7,248 research outputs found
Formation of the Galactic globular clusters with He-rich stars in low-mass halos virialized at high redshift
Recent observations have reported that the Galactic globular clusters (GCs)
with unusually extended horizontal-branch (EHB) morphologies show a
significantly lower velocity dispersion compared with that of the entire
Galactic GC system. We consider that the observed distinctive kinematics of GCs
with EHB has valuable information on the formation epochs of GCs and
accordingly discuss this observational result based on cosmological N-body
simulations with a model of GC formation. We assume that GCs in galaxies were
initially formed in low-mass halos at high redshifts and we investigate final
kinematics of GCs in their host halos at . We find that GCs formed in
halos virialized at z>10 show lower velocity dispersions on average than those
formed at z>6 for halos with GCs at z=0. We thus suggest that the origin of the
observed lower velocity dispersion for the Galactic GCs with EHBs is closely
associated with earlier formation epochs (z>10) of halos initially hosting the
GCs in the course of the Galaxy formation. Considering that the origin of EHBs
can be due to the presence of helium-enhanced second-generation stars in GCs,
we discuss the longstanding second parameter problem of GCs in the context of
different degrees of chemical pollution in GC-forming gas clouds within
low-mass halos virialized at different redshifts.Comment: 5 pages, 3 figures, accepted by MNRAS Letter
Prepotentials for local mirror symmetry via Calabi-Yau fourfolds
In this paper, we first derive an intrinsic definition of classical triple
intersection numbers of K_S, where S is a complex toric surface, and use this
to compute the extended Picard-Fuchs system of K_S of our previous paper,
without making use of the instanton expansion. We then extend this formalism to
local fourfolds K_X, where X is a complex 3-fold. As a result, we are able to
fix the prepotential of local Calabi-Yau threefolds K_S up to polynomial terms
of degree 2. We then outline methods of extending the procedure to non
canonical bundle cases.Comment: 42 pages, 7 figures. Expanded, reorganized, and added a theoretical
background for the calculation
On the Origin of Mass--Metallicity Relations, Blue Tilts, and Scaling Relations for Metal-poor Globular Cluster Systems
We investigate formation processes and physical properties of globular
cluster systems (GCSs) in galaxies based on high-resolution cosmological
simulations with globular clusters. We focus on metal-poor clusters (MPCs) and
correlations with their host galaxies by assuming that MPC formation is
truncated at a high redshift (z_trun > 6). We find that the correlation between
mean metallicities (Z_gc) of MPCs and their host galaxy luminosities (L)
flattens from z=z_trun to z=0. We also find that the observed relation (Z_gc ~
L^0.15) in MPCs can be reproduced well in the models with Z_gc ~ L^0.5 at
z=z_trun when z_trun ~ 10, if mass-to-light-ratios are assumed to be constant
at z=z_trun. However, better agreement with the observed relation is found for
models with different mass-to-light-ratios between z=z_trun and z=0. It is also
found that the observed color-magnitude relation of luminous MPCs (i.e., ``blue
tilts'') may only have a small contribution from the stripped stellar nuclei of
dwarf galaxies, which have nuclei masses that correlate with their total mass
at z=z_trun. The simulated blue tilts are found to be seen more clearly in more
massive galaxies, which reflects the fact that more massive galaxies at z=0 are
formed from a larger number of dwarfs with stellar nuclei formed at z>z_trun.
The half-number radii (R_e) of GCSs, velocity dispersions of GCSs (sigma), and
their host galaxy masses (M_h) are found to be correlated with one another such
that R_e ~ M_h^{0.57} and sigma ~ M_h^{0.32}.Comment: 15 pages, 20 figures, accepted by MNRA
WMAP Haze: Directly Observing Dark Matter?
