43 research outputs found
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
A photometric survey for Lyalpha-HeII dual emitters: Searching for Population III stars in high-redshift galaxies
We present a new photometric search for high-z galaxies hosting Population
III (PopIII) stars based on deep intermediate-band imaging observations
obtained in the Subaru Deep Field (SDF), by using Suprime-Cam on the Subaru
Telescope. By combining our new data with the existing broad-band and
narrow-band data, we searched for galaxies which emit strongly both in Ly_alpha
and in HeII 1640 (``dual emitters'') that are promising candidates for
PopIII-hosting galaxies, at 3.93<z<4.01 and 4.57<z<4.65. Although we found 10
``dual emitters'', most of them turn out to be [OII]-[OIII] dual emitters or
H_beta-(H_alpha+[NII]) dual emitters at z<1, as inferred from their broad-band
colors and from the ratio of the equivalent widths. No convincing candidate of
Ly_alpha-HeII dual emitter of SFR_PopIII > 2 Msun/yr was found by our
photometric search in 4.03 x 10^5 Mpc^3 in the SDF. This result disfavors low
feedback models for PopIII star clusters, and implies an upper-limit of the
PopIII SFR density of SFRD_PopIII < 5 x 10^-6 Msun/yr/Mpc^3. This new selection
method to search for PopIII-hosting galaxies should be useful in future
narrow-band surveys to achieve the first observational detection of
PopIII-hosting galaxies at high redshifts.Comment: 24 pages, 10 figures, accepted for publication in Ap
Radio and millimeter properties of Ly emitters in the COSMOS field: limits on radio AGN, submm galaxies, and dust obscuration
We present observations at 1.4 and 250 GHz of the Ly
emitters (LAE) in the COSMOS field found by Murayama et al.. At 1.4 GHz there
are 99 LAEs in the lower noise regions of the radio field. We do not detect any
individual source down to 3 limits of Jy beam at 1.4
GHz, nor do we detect a source in a stacking analysis, to a 2 limit of
Jy beam. At 250 GHz we do not detect any of the 10 LAEs that are
located within the central regions of the COSMOS field covered by MAMBO () to a typical 2 limit of mJy. The radio data
imply that there are no low luminosity radio AGN with W Hz in the LAE sample. The radio and millimeter observations
also rule out any highly obscured, extreme starbursts in the sample, ie. any
galaxies with massive star formation rates M year in
the full sample (based on the radio data), or 500 M year for the
10% of the LAE sample that fall in the central MAMBO field. The stacking
analysis implies an upper limit to the mean massive star formation rate of
M year.Comment: 11 pages AAStex format 3 figures. ApJ COSMOS Special Issue. Changes:
Added 'Note added in proof' to reflect nine new sources in the LAE sampl
The HST Cosmos Project: Contribution from the Subaru Telescope
The Cosmic Evolution Survey (COSMOS) is a Hubble Space Telescope (HST)
treasury project.The COSMOS aims to perform a 2 square degree imaging survey of
an equatorial field in (F814W) band, using the Advanced Camera for Surveys
(ACS). Such a wide field survey, combined with ground-based photometric and
spectroscopic data, is essential to understand the interplay between large
scale structure, evolution and formation of galaxies and dark matter. In 2004,
we have obtained high-quality, broad band images of the COSMOS field ( and ) using Suprime-Cam on the Subaru
Telescope, and we have started our new optical multi-band program, COSMOS-21 in
2005. Here, we present a brief summary of the current status of the COSMOS
project together with contributions from the Subaru Telescope. Our future
Subaru program, COSMOS-21, is also discussed briefly.Comment: 4 pages, 3 figures, to appear in the Proceedings of the 6th East
Asian Meeting on Astronomy, JKAS, 39, in pres
Lyman Alpha Emitters at Redshift 5.7 in the COSMOS Field
We present results from a narrow-band optical survey of a contiguous area of
1.95 deg^2, covered by the Cosmic Evolution Survey (COSMOS). Both optical
narrow-band (lambda_c = 8150 AA and Delta_lambda = 120 AA) and broad-band (B,
V, g', r', i', and z') imaging observations were performed with the Subaru
prime-focus camera, Suprime-Cam on the Subaru Telescope. We provide the largest
contiguous narrow-band survey, targetting Ly alpha emitters (LAEs) at z~5.7. We
find a total of 119 LAE candidates at z~5.7. Over the wide-area covered by this
survey, we find no strong evidence for large scale clustering of LAEs. We
estimate a star formation rate (SFR) density of ~7*10^-4 M_sun yr^-1 Mpc^-3 for
LAEs at z~5.7, and compare it with previous measurements.Comment: 26 pages, 19 figures. to appear in the ApJ Supplement COSMOS Special
Issu
A Potential Galaxy Threshing System in the Cosmos Field
We report on the discovery of a new potential galaxy threshing system in the
COSMOS 2 square degree field using the prime-focus camera, Suprime-Cam, on the
8.2 m Subaru Telescope. This system consists of a giant elliptical galaxy with
and a tidally disrupted satellite galaxy with at a photometric redshift of . This redshift is
consistent with the spectroscopic redshift of 0.079 for the giant elliptical
galaxy obtained from the Sloan Digital Sky Survey (SDSS) archive. The
luminosity masses of the two galaxies are
and , respectively. The distance between the
two galaxies is greater than 100 kpc. The two tidal tails emanating from the
satellite galaxy extend over 150 kpc. This system would be the second
well-defined galaxy threshing system found so far.Comment: 17 pages, 7 figures, accepted for the COSMOS special issue of ApJ
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