214 research outputs found
Study on a Mathematical Basis of Critical Path Method and its Application
This paper is concerned with establishing the mathematical basis of the Critical Path Method—a new tool for planning and scheduling projects. The mathematical model upon which the Critical Path Method is based is a parametric linear program that has the objective of computing the utility of a project as a function of its duration. In order to solve the parametric linear program, primal dual algorithm may effectively be used and be solved efficiently by network flow method. This paper contains also the application of this algorithm to the scheduling of quaywall construction at Pier No.8E, Port of Kobe
"Direct" Gas-phase Metallicities, Stellar Properties, and Local Environments of Emission-line Galaxies at Redshift below 0.90
Using deep narrow-band (NB) imaging and optical spectroscopy from the Keck
telescope and MMT, we identify a sample of 20 emission-line galaxies (ELGs) at
z=0.065-0.90 where the weak auroral emission line, [OIII]4363, is detected at
>3\sigma. These detections allow us to determine the gas-phase metallicity
using the "direct'' method. With electron temperature measurements and dust
attenuation corrections from Balmer decrements, we find that 4 of these
low-mass galaxies are extremely metal-poor with 12+log(O/H) <= 7.65 or
one-tenth solar. Our most metal-deficient galaxy has 12+log(O/H) =
7.24^{+0.45}_{-0.30} (95% confidence), similar to some of the lowest
metallicity galaxies identified in the local universe. We find that our
galaxies are all undergoing significant star formation with average specific
star formation rate (SFR) of (100 Myr)^{-1}, and that they have high central
SFR surface densities (average of 0.5 Msun/yr/kpc^2. In addition, more than
two-thirds of our galaxies have between one and four nearby companions within a
projected radius of 100 kpc, which we find is an excess among star-forming
galaxies at z=0.4-0.85. We also find that the gas-phase metallicities for a
given stellar mass and SFR lie systematically below the local M-Z-(SFR)
relation by \approx0.2 dex (2\sigma\ significance). These results are partly
due to selection effects, since galaxies with strong star formation and low
metallicity are more likely to yield [OIII]4363 detections. Finally, the
observed higher ionization parameter and electron density suggest that they are
lower redshift analogs to typical z>1 galaxies.Comment: Accepted for publication in the Astrophysical Journal (15 November
2013). 31 pages in emulateapj format with 16 figures and 7 tables. Revised to
address referee's comments, which include discussion on selection effects,
similarities to green pea galaxies, and nebular continuum contribution.
Modifications were made for some electron temperature and metallicity
measurement
Physical conditions of the interstellar medium in star-forming galaxies at z~1.5
We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118
star-forming galaxies at in the Subaru Deep Field. These galaxies
are selected as [OII]3727 emitters at 1.47 and 1.62 from
narrow-band imaging. We detect H emission line in 115 galaxies,
[OIII]5007 emission line in 45 galaxies, and H,
[NII]6584, and [SII]6716,6731 in 13, 16, and 6
galaxies, respectively. Including the [OII] emission line, we use the six
strong nebular emission lines in the individual and composite rest-frame
optical spectra to investigate physical conditions of the interstellar medium
in star-forming galaxies at 1.5. We find a tight correlation between
H and [OII], which suggests that [OII] can be a good star formation
rate (SFR) indicator for galaxies at . The line ratios of
H/[OII] are consistent with those of local galaxies. We also find that
[OII] emitters have strong [OIII] emission lines. The [OIII]/[OII] ratios are
larger than normal star-forming galaxies in the local Universe, suggesting a
higher ionization parameter. Less massive galaxies have larger [OIII]/[OII]
ratios. With evidence that the electron density is consistent with local
galaxies, the high ionization of galaxies at high redshifts may be attributed
to a harder radiation field by a young stellar population and/or an increase in
the number of ionizing photons from each massive star.Comment: Fixed a minor issue with LaTeX table numberin
A Search for Molecular Gas toward a BzK-selected Star-forming Galaxy at z = 2.044
We present a search for CO(3-2) emission in SDF-26821, a BzK-selected
star-forming galaxy (sBzK) at z = 2.044, using the 45-m telescope of the
Nobeyama Radio Observatory and the Nobeyama Millimeter Array. We do not detect
significant emission and derive 2 \sigma limits: the CO luminosity of L'CO <
3.1 x 10^10 K km s^{-1} pc^{-2}, the ratio of far-infrared luminosity to CO
luminosity of L_FIR/L'CO > 57 Lsun (K km s^{-1} pc^{-2})^{-1}, and the
molecular gas mass of M_H2 < 2.5 x 10^10 Msun, assuming a velocity width of 200
km s^{-1} and a CO-to-H2 conversion factor of alpha_CO=0.8 Msun (K km s^{-1}
pc^{-2})^{-1}. The ratio of L_FIR/L'CO, a measure of star formation efficiency
(SFE), is comparable to or higher than the two z ~ 1.5 sBzKs detected in
CO(2-1) previously, suggesting that sBzKs can have a wide range of SFEs.
