16,903 research outputs found
JHK Spectra of the z=2.39 Radio Galaxy 53W002
We present low-resolution, near-IR JHK spectra of the weak z=2.39 radio
galaxy 53W002, obtained with the OH-airglow Suppressor spectrograph (OHS) and
Cooled Infrared Spectrograph and Camera for OHS (CISCO) on the Subaru
Telescope. They cover rest-frame wavelengths of 3400-7200 A, and the emission
lines of [O II]3727, Hb, [O III]4959, 5007, Ha, [N II]6548, 6583 and [S
II]6716, 6731 were detected. Using the Ha/Hb line ratio, we find an extinction
of E(B-V)=0.14. The emission-line ratios are reproduced by a cloud of electron
density n_e=1x10^{3-4}(/cm3) with solar metallicity, ionized by an alpha=-0.7
power-law continuum with ionizing parameter U=1x10^-3. In addition to these
emission lines, we make the first spectroscopic confirmation of the Balmer
discontinuity in a high-z radio galaxy. Together with rest-frame UV photometry
from the literature, we show that at least 1/3 of the present stellar mass was
formed in the current starburst. The stellar mass was estimated to be
(1-1.4)x10^11 M_sol by one-component model fitting, which is smaller than that
of typical z~1 B2/6C radio galaxies. We suggest that 53W002 is currently
assembling a large part of its stellar mass through merger events with the
surrounding sub-galactic clumps, some of which can be identified with the Lya
emitters detected in narrow-band imaging. After a few such events over the next
few Gyr, 53W002 will evolve into a massive elliptical galaxy.Comment: 10 pages, including 11 figures. Accepted for publication in
PASJ(2001). Revised 5/15/200
Investigation of ion induced bending mechanism for nanostructures
Ion induced bending is a promising controlled technique for manipulating nanoscale structures. However, the underlying mechanism of the process is not well understood. In this letter, we report a detailed study of the bending mechanism of Si nanowires (NWs) under Ga+ irradiation. The microstructural changes in the NW due to ion beam irradiation are studied and molecular dynamics simulations are used to explore the ion–NW interaction processes. The simulation results are compared with the microstructural studies of the NW. The investigations inform a generic understanding of the bending process in crystalline materials, which we suggest to be feasible as a versatile manipulation and integration technique in nanotechnology
Lifetimes of ultralong-range strontium Rydberg molecules in a dense BEC
The lifetimes and decay channels of ultralong-range Rydberg molecules created
in a dense BEC are examined by monitoring the time evolution of the Rydberg
population using field ionization. Studies of molecules with values of
principal quantum number, , in the range to that contain tens
to hundreds of ground state atoms within the Rydberg electron orbit show that
their presence leads to marked changes in the field ionization characteristics.
The Rydberg molecules have lifetimes of s, their destruction
being attributed to two main processes: formation of Sr ions through
associative ionization, and dissociation induced through -changing
collisions. The observed loss rates are consistent with a reaction model that
emphasizes the interaction between the Rydberg core ion and its nearest
neighbor ground-state atom. The measured lifetimes place strict limits on the
time scales over which studies involving Rydberg species in cold, dense atomic
gases can be undertaken and limit the coherence times for such measurements.Comment: 9 pages, 8 figure
ASCA Discovery of an X-ray Pulsar in the Error Box of SGR1900+14
We present a 2 - 10 keV ASCA observation of the field around the soft gamma
repeater SGR1900+14. One quiescent X-ray source was detected in this
observation, and it was in the SGR error box. In 2 - 10 keV X-rays, its
spectrum may be fit by a power law with index -2.2, and its unabsorbed flux is
9.6 x 10^-12 erg cm^-2 s^-1. We also find a clear 5.16 s period. The properties
of the three well-studied soft gamma repeaters are remarkably similar to one
another, and provide evidence that all of them are associated with young,
strongly magnetized neutron stars in supernova remnants.Comment: Accepted for publication in the Astrophysical Journal Letter
[OII]3727 Emission from the Companion to the Quasar BR 1202-0725 at z=4.7
Results of a narrow-band imaging for the redshifted [OII]3727 emission around
a quasar at z=4.7 obtained with the Subaru telescope and CISCO (a Cassegrain
near infrared camera) are presented. A significant emission line is detected in
the narrow-band H_2 (v=1-0 S(1)) filter at a location 2.4" northwest from the
quasar, where the presence of a companion has been reported in Lyman alpha
emission and the rest-frame UV continuum. We identify this line as [OII]3727
emission and confirm that the source really is a companion at z=4.7. The
[OII]3727 flux from the companion is estimated to be 2.5 x 10^{-17} erg s^{-1}
cm^{-2}. If the companion is a star forming object, the inferred star formation
rate is as high as 45-230 M_{solar} yr^{-1} even without assuming the
extinction correction. This value is higher than those derived from the Lyman
alpha emission or from the UV continuum. Thus, provided that the difference is
caused by dust extinction, the extinction corrected star formation rate is
calculated to be 45 to 2300 M_{solar} yr^{-1} depending on the assuming
extinction curves.Comment: 15 pages including 3 figures. Accepted for publication in PAS
- …