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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 - PowerPoint PPT Presentation
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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
September 2, 2013 222
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 333
Density profiles from simulations:
September 2, 2013 444
Selected regions of the SDSS-FoV
Subslices
330x250 Mpc/h
September 2, 2013 555
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
September 2, 2013 666
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 777
Reliability and completeness:
September 2, 2013 888
Group mass range during iteration:
Typically virial masses of groups between 1013 and 1014 Msun
September 2, 2013 999
Mass-multiplicity relation:
Only for groups near preselected halos: upper linear bound of multiplicities
September 3, 2013 101010
Comparison with input from Millenium catalogs:
September 2, 2013 111111
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 121212
Purity fp
Contamination by interlopers fi
Completeness fc
Evaluation: