Spiral Graph: Cluster Buster - A Participatory Science Project to Improve the Identification of Spiral Arms from All-Sky Survey Galaxy Images

Project Summary:

Compelling evidence exists for two classes of black holes (BHs), stellar-mass and supermassive. The Milky Way is expected to have 10^8 stellar-mass BHs, ranging in mass from ~10^1 to 10^2 times that of the Sun. Supermassive black holes (SMBHs) are found in the centers of nearly every large galaxy, including the Milky Way, and range from ~10^6 to 10^9 solar masses. Observations by the James Webb Space Telescope have revealed galaxies that host SMBHs within the first 5x10^8 years after the Big Bang. However, the origin of SMBHs is unclear since they must grow rapidly in a relatively short time.

Clues to the origin of common SMBHs may lie in the rare galaxies harboring central intermediate-mass black holes (IMBHs) having masses between stellar-mass and SMBHs (~10^3 to 10^5 solar masses). The discovery and analysis of these galaxies could elucidate the co-evolution of SMBHs and their galaxies. Observationally confirming an IMBH in a galaxy center requires significant telescope resources, so targeting likely candidates is imperative. One method of identifying potential targets is by using easily observable parameters of a galaxy that link to the central BH mass. One such relation is between SMBH mass and the degree of winding of spiral
arms in a galaxy (known as pitch angle or PA). Spiral galaxies with tightly wrapped arms, or small PA, are found to have larger SMBH mass and vice versa. The existence of large sets of all-sky survey image data makes measuring PA a more time efficient process for estimating the central BH mass of a spiral galaxy.

Previously, we ran a participatory science project called Spiral Graph (SG) that asked volunteers to trace the spiral structure in relatively low contrast all-sky survey images of tens of thousands of galaxies. Those tracings effectively increased the signal-to-noise ratio of the arms relative to the background, allowing us to measure the PA via software called P2DFFT. Since many spiral galaxies are not perfectly symmetric, a single fit to all the arms is not realistic and our results showed us that greater accuracy is needed in determining a "global" PA. This can be achieved by measuring the PA of each arm individually and combining the weighted results into a global value. Disentangling the independent tracings from multiple volunteers of each galaxy is not trivial so we developed a line clustering algorithm (LCA), based on a set of hyperparameters (HPs), that is able to group similar tracings into individual arm clusters while eliminating outliers. The LCA produces good results with most clear cases, but it requires dynamic adjustments to the HPs in order to fit a variety of cases correctly.

This proposal is for the development of a participatory science project called Spiral Graph: Cluster Buster (SG:CB) on the Zooniverse platform. Specifically, we will: (1) run the LCA with a set of HPs on a series of galaxy tracings obtained via SG; (2) color code the line clusters and present both clustered and unclustered tracing images to volunteers via SG:CB; (3) ask the volunteers to evaluate if the LCA properly clustered all the perceived arms; and (4) adjust the HPs for reapplying steps (1) - (4). This will lead to a comprehensive dataset of LCA HPs for galaxy tracings, allowing us to develop and train an AI algorithm that dynamically selects appropriate LCA HPs. This will result in proper clustering for any galaxy arm tracings and allow PA measurements of individual arms.

This proposed project directly addresses the goal of the CSSFP in contributing to the building of a scientifically literate nation by providing opportunities for all participatory scientists (PS), encouraging volunteers who can benefit NASA, leveraging existing PS communities, and connecting PSs with subject matter experts. It also aligns with NASA's Astrophysics Division's interests in understanding the history of galaxies, revealing the extremes of nature, and public engagement with astronomy learners.