285 research outputs found
UV excess galaxies: Wolf-Rayet galaxies
We discuss V and R band photometry for 67% of the Sullivan et al. 2000 SA57
ultraviolet-selected galaxy sample. In a sample of 176 UV-selected galaxies,
Sullivan et al. 2000 find that 24% have (UV-B) colors too blue for consistency
with starburst spectral synthesis models. We propose that these extreme blue,
UV excess galaxies are Wolf-Rayet (WR) galaxies, starburst galaxies with strong
UV emission from WR stars. We measure a median (V-R)=0.38+-0.06 for the
UV-selected sample, bluer than a sample optically selected at R but consistent
with starburst and WR galaxy colors. We demonstrate that redshifted WR emission
lines can double or triple the flux through the UV bandpass at high redshifts.
Thus the (UV-B) color of a WR galaxy can be up to 1.3 mag bluer at high
redshift, and the expected selection function is skewed to larger redshifts.
The redshift distribution of the extreme blue, UV excess galaxies matches the
selection function we predict from the properties of WR galaxies.Comment: 4 pages, including 4 figures. Uses AASTeX and emulateapj5.sty.
Includes referee change
Redshifts for 2410 Galaxies in the Century Survey Region
The `Century Survey' strip covers 102 square degrees within the limits 8.5h
\leq \alpha_{1950} \leq 16.5h, 29.0 degrees \leq \delta_{1950} \leq 30.0
degrees. The strip passes through the Corona Borealis supercluster and the
outer region of the Coma cluster.
Within the Century Survey region, we have measured 2410 redshifts which
constitute four overlapping complete redshift surveys: (1) 1728 galaxies with
Kron-Cousins R_{phot} \leq 16.13 covering the entire strip, (2) 507 galaxies
with R_{phot} \leq 16.4 in the right ascension range 8h 32m \leq \alpha_{1950}
\leq 10h 45m, (3) 1251 galaxies with absorption- and K-corrected R_{CCD, corr}
\leq 16.2 covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h
and (4) 1255 galaxies with absorption- and K-corrected V_{CCD, corr} \leq 16.7
also covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h. All
of these redshift samples are more than 98 % complete to the specified
magnitude limit.Comment: 18 pages, 9 figures, 3 tables, 2 abbreviated tables. In press, to
appear in Astronomical Journal, Dec. 2001 issu
Quantization of Superflow Circulation and Magnetic Flux with a Tunable Offset
Quantization of superflow-circulation and of magnetic-flux are considered for
systems, such as superfluid He-A and unconventional superconductors, having
nonscalar order parameters. The circulation is shown to be the anholonomy in
the parallel transport of the order parameter. For multiply-connected samples
free of distributed vorticity, circulation and flux are predicted to be
quantized, but generically to nonintegral values that are tunably offset from
integers. This amounts to a version of Aharonov-Bohm physics. Experimental
settings for testing these issues are discussed.Comment: 5 two-column pages, ReVTeX, figure available upon request (to
[email protected]
Electron spin evolution induced by interaction with nuclei in a quantum dot
We study the decoherence of a single electron spin in an isolated quantum dot
induced by hyperfine interaction with nuclei for times smaller than the nuclear
spin relaxation time. The decay is caused by the spatial variation of the
electron envelope wave function within the dot, leading to a non-uniform
hyperfine coupling . We show that the usual treatment of the problem based
on the Markovian approximation is impossible because the correlation time for
the nuclear magnetic field seen by the electron spin is itself determined by
the flip-flop processes.
The decay of the electron spin correlation function is not exponential but
rather power (inverse logarithm) law-like. For polarized nuclei we find an
exact solution and show that the precession amplitude and the decay behavior
can be tuned by the magnetic field. The decay time is given by ,
where is the number of nuclei inside the dot. The amplitude of precession,
reached as a result of the decay, is finite. We show that there is a striking
difference between the decoherence time for a single dot and the dephasing time
for an ensemble of dots.Comment: Revtex, 11 pages, 5 figure
Conductance fluctuations in diffusive rings: Berry phase effects and criteria for adiabaticity
We study Berry phase effects on conductance properties of diffusive
mesoscopic conductors, which are caused by an electron spin moving through an
orientationally inhomogeneous magnetic field. Extending previous work, we start
with an exact, i.e. not assuming adiabaticity, calculation of the universal
conductance fluctuations in a diffusive ring within the weak localization
regime, based on a differential equation which we derive for the diffuson in
the presence of Zeeman coupling to a magnetic field texture. We calculate the
field strength required for adiabaticity and show that this strength is reduced
by the diffusive motion. We demonstrate that not only the phases but also the
amplitudes of the h/2e Aharonov-Bohm oscillations are strongly affected by the
Berry phase. In particular, we show that these amplitudes are completely
suppressed at certain magic tilt angles of the external fields, and thereby
provide a useful criterion for experimental searches. We also discuss Berry
phase-like effects resulting from spin-orbit interaction in diffusive
conductors and derive exact formulas for both magnetoconductance and
conductance fluctuations. We discuss the power spectra of the
magnetoconductance and the conductance fluctuations for inhomogeneous magnetic
fields and for spin-orbit interaction.Comment: 18 pages, 13 figures; minor revisions. To appear in Phys. Rev.
