215 research outputs found
Effects of large-scale environment on the assembly history of central galaxies
We examine whether large-scale environment affects the mass assembly history
of their central galaxies. To facilitate this, we constructed dark matter halo
merger trees from a cosmological N-body simulation and calculated the formation
and evolution of galaxies using a semi-analytic method. We confirm earlier
results that smaller halos show a notable difference in formation time with a
mild dependence on large-scale environment. However, using a semi-analytic
model, we found that on average the growth rate of the stellar mass of central
galaxies is largely insensitive to large-scale environment. Although our
results show that the star formation rate (SFR) and the stellar mass of central
galaxies in smaller halos are slightly affected by the assembly bias of halos,
those galaxies are faint, and the difference in the SFR is minute, and
therefore it is challenging to detect it in real galaxies given the current
observational accuracy. Future galaxy surveys, such as the BigBOSS experiment
and the Large Synoptic Survey Telescope, which are expected to provide
observational data for fainter objects, will provide a chance to test our model
predictions.Comment: 7 pages, 5 figure
Explaining the Color Distributions of Globular Cluster Systems in Elliptical Galaxies
The colors of globular clusters in most of large elliptical galaxies are
bimodal. This is generally taken as evidence for the presence of two cluster
subpopulations that have different geneses. However, here we find that, because
of the non-linear nature of the metallicity-to-color transformation, a coeval
group of old clusters with a unimodal metallicity spread can exhibit color
bimodality. The models of cluster colors indicate that the horizontal-branch
stars are the main drivers behind the empirical non-linearity. We show that the
scenario gives simple and cohesive explanations for all the key observations,
and could simplify theories of elliptical galaxy formation.Comment: Science, 311, 1129; Minor changes to text to match the published
version (9 pages, 3 figures
Merger relics of cluster galaxies
Context. Sheen and collaborators recently found that a surprisingly large
portion (38%) of massive early-type galaxies in heavy clusters show strong
merger-related disturbed features. This contradicts the general understanding
that massive clusters are hostile environments for galaxy mergers. Considering
the significance of mergers in galaxy evolution, it is important to understand
this. Aims. We aim to present a theoretical foundation that explains galaxy
mergers in massive clusters. Methods. We used the N-body simulation technique
to perform a cosmological-volume simulation and derive dark-halo merger trees.
Then, we used the semi-analytic modeling technique to populate each halo with
galaxies. We ran hydrodynamic simulations of galaxy mergers to estimate the
lifetime of merger features for the imaging condition used by Sheen and
collaborators. We applied this merger feature lifetime to our semi-analytic
models. Finally, we counted the massive early-type galaxies in heavy model
clusters that would show strong merger features. Results. While there still are
substantial uncertainties, our preliminary results are remarkably close to the
observed fraction of galaxies with merger features. Key ingredients for the
success are twofold: firstly, the subhalo motion in dark haloes has been
accurately traced, and, second, the lifetime of merger features has been
properly estimated. As a result, merger features are expected to last very long
in cluster environments. Many massive early-type galaxies in heavy clusters
therefore show merger features not because they experience mergers in the
current clusters in situ, but because they still carry their merger features
from their previous halo environments. Conclusions. Investigating the merger
relics of cluster galaxies is potentially important, because it uniquely allows
us to backtrack the halo merger history.Comment: 4 pages, 3 figures, accepted for publication in A&A Research Not
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