Tully-Fisher Relation

For our last blog post, given the option of MOND, Mass-Luminosity, and Tully-Fisher it seems that MOND has been the most popular. I figured I'd mix things up just a bit. After scouring through at least a solar mass worth of articles of both Mass-Luminosity and Tully-Fisher, I picked out this one from a few years back.

The full article can be accessed here.

The data they're using here comes from AEGIS. The All-wavelength Extended Groth strip International Survey was an international collaboration between scientists and observatories in order to bring together larger data sets than any one had access to. The NRAO's, Very Large Array radio telescope from New Mexico, NASA's infrared Spitzer Space Telescope, Caltech's Palomar Observatory telescopes, the three imaging processors at the aptly-named Canada-France-Hawaii Telescope on Mauna Kea, the optical telescope at Keck Observatory also on Mauna Kea, NASA's Hubble Space Telescope, NASA's ultraviolet GALEX satellite, and NASA's Chandra X-ray Observatory satellite. Data taken from various spots on Earth as well as from orbit in a multitude of wavelengths and methodologies allowed for a rather varied data set from AEGIS.

We've learned that there is a good relationship between the rotation velocity and the luminosity of a galaxy. To be more precise, there is a relationship between rotation velocity and mass but there is also a relationship between mass and luminosity; hence, there is a relationship between rotation velocity and luminosity as well.



This diagram shows us the basic idea behind the relationship, its measurements, and how we've used it to determine the Hubble constant. As we all experienced in our own rotational velocity curves and trying to best fit the graphs, not all methods were equally successful. This articles provides a closer-fit line because they're using measurements for baryonic mass instead of using luminosity alone to infer the mass. Furthermore, they're considering more than pure rotation velocity by adding in the velocity dispersion. The velocity dispersion is what all the σ measurements refer to and allows a more accurate assessment of the true energies involved. As they slowly modify their constants, re-define their data, more and more evidence is added to the relationship and the best-fit line becomes increasingly more precise. I am curious as to how they were able to estimate the baryonic mass. It seems like they did achieve a greater level of precision given their ability to fit their data appropriately, but the article itself claims that this is beyond the scope of their publication.

This relationship and this data set has also been a part of the development of the current understanding of galaxy evolution and predicting mergers. As a lot of this data came from Mauna Kea observatories, the University of Hawaii's observatory also put together some of the information. That website can be found here but the most interesting video is below.