Spiral Graph: Pitch Angle Measurements of Spiral Galaxies from Data Collected by Citizen Scientists

Spiral Graph is a citizen science project developed on the Zooniverse platform in order to help determine the spiral arm pitch angle (𝜙) of galaxies. g-band images, taken primarily from DECaLS DR8 or secondarily from SDSS, of the stellar mass-complete sample of 6222 spiral galaxies from Hart et al. (2017) were deprojected, uploaded, and presented to volunteers. The volunteers were first asked to confirm that the object centered in the image is indeed a non-interacting spiral galaxy. If confirmed, they were then tasked with tracing over the visible arms, ignoring the bulge and any bar, ring, or foreground star. The resultant tracings from at least 15 different volunteers were aggregated and input into P2DFFT, an algorithm used to measure 𝜙. We compare the results of this pitch angle measurement process (𝜙_SG) to other methods including those determined by SpArcFiRe (𝜙_SF; as reported by Hart et al. 2017), Spirality (𝜙_SY), and manually overlaying logarithmic spirals of known pitch angle (𝜙_OL). We find that 𝜙_SG most strongly correlates with 𝜙_OL and correlates least with 𝜙_SY.