226,529 research outputs found
Prospect for relic neutrino searches
Unlike the relic photons, relic neutrinos have not so far been observed. The
Cosmic Neutrino Background (CB) is the oldest relic from the Big Bang,
produced a few seconds after the Bang itself. Due to their impact in cosmology,
relic neutrinos may be revealed indireclty in the near future through
cosmological observations. In this talk we concentrate on other proposals, made
in the last 30 years, to try to detect the CB directly, either in
laboratory searches (through tiny accelerations they produce on macroscopic
targets) or through astrophysical observations (looking for absorption dips in
the flux of Ultra-High Energy neutrinos, due to the annihilation of these
neutrinos with relic neutrinos at the Z-resonance). We concentrate mainly on
the first of these two possibilities.Comment: Talk given at the Nobel Symposium on Neutrino Physics, Enkoping,
Sweden, Augus 19-24, 2004; 16 page
High Spatial Resolution KAO Far-Infrared Observations of the Central Regions of Infrared-Bright Galaxies
We present new high spatial resolution Kuiper Airborne Observatory 50 micron
and/or 100 micron data for 11 infrared-bright galaxies. We also tabulate
previously published KAO data for 11 other galaxies, along with the IRAS data
for the bulges of M 31 and M 81. We find that L(FIR)/L(B) and L(FIR)/L(H)
correlate with CO (1 - 0) intensity and tau(100). Galaxies with optical or
near-infrared signatures of OB stars in their central regions have higher
values of I(CO) and tau(100), as well as higher far-infrared surface
brightnesses and L(FIR)/L(B) and L(FIR)/L(H) ratios. L(FIR)/L(H(alpha)) does
not correlate strongly with CO and tau(100). These results support a scenario
in which OB stars dominate dust heating in the more active galaxies and older
stars are important in quiescent bulges.Comment: 45 pages, to appear in Ap.J. vol. 468 (Sept. 1996). 17 postscript
figures and 10 postscript tables available at
ftp://ipac.caltech.edu/science/bsmith/ka
Viscous relaxation and collective oscillations in a trapped Fermi gas near the unitarity limit
The viscous relaxation time of a trapped two-component gas of fermions in its
normal phase is calculated as a function of temperature and scattering length,
with the collision probability being determined by an energy-dependent s-wave
cross section. The result is used for calculating the temperature dependence of
the frequency and damping of collective modes studied in recent experiments,
starting from the kinetic equation for the fermion distribution function with
mean-field effects included in the streaming terms.Comment: 10 pages, 9 figures; proof version, corrected typo in Eq. (23);
accepted for publication in PR
Time-Series BVI Photometry for the Globular Cluster NGC 6981 (M72)
We present new BVI photometry of the globular cluster NGC 6981 (M72), based
mostly on ground-based CCD archive images. We present a new color-magnitude
diagram (CMD) that reaches almost four magnitudes below the turn-off level. We
performed new derivations of metallicity and morphological parameters of the
evolved sequences, in good agreement with previous authors, obtaining a value
of [Fe/H] ~ -1.50 in the new UVES scale. We also identify the cluster's blue
straggler population. Comparing the radial distribution of these stars with the
red giant branch population, we find that the blue stragglers are more
centrally concentrated, as found in previous studies of blue stragglers in
globular clusters. Taking advantage of the large field of view covered by our
study, we analyzed the surface density profile of the cluster, finding
extratidal main sequence stars out to r ~ 14.1 arcmin or about twice the tidal
radius. We speculate that this may be due to tidal disruption in the course of
M72's orbit, in which case tidal tails associated with the cluster may exist.
We also take a fresh look at the variable stars in the cluster, recovering all
previous known variables, including three SX Phoenicis stars, and adding three
previously unknown RR Lyrae (1 c-type and 2 ab-type) to the total census.
Finally, comparing our CMD with unpublished data for M3 (NGC 5272), a cluster
with similar metallicity and horizontal branch morphology, we found that both
objects are essentially coeval.Comment: Accepted for publication in A
A Possible Formation Scenario for Dwarf Spheroidal Galaxies - II: A Parameter Study
Dwarf spheroidal (dSph) galaxies are considered the basic building blocks of
the galaxy formation process in the LCDM (Lambda Cold Dark Matter) hierarchical
cosmological model. These galaxies are believed to be the most dark matter (DM)
dominated systems known, have the lowest stellar content, and are poor in gas.
Many theories attempt to explain the formation of dSph galaxies resorting to
the fact that these galaxies are mainly found orbiting large galaxies or
invoking other mechanisms of interactions. Here we show the full set of
simulation as an extension of our fiducial model, where we study the formation
of classical dSph galaxies in isolation by dissolving star clusters within the
DM halo of the dwarf galaxy. In our parameter survey we adopt cored and cusped
DM halo profiles and consider different numbers of dissolving star clusters. We
investigate the dependency of observable quantities with different masses and
scale-lengths of the DM halo and different star formation efficiencies (SFE).
We find that our proposed scenario explains many features of the classical dSph
galaxies of the Milky Way, like their morphology and their dynamics. We see
trends how the surface brightness and the scale-length of the luminous
component vary with the parameters of our simulations. We also identify how
irregularities in their shape, i.e. clumpiness and ellipticity vary in our
simulations. In velocity space, we identify the parameters leading to flat
velocity dispersions curves. We recognize kinematically cold substructures in
velocity space, named fossil remnants and stemming from our unique initial
conditions, which alter the expected results. These streaming motions are
considered as a key feature for future observation with high resolution to
validate our scenario.Comment: 23 pages, 9 figures, 4 Tables, accepted for publication in MNRA
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