11 research outputs found
Evolution of Clusters of Galaxies: Mass Stripping from Galaxies and Growth of Common Halos
We investigated the evolution of clusters of galaxies using self-consistent
-body simulations in which each galaxy was modeled by many particles. We
carried out simulations for about 20 cases using different initial conditions.
In all simulations, clusters were initially in virial equilibrium. We found
that more than half of the total mass escaped from individual galaxies within a
few crossing times of the cluster, and that a diffuse halo was formed. The
growth rate of the common halo depended on the size of individual galaxies only
weakly. The stripping of the mass from galaxies was mainly due to the
interaction of galaxies, not due to the effect of the tidal field of the
cluster potential. The amount of stripped mass was larger for galaxies in the
central region than for those in the outer region, since the interactions were
more frequent in the central region. As a result, a positive correlation
between the distance from the center and the mass of the galaxy developed. The
volume-density profile of the common halo is expressed as
in the central region. This mass distribution is consistent with the mass
distribution in clusters estimated using X-ray observations.Comment: 12 pages with 12 figures; accepted for publication in PAS
Collisional Evolution of Galaxy Clusters and the Growth of Common Halos
We investigated the dynamical evolution of clusters of galaxies in virial
equilibrium using Fokker-Planck models and self-consistent N-body models. In
particular, we focused on the growth of a common halo, which is a cluster-wide
halo formed by matter stripped from galaxies, and the development of a central
density cusp. The Fokker-Planck models include the effects of two-body
gravitational encounters both between galaxies and between galaxies and common
halo particles. The effects of tidal mass stripping from the galaxies due to
close galaxy-galaxy encounters and accompanying dissipation of the orbital
kinetic energies of the galaxies were also taken into account in the
Fokker-Planck models. We find that the results of the Fokker-Planck models are
in excellent agreement with those of the N-body models regarding the growth of
the common halo mass and the evolution of the cluster density profiles. In the
central region of the cluster, a shallow density cusp, approximated by ( 1), develops. This shallow cusp results
from the combined effects of two-body relaxation and tidal stripping. The cusp
steepness, , weakly depends on the relative importance of the tidal
stripping. When the effect of stripping is important, the central velocity
dispersion decreases as the central density increases and, consequently, a
shallow () cusp is formed. In the limit of no stripping, usual
gravothermal core collapse occurs, i.e. the central velocity dispersion
increases as the central density increases with a steep () cusp
left. We conclude from our consideration of the origin of the cusp demonstrated
here that shallow cusps should develop in real galaxy clusters.Comment: revised, 21 pages, 16 figures, to appear in PASJ, 54, No.1 (2002
Structural Evidence for Environment-Driven Transformation of the Blue Galaxies in Local Abell Clusters - A85, A496, and A754
We compare V-band structural properties of cluster and field galaxies, to
test whether much of the current cluster membership resulted from the
transformation of infalling spirals into red early types. We use 140 galaxies
from 3 z<0.6 Abell clusters (A85,A496,A754 - spectroscopic membership) with
blue colors, and compare them to 80 field galaxies with similar colors and
luminosities. Our previous work (McIntosh et al. 2004, ApJ submitted) shows
that the blue galaxies in these local clusters are a recently infalling
population that has yet to encounter the dense core. We quantify galaxy
internal structure from 2D B/D decompositions using GIM2D. We observe
structural differences between blue galaxies in clusters, compared to the
field. Most blue cluster members are physically smaller and fainter than their
field counterparts. At a matched size and luminosity, recent arrivals are
smoother in appearance, yet their total light is as disk-dominated as in normal
field spirals. Moreover, 50% of blue cluster galaxies have blue cores or
globally blue color profiles, in contrast with field spirals that have
typically red color gradients. Without environment dependent evolution outside
of cluster cores, we expect blue disk galaxies in clusters and the field to
have similar morphologies, sizes, and color gradients. We show conclusively
that galaxy properties do reflect the environment in which the galaxy is found.
The data show that the transformation of accreted galaxies is not confined to
the dense cluster core. The overall properties of bluer cluster galaxies are
best explained by environment-driven transformation of accreted field spirals,
and our results suggest that the processes that govern color and morphological
evolution occur separately. (abridged)Comment: Accepted for publication in ApJ, 23 pages, Latex using
emulateapj5.sty and onecolfloat.sty (included), 15 figures, version with full
resolution Figs. 2 and 5 at
http://www.astro.umass.edu/~dmac/Papers/transf.hires.ps Substantial revisions
of Introduction and Discussion; extensive minor changes throughout paper
following recommendations by referee; conclusions unchanged except for
removal of pre-processing interpretatio
Separation of recoiling chromium(II) ion from neutron-irradiated chromium (III) ion by the dynamic extraction method using ion-exchanger
Benefits of group compassion-focused therapy for treatment-resistant depression: A pilot randomized controlled trial
Major depression is one of the most common mental health problems worldwide. More than one-third of patients suffer from treatment-resistant depression (TRD). In this study, we explored the feasibility of group compassion-focused therapy (CFT) for TRD using a randomized controlled trial with two parallel groups. Eighteen participants were randomly allocated to the intervention group (CFT and usual care) and control group (usual care alone) and a participant in each group withdrew. Participants in the intervention group received a 1.5-h session every week for 12 weeks. The effects of the intervention on the participantsâ scores were calculated using a linear mixed model. There was a larger reduction in their depressive symptoms and fears of compassion for self and a greater increase in their compassion for self compared to the control group participants. The reliable clinical indices showed that in the CFT (intervention) group, three of nine participants recovered (33%), two improved (22%), two recovered but non-reliably (22%), and the condition of two remained unchanged (22%). These findings indicate adequate feasibility of group CFT for TRD in Japanese clinical settings