53 research outputs found
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
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
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
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
Near-Infrared Spectroscopy of the Cool Brown Dwarf, SDSS 1624+00
Using the Subaru Telescope, we have obtained multiple near-infrared spectra
of the cool brown dwarf, SDSS 1624+00, in search of spectral variability in an
80 minute time span. We have found the suspected variability of water vapor
absorption throughout the observations, which requires confirmation by a longer
time baseline. After coadding the spectra, we have obtained a high-quality
spectrum covering 1.05 to 1.8 um. Three kinds of spectral indicators, the water
vapor bands, methane band, and KI lines in J band, suggest that SDSS 1624+00 is
warmer and dustier than Gl 229B.Comment: 6 figures, to appear in PAS
Diffuse Extragalactic Background Light versus Deep Galaxy Counts in the Subaru Deep Field: Missing Light in the Universe?
Deep optical and near-infrared galaxy counts are utilized to estimate the
extragalactic background light (EBL) coming from normal galactic light in the
universe. Although the slope of number-magnitude relation of the faintest
counts is flat enough for the count integration to converge, considerable
fraction of EBL from galaxies could still have been missed in deep galaxy
surveys because of various selection effects including the cosmological dimming
of surface brightness of galaxies. Here we give an estimate of EBL from galaxy
counts, in which these selection effects are quantitatively taken into account
for the first time, based on reasonable models of galaxy evolution which are
consistent with all available data of galaxy counts, size, and redshift
distributions. We show that the EBL from galaxies is best resolved into
discrete galaxies in the near-infrared bands (J, K) by using the latest data of
the Subaru Deep Field; more than 80-90% of EBL from galaxies has been resolved
in these bands. Our result indicates that the contribution by missing galaxies
cannot account for the discrepancy between the count integration and recent
tentative detections of diffuse EBL in the K-band (2.2 micron), and there may
be a very diffuse component of EBL which has left no imprints in known galaxy
populations.Comment: ApJ Letters in press. Two new reports on the diffuse EBL at 1.25 and
2.2 microns are added to the reference list and Table
A Study of Selection Methods for H alpha Emitting Galaxies at z~1.3 for the Subaru/FMOS Galaxy Redshift Survey for Cosmology (FastSound)
The efficient selection of high-redshift emission galaxies is important for
future large galaxy redshift surveys for cosmology. Here we describe the target
selection methods for the FastSound project, a redshift survey for H alpha
emitting galaxies at z=1.2-1.5 using Subaru/FMOS to measure the linear growth
rate f\sigma 8 via Redshift Space Distortion (RSD) and constrain the theory of
gravity. To select ~400 target galaxies in the 0.2 deg^2 FMOS field-of-view
from photometric data of CFHTLS-Wide (u*g'r'i'z'), we test several different
methods based on color-color diagrams or photometric redshift estimates from
spectral energy distribution (SED) fitting. We also test the improvement in
selection efficiency that can be achieved by adding near-infrared data from the
UKIDSS DXS (J). The success rates of H alpha detection with FMOS averaged over
two observed fields using these methods are 11.3% (color-color, optical), 13.6%
(color-color, optical+NIR), 17.3% (photo-z, optical), and 15.1% (photo-z,
optical+NIR). Selection from photometric redshifts tends to give a better
efficiency than color-based methods, although there is no significant
improvement by adding J band data within the statistical scatter. We also
investigate the main limiting factors for the success rate, by using the sample
of the HiZELS H alpha emitters that were selected by narrow-band imaging.
Although the number density of total H alpha emitters having higher H alpha
fluxes than the FMOS sensitivity is comparable with the FMOS fiber density, the
limited accuracy of photometric redshift and H alpha flux estimations have
comparable effects on the success rate of <~20% obtained from SED fitting.Comment: 12 pages, 7 figures, accepted to PAS
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