466 research outputs found
SuprimeCam Observation of Sporadic Meteors during Perseids 2004
We report the serendipitous findings of 13 faint meteors and 44 artificial
space objects by Subaru SuprimeCam imaging observations during 11-16 August
2004. The meteors, at about 100km altitude, and artificial satellites/debris in
orbit, at 500km altitude or higher, were clearly discriminated by their
apparent defocused image sizes. CCD photometry of the 13 meteors, including 1
Perseid, 1 Aquarid, and 11 sporadic meteors, was performed. We defined a peak
video-rate magnitude by comparing the integrated photon counts from the
brightest portion of the track traversed within 33ms to those from a 0-mag star
during the same time duration. This definition gives magnitudes in the range
4.0< V_{vr} <6.4 and 4.1< I_{vr}<5.9 for these 13 meteors. The corresponding
magnitude for virtual naked-eye observers could be somewhat fainter especially
for the V-band observation, in which the [OI] 5577 line lasting about 1 sec as
an afterglow could contribute to the integrated flux of the present 5-10 min
CCD exposures. Although the spatial resolution is insufficient to resolve the
source size of anything smaller than about 1 m, we developed a new estimate of
the collisionally excited column diameter of these meteors. A diameter as small
as a few mm was derived from their collisionally excited photon rates, meteor
speed, and the volume density of the oxygen atoms at the 100km altitude. The
actual column diameter of the radiating zone, however, could be as large as few
100m because the excited atoms travel that distance before they emit forbidden
lines in 0.7 sec of its average lifetime. Among the 44 artificial space
objects, we confirmed that 17 were cataloged satellites/space debris.Comment: 14 pages, 13 figures, 5 tables, submitted to PAS
Morphologies and Color Gradients of Luminous Evolved Galaxies at z~1.5
We have examined in detail the morphologies of seven z~1.5 passively evolving
luminous red galaxies using high resolution HST NICMOS and ACS imaging data.
Almost all of these galaxies appear to be relaxed systems, with smooth
morphologies at both rest-frame UV and visible wavelengths. Previous results
from spectral synthesis modeling favor a single burst of star formation more
than 1 Gyr before the observed epoch. The prevalence of old stellar
populations, however, does not correlate exclusively with early-type
morphologies as it does in the local universe; the light profiles for some of
these galaxies appear to be dominated by massive exponential disks. This
evidence for massive old disks, along with the apparent uniformity of stellar
age across the disk, suggests formation by a mechanism better described as a
form of monolithic collapse than as a hierarchical merger. These galaxies could
not have undergone a single major merging event since the bulk of their stars
were formed, more than 1 Gyr earlier. There is at least one case, however, that
appears to be undergoing a "dry merger", which may be an example of the process
that converts these unusual galaxies into the familiar spheroids that dominate
galaxies comprising old stellar populations at the present epoch.Comment: 16 pages, 9 figures (8 in color), accepted for publication in Ap
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
Pressure dependence of the superconducting transition temperature in CYb and CCa
We have studied the evolution, with hydrostatic pressure, of the recently
discovered superconductivity in the graphite intercalation compounds CYb
and CCa. We present pressure-temperature phase diagrams, for both
superconductors, established by electrical transport and magnetization
measurements. In the range 0-1.2 GPa the superconducting transition temperature
increases linearly with pressure in both materials with
and for CYb and CCa respectively. The
transition temperature in CYb, which has beenmeasured up to 2.3 GPa,
reaches a peak at around 1.8 GPa and then starts to drop. We also discuss how
this pressure dependence may be explained within a plasmon pairing mechanism.Comment: 4 pages, 3 figure
Spectroscopy of i-Dropout Galaxies with an NB921-Band Depression in the Subaru Deep Field
We report new spectroscopy of two star-forming galaxies with strong Ly_alpha
emission at z=6.03 and z=6.04 in the Subaru Deep Field. These two objects are
originally selected as i'-dropouts (i'-z' > 1.5) showing an interesting
photometric property, the ``NB921 depression''. The NB921-band (centered at
9196A) magnitude is significantly depressed with respect to the z'-band
magnitude. The optical spectra of these two objects exhibit asymmetric
emission-lines at lambda_obs ~ 8540A and ~ 8560A, suggesting that these objects
are Ly_alpha emitters at z~6. The rest-frame equivalent widths of the Ly_alpha
