A halo-based galaxy group finder: calibration and application to the 2dFGRS

Abstract

We use the halo occupation model to calibrate galaxy group finders in magnitude limited redshift surveys. Because, according to the current scenario of structure formation, galaxy groups are associated with cold dark matter (CDM) haloes, we make use of the properties of the halo population in the design of our group finder. The method starts with an assumed mass-to-light ratio to assign a tentative mass to each group. This mass is used to estimate the size and velocity dispersion of the underlying halo that hosts the group, which in turn is used to determine group membership (in redshift space). This procedure is repeated until no further changes occur in group memberships. We find that the final groups selected this way are insensitive to the mass-to-light ratio assumed. We use mock catalogues, constructed using the conditional luminosity function (CLF), to test the performance of our group finder in terms of completeness of true members and contamination by interlopers. Our group finder is more successful than the conventional friends-of-friends (FOF) group finder in assigning galaxies in common dark matter haloes to a single group. We apply our group finder to the 2-degree Field Galaxy Redshift Survey (2dFGRS) and compare the resulting group properties with model predictions based on the CLF. For the CDM concordance cosmology, we find a clear discrepancy between the model and data in the sense that the model predicts too many rich groups. In order to match the observational results, we have to either increase the mass-to-light ratios of rich clusters to a level significantly higher than current observational estimates, or to assume σ 8 0.7, compared with the concordance value of 0.9.

The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results From the Cos-Gass+cos-Halos Surveys

“…Also, the COS-Halos sample was selected to be all centrals (with a couple of non-centrals Tumlinson et al 2013, Section 2.5). This is not one of the criteria for COS-GASS, although the mass range of the galaxies ensured that most of the COS-GASS galaxies (34/45) are centrals (based on the group catalog by Yang et al 2005Yang et al , 2007. Thus, the combined sample is 85% centrals.…”

Galaxy groups in the low-redshift Universe

“…The group finder of Y05 has been applied to redshift surveys such as the 2dFGRS (e.g. Yang et al 2005), the SDSS (e.g. Weinmann et al 2006;Yang et al 2007), and the 2MRS (e.g.…”

Revisiting the screening mechanism inf(R)gravity

“…In the case of f R ¼ −10 −6 , although the criterion in Eq. (41) no longer guarantees that all the selected haloes are completely unscreened, it does cleanly separates unscreened haloes from the well-screened ones, and the contamination of the unscreened samples is very low. We point out that the way we separate self and environmental screenings of dark matter haloes is slightly different from some works in the literature.…”

“…(i) First, a global map of ϕ N can be easily constructed in real galaxy surveys if a group catalog [41] is available because ϕ N satisfies the linear equation [Eq. (26)].…”