195 research outputs found
Lyman Break Galaxies at z~5: Rest-frame UV Spectra II
We present the results of spectroscopy of Lyman Break Galaxies (LBGs) at z~5
in the J0053+1234 field with the Faint Object Camera and Spectrograph on the
Subaru telescope. Among 5 bright candidates with z' < 25.0 mag, 2 objects are
confirmed to be at z~5 from their Ly alpha emission and the continuum
depression shortward of Ly alpha. The EWs of Ly alpha emission of the 2 LBGs
are not so strong to be detected as Ly alpha emitters, and one of them shows
strong low-ionized interstellar (LIS) metal absorption lines. Two faint objects
with z' \geq 25.0 mag are also confirmed to be at z~5, and their spectra show
strong Ly alpha emission in contrast to the bright ones. These results suggest
a deficiency of strong Ly alpha emission in bright LBGs at z~5, which has been
discussed in our previous paper. Combined with our previous spectra of LBGs at
z~5 obtained around the Hubble Deep Field-North (HDF-N), we made a composite
spectrum of UV luminous (M_1400 \leq -21.5 mag) LBGs at z~5. The resultant
spectrum shows a weak Ly alpha emission and strong LIS absorptions which
suggests that the bright LBGs at z~5 have chemically evolved at least to ~0.1
solar metallicity. For a part of our sample in the HDF-N region, we obtained
near-to-mid infrared data, which constraint stellar masses of these objects.
With the stellar mass and the metallicity estimated from LIS absorptions, the
metallicities of the LBGs at z~5 tend to be lower than those of the galaxies
with the same stellar mass at z \lesssim 2, although the uncertainty is very
large.Comment: 17 pages, 5 figures, accepted for publication in PAS
Seismological evidence of simultaneous mountain-building and crust-thickening from the 1999 Taiwan Chi-Chi earthquake (Mw=7.6)
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
Lyman Break Galaxies at : Rest-Frame UV Spectra
We report initial results for spectroscopic observations of candidates of
Lyman Break Galaxies (LBGs) at in a region centered on the Hubble Deep
Field-North by using the Faint Object Camera and Spectrograph attached to the
Subaru Telescope. Eight objects with mag, including one AGN, are
confirmed to be at . The rest-frame UV spectra of seven LBGs
commonly show no or weak Lyalpha emission line (rest-frame equivalent width of
0-10\AA) and relatively strong low-ionization interstellar metal absorption
lines of SiII 1260, OI+SiII 1303, and CII 1334 (mean
rest-frame equivalent widths of them are \AA). These
properties are significantly different from those of the mean rest-frame UV
spectrum of LBGs at , but are quite similar to those of subgroups of
LBGs at with no or weak Lyalpha emission. The weakness of Lyalpha
emission and strong low-ionization interstellar metal absorption lines may
indicate that these LBGs at are chemically evolved to some degree and
have a dusty environment. Since the fraction of such LBGs at in our
sample is larger than that at , we may witness some sign of evolution
of LBGs from to , though the present sample size is very
small. It is also possible, however, that the brighter LBGs tend to show no or
weak Lyalpha emission, because our spectroscopic sample is bright (brighter
than ) among LBGs at . More observations are required to
establish spectroscopic nature of LBGs at .Comment: 16 pages, 3 figures, accepted by Ap
GPS Medium-Range Kinematic Positioning for the Seafloor Geodesy of Eastern Taiwan
To realize the plate motion of the Philippine Sea Plate (PSP) and the characteristics of crustal deformation in the plate boundary zone between the PSP and Eurasia Plate, three seafloor geodetic arrays using a combination of GPS kinematic positioning and acoustic ranging techniques have been established off eastern Taiwan since 2008. Each array is composed of three transponders deployed on the ocean bottom in a triangular shape and has been observed at least two times since 2009. The GPS kinematic positioning in the relative distance ranging from 80 to 120 km off the eastern coast of Taiwan plays a main role in the whole seafloor geodetic deformation system. Seven stations from Taiwan Continuous GPS Array are taken as reference sites and three or four rover GPS units are set up on the vessel or buoy. Both on-land reference and onboard rover receivers record data in sampling rates of 1 and 5 Hz to determine the instantaneous positions of transducer onboard which transmits and receives the acoustic signal to and from seafloor transponders and the attitude of vessel or buoy in kinematic mode. We compare the results of medium-range kinematic positioning between the on-land reference stations and rovers onboard by the GrafNav and Bernese V5.0 software, respectively. In addition, we determine the attitude at all times by way of computing the inter-distance of rover receivers onboard. Hence there are two positioning results can be estimated which are direct (by short relative distances from onboard) and indirect (by medium-range kinematic mode for each GPS unit from on-land continuous stations) methods, and the difference reveals in decimeter level
CO Observations of a FeLoBAL Quasar with an H alpha Absorption Line at z=2.3
SDSS J083942.11+380526.3 is an Iron Low-ionization Broad Absorption Line