emission of the two objects are 94A and 236A; the latter one is the Ly_alpha
emitter with the largest Ly_alpha equivalent width at z > 6 ever
spectroscopically confirmed. The spectroscopically measured Ly_alpha fluxes of
these two objects are consistent with the interpretation that the NB921
depression is caused by the contribution of the strong Ly_alpha emission to the
z'-band flux. Most of the NB921-depressed i'-dropout objects are thought to be
strong Ly_alpha emitters at 6.0 < z < 6.5; Galactic L and T dwarfs and
NB921-dropout galaxies at z > 6.6 do not dominate the NB921-depressed
i'-dropout sample. Thus the NB921-depression method is very useful for finding
high-z Ly_alpha emitters with a large Ly_alpha equivalent width over a large
redshift range, 6.0 < z < 6.5. Although the broadband-selected sample at z ~ 3
contains only a small fraction of objects with a Ly_alpha equivalent width
larger than 100A, the i'-dropout sample of the Subaru Deep Field contains a
much larger fraction of such strong Ly_alpha emitters. This may imply a strong
evolution of the Ly_alpha equivalent width from z > 6 to z ~ 3.Comment: 21 pages, 6 figures, to appear in The Astrophysical Journa
Discovery of H alpha absorption in the unusual broad absorption line quasar SDSS J083942.11+380526.3
We discovered an H alpha absorption in a broad H alpha emission line of an
unusual broad absorption line quasar, SDSS J083942.11+380526.3 at z=2.318, by
near-infrared spectroscopy with the Cooled Infrared Spectrograph and Camera for
OHS (CISCO) on the Subaru telescope. The Presence of non-stellar H alpha
absorption is known only in the Seyfert galaxy NGC 4151 to date, thus our
discovery is the first case for quasars. The H alpha absorption line is
blueshifted by 520 km/s relative to the H alpha emission line, and its redshift
almost coincides with those of UV low-ionization metal absorption lines. The
width of the H alpha absorption (~ 340 km/s) is similar to those of the UV
low-ionization absorption lines. These facts suggest that the H alpha and the
low-ionization metal absorption lines are produced by the same low-ionization
gas which has a substantial amount of neutral gas. The column density of the
neutral hydrogen is estimated to be ~ 10^18 cm^-2 by assuming a gas temperature
of 10,000 K from the analysis of the curve of growth. The continuum spectrum is
reproduced by a reddened (E(B-V) ~ 0.15 mag for the SMC-like reddening law)
composite quasar spectrum. Furthermore, the UV spectrum of SDSS
J083942.11+380526.3 shows a remarkable similarity to that of NGC 4151 in its
low state, suggesting the physical condition of the absorber in SDSS
J083942.11+380526.3 is similar to that of NGC 4151 in the low state. As
proposed for NGC 4151, SDSS J083942.11+380526.3 may be also seen through the
close direction of the surface of the obscuring torus.Comment: Accepted for publication in Ap
The Number Density of Old Passively-Evolving Galaxies at z=1 in the Subaru/XMM-Newton Deep Survey Field
We obtained the number counts and the rest-frame B-band luminosity function
of the color-selected old passively-evolving galaxies (OPEGs) at z=1 with very
high statistical accuracy using a large and homogeneous sample of about 4000
such objects with z' <25 detected in the area of 1.03 deg^2 in the
Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined
on the i'-z' and R-z' color-magnitude plane so that OPEGs at z=0.9-1.1 with
formation redshift z_f=2-10 are properly sampled. The limiting magnitude
corresponds to the luminosity of galaxies with M_*+3 at z=0. We made a pilot
redshift observations for 99 OPEG candidates with 19 < z' < 22 and found that
at least 78% (73/93) of the entire sample, or 95% (73/77) of these whose
redshifts were obtained are indeed lie between z=0.87 and 1.12 and the most of
their spectra show the continuum break and strong Ca H and K lines, indicating
that these objects are indeed dominated by the old stellar populations. We then
compare our results with the luminosity functions of the color- or the
morphologically-selected early type galaxies at z=0 taking the evolutionary
factor into account and found that the number density of old passive galaxies
with sim M_* magnitude at z~1 averaged over the SXDS area is 40-60% of the
equivalently red galaxies and 60-85% of the morphologically-selected E/S0
galaxies at z=0 depending on their luminosity evolution. It is revealed that
more than half, but not all, of the present-day early-type galaxies had already
been formed into quiescent passive galaxies at z=1.Comment: 28 pages, accepted for publication in Astrophysical Journal. The full
version of the paper including Fig.3 and Fig.4 (large size) in full
resolution is put at
http://optik2.mtk.nao.ac.jp/~yamada/astronomy/sxdsred.htm
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