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September 2, 2013

An adaptive friends-of-friends group finder. Volker M üller Leibniz-Institut für Astrophysik Potsdam (AIP) with Juan Carlos Munoz (Medellin). September 2, 2013. 1. 1. Starting point: High-resolution simulations demonstrate self-similar density profiles around fof-halos

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September 2, 2013

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  1. An adaptive friends-of-friends group finder Volker Müller Leibniz-Institut für Astrophysik Potsdam (AIP) with Juan Carlos Munoz (Medellin) September 2, 2013 1 1

  2. 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 September 2, 2013 2 2

  3. Density profiles from simulations: September 2, 2013 3 3

  4. Selected regions of the SDSS-FoV Subslices 330x250 Mpc/h September 2, 2013 4 4

  5. Algorithm: 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 log (Mhalo//Msun) September 2, 2013 5 5

  6. 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) September 2, 2013 6 6

  7. Reliability and completeness: September 2, 2013 7 7

  8. Group mass range during iteration: Typically virial masses of groups between 1013 and 1014 Msun September 2, 2013 8 8

  9. Mass-multiplicity relation: Only for groups near preselected halos: upper linear bound of multiplicities September 2, 2013 9 9

  10. Comparison with input from Millenium catalogs: September 3, 2013 10 10

  11. 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 September 2, 2013 11 11

  12. Evaluation: Purity fp Contamination by interlopers fi Completeness fc September 2, 2013 12 12

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