478 research outputs found
C32, A Young Star Cluster in IC 1613
The Local Group irregular galaxy IC 1613 has remained an enigma for many
years because of its apparent lack of star clusters. We report the successful
search for clusters among several of the candidate objects identified many
years ago on photographic plates. We have used a single HST WFPC2 pointing and
a series of images obtained with the WIYN telescope under exceptional seeing
conditions, examining a total of 23 of the previously published candidates. All
but six of these objects were found to be either asterisms or background
galaxies. Five of the six remaining candidates possibly are small, sparse
clusters and the sixth, C32, is an obvious cluster. It is a compact, young
object, with an age of less than 10 million years and a total absolute
magnitude of M_V = -5.78+/-0.16 within a radius of 13 pc.Comment: 5 pages, 5 figures, to be published in the May 2000 issue of the PAS
Acoustic Faraday effect in TbGaO
The transverse acoustic wave propagating along the [100] axis of the cubic
TbGaO (acoustic mode) is doubly degenerate. A magnetic
field applied in the direction of propagation lifts this degeneracy and leads
to the rotation of the polarization vector - the magneto-acoustic Faraday
rotation. Here, we report on the observation and analysis of the
magneto-acoustic Faraday-effect in TbGaO in static and pulsed
magnetic fields. We present also a theoretical model based on magnetoelastic
coupling of 4 electrons to both, acoustic and optical phonons and an
effective coupling between them. This model explains the observed linear
frequency dependence of the Faraday rotation angle
The GALEX-SDSS NUV & FUV Flux Density and Local Star-Formation Rate
We calculate the local UV flux density in the GALEX MIS FUV and NUV bands
using redshifts provided by SDSS DR7. Luminosity functions are calculated for
the overlapping MIS and SDSS sample, allowing flux densities to be measured and
the local star formation rate (SFR) to be calculated using volumes much larger
than previous FUV based estimates. We calculate flux densities for a dust
corrected low redshift (0.013 < z < 0.1) sample of f[FUV] = 22.24 \pm 3.13
\times 10^25 h ergs s^-1 Hz^-1 Mpc^-3, f[NUV] = 38.54 \pm 5.30 \times 10^25 h
ergs s^-1 Hz^-1 Mpc^-3. The star formation rate density found is
0.0312\pm0.0045 h M\odot yr^-1 Mpc^-3. This is larger than published rates
recently found using the UV implied SFR, though the major discrepancy is the
correction made for dust attenuation and once this is dealt with consistently
the results agree well. These values are also consistent with recent Halpha
derived SFRs. Once cosmic variance is taken into account most of the recent
SFRs at low redshift (z < 0.3) found in the literature can be brought into
agreement, however the lowest redshift values (z < 0.045) do appear to be
significantly lower.Comment: 14 pages, 10 figures, accepted for publication in MNRA
Electronic Transport Through a Nuclear-Spin-Polarization-Induced Quantum Wire
Electron transport in a low-dimensional structureâthe nuclear-spin-polarization-induced quantum wire is theoretically studied. In the proposed system the local nuclear-spin polarization creates the effective hyperfine field that confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear-spin polarization. The influence of the nuclear-spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed
The kinematics of ionized gas in lyman-break analogs at z ~ 0.2
We present results for 19 âLyman-break analogsâ observed with Keck/OSIRIS with an adaptive-optics-assisted
spatial resolution of less than 200 pc. We detect satellites/companions, diffuse emission, and velocity shear, all
with high signal-to-noise ratios. These galaxies present remarkably high velocity dispersion along the line of sight
(~70 km s^(â1)), much higher than standard star-forming spirals in the low-redshift universe. We artificially redshift
our data to z ~ 2.2 to allow for a direct comparison with observations of high-z Lyman-break galaxies and find
striking similarities between both samples. This suggests that either similar physical processes are responsible
for their observed properties, or, alternatively, that it is very difficult to distinguish between different mechanisms
operating in the low- versus high-redshift starburst galaxies based on the available data. The comparison between
morphologies in the UV/optical continuum and our kinemetry analysis often shows that neither is by itself sufficient
to confirm or completely rule out the contribution from recent merger events. We find a correlation between the
kinematic properties and stellar mass, in that more massive galaxies show stronger evidence for a disk-like structure.
This suggests a co-evolutionary process between the stellar mass buildup and the formation of morphological and
dynamical substructure within the galaxy
Quenching Star Formation at Intermediate Redshifts: Downsizing of the Mass Flux Density in the Green Valley
The bimodality in galaxy properties has been observed at low and high redshifts, with a clear distinction between star-forming galaxies in the blue cloud and passively evolving objects in the red sequence; the absence of galaxies with intermediate properties indicates that the quenching of star formation and subsequent transition between populations must happen rapidly. In this paper, we present a study of over 100 transiting galaxies in the so-called green valley at intermediate redshifts (z ~ 0.8). By using very deep spectroscopy with the DEIMOS instrument at the Keck telescope we are able to infer the star formation histories of these objects and measure the stellar mass flux density transiting from the blue cloud to the red sequence when the universe was half its current age. Our results indicate that the process happened more rapidly and for more massive galaxies in the past, suggesting a top-down scenario in which the massive end of the red sequence is forming first. This represents another aspect of downsizing, with the mass flux density moving toward smaller galaxies in recent times
Electronic transport through nuclear-spin-polarization-induced quantum wire
Electron transport in a new low-dimensional structure - the nuclear spin
polarization induced quantum wire (NSPI QW) is theoretically studied. In the
proposed system the local nuclear spin polarization creates the effective
hyperfine field which confines the electrons with the spins opposite to the
hyperfine field to the regions of maximal nuclear spin polarization. The
influence of the nuclear spin relaxation and diffusion on the electron energy
spectrum and on the conductance of the quantum wire is calculated and the
experimental feasibility is discussed.Comment: 5 pages, 4 figure
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