29 research outputs found
Lyman Emitters beyond Redshift 5:The Dawn of Galaxy Formation
The 8m class telescopes in the ground-based optical astronomy together with
help from the ultra-sharp eye of the Hubble Space Telescope have enabled us to
observe forming galaxies beyond redshift . In particular, more than twenty
Ly-emitting galaxies have already been found at . These findings
provide us with useful hints to investigate how galaxies formed and then
evolved in the early universe. Further, detailed analysis of Ly
emission line profiles are useful in exploring the nature of the intergalactic
medium because the trailing edge of cosmic reionization could be close to -- 7, at which forming galaxies have been found recently. We also
discuss the importance of superwinds from forming galaxies at high redshift,
which has an intimate relationship between galaxies and the intergalactic
medium. We then give a review of early cosmic star formation history based on
recent progress in searching for Ly-emitting young galaxies beyond
redshift 5.Comment: 23 pages, 12 figures, jkas35.sty. To appear in the proceedings of the
APCTP WoFormation and Interaction of Galaxies, edited by Hyung Mok Leerkshop
o
The Halpha Luminosity Function of the Galaxy Cluster Abell 521 at z = 0.25
We present an optical multicolor-imaging study of the galaxy cluster Abell
521 at , using Suprime-Cam on the Subaru Telescope, covering an area
of arcmin ( Mpc at ). Our imaging data taken with both a narrow-band filter,
(\AA and \AA), and broad-band filters,
, and allow us to find 165 H
emitters. We obtain the H luminosity function (LF) for the cluster
galaxies within 2 Mpc; the Schechter parameters are ,
Mpc, and erg s. Although the faint end slope, , is consistent with
that of the local cluster H LFs, the characteristic luminosity,
, is about 6 times (or mag) brighter. This strong
evolution implies that Abell 521 contains more active star-forming galaxies
than the local clusters, being consistent with the observed Butcher-Oemler
effect. However, the bright of Abell 521 may be, at least in part,
due to the dynamical condition of this cluster.Comment: 21 pages, 7 figures, ApJ, Part 1, in pres
The Effects of Resonant Tunneling on Magnetoresistance through a Q uantum Dot
The effect of resonant tunneling on magnetoresistance (MR) is studied
theoretically in a double junction system. We have found that the ratio of the
MR of the resonant peak current is reduced more than that of the single
junction, whereas that of the valley current is enhanced depending on the
change of the discrete energy-level under the change of magnetic field. We also
found that the peak current-valley current (PV) ratio decreases when the
junction conductance increases.Comment: 11 pages, 3 figures(mail if you need), use revtex.st
Are Two z~6 Quasars Gravitationally Lensed ?
Several high-z (z > 5.7) quasars have been found in the course of Sloan
Digital Sky Survey. The presence of such very high-z quasars is expected to
give constraints on early structure formation. On one hand, it is suggested
that these most luminous objects at high redshift are biased toward the highly
magnified objects by gravitational lensing. To clarify the effect of
gravitational lensing on the high-z quasars, we began the imaging survey of
intervening lensing galaxies. Indeed our previous optical image showed that
SDSSp J104433.04+012502.2 at z=5.74 is gravitationally magnified by a factor 2.
In this paper, we report our new optical imaging of other two high-z quasars,
SDSSp J103027.10+052455.0 at z=6.28 and SDSSp J130608.26+035626.3 at z=5.99.
Since we find neither intervening galaxy nor counter image with i^{\prime} <
25.4-25.8 around each quasar, we conclude that they are not strongly magnified
regardless that a lens galaxy is dusty.Comment: 10 pages, 8 figures, Accepted for PAS
SDSSp J104433.04012502.2 at is Gravitationally Magnified by an Intervening Galaxy
During the course of our optical deep survey program on L emitters at
in the sky area surrounding the quasar SDSSp
J104433.04012502.2 at , we found that a faint galaxy with (AB)
is located at \timeform{1".9} southwest of the quasar. Its
broad-band color properties from to suggest that the galaxy is
located at a redshift of -- 2.5. This is consistent with no strong
emission line in our optical spectroscopy. Since the counter image of the
quasar cannot be seen in our deep optical images, the magnification factor
seems not to be very high. Our modest estimate is that this quasar is
gravitationally magnified by a factor of 2.Comment: 11 pages, 5 figures, PASJ, in pres
The Discovery of a Very Narrow-Line Star Forming Obat a Redshift of 5.66ject
We report on the discovery of a very narrow-line star forming object beyond
redshift of 5. Using the prime-focus camera, Suprime-Cam, on the 8.2 m Subaru
telescope together with a narrow-passband filter centered at
= 8150 \AA with passband of = 120 \AA, we have obtained a very
deep image of the field surrounding the quasar SDSSp J104433.04012502.2 at a
redshift of 5.74. Comparing this image with optical broad-band images, we have
found an object with a very strong emission line. Our follow-up optical
spectroscopy has revealed that this source is at a redshift of
, forming stars at a rate
yr. Remarkably, the velocity dispersion of Ly-emitting gas is
only 22 km s. Since a blue half of the Ly emission could be
absorbed by neutral hydrogen gas, perhaps in the system, a modest estimate of
the velocity dispersion may be 44 km s. Together with a linear
size of 7.7 kpc, we estimate a lower limit of the dynamical mass
of this object to be . It is thus suggested that
LAE J10440123 is a star-forming dwarf galaxy (i.e., a subgalactic object or
a building block) beyond redshift 5 although we cannot exclude a possibility
that most Ly emission is absorbed by the red damping wing of neutral
intergalactic matter.Comment: 6 pages, 2 figures. ApJ Letters, in pres
The HI content of star-forming galaxies at z = 0.24
We use observations from the Giant Metrewave Radio Telescope (GMRT) to
measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24
(i.e. a look-backtime of ~3 Gyr). The sample of galaxies studied were selected
from Halpha-emitting field galaxies detected in a narrow-band imaging survey
with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain
precise optical redshifts for these galaxies. We then coadded the HI 21 cm
emission signal for all the galaxies within the GMRT spectral line data cube.
