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Title: Velocity segregation and systematic biases in velocity dispersion estimates with the SPT-GMOS spectroscopic survey

The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel'dovich (SZ) selected galaxy clusters spanning $ 0.28 < z < 1.08$. Our sample is primarily draw from the SPT-GMOS spectroscopic survey, supplemented by additional published spectroscopy, resulting in a final spectroscopic sample of 4148 galaxy spectra---2868 cluster members. The velocity dispersion of star-forming cluster galaxies is $$17\pm4$$% greater than that of passive cluster galaxies, and the velocity dispersion of bright ($$m < m^{*}-0.5$$) cluster galaxies is $$11\pm4$$% lower than the velocity dispersion of our total member population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive vs. star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations in which suggests that our dispersions are systematically low by as much as 3\% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Here, by measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.
ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ORCiD logo [5] ; ORCiD logo [1] ; ORCiD logo [6] ;  [7] ;  [8] ; ORCiD logo [1] ;  [9] ;  [7] ;  [10] ; ORCiD logo [11] ; ORCiD logo [7] ; ORCiD logo [12] ;  [13]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. Colby College, Waterville, ME (United States)
  3. Harvard Univ., Cambridge, MA (United States)
  4. Univ. of Chicago, Chicago, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  5. Univ. of Chicago, Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
  6. Univ. of Missouri, Kansas City, MO (United States)
  7. Ludwig-Maximilians-Univ., Munich (Germany); Excellence Cluster Universe, Garching (Germany)
  8. Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taipei (Taiwan)
  9. Univ. of Colorado, Boulder, CO (United States); NASA Ames Research Center (ARC), Moffett Field, CA (United States)
  10. Univ. of Hawaii, Honolulu, HI (United States)
  11. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
  12. Harvard Univ., Cambridge, MA (United States); Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
  13. Cerro Tololo Inter-American Observatory, La Serena (Chile)
Publication Date:
Report Number(s):
FERMILAB-PUB-16-610-AE; arXiv:1612.02827
Journal ID: ISSN 1538-4357; 1502585
Grant/Contract Number:
AC02-07CH11359; AC02-06CH11357
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 837; Journal Issue: 1; Journal ID: ISSN 1538-4357
Institute of Physics (IOP)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); National Aeronautic and Space Administration (NASA)
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; cosmology: observations; galaxies: clusters: general; galaxies: distances and redshifts; galaxies: evolution; galaxies: kinematics and dynamics
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1372092