A Mass Census of the Nearby Universe with RESOLVE and ECO
Abstract
The low-mass slope of the galaxy stellar mass function is significantly shallower than that of the theoretical dark matter halo mass function, leading to several possible interpretations including: 1) stellar mass does not fully represent galaxy mass, 2) galaxy formation becomes increasingly inefficient in lower mass halos, and 3) environmental effects, such as stripping and merging, may change the mass function. To investigate these possible scenarios, we present the census of stellar, baryonic (stars + cold gas), and dynamical masses of galaxies and galaxy groups for the RESOLVE and ECO surveys. RESOLVE is a highly complete volume-limited survey of ~1500 galaxies, enabling direct measurement of galaxy mass functions without statistical completeness corrections down to baryonic mass Mb ~ 10^9 Msun. ECO provides a larger data set (~10,000 galaxies) complete down to Mb ~ 10^9.4 Msun. We show that the baryonic mass function has a steeper low-mass slope than the stellar mass function due to the large population of low-mass, gas-rich galaxies. The baryonic mass function’s low-mass slope, however, is still significantly shallower than that of the dark matter halo mass function. A more direct probe of total galaxy mass is its characteristic velocity, and we present RESOLVE’s preliminary galaxy velocity function, which combines ionized-gas rotation curves, stellar velocity dispersions, and estimates from scaling relations. The velocity function also diverges from the dark matter halo velocity function at low masses. To study the effect of environment, we break the mass functions into different group halo mass bins, finding complex substructure, including a depressed and flat low-mass slope for groups with halo masses ~10^11.4-12 Msun, which we refer to as the nascent group regime, with typical membership of 2-4 galaxies. This substructure is suggestive of efficient merging or gas stripping in nascent groups, which we find also have large scatter in their cold-baryon fractions, possibly pointing to diversity in hot halo gas content in this regime. This work is supported by NSF grant AST-0955368, the NC Space Grant Graduate Research Fellowship Program, and a UNC Royster Society Dissertation Completion Fellowship.
- Publication:
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American Astronomical Society Meeting Abstracts #229
- Pub Date:
- January 2017
- Bibcode:
- 2017AAS...22912802E