(FeLoBAL) quasar at z = 2.3, and Aoki et al. (2006) recently found the presence
of an H alpha absorption line in the broad H alpha emission line. Motivated by
an idea that this quasar may be a huge molecular gas reservoir in the early
phase of quasar evolution, we made CO(J=3-2) observations of it using the
Nobeyama Millimeter Array. No significant CO emission was detected; although an
emission-like feature (2.5 sigma) was seen close (~ 2") to the quasar, we
regard it as a noise. The obtained 3 sigma upper limit on the CO luminosity is
L'_{{\rm CO}(J=3-2)} = 4.5 \times 10^{10} K km/s pc^2, which corresponds to
M({\rm H}_2) = 3.6 times 10^10 M_{\odot} if we adopt the CO-to-H_2 conversion
factor of 0.8 M_{\odot} (K km/s pc^2)^{-1}. This upper limit is comparable to
L'_{{\rm CO}(J=3-2)} (and thus the molecular gas mass) detected in quasars and
BAL quasars at z=1-3, and no sign of the presence of the huge amount of
molecular gas in this FeLoBAL quasar was obtained.Comment: 7 pages, 1 figure. Accepted by PAS
Earthquake Doublet Sequences: Evidence of Static Triggering in the Strong Convergent Zones of Taiwan
Three earthquake sequences, each with two main earthquakes of almost the same magnitudes (ML from 5.9 to 7.0 with differences less than 0.1), have recently been observed in Taiwan. The two largest earthquakes in each sequence occurred with a short delay time between them, were strikingly similar in terms of magnitude, location and/or focal mechanism and are referred to as doublets. They were markedly distinct from typical single mainshock sequences. Our estimated static stress field generated by the first shock in the doublet shows that the second shock and most of their aftershocks were located within a region where static stress increased substantially. Thus, a possible explanation for earthquake doublet is that seismic energy for each shock had accumulated independently within adjacent crustal volumes, separated by an asperity, and that the second shock is triggered by the increased static stress after the first one. An important implication of doublet sequence is that works by emergency response teams after the first earthquake could be made more hazardous by the second
The potential for a great earthquake along the southernmost Ryukyu subduction zone
Interseismic GPS data along the Hualien-Suao coast
(NE Taiwan) shows a pattern of strain accumulation that is
consistent with a potential future large shallow earthquake
along the southernmost Ryukyu subduction zone. The
measured shortening rate parallel to the Ryukyu Trench
is 80 mm/yr, about twice of the shortening rate perpendicular to the Ryukyu Trench. We invert for slip-deficit rates and the geometric configuration of the plate interface. Our preferred fault model dips 10° northward and extends about 70 km from the Ryukyu Trench to a depth of 13 km. The slip deficit rate exhibits a left-lateral motion of 78 mm/yr and a normal motion of 36 mm/yr on a 290°-trending fault. The slip rate budget of the southernmost Ryukyu subduction zone is close to the plate convergence rate, suggesting the plate interface is fully locked. Assessments of seismic hazard in this region need to consider the potential threat from M_w 7.5~8.7 tsunami earthquakes generated by shallow ruptures
Adaptive Optics Rest-Frame V-band Imaging of Lyman Break Galaxies at z~3: High-surface Density Disk-like Galaxies ?
In order to reveal the rest-frame V-band morphology of galaxies at z~3, we
conducted AO-assisted K-band imaging observations of z~3 LBGs with Mv*-0.5 to
Mv*+3.0 mag. LBGs brighter than Mv* have larger rHL (0.40") than the fainter
LBGs (0.23") on average, and there is no bright LBGs with a small rHL. The LBGs
brighter than Mv* have red rest-frame U-V colors (average of 0.2 mag) and most
of the fainter LBGs show blue rest-frame U-V colors (average of -0.4 mag). The
K-band peaks of some of the LBGs brighter than K=22.0 mag show significant
shift from those in the optical images. The images of all but one of the LBGs
with K<21.5 mag are fitted well with Sersic profile with n index less than 2,
similar to disk galaxies in the local universe. Assuming that the LBGs have a
disk-shape, we compared their size-luminosity and size-stellar mass relation
with those of z=0 and z=1 disk galaxies. The LBGs are brighter than z=0 and z=1
disk galaxies at the same effective radius. The rest-frame V-band surface
brightness of the LBGs are 2.2-2.9 mag and 1.2-1.9 mag brighter than the disk
galaxies at z=0 and z=1, respectively. The size-stellar mass relation of the
LBGs shows that the effective radii of the LBGs do not depend on their stellar
mass. For the LBGs brighter than Mv*, the average surface stellar mass density
is 3-6 times larger than those of the z=0 and z=1 disk galaxies. We also
examine the profiles of the serendipitously observed DRGs. They are also fitted
with the Sersic profiles with n<2. The implications of the dominance of n<2
population among galaxies at z~3 and the presence of the high surface stellar
mass density disk systems are discussed.Comment: Accepted for publication in Astrophysical Journal Supplement. 38
pages, 26 postscript figures. Original version with high resolution figures
is available from http://www.naoj.org/staff/akiyama/papers/LBG_AO.pd
- …