11,818 research outputs found
HST Images of a Galaxy Group at z=2.81, and the Sizes of Damped Lyman Alpha Galaxies
We present HST WFPC2 observations in three bands (F450W, F467M and F814W) of
a group of three galaxies at z=2.8 discovered in a ground-based narrow-band
search for Lyman alpha emission near the z=2.8 quasar PKS0528-250. One of the
galaxies is a damped (DLA) absorber and these observations bear on the relation
between the DLA clouds and the Lyman-break galaxies and the stage in the
evolution of galaxies they represent. We describe a procedure for combining the
undersampled WFPC2 images pointed on a sub-pixel grid, which largely recovers
the full sampling of the WFPC2 point spread function (psf). These three
galaxies have similar properties to the Lyman-break galaxies except that they
have strong Lyman alpha emission. The three galaxies are detected in all three
bands, with average B~26, I~25. Two of the galaxies are compact with intrinsic
(i.e. after correcting for the effect of the psf) half-light radii of ~0.1
arcsec (~0.4/h kpc, q_o=0.5). The third galaxy comprises two similarly compact
components separated by 0.3 arcsec. The HST images and a new ground-based Lyman
alpha image of the field provide evidence that the three galaxies are more
extended in the light of Lyman alpha than in the continuum. The measured impact
parameters for this DLA galaxy (1.17 arcsec), for a second confirmed system,
and for several candidates, provide a preliminary estimate of the
cross-section-weighted mean radius of the DLA gas clouds at z~3 of less than
13/h kpc, for q_o=0.5. Given the observed sky covering factor of the absorbers
this implies that for q_o=0.5 the space density of DLA clouds at these
redshifts is more than five times the space density of spiral galaxies locally,
with the actual ratio probably considerably greater. For q_o=0.0 there is no
evidence as yet that DLA clouds are more common than spiral galaxies locally.Comment: 11 pages, LaTeX, 6 Figures total (4 colour GIF-format, 2 PostScript),
accepted for publication in MNRA
Macroscopic-Microscopic Mass Models
We discuss recent developments in macroscopic-microscopic mass models,
including the 1992 finite-range droplet model, the 1992 extended-Thomas-Fermi
Strutinsky-integral model, and the 1994 Thomas-Fermi model, with particular
emphasis on how well they extrapolate to new regions of nuclei. We also address
what recent developments in macroscopic-microscopic mass models are teaching us
about such physically relevant issues as the nuclear curvature energy, a new
congruence energy arising from a greater-than-average overlap of neutron and
proton wave functions, the nuclear incompressibility coefficient, and the
Coulomb redistribution energy arising from a central density depression. We
conclude with a brief discussion of the recently discovered rock of metastable
superheavy nuclei near 272:110 that had been correctly predicted by
macroscopic-microscopic models, along with a possible new tack for reaching an
island near 290:110 beyond our present horizon.Comment: 10 pages. LaTeX. Presented at International Conference on Exotic
Nuclei and Atomic Masses (ENAM 95), Arles, France, June 19-23, 1995. To be
published in conference proceedings by Les Editions Frontieres, Gif sur
Yvette, France. Seven figures not included here. PostScript version with
figures available at http://t2.lanl.gov/pub/publications/publications.html or
by anonymous ftp at ftp://t2.lanl.gov/pub/publications/enam9
Self-shrinkers with a rotational symmetry
In this paper we present a new family of non-compact properly embedded,
self-shrinking, asymptotically conical, positive mean curvature ends
that are hypersurfaces of revolution with
circular boundaries. These hypersurface families interpolate between the plane
and half-cylinder in , and any rotationally symmetric
self-shrinking non-compact end belongs to our family. The proofs involve the
global analysis of a cubic-derivative quasi-linear ODE. We also prove the
following classification result: a given complete, embedded, self-shrinking
hypersurface of revolution is either a hyperplane ,
the round cylinder of radius , the
round sphere of radius , or is diffeomorphic to an (i.e. a "doughnut" as in [Ang], which when is a torus). In
particular for self-shrinkers there is no direct analogue of the Delaunay
unduloid family. The proof of the classification uses translation and rotation
of pieces, replacing the method of moving planes in the absence of isometries.Comment: Trans. Amer. Math. Soc. (2011), to appear; 23 pages, 1 figur
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