Finding Galaxy Groups in the Early Stages of Formation in the RESOLVE Survey
Abstract
The most common galaxy group finding algorithm, Friends-of-Friends (FoF), finds settled groups that share a common dark matter halo but misses groups that are in earlier stages of formation and have not yet merged halos. We present a new algorithm that is designed to find small "proto-groups" like the Local Group that are gravitationally bound but do not yet share a common halo and are not identified as FoF groups. We use the escape velocity to test whether a galaxy is bound in a proto-group or to a separate, already settled group. We apply this boundness criterion to RESOLVE, a large volume limited survey of galaxies in the local universe. A large volume limited survey is ideal for studying galaxy groups since the population of groups that we identify should accurately reflect the population of groups in the broader universe. Using our boundness criterion increases the number of multiple galaxy systems that are identified from 235 to 312, and decreases the number of single galaxy systems from 916 to 416. To determine how well we find systems like the Local Group, we identify a population of Local Group analogues using a Mock Catalog. FoF finds 20% of the Local Group analogues, whereas using a boundness criterion expands this to 80%. We examine different categories of bound systems in RESOLVE, focusing on the evolutionary connection between groups and proto-groups. We compare properties such as the diameters, colors, gas content, and large scale environments of proto-groups and small settled groups (FoF groups with halo mass less than 1012 M⊙). We use metrics such as virialization state, compactness, and color dispersion to quantify the evolutionary state of each group. Our results provide a foundation for studies of the evolution of groups over cosmic time. This research has been supported by National Science Foundation grant AST-1814486.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23520736C