system! Conservation of angular momentum makes this quite difficult!
To give away the punch line, there are known mechanisms for getting the gas down to ~100 parsec (pc), and from getting the gas from ~1 pc into the black hole. Getting the gas from 100 pc to 1pc turns out to be difficult! There are some ideas (supernovae, magnetic fields?, etc), but no obvious method.
Putting observational constraints on this also turns out to be difficult. Most active galactic nuclei lie at such large distances that current telescopes are unable to resolve this crucial region. So the mechanism must be inferred from other observations. Large datasets like the Sloan Digital Sky Survey, which have data on many quasars and other AGN, will hopefully shed some light on the issue.
… models.
I’ve been working quite a bit lately on my thesis. Fleshing out chapters and adding figures. One part of this is discussing the models of starbursts and active galactic nuclei that I’m using to study Cygnus A. So, I’ve made a couple plots showing the effect changing the parameters has on the models.
This plot shows the energy re-radiated by a clumpy torus in an active galaxy. The various panels show how the emission changes with the variety of parameters. More information on the model is available at https://newton.pa.uky.edu/~clumpyweb/. I’ll also have a bit of a writeup in my thesis eventually…
After 5 years in college, I’m finally about to embark on my first “real” school vacation. RIT never celebrated any holidays (nevermind starting classes on Labor Day! =-o ). UVa however, gives us 2 “reading days” for Columbus Day and the day after. I’m planning on taking advantage of it by going mountain biking for a morning, but most of the time will be spent doing research. It’ll be nice to have a break from homework so I can get some research done.
I’m starting to learn more about my research here. I don’t know details and I don’t yet have the real data, but basically what I’ll be doing is studying interactions between the radio jets and the ambient gas in Seyfert galaxies. Basically, Seyferts are galaxies with a black hole that’s actively swallowing gas. However, unlike radio galaxies, Seyferts don’t have strong radio emission. They do show weak emission and low power jets, but not nearly as strong as their radio-loud counterparts.
So I’ll be using data from the Hubble Space Telescope to look at the physical conditions of the gas in the galaxy. I’ll go into more detail later, but basically this involves comparing the amount of light emitted by various elements in various states. Data will also come from the Very Large Array. This will enable me to measure properties of the radio jet and compare them with the information derived from the optical HST data.
I’ll be posting more detailed information about the methods I’ll be using once I get acquainted with the data.
There were two astronomy colloquia this past week, both held at NRAO up the road from the astronomy building. The first was about the Austrailian Square Kilometer Array Technology Demonstrator (ASKAP) and the second was a talk about feedback between active galactic nuclei and the environment and consequences for galaxy formation. Both were quite interesting talks.
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