897 research outputs found
Goto's generalized Kaehler stability theorem
In these notes we give a shortened and more direct proof of Goto's
generalized Kaehler stability theorem stating that if (J_1,J_2) is a
generalized kaehler structure for which J_2 is determined by a nowhere
vanishing closed form, then small deformations of J_1 can be coupled with small
deformations of J_2 so that the pair remains a generalized Kaehler structure.Comment: 9 pages, 5 figure
Galaxies Inside Stromgren Spheres of Luminous Quasars at z>6: Detection of The First Galaxies
The intrinsic Lyman-alpha emission lines of normal galaxies before
reionization are much absorbed by the damping wing of the Gunn-Peterson trough,
rendering their direct detection nearly impossible, if their intrinsic line
widths are less than ~100km/s. High redshift luminous quasars prior to the
completion of cosmological reionization at z~6, on the other hand, are capable
of producing large HII regions around them (Stromgren spheres) to allow their
intrinsic Lyman-alpha emission lines to be transmitted without overwhelming
absorption (Cen & Haiman 2000). We suggest that targeted observations at the
Stromgren spheres of known luminous quasars at z >= 6 would be able to detect
Lyman-alpha emission lines of galaxies inside the Stromgren spheres largely
unattenuated. A tunable, very narrowband filter of \Delta\lambda\over \lambda ~
0.1% or a narrowband filter of \Delta\lambda\over \lambda ~1% with follow-up
spectroscopic identifications will be required. Such observations could
directly observe the sources of cosmological reionization including possibly
the Pop III galaxies at z=6-20 by JWST. Possible applications include
determinations of the ionization state of the intergalactic medium, the sizes
of the Stromgren spheres, the ages of the quasars, the luminosity function of
high redshift galaxies and its evolution, the spatial distribution of galaxies
and its evolution, the biased distribution of galaxies around quasars and the
anisotropy of quasar emission. Observations using Keck-class telescopes may
already be made to enable a differentiation between a fully neutral and a 10%
neutral intergalactic medium at z>6.Comment: Submitted to ApJ Letters, 10 page
Compact Star Clusters in the M31 Disk
We have carried out a survey of compact star clusters (apparent size <3
arcsec) in the southwest part of the M31 galaxy, based on the high-resolution
Suprime-Cam images (17.5 arcmin x 28.5 arcmin), covering ~15% of the
deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V
< 20.5 mag) was performed using frames of the Local Group Galaxies Survey. The
final sample, containing 238 high probability star cluster candidates (typical
half-light radius r_h ~ 1.5 pc), was selected by specifying a lower limit of
r_h > 0.15 arcsec (>0.6 pc). We derived cluster parameters based on the
photometric data and multiband images by employing simple stellar population
models. The clusters have a wide range of ages from ~5 Myr (young objects
associated with 24 um and/or Ha emission) to ~10 Gyr (globular cluster
candidates), and possess mass in a range of 3.0 < log(m/M_sol) < 4.3 peaking at
m ~ 4000 M_sol. Typical age of these intermediate-mass clusters is in the range
of 30 Myr < t < 3 Gyr, with a prominent peak at ~70 Myr. These findings suggest
a rich intermediate-mass star cluster population in M31, which appears to be
scarce in the Milky Way galaxy.Comment: 16 pages, 8 figures, 1 table, accepted for publication in Ap
Deformations of Oka manifolds
We investigate the behaviour of the Oka property with respect to deformations
of compact complex manifolds. We show that in a family of compact complex
manifolds, the set of Oka fibres corresponds to a G-delta subset of the base.
We give a necessary and sufficient condition for the limit fibre of a sequence
of Oka fibres to be Oka in terms of a new uniform Oka property. We show that if
the fibres are tori, then the projection is an Oka map. Finally, we consider
holomorphic submersions with noncompact fibres
Constraints on the equation of state of dark energy and the Hubble constant from stellar ages and the CMB
We place tight constraints on the redshift-averaged, effective value of the
equation of state of dark energy, w, using only the absolute ages of Galactic
stars and the observed position of the first peak in the angular power spectrum
of the CMB. We find w<-0.8 at the 68% confidence level. If we further consider
that w > -1, this finding suggests that within our uncertainties, dark energy
is indistinguishable from a classical vacuum energy term.
We detect a correlation between the ages of the oldest galaxies and their
redshift. This opens up the possibility of measuring w(z) by computing the
relative ages of the oldest galaxies in the universe as a function of redshift,
dz/dt. We show that this is a realistic possibility by computing dz/dt at z~0
from SDSS galaxies and obtain an independent estimate for the Hubble constant,
H_0 = 69 \pm 12 km s-1 Mpc-1. The small number of galaxies considered at z>0.2
does not yield, currently, a precise determination of w(z), but shows that the
age--redshift relation is consistent with a Standard LCDM universe with .Comment: Submitted to Ap
Complex p p waves and the nonlinear graviton construction
This is the published version, also available here: http://dx.doi.org/10.1063/1.523578.We show how to construct all of the complex p p waves using the nonlinear graviton construction of Penrose
RAPTOR observations of delayed explosive activity in the high-redshift gamma-ray burst GRB 060206
The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos
National Laboratory observed GRB 060206 starting 48.1 minutes after gamma-ray
emission triggered the Burst Alert Telescope (BAT) on-board the Swift
satellite. The afterglow light curve measured by RAPTOR shows a spectacular
re-brightening by ~1 mag about 1 h after the trigger and peaks at R ~ 16.4 mag.
Shortly after the onset of the explosive re-brightening the OT doubled its flux
on a time-scale of about 4 minutes. The total R-band fluence received from GRB
060206 during this episode is 2.3e-9 erg/cm2. In the rest frame of the burst (z
= 4.045) this yields an isotropic equivalent energy release of ~0.7e50 erg in
just a narrow UV band 130 +/- 22 nm. We discuss the implications of RAPTOR
observations for untriggered searches for fast optical transients and studies
of GRB environments at high redshift.Comment: Submitted to ApJ Letter
Knots, Braids and BPS States in M-Theory
In previous work we considered M-theory five branes wrapped on elliptic
Calabi-Yau threefold near the smooth part of the discriminant curve. In this
paper, we extend that work to compute the light states on the worldvolume of
five-branes wrapped on fibers near certain singular loci of the discriminant.
We regulate the singular behavior near these loci by deforming the discriminant
curve and expressing the singularity in terms of knots and their associated
braids. There braids allow us to compute the appropriate string junction
lattice for the singularity and,hence to determine the spectrum of light BPS
states. We find that these techniques are valid near singular points with N=2
supersymmetry.Comment: 38 page
- …