September 2, 2013

September 2, 2013 11

An adaptive friends-of-friends group finder

Volker Müller

Leibniz-Institut für Astrophysik Potsdam (AIP)

with

Juan Carlos Munoz (Medellin)

1


Starting point:

•High-resolution simulations demonstrate self-similar density profiles around fof-halos

•Extension of the profile into the zone-of-influence

•“Halo based reconstruction of the cosmic mass density field” of SDSS Main sample (Munoz-Cuartas, M., Forero-Romero, 2011)

•Web-classification into filaments, sheets, and voids provides reasonable volume and mass fractions

•Construction of a group catalog most likely reproducing the underlying dark-matter halos (Munoz-Cuarta, M. 2012)

•Precursor are is the group finder by Yang, Mo, and van den Bosch (2008), but we do not use a initially selected linking length, and no assumption on the M/L ratio of the galaxy halos


Density profiles from simulations:


Selected regions of the SDSS-FoV

Subslices

330x250 Mpc/h


Algorithm:

log (Mhalo//Msun)

log (nhalo/ / h3 Mpc-3)

•N luminosity ordered galaxies enclosed in halos with a given mass function nDM(M) (specified by the standard cosmology) and M < Mlim

•FoF of halos with ellipsoidal search range


Iteration:

•Mlim -> Mlim + Δmlim and assigning halos to mass-ordered groups from the specified mass function

•FoF of halos till closure condition:

(typically 5 – 10 iterations are sufficient)


Reliability and completeness:


Group mass range during iteration:

Typically virial masses of groups between 1013 and 1014 Msun


Mass-multiplicity relation:

Only for groups near preselected halos: upper linear bound of multiplicities

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Comparison with input from Millenium catalogs:

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Conclusions:•We use a FoF / percolation method that takes local linking lengths, dependent on the locally assembled mass of suspected halos.

•No free parameters besides the specified cosmology.

•No assumption on a M/L-ratio of galaxies or an initial linking length

•Tendendies

- of faint halos to be included in larger groups

- of massive halos to not encompassing all halo galaxies

-> steepening of the halo mass function

•Earlier tests of our group finder with Millenium mock samples

- Ni true group members, Nf number identified with the group

finder, Nc number common in both samples

- purity fp = Nf/Ni completeness fc = Nc/Ni

contamination fi = |Nf - Ni|/Ni

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Purity fp

Contamination by interlopers fi

Completeness fc

Evaluation:

September 2, 2013

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