The main goal of our research is to map out the density structure of matter in the local universe. To do so, we need to measure the relative velocity of galaxies, known as peculiar velocities. However, as we observe galaxies from the Earth, the measured radial velocity of a galaxy is a superposition of the global Hubble expansion rate and the peculiar velocities.
This means that to extract galaxies peculiar velocities, we need to measure their physical distances, and then subtract the resulting Hubble expansion rate from the measured radial velocities. Using the resulting peculiar velocities, later we can recover the underlying density field and discover structures like our home supercluster known as Laniakea.
With all of that in mind, to achieve our goal we need to measure two different quantities. First, we need to measure the rotation velocity of galaxies, which results in their absolute luminosity if we use the Tully-Fisher relationship that connects rotation rate and luminosity. Second, we need to measure the apparent magnitude of galaxies, which together with the obtained absolute luminosity from the previous step, it gives us distances to galaxies.
Spiral galaxies are late-type galaxies with a lot of atomic Hydrogen gas which undergoes star formation. The hydrogen atom consists of one proton and one electron. Each hydrogen atom can be found in two different states. In one state, both electron and proton have the same spin directions, and in the other state, electron and proton have opposite spin directions. The opposite spin direction has slightly lower energy level and the transition from high to low energy states produces radio emission that can be observed at 21 cm.
So far, all users together have spent more than 1,100 hours on this project. About 5,000 galaxies have been already rejected due to the poor quality of images or bad HI profiles which made them bad candidates for the distance measurements using TF relationship. For those galaxies that have not been rejected, we have made sure that there are at least 3 different measurements done by different users. This increases the accuracy of the final results as we use the median of all measurements. If a user makes a terrible mistake and introduces an outlier which is not consistent with other measurements, that measurement would be later removed.
At this time, we have enough information and data to move on to the next level of analysis and prepare the next generation of distance catalog using which we can find more local galaxy structures, like Laniakea. I would like to thank all of those who have already participated or will participate in this project. With more measurements, we can better understand the nature of uncertainties and minimize them, which leads us to better and more accurate distance measurements required for Cosmicflows calculations. All the final products and data catalogs would be available to public through the Extra-Galactic Distance Data-Base. I appreciate all of your comments and suggestions that help us with improving this process.