Comparisons of far-infrared luminosity, gas mass, and stellar mass among the
sBzKs suggest that SDF-26821 is at an earlier stage of forming stars with a
similar SFE and/or more efficiently forming stars than the two z ~ 1.5 sBzKs.
The higher SFEs and specific star formation rates of the sBzKs compared to
local spirals are indicative of the difference in star formation modes between
these systems, suggesting that sBzKs are not just scaled-up versions of local
spirals.Comment: 4 pages, 4 figures, Accepted for publication in PAS
Large-scale Filamentary Structure around the Protocluster at Redshift z=3.1
We report the discovery of a large-scale coherent filamentary structure of
Lyman alpha emitters in a redshift space at z=3.1. We carried out spectroscopic
observations to map the three dimensional structure of the belt-like feature of
the Lyman alpha emitters discovered by our previous narrow-band imaging
observations centered on the protocluster at z=3.1. The feature was found to
consist of at least three physical filaments connecting with each other. The
result is in qualitative agreement with the prediction of the 'biased'
galaxy-formation theories that galaxies preferentially formed in large-scale
filamentary or sheet-like mass overdensities in the early Universe. We also
found that the two known giant Lyman alpha emission-line nebulae showing high
star-formation activities are located near the intersection of these filaments,
which presumably evolves into a massive cluster of galaxies in the local
Universe. This may suggest that massive galaxy formation occurs at the
characteristic place in the surrounding large-scale structure at high redshift.Comment: 11 pages, 3 figures, accepted for publication in ApJ Letter
Keck Spectroscopy of Lyman-break Galaxies and its Implications for the UV-continuum and Ly_alpha Luminosity Functions at z>6
We present Keck spectroscopic observations of z>6 Lyman-break galaxy (LBG)
candidates in the Subaru Deep Field (SDF). The candidates were selected as
i'-dropout objects down to z'=27 AB magnitudes from an ultra-deep SDF z'-band
image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly_alpha
emission lines at 6< z < 6.4. The median value of the Ly_alpha rest-frame
equivalent widths (EWs) is ~50 A, with four EWs >100 A. This well-defined
spectroscopic sample spans a UV-continuum luminosity range of -21.8<
M_{UV}<-19.5 (0.6~5 L*_{UV}) and a Ly_alpha luminosity range of (0.3~3) x
10^{43} erg s^{-1} (0.3~3 L*_ {Ly_alpha}). We derive the UV and Ly_alpha
luminosity functions (LFs) from our sample at ~6.2 after we correct for
sample incompleteness. We find that our measurement of the UV LF is consistent
with the results of previous studies based on photometric LBG samples at 5<z<7.
Our Ly_alpha LF is also generally in agreement with the results of
Ly_alpha-emitter surveys at z~5.7 and 6.6. This study shows that deep
spectroscopic observations of LBGs can provide unique constraints on both the
UV and Ly_alpha LFs at z>6.Comment: 14 pages, 7 figures, accepted for publication in Ap
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
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