7,542 research outputs found
Multiple merging in the Abell cluster 1367
We present a dynamical analysis of the central ~1.3 square degrees of the
cluster of galaxies Abell 1367, based on 273 redshift measurements (of which
119 are news). From the analysis of the 146 confirmed cluster members we derive
a significantly non-Gaussian velocity distribution, with a mean location C_{BI}
= 6484+/-81 km/s and a scale S_{BI} = 891+/-58 km/s. The cluster appears
elongated from the North-West to the South-East with two main density peaks
associated with two substructures. The North-West subcluster is probably in the
early phase of merging into the South-East substructure (~ 0.2 Gyr before core
crossing). A dynamical study of the two subclouds points out the existence of a
group of star-forming galaxies infalling into the core of the South-East
subcloud and suggests that two other groups are infalling into the NW and SE
subclusters respectively. These three subgroups contain a higher fraction of
star-forming galaxies than the cluster core, as expected during merging events.
Abell 1367 appears as a young cluster currently forming at the intersection of
two filaments.Comment: 15 pages, 13 figures, 7 tables. Accepted for publication on A&A. High
resolution figures at http://goldmine.mib.infn.it/papers/a1367.htm
Critical behavior of 3D Z(N) lattice gauge theories at zero temperature
Three-dimensional lattice gauge theories at zero temperature are
studied for various values of . Using a modified phenomenological
renormalization group, we explore the critical behavior of the generalized
model for . Numerical computations are used to simulate
vector models for for lattices with linear extension up
to . We locate the critical points of phase transitions and establish
their scaling with . The values of the critical indices indicate that the
models with belong to the universality class of the three-dimensional
model. However, the exponent derived from the heat capacity is
consistent with the Ising universality class. We discuss a possible resolution
of this puzzle. We also demonstrate the existence of a rotationally symmetric
region within the ordered phase for all at least in the finite
volume.Comment: 25 pages, 4 figures, 8 table
Goals, usefulness and abstraction in value-based choice
Colombian drug lord Pablo Escobar, while on the run, purportedly burned two million dollars in banknotes to keep his daughter warm. A stark reminder that, in life, circumstances and goals can quickly change, forcing us to reassess and modify our values on-the-fly. Studies in decision-making and neuroeconomics have often implicitly equated value to reward, emphasising the hedonic and automatic aspect of the value computation, while overlooking its functional (concept-like) nature. Here we outline the computational and biological principles that enable the brain to compute the usefulness of an option or action by creating abstractions that flexibly adapt to changing goals. We present different algorithmic architectures, comparing ideas from artificial intelligence (AI) and cognitive neuroscience with psychological theories and, when possible, drawing parallels
Beyond galaxy bimodality: the complex interplay between kinematic morphology and star formation in the local Universe
It is generally assumed that galaxies are a bimodal population in both star
formation and structure: star-forming galaxies are disks, while passive
galaxies host large bulges or are entirely spheroidal. Here, we test this
scenario by presenting a full census of the kinematic morphologies of a
volume-limited sample of galaxies in the local Universe extracted from the
MaNGA galaxy survey. We measure the integrated stellar line-of-sight velocity
to velocity dispersion ratio () for 4574 galaxies in the stellar mass
range . We show that at fixed
stellar mass, the distribution of is not bimodal, and that a simple
separation between fast and slow rotators is over-simplistic. Fast rotators are
a mixture of at least two populations, referred to here as dynamically-cold
disks and intermediate systems, with disks dominating in both total stellar
mass and number. When considering star-forming and passive galaxies separately,
the star-forming population is almost entirely made up of disks, while the
passive population is mixed, implying an array of quenching mechanisms. Passive
disks represent 30% (both in number and mass) of passive galaxies, nearly
a factor of two higher than that of slow rotators, reiterating that these are
an important population for understanding galaxy quenching. These results paint
a picture of a local Universe dominated by disky galaxies, most of which become
somewhat less rotation-supported upon or after quenching. While spheroids are
present to a degree, they are certainly not the evolutionary end-point for the
majority of galaxies.Comment: 17 pages (incl. 5 of appendix), accepted for publication in Ap
The phase transitions in 2D Z(N) vector models for N>4
We investigate both analytically and numerically the renormalization group
equations in 2D Z(N) vector models. The position of the critical points of the
two phase transitions for N>4 is established and the critical index \nu\ is
computed. For N=7, 17 the critical points are located by Monte Carlo
simulations and some of the corresponding critical indices are determined. The
behavior of the helicity modulus is studied for N=5, 7, 17. Using these and
other available Monte Carlo data we discuss the scaling of the critical points
with N and some other open theoretical problems.Comment: 19 pages, 8 figures, 10 tables; version to appear on Phys. Rev.
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