AGN Spectroscopy
By: Brent H.
Grosse Pointe North High School
Abstract:
Using 122 sources from RBSE, the researcher identified and studied quasars and elliptical galaxies. For each of these quasars and elliptical galaxies a redshift was calculated. An analysis of the findings proved that the elliptical galaxies are considerably closer than any quasars. As strange as these objects may seem to be in the radio range of their spectra, they are quite normal when it comes to where they are located in the universe.
Introduction:
The research herein originated from a collection of data that RBSE had compiled. The people at RBSE found 122 sources that were "unusual." These sources were unusual because of their spectra in the radio frequencies. When measured at two different points in the radio spectrum, these objects were found to have the same amplitude. This classifies these objects as having "flat" radio spectra. The spectra of these sources were compiled onto a CD, which was then sent out to any willing researchers. These sources were completely raw, as it were. They were unclassified as to what type of source they were. All there was to work with were the 122 spectra in the visible range, with a little bit of data from the UV and IR areas of the spectrum. The first step was to look over each of the many spectra and store any traits it might have in a database. Using these traits and a flowchart, one would then classify each of the aforementioned sources. Having classified them all, it is the next logical step to find a redshift for each. The steps that followed took a lot of thought. Now that this veritable mountain of data had been compiled, what was one to do with it? Quasars were the majority of the sources by far. The next highest amount of sources was elliptical galaxies. This led to the decision to narrow the focus to quasars and elliptical galaxies.
Problem:
It is to be expected that the quasars would have an enormously obvious difference in redshifts, being farther away in the universe than the elliptical galaxies. These objescts, however, have a different spectrum in the radio range than most objects in their class. This leave room to wonder if they might act differently in the universe. The idea behind this project is to discover whether the objects have noticably different redshifts than would be expected, or if they interact with each other differently in the universe.
Procedure:
The first step is classification of the objects. To do this, one must compile known traits of each kind of AGN source. To organize this data, a researcher must create a flowchart. This flowchart must enable the researcher to classify a source based on the traits of its spectrum in the visual range. One must then create a database for the known traits of these sources. One at a time, the researcher must observe the spectra of each of the 122 given sources, recording the traits it has. After this task is completed, one must use the flowchart to identify each of the sources. Reviewing each of the spectra is necessary for double-checking to making sure the classification is reasonable. The flowchart needed quite a bit of revision before it was actually able to flawlessly identify a source.
After the classification process is complete, it is time to separate the quasars and elliptical galaxies. Sorting the data by classification easily does this. For each of these objects a redshift was calculated. This is done by first identifying emission lines in the spectra. To do this, one must compare a simulated quasar at rest to the observed quasar spectrum. When two "spikes" or "dips" have been tentatively chosen, it is time to check if the selected emission lines are actually what the observer had hypothesized. To do this, one must find the ratio greater than 1 of the two lines at rest. Then, find the same ratio for the lines at their observed wavelength. If these two ratios are extremely close, then the lines were correctly identified. If not, then they were not identified correctly, and must be reexamined and correctly identified before a redshift can be determined. Once the lines have been identified, the equation:
1 + z = (observed wavelength) / (wavelength at rest)
This must be done for each of the two lines. After a redshift has been found for each line, the two must be averaged to give a more reliable calculation. These redshifts are varying in range, but this equation suits redshifts of any object.
Analysis:
Quasars and elliptical galaxies are two very different types of objects in the universe. This is true for many of their traits, and redshift is an obvious example. These objects may have been strange in some ways, but as far as the expected trends related to redshift, they follow all of the rules. The average quasar is known to have a redshift anywhere from 0.06 to 5.5. A common Elliptical Galaxy has a redshift from a little over 0 to a little over 1. The quasars in this investigation had redshifts averaging about 1. Although this is low end, it is well within the parameters of a normal quasar. The Elliptical Galaxies averaged about 0.15. When compared on a line graph as two different series of data, it is blatantly obvious that the slowest moving of all the quasars in still moving away from us at a far greater rate than any of the elliptical galaxies.
Conclusion:
It is quite clear that these objects follow trends of other objects of the same type in the universe when it comes to redshift. Whatever it is about them that may or may not be effected by the fact that they have flat spectra in the radio range, it is certainly not that they move comparatively faster or slower away from us than they would be expected to. As is the case for even the more "normal" objects in the universe, a quasar is moving away from us at a far greater rate than any galaxy.
Bibliography:
Kembhavi, Ajit, and Jayant V. Narlikar. Quasars and Active Galactic Nuclei. New York: Cambridge Press, 1999.
Kraus, John D. Radio Astronomy 2nd Edition. Ohio: Cygnus-Quasar Books, 1986.
Zombeck, Martin V. Handbook of Space Astronomy & Astrophysics Second Edition. New York: Cambridge Press, 1990.