10,314 research outputs found
Bulge plus disc and S\'ersic decomposition catalogues for 16,908 galaxies in the SDSS Stripe 82 co-adds: A detailed study of the structural measurements
Quantitative characterization of galaxy morphology is vital in enabling
comparison of observations to predictions from galaxy formation theory.
However, without significant overlap between the observational footprints of
deep and shallow galaxy surveys, the extent to which structural measurements
for large galaxy samples are robust to image quality (e.g., depth, spatial
resolution) cannot be established. Deep images from the Sloan Digital Sky
Survey (SDSS) Stripe 82 co-adds provide a unique solution to this problem -
offering magnitudes improvement in depth with respect to SDSS Legacy
images. Having similar spatial resolution to Legacy, the co-adds make it
possible to examine the sensitivity of parametric morphologies to depth alone.
Using the Gim2D surface-brightness decomposition software, we provide public
morphology catalogs for 16,908 galaxies in the Stripe 82 co-adds. Our
methods and selection are completely consistent with the Simard et al. (2011)
and Mendel et al. (2014) photometric decompositions. We rigorously compare
measurements in the deep and shallow images. We find no systematics in total
magnitudes and sizes except for faint galaxies in the -band and the
brightest galaxies in each band. However, characterization of bulge-to-total
fractions is significantly improved in the deep images. Furthermore, statistics
used to determine whether single-S\'ersic or two-component (e.g., bulge+disc)
models are required become more bimodal in the deep images. Lastly, we show
that asymmetries are enhanced in the deep images and that the enhancement is
positively correlated with the asymmetries measured in Legacy images.Comment: 27 pages, 14 figures. MNRAS accepted. Our catalogs are available in
TXT and SQL formats at
http://orca.phys.uvic.ca/~cbottrel/share/Stripe82/Catalogs
Galactic Cosmic Rays from Supernova Remnants: II Shock Acceleration of Gas and Dust
This is the second paper (the first was astro-ph/9704267) of a series
analysing the Galactic Cosmic Ray (GCR) composition and origin. In this we
present a quantitative model of GCR origin and acceleration based on the
acceleration of a mixture of interstellar and/or circumstellar gas and dust by
supernova remnant blast waves. We present results from a nonlinear shock model
which includes (i) the direct acceleration of interstellar gas-phase ions, (ii)
a simplified model for the direct acceleration of weakly charged dust grains to
energies of order 100keV/amu simultaneously with the gas ions, (iii) frictional
energy losses of the grains colliding with the gas, (iv) sputtering of ions of
refractory elements from the accelerated grains and (v) the further shock
acceleration of the sputtered ions to cosmic ray energies. The calculated GCR
composition and spectra are in good agreement with observations.Comment: to appear in ApJ, 51 pages, LaTeX with AAS macros, 9 postscript
figures, also available from ftp://wonka.physics.ncsu.edu/pub/elliso
Entropy-driven formation of the gyroid cubic phase
We show, by computer simulation, that tapered or pear-shaped particles, interacting through purely repulsive interactions, can freely self-assemble to form the three-dimensionally periodic, gyroid cubic phase. The Ia3d gyroid cubic phase is formed by these particles both on compression of an isotropic configuration and on expansion of a smectic A bilayer arrangement. For the latter case, it is possible identify the steps by which the topological transformation from non-intersecting planes to fully interpenetrating, periodic networks takes place</p
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