The influence of halo assembly on galaxies and galaxy groups

ZAPATA T., PEREZ J., PADILLA N. AND TISSERA, P.

Passa Quatro, Minas Gerais, Brazil

Congreso; XXXIV Annual meeting of the Brazilian Astronomical Society; 2008

Recent studies on clustering of dark-matter haloes found that the age and assembly history of haloes of similar mass influence their clustering amplitude. The assembly bias has also been detected in observations by Wang et al. (2008), which study associate group colour with his age. Our aim is to detect the effects of halo assembly on the galaxy population and find other observational parameters that can be used as an indicator of halo age. We compare galaxy groups from SDSS-DR6 real data with a mock SDSS simulated catalogue (from Semi-Analytic Model (SAM), De Lucia et al. (2006)). We apply exactly the samefriend-of-friend group detection algorithm to both samples and we calculated groups properties for two different narrow (0.4 dex wide) ranges of halo mass. Using mock SDSS group catalogue, we found that higher concentration and isolation indicate that groups are older, where concentration is mesured as the proyected density using the fifth closest galaxy to the group centre and isolation is defined a the distance to the nearest neighbor in terms of its virial radius. Analysing the mean spectral type of SDSS groups, we find that while SDSS massive groups confirm the predicted correlation concentration-age, they disagree