Mass and Light distributions in Clusters of Galaxies - Henry A ...

Mass and Light of A1703, A370 & RXJ1347-11
galaxies are dynamically affected to a varying degree based on their formation
times and spatial locations in their parent systems. This process can
be described by the excursion set formalism (Lacey & Cole 1993) with more
detailed insight gained from hydrodynamical simulations. It has been clearly
demonstrated that during these merger events DM halos suffer pronounced
tidal stripping (e.g., Moore et al. 1996). Detailed N-body simulations indicate
that up to 70% of the mass may be stripped from halos orbiting close to
the center of massive clusters when integrated over the Hubble time, and with
∼ 20% loss even near the virial radius (Nagai & Kravtsov 2005). Statistical
evidence for halo truncation is claimed also from lensing based measurements
(Natarajan et al. 2002, 2009).
As can be expected, simulations show that despite the substantial effect of
tidal forces in removing the outer DM from galaxy halos, the stellar content
of early-type galaxies is only weakly affected by tidal interactions due to the
centralized location of most stars within the DM halos (Nagai & Kravtsov
2005; Reed et al. 2005). Hence, the ratio of total mass to galaxy luminosity
is predicted to be approximately independent of radius in this context. In
detail, the above simulations show a mild radial decline of the ratio of the
total mass density over the number density of DM halos, M/n, as shown in
Fig. 3.13 (dashed curve). The relatively gentle declining trend in this ratio is
the result of tidal forces (Nagai & Kravtsov 2005; Reed et al. 2005), which act
over time to reduce the number of sub halos in the inner region as compared
to the cluster outskirts.
This M/n ratio is a very useful prediction of the simulations which may
be readily compared to our data. For each cluster we indeed find a gentle
decline in the ratio of the total mass to the number of early type galaxies, the
mean slope of which is in very good agreement with the prediction as shown
in Fig. 3.13. The declining trend in this ratio is seen in the region 0.1−1 r vir ,
in good agreement with the prediction by Nagai & Kravtsov (2005).
As we showed in § 3.9 the ratio of the total mass density to bluer cluster
members light density has a very steep decline with radius – much greater
than the mild trend observed above for early-type red sequence galaxies. The
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