From the coadded signal of 121 galaxies, we measure an average atomic
hydrogen gas mass of (2.26 +- 0.90)*10^9 solar masses. We translate this HI
signal into a cosmic density of neutral gas at z = 0.24 of Omega_gas = (0.91 +-
0.42)*10^-3. This is the current highest redshift at which Omega_gas has been
constrained from 21 cm emission and our value is consistent with that estimated
from damped Lyman-alpha systems around this redshift. We also find that the
correlations between the Halpha luminosity and the radio continuum luminosity
and between the star formation rate and the HI gas content in star-forming
galaxies at z = 0.24 are consistent with the correlations found at z = 0. These
two results suggest that the star formation mechanisms in field galaxies ~3 Gyr
ago were not substantially different from the present, even though the star
formation rate is 3 times higher.Comment: 11 pages, contains 9 figures and 1 table. Accepted for publishing in
MNRAS 2007 January 22. Received 2007 January 22; in original form 2006
November 3
A Subaru Search for Lyman-Alpha Emitters at z=5.8 with an Intermediate-Band Filter
We present the results of a survey for Ly-alpha emitters at z ~ 5.8 using a
new intermediate-band filter centered at lambda_c = 8275 AA with
Delta-lambda_FWHM = 340 AA (i.e., the spectroscopic resolution is R ~ 23) with
a combination with a traditional narrow-band centered at lambda_c = 8150 AA
with
Delta-lambda_FWHM = 120 AA (R ~ 68). Our observations were made with use of
the Subaru Prime Focus Camera, Suprime-Cam, on the 8.2 m Subaru telescope in a
sky area surrounding the high redshift quasar, SDSSp J104433.04-012522.2 at
z=5.74, covering an effective sky area with ~ 720 arcmin^2. In this survey, we
have found four Ly-alpha-emitter candidates from the intermediate-band image (z
\~ 5.8 with Delta z ~ 0.3). Combined with our previous results based on the
NB816 imaging, we discuss the star formation activity in galaxies between z ~
5.7 and z ~ 5.9.Comment: 8 pages, 8 figures. Accepted for publication in PAS
The Subaru Deep Field Project: Lyman Emitters at Redshift of 6.6
We present new results of a deep optical imaging survey using a narrowband
filter () centered at 9196 \AA ~ together with , ,
, , and broadband filters in the sky area of the Subaru
Deep Field which has been promoted as one of legacy programs of the 8.2m Subaru
Telescope. We obtained a photometric sample of 58 Ly emitter candidates
at 6.5 -- 6.6 among strong -excess () objects together with a color criterion of . We then obtained optical spectra of 20 objects in our -excess
sample and identified at least nine Ly emitters at -- 6.6
including the two emitters reported by Kodaira et al. (2003). Since our
Ly emitter candidates are free from strong amplification of
gravitational lensing, we are able to discuss their observational properties
from a statistical point of view. Based on these new results, we obtain a lower
limit of the star formation rate density of yr Mpc at , being
consistent with our previous estimate. We discuss the nature of star-formation
activity in galaxies beyond .Comment: 49 pages, 16 figures, PASJ, Vol. 57, No. 1, in pres
A Subaru Search for Lyman Emitters at Redshift 5.7
We present the results of a survey for Ly emitters at
based on optical narrow-band ( \AA ~ and \AA), and broad-band (, , , and )
observations of the field surrounding the high redshift quasar, SDSSp
J104433.04012522.2, on the 8.2 m Subaru Telescope with the Subaru Prime
Focus Camera, Suprime-Cam. This survey covers a sky area of
arcmin and a co-moving volume of
Mpc. We have found 20 candidates of Ly emitters at 5.7
with . Two of them have been confirmed star-forming
galaxies at and from our follow-up optical spectroscopy. We
discuss star-formation properties of the 20 objects from a statistical point of
view. Our survey leads to a new estimate of the star formation rate density at
, yr
Mpc.Comment: 18 pages, 19 figures, accepted for A