IDENTIFYING DIFFUSE GALAXIES THROUGH CITIZEN SCIENCE

Abstract

We present a catalog of 642 diffuse galaxies (DGs) identified through a citizen science search of the Fornax cluster, of which we estimate 21.8% are nucleated. These DGs were visually identified using a combination of the Fornax Deep Survey (FDS) and Dark Energy Camera Legacy Survey (DECaLS) imaging. With the help of over 700 volunteers on Zooniverse, we examined nearly 15,000 image cutouts (spanning 26 deg^2) in 30 days, averaging 1.15 days per square degree. Our catalog recovers > 90% of the objects from prior dwarf galaxy catalogs in the parameter space explored by our search. We achieve higher completeness than existing automated detection algorithms, resulting in numerous additional detections, particularly near bright stars and galaxies. Three of the DG candidates we identify are previously undiscovered objects (in any existing search, automated or visual) that should be further investigated to determine cluster membership. A potential drop in the number density of non-nucleated DGs is observed near the cluster center. We propose that this decline may suggest a higher likelihood of forming a nuclear star cluster (NSC) via globular cluster inspiral in the cluster core. We also identify an apparent spike in the nucleated density around 400 kpc, which is not associated with any obvious structure in the cluster or in the imaging dataset and requires further investigation. The efficiency and completeness of our citizen science methodology makes it a valuable tool for mapping DG populations in future sky surveys, such as the Legacy Survey of Space and Time (LSST).