7,339 research outputs found
Planetary nebulae and stellar kinematics in the flattened elliptical galaxy NGC 1344
We present photometric and kinematic information obtained by measuring 197
planetary nebulae (PNs) discovered in the flattened Fornax elliptical galaxy
NGC 1344 (also known as NGC 1340) with an on-band, off-band, grism + on-band
filter technique. We build the PN luminosity function (PNLF) and use it to
derive a distance modulus m-M=31.4, slightly smaller than, but in good
agreement with, the surface brightness fluctuation distance. The PNLF also
provides an estimate of the specific PN formation rate: 6x10^-12 PNs per year
per solar luminosity. Combining the positional information from the on-band
image with PN positions measured on the grism + on-band image, we can measure
the radial velocities of 195 PNs, some of them distant more than 3 effective
radii from the center of NGC 1344. We complement this data set with stellar
kinematics derived from integrated spectra along the major and minor axes, and
parallel to the major axis of NGC 1344. The line-of-sight velocity dispersion
profile indicates the presence of a dark matter halo around this galaxy.Comment: 45 pages, 18 figures, accepted for publication in Ap
Shot Noise Enhancement in Resonant Tunneling Structures in a Magnetic Field
We have observed that the shot noise of tunnel current, I, in
GaSb-AlSb-InAs-AlSb-GaSb double-barrier structure under a magnetic field can
exceed 2qI. The measurements were done at T=4K in fields up to 5T parallel to
the current. The noise enhancement occurred at each of the several
negative-differential conductance regions induced by the tunneling of holes
through Landau levels in the InAs quantum well. The amount of the enhancement
increased with the strength of the negative conductance and reached values up
to 8qI. These results are explained qualitatively by fluctuations of the
density of states in the well, but point out the need for a detailed theory of
shot noise enhancement in resonant tunneling devices.Comment: 4 pages, RevTex, 3 figure
Magnetic confinement of the superconducting condensate in superconductor/ferromagnet hybrid composites
The influence of an inhomogeneous magnetic field on the magnetoresistance of
thin Al films, used in different superconductor/ferromagnet hybrids, has been
investigated. Two contrasting magnetic textures with out-of-plane magnetization
are explored, namely (i) a plain film in a multidomain state and (ii) an array
of micro-sized dots. The stray fields of the ferromagnetic structures confine
the superconducting condensate and, accordingly, modify the condition for the
nucleation of superconductivity. By switching between different magnetic states
of the ferromagnet, this confinement can be tuned at will, hereby reversibly
changing the dependence of the critical temperature Tc on an external magnetic
field H. In particular, the continuous evolution from a conventional linear
Tc(H) dependence with a single maximum to a reentrant superconducting phase
boundary with multiple Tc peaks has been demonstrated
Suppression of hole-hole scattering in GaAs/AlGaAs heterostructures under uniaxial compression
Resistance, magnetoresistance and their temperature dependencies have been
investigated in the 2D hole gas at a [001] p-GaAs/AlGaAs
heterointerface under [110] uniaxial compression. Analysis performed in the
frame of hole-hole scattering between carriers in the two spin splitted
subbands of the ground heavy hole state indicates, that h-h scattering is
strongly suppressed by uniaxial compression. The decay time of the
relative momentum reveals 4.5 times increase at a uniaxial compression of 1.3
kbar.Comment: 5 pages, 3 figures. submitted to Phys.Rev.
Vibrating soap films: An analog for quantum chaos on billiards
We present an experimental setup based on the normal modes of vibrating soap
films which shows quantum features of integrable and chaotic billiards. In
particular, we obtain the so-called scars -narrow linear regions with high
probability along classical periodic orbits- for the classically chaotic
billiards. We show that these scars are also visible at low frequencies.
Finally, we suggest some applications of our experimental setup in other
related two-dimensional wave phenomena.Comment: 5 pages, 7 figures. Better Postscript figures available on reques
Electric-Field Tuning of Spin-Dependent Exciton-Exciton Interactions in Coupled Quantum Wells
We have shown experimentally that an electric field decreases the energy
separation between the two components of a dense spin-polarized exciton gas in
a coupled double quantum well, from a maximum splitting of meV to
zero, at a field of 35 kV/cm. This decrease, due to the field-induced
deformation of the exciton wavefunction, is explained by an existing
calculation of the change in the spin-dependent exciton-exciton interaction
with the electron-hole separation. However, a new theory that considers the
modification of screening with that separation is needed to account for the
observed dependence on excitation power of the individual energies of the two
exciton components.Comment: 5 pages, 4 eps figures, RevTeX, Physical Review Letters (in press
Peanut-shaped bulges in face-on disk galaxies
We present high resolution absorption-line spectroscopy of 3 face-on
galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for
box/peanut (B/P)-shaped bulges. These observations test and confirm the
prediction of Debattista et al. (2005) that face-on B/P-shaped bulges can be
recognized by a double minimum in the profile of the fourth-order Gauss-Hermite
moment h_4. In NGC 1703, which is an unbarred control galaxy, we found no
evidence of a B/P bulge. In NGC 98, a clear double minimum in h_4 is present
along the major axis of the bar and before the end of the bar, as predicted. In
contrast, in NGC 600, which is also a barred galaxy but lacks a substantial
bulge, we do not find a significant B/P shape.Comment: 4 pages, 1 figure. To appear in "Tumbling, twisting, and winding
galaxies: Pattern speeds along the Hubble sequence", E. M. Corsini and V. P.
Debattista (eds.), Memorie della Societa` Astronomica Italian
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