Kinematics and Mass Profile of AWM 7
We have measured 492 redshifts (311 new) in the direction of the poor cluster
AWM~7 and have identified 179 cluster members (73 new). We use two independent
methods to derive a self-consistent mass profile, under the assumptions that
the absorption-line galaxies are virialized and that they trace an underlying
Navarro, Frenk & White (1997) dark matter profile: (1) we fit such an NFW
profile to the radial distribution of galaxy positions and to the velocity
dispersion profile; (2) we apply the virial mass estimator to the cluster. With
these assumptions, the two independent mass estimates agree to \sim 15% within
1.7 h^{-1} Mpc, the radial extent of our data; we find an enclosed mass \sim
(3+-0.5)\times 10^{14} h^{-1} M_\odot. The largest potential source of
systematic error is the inclusion of young emission-line galaxies in the mass
estimate.
We investigate the behavior of the surface term correction to the virial mass
estimator under several assumptions about the velocity anisotropy profile,
still within the context of the NFW model, and remark on the sensitivity of
derived mass profiles to outliers. We find that one must have data out to a
large radius in order to determine the mass robustly, and that the surface term
correction is unreliable at small radii.Comment: LaTeX, 5 tables, 7 figures, appeared as 2000 AJ 119 44; typos and Eq.
9 corrected; results are unaffecte
Superconductor coupled to two Luttinger liquids as an entangler for electron spins
We consider an s-wave superconductor (SC) which is tunnel-coupled to two
spatially separated Luttinger liquid (LL) leads. We demonstrate that such a
setup acts as an entangler, i.e. it creates spin-singlets of two electrons
which are spatially separated, thereby providing a source of electronic
Einstein-Podolsky-Rosen pairs. We show that in the presence of a bias voltage,
which is smaller than the energy gap in the SC, a stationary current of
spin-entangled electrons can flow from the SC to the LL leads due to Andreev
tunneling events. We discuss two competing transport channels for Cooper pairs
to tunnel from the SC into the LL leads. On the one hand, the coherent
tunneling of two electrons into the same LL lead is shown to be suppressed by
strong LL correlations compared to single-electron tunneling into a LL. On the
other hand, the tunneling of two spin-entangled electrons into different leads
is suppressed by the initial spatial separation of the two electrons coming
from the same Cooper pair. We show that the latter suppression depends
crucially on the effective dimensionality of the SC. We identify a regime of
experimental interest in which the separation of two spin-entangled electrons
is favored. We determine the decay of the singlet state of two electrons
injected into different leads caused by the LL correlations. Although the
electron is not a proper quasiparticle of the LL, the spin information can
still be transported via the spin density fluctuations produced by the injected
spin-entangled electrons.Comment: 15 pages, 2 figure
High-fidelity indirect readout of trapped-ion hyperfine qubits
We propose and demonstrate a protocol for high-fidelity indirect readout of
trapped ion hyperfine qubits, where the state of a qubit ion is
mapped to a readout ion using laser-driven Raman
transitions. By partitioning the ground state hyperfine
manifold into two subspaces representing the two qubit states and choosing
appropriate laser parameters, the protocol can be made robust to spontaneous
photon scattering errors on the Raman transitions, enabling repetition for
increased readout fidelity. We demonstrate combined readout and back-action
errors for the two subspaces of and
with 68% confidence while avoiding decoherence
of spectator qubits due to stray resonant light that is inherent to direct
fluorescence detection.Comment: 7 + 6 pages, 3 + 1 figure
A Photometric and Kinematic Study of AWM 7
We have measured redshifts and Kron-Cousins R-band magnitudes for a sample of
galaxies in the poor cluster AWM 7. We have measured redshifts for 172
galaxies; 106 of these are cluster members.
We determine the luminosity function from a photometric survey of the central
1.2 h^{-1} x 1.2 h^{-1} Mpc. The LF has a bump at the bright end and a
faint-end slope of \alpha = -1.37+-0.16, populated almost exclusively by
absorption-line galaxies.
The cluster velocity dispersion is lower in the core (\sim 530 km/s) than at
the outskirts (\sim 680 km/s), consistent with the cooling flow seen in the
X-ray. The cold core extends \sim 150 h^{-1} kpc from the cluster center. The
Kron-Cousins R-band mass-to-light ratio of the system is 650+-170 h
M_\odot/L_\odot, substantially lower than previous optical determinations, but
consistent with most previous X-ray determinations.
We adopt H_0 = 100 h km/s/Mpc throughout this paper; at the mean cluster
redshift, (5247+-76 km/s), 1 h^{-1} Mpc subtends 65\farcm5.Comment: 37 pages, LaTeX, including 12 Figures and 1 Table. Accepted for
publication in the Astronomical Journa
Aharonov-Bohm effect in the chiral Luttinger liquid
Edge states of the quantum Hall fluid provide an almost unparalled
opportunity to study mesoscopic effects in a highly correlated electron system.
In this paper we develop a bosonization formalism for the finite-size edge
state, as described by chiral Luttinger liquid theory, and use it to study the
Aharonov-Bohm effect. The problem we address may be realized experimentally by
measuring the tunneling current between two edge states through a third edge
state formed around an antidot in the fractional quantum Hall effect regime. A
renormalization group analysis reveals the existence of a two-parameter
universal scaling function G(X,Y) that describes the Aharonov-Bohm resonances.
We also show that the strong renormalization of the tunneling amplitudes that
couple the antidot to the incident edge states, together with the nature of the
Aharonov-Bohm interference process in a chiral system, prevent the occurrence
of perfect resonances as the magnetic field is varied, even at zero
temperature.Comment: 16 pages, Revtex, 5 figures available from [email protected]
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