746 research outputs found
FeII/MgII Emission Line Ratios of QSOs. II. z>6 Objects
Near-infrared spectra of four QSOs located at are obtained with the
OH-airglow suppressor mounted on the Subaru telescope. The FeII/MgII
emission-line ratios of these QSOs are examined by the same fitting algorithm
as in our previous study of QSOs. The fitting results show that two out
of the four QSOs have significant FeII emission in their rest-UV spectra,
while the other two have almost no FeII features. We also applied our fitting
algorithm to more than 10,000 SDSS QSOs and found two trends in the
distribution of FeII/MgII against redshift: (1) the upper envelope of the
FeII/MgII distribution at shows a probable declination toward high
redshift, and (2) the median distribution settles into lower ratios at with small scatter compared to the other redshift. We discuss an Fe/Mg
abundance evolution of QSOs with a substantial contribution from the diverse
nature of the broad-line regions in high-redshift QSOs.Comment: 12 pages, 2 figures. Accepted for publication in ApJ (10 October
2004, v614
OHS: OH-airglow Suppressor for the Subaru Telescope
This paper describes an OH-airglow Suppressor (OHS) for the infrared Nasmyth
focus of the Subaru telescope. OHS has the capability of eliminating 224
airglow-lines in the - and -bands, which are major sources of background
radiation at near-infrared wavelengths up to 2 m. Specifically, it is a
pre-optics system installed between the telescope and an infrared
camera/spectrograph (CISCO). The suppressor reduces sky background emissions to
1/25 and its throughput is 40%. As a result, the S/N gain achieved with OHS is
more than 1 mag compared to the typical spectroscopic approach. The limiting
magnitude measured during a test observing run was found to be = 21.1 mag
( = 210, S/N = 5) in the standard 4000 s exposure
sequence.Comment: 6 pages, 9 figures. Accepted for publication in PASJ(2001
Nature of a Strongly-Lensed Submillimeter Galaxy SMM J14011+0252
We have carried out near-infrared JHK spectroscopy of a gravitationally
lensed submillimeter galaxy SMM J14011+0252 at z=2.565, using OHS and CISCO on
the Subaru telescope. This object consists of two optical components, J1 and
J2, which are lensed by the cluster Abell 1835. J1 suffers additional strong
lensing by a foreground galaxy at z=0.25 in the cluster. The rest-optical
H-alpha, H-beta, and [O II]3727 lines are detected in both J1 and J2, and [N
II]6548,6583 lines are also detected in J1. A diagnosis of emission-line ratios
shows that the excitation source of J1 is stellar origin, consistent with
previous X-ray observations. The continua of J1 and J2 show breaks at rest
4000A, indicating relatively young age. Combined with optical photometry, we
have carried out model spectrum fitting of J2 and find that it is a very young
(~50 Myr) galaxy of rather small mass (~10e8 M_sol) which suffers some amount
of dust extinction. A new gravitational lensing model is constructed to assess
both magnification factor and contamination from the lensing galaxy of the
component J1, using HST-F702W image. We have found that J1 suffers strong
lensing with magnification of ~30, and its stellar mass is estimated to be <
10e9 M_sol. These results suggest that SMM J14011+0252 is a major merger system
at high redshift that undergoes intense star formation, but not a formation
site of a giant elliptical. Still having plenty of gas, it will transform most
of the gas into stars and will evolve into a galaxy of < 10e10 M_sol.
Therefore, this system is possibly an ancestor of a less massive galaxy such as
a mid-sized elliptical or a spiral at the present.Comment: 21 pages, 11 figures. Accepted for publication in Astronomical
Journa
The relation between quasars' optical spectra and variability
This work aimed to find the relationship between quasars' optical variability
and spectral features to reveal the regularity behind the random variation. It
is known that quasar's FeII/Hbeta flux ratio and equivalent width of [OIII]5007
are negatively correlated, called Eigenvector 1. In this work, we visualized
the relationship between the position on this Eigenvector 1 (EV1) plane and how
they had changed their brightness after ~10 years. We conducted three analyses
using different quasar samples each. The first analysis showed the relation
between their distributions on the EV1 plane and how much they had changed
brightness, using 13,438 Sloan Digital Sky Survey quasars. This result shows
how brightness changes later are clearly related to the position on the EV1
plane. In the second analysis, we plotted the sources reported as
Changing-Look(State) Quasars on the EV1 plane. This result shows that the
position on the EV1 plane corresponds activity level of each source, the bright
or dim state of them are distributed on the opposite sides divided by the
typical quasar distribution. In the third analysis, we examined the transition
vectors on the EV1 plane using sources with multiple-epoch spectra. This result
shows that the brightening and dimming sources move on the similar path and
they turn into the position corresponding to the opposite activity level. We
also found this trend is opposite to the empirical rule that RFeII positively
correlated with the Eddington ratio, which has been proposed based on the
trends of a large number of quasars. From all these analyses, it is indicated
that quasars tend to oscillate between both sides of the distribution ridge on
the EV1 plane; each of them corresponds to a dim state and a bright state. This
trend in optical variation suggests that significant brightness changes, such
as Changing-Look quasars, are expected to repeat.Comment: 12 pages, 4 figures, 1 table. Accepted for publication in PAS
Constraint on the inflow/outflow rates in star-forming galaxies at z~1.4 from molecular gas observations
We constrain the rate of gas inflow into and outflow from a main-sequence
star-forming galaxy at z~1.4 by fitting a simple analytic model for the
chemical evolution in a galaxy to the observational data of the stellar mass,
metallicity, and molecular gas mass fraction. The molecular gas mass is derived
from CO observations with a metallicity-dependent CO-to-H2 conversion factor,
and the gas metallicity is derived from the H{\alpha} and [NII]{\lambda} 6584
emission line ratio. Using a stacking analysis of CO integrated intensity maps
and the emission lines of H{\alpha} and [NII], the relation between stellar
mass, metallicity, and gas mass fraction is derived. We constrain the inflow
and outflow rates with least-chi-square fitting of a simple analytic chemical
evolution model to the observational data. The best-fit inflow and outflow
rates are ~1.7 and ~0.4 in units of star-formation rate, respectively. The
inflow rate is roughly comparable to the sum of the star-formation rate and
outflow rate, which supports the equilibrium model for galaxy evolution; i.e.,
all inflow gas is consumed by star formation and outflow.Comment: 5 pages, 2 figures, Accepted for publication in the Ap
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