1,868 research outputs found
Kinematic decomposition of IllustrisTNG disk galaxies: morphology and relation with morphological structures
We recently developed an automated method, auto-GMM to decompose simulated
galaxies. It extracts kinematic structures in an accurate, efficient, and
unsupervised way. We use auto-GMM to study the stellar kinematic structures of
disk galaxies from the TNG100 run of IllustrisTNG. We identify four to five
structures that are commonly present among the diverse galaxy population.
Structures having strong to moderate rotation are defined as cold and warm
disks, respectively. Spheroidal structures dominated by random motions are
classified as bulges or stellar halos, depending on how tightly bound they are.
Disky bulges are structures that have moderate rotation but compact morphology.
Across all disky galaxies and accounting for the stellar mass within 3
half-mass radii, the kinematic spheroidal structures, obtained by summing up
stars of bulges and halos, contribute ~45% of the total stellar mass, while the
disky structures constitute 55%. This study also provides important insights
about the relationship between kinematically and morphologically derived
galactic structures. Comparing the morphology of kinematic structures with that
of traditional bulge+disk decomposition, we conclude: (1) the morphologically
decomposed bulges are composite structures comprised of a slowly rotating
bulge, an inner halo, and a disky bulge; (2) kinematically disky bulges, akin
to what are commonly called pseudo bulges in observations, are compact
disk-like components that have rotation similar to warm disks; (3) halos
contribute almost 30% of the surface density of the outer part of morphological
disks when viewed face-on; and (4) both cold and warm disks are often truncated
in central regions.Comment: 20 pages, 14 figures. Accepted for publication in ApJ. The mass
fraction catalogue and images of the kinematically derived galactic
structures are publicly available
(https://www.tng-project.org/data/docs/specifications/#sec5m
Unsupervised Learning of Complex Articulated Kinematic Structures combining Motion and Skeleton Information
In this paper we present a novel framework for unsupervised kinematic structure learning of complex articulated objects from a single-view image sequence. In contrast to prior motion information based methods, which estimate relatively simple articulations, our method can generate arbitrarily complex kinematic structures with skeletal topology by a successive iterative merge process. The iterative merge process is guided by a skeleton distance function which is generated from a novel object boundary generation method from sparse points. Our main contributions can be summarised as follows: (i) Unsupervised complex articulated kinematic structure learning by combining motion and skeleton information. (ii) Iterative fine-to-coarse merging strategy for adaptive motion segmentation and structure smoothing. (iii) Skeleton estimation from sparse feature points. (iv) A new highly articulated object dataset containing multi-stage complexity with ground truth. Our experiments show that the proposed method out-performs state-of-the-art methods both quantitatively and qualitatively
Multi-frequency Studies of Massive Cores with Complex Spatial and Kinematic Structures
Five regions of massive star formation have been observed in various
molecular lines in the frequency range GHz. The studied regions
possess dense cores, which host young stellar objects. The physical parameters
of the cores are estimated, including kinetic temperatures ( K),
sizes of the emitting regions ( pc), and virial masses (). Column densities and abundances of various molecules are
calculated in the local thermodynamical equilibrium approximation. The core in
99.982+4.17, associated with the weakest IRAS source, is characterized by
reduced molecular abundances. Molecular line widths decrease with increasing
distance from the core centers (). For b\ga 0.1~pc, the dependences
are close to power laws (), where varies from
to , depending on the object. In four cores, the
asymmetries of the optically thick HCN(1--0) and HCO(1--0) lines indicate
systematic motions along the line of sight: collapse in two cores and expansion
in two others. Approximate estimates of the accretion rates in the collapsing
cores indicate that the forming stars have masses exceeding the solar mass.Comment: 18 pages, 7 figures, 6 table
The One-loop Open Superstring Massless Five-point Amplitude with the Non-Minimal Pure Spinor Formalism
We compute the massless five-point amplitude of open superstrings using the
non-minimal pure spinor formalism and obtain a simple kinematic factor in pure
spinor superspace, which can be viewed as the natural extension of the
kinematic factor of the massless four-point amplitude. It encodes bosonic and
fermionic external states in supersymmetric form and reduces to existing
bosonic amplitudes when expanded in components, therefore proving their
equivalence. We also show how to compute the kinematic structures involving
fermionic states.Comment: 38 pages, harvmac TeX, v2: fix typo in (4.2) and add referenc
Harassment Origin for Kinematic Substructures in Dwarf Elliptical Galaxies?
We have run high resolution N-body models simulating the encounter of a dwarf
galaxy with a bright elliptical galaxy. The dwarf absorbs orbital angular
momentum and shows counter-rotating features in the external regions of the
galaxy. To explain the core-envelope kinematic decoupling observed in some
dwarf galaxies in high-density environments requires nearly head-on collisions
and very little dark matter bound to the dwarf. These kinematic structures
appear under rather restrictive conditions. As a consequence, in a cluster like
Virgo ~1% of dwarf galaxies may present counter-rotation formed by harassment.Comment: 10 pages, 7 figures; Accepted for publication in Astronomy and
Astrophysic
Generic multiloop methods and application to N=4 super-Yang-Mills
We review some recent additions to the tool-chest of techniques for finding
compact integrand representations of multiloop gauge-theory amplitudes -
including non-planar contributions - applicable for N=4 super-Yang-Mills in
four and higher dimensions, as well as for theories with less supersymmetry. We
discuss a general organization of amplitudes in terms of purely cubic graphs,
review the method of maximal cuts, as well as some special D-dimensional
recursive cuts, and conclude by describing the efficient organization of
amplitudes resulting from the conjectured duality between color and kinematic
structures on constituent graphs.Comment: 42 pages, 18 figures, invited review for a special issue of Journal
of Physics A devoted to "Scattering Amplitudes in Gauge Theories", v2 minor
corrections, v3 added reference
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