In this paper we show that dark matter in the form of dense matter/antimatter
nuggets could provide a natural and unified explanation for several distinct
bands of diffuse radiation from the core of the Galaxy spanning over 12 orders
of magnitude in frequency. We fix all of the phenomenological properties of
this model by matching to x-ray observations in the keV band, and then
calculate the unambiguously predicted thermal emission in the microwave band,
at frequencies smaller by 10 orders of magnitude. Remarkably, the intensity and
spectrum of the emitted thermal radiation are consistent with--and could
entirely explain--the so-called "WMAP haze": a diffuse microwave excess
observed from the core of our Galaxy by the Wilkinson Microwave Anisotropy
Probe (WMAP). This provides another strong constraint of our proposal, and a
remarkable nontrivial validation. If correct, our proposal identifies the
nature of the dark matter, explains baryogenesis, and provides a means to
directly probe the matter distribution in our Galaxy by analyzing several
different types of diffuse emissions.Comment: 16 pages, REVTeX4. Updated to correspond with published version:
includes additional appendices discussing finite-size effect
Designs for graphs with six vertices and ten edges
The design spectrum has been determined for two of the 15 graphs with six vertices and ten edges. In this paper we completely solve the design spectrum problem for a further eight of these graphs.</p
A kinematical approach to gravitational lensing using new formulae for refractive index and acceleration
This paper uses the Schwarzschild metric to derive an effective refractive
index and acceleration vector that account for relativistic deflection of light
rays, in an otherwise classical kinematic framework. The new refractive index
and the known path equation are integrated to give accurate results for travel
time and deflection angle, respectively. A new formula for coordinate
acceleration is derived which describes the path of a massless test particle in
the vicinity of a spherically symmetric mass density distribution. A standard
ray-shooting technique is used to compare the deflection angle and time delay
predicted by this new formula with the previously calculated values, and with
standard first order approximations. Finally, the ray shooting method is used
in theoretical examples of strong and weak lensing, reproducing known
observer-plane caustic patterns for multiple masses.Comment: 11 pages, 7 figures, MNRAS accepte
Far-Infrared Emission From E and E/S0 Galaxies
Studies of cold material through IRAS 60um and 100um observations indicated
that half of ordinary E and E/S0 galaxies were detected above the 3 sigma
level, indicating that cold gas is common, although no correlation was found
between the optical and far- infrared fluxes. Most detections were near the
instrumental threshold, and given an improved understanding of detection
confidence, we reconsider the 60um and 100um detection rate. After excluding
active galactic nuclei, peculiar systems, and background contamination, only 15
non-peculiar E and E/S0 galaxies from the RSA catalog are detected above the
98% confidence level, about 12% of the sample. An unusually high percentage of
these 15 galaxies possess cold gas (HI, CO) and optical emission lines
(Halpha), supporting the presence of gas cooler than 10E4 K. The 60um to 100um
flux ratios imply a median dust temperature for the sample of 30 K, with a
range of 23-38 K.
These detections define the upper envelope of the optical to far-infrared
relationship, F_fir propto F_B^0.24+/-0.08, showing that optically bright
objects are also brighter in the infrared, although with considerable
dispersion. A luminosity correlation is present with L_fir propto
L_B^1.65+/-0.28, but the dust temperature is uncorrelated with luminosity.
Models that contain large dust grains composed of amorphous carbon plus
silicates come close to reproducing the typical 60um to 100um flux ratios, the
far-infrared luminosity, and the L_fir - L_B relationship.Comment: 10 postscript pages, 2 tables, and 2 figure
Ground‐based measurements of NOx and total reactive oxidized nitrogen (NOy) at Sable Island, Nova Scotia, during the NARE 1993 summer intensive
Measurements of NO, NO2, and total reactive oxidized nitrogen (NOy) were added to ongoing measurements of aerosols, CO, and O3 at Sable Island (43°55′N, 60°01′W), Nova Scotia, during the North Atlantic Regional Experiment (NARE) 1993 summer intensive. Ambient levels of NOx and NOy were found to be highly variable, and elevated levels can be attributed to the transport of polluted continental air or presumably to relatively fresh emissions from sources upwind (e.g., ship traffic). The median values for NOx and NOy are 98 and 266 parts per trillion by volume (pptv), respectively. A multiday pollution episode occurred during which elevated NOx and NOy were observed with enhanced levels of O3, CO, and condensation nuclei. Air masses of recent tropical marine origin characterized by low and constant levels of O3 and CO were sampled after Hurricane Emily. The correlation between ozone and CO is reasonably good, although the relation is driven by the single pollution episode observed during the study. The correlation of O3 with NOy and with NOy‐NOx is complicated by the presumed NOy removal processes in the marine boundary layer. Examination of the radiosonde data and comparisons of the surface data with those obtained on the overflying aircraft provide clear indications of vertical stratification above the site
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