68 research outputs found
CO Multi-line Imaging of Nearby Galaxies (COMING). IX. CO(=2-1)/CO(=1-0) line ratio on kiloparsec scales
While molecular gas mass is usually derived from CO(=1-0) - the
most fundamental line to explore molecular gas - it is often derived from
CO(=2-1) assuming a constant CO(=2-1)/CO(=1-0)
line ratio (). We present variations of and effects of the
assumption that is a constant in 24 nearby galaxies using CO
data obtained with the Nobeyama 45-m radio telescope and IRAM 30-m telescope.
The median of for all galaxies is 0.61, and the weighted mean of
by CO(=1-0) integrated-intensity is 0.66 with a standard
deviation of 0.19. The radial variation of shows that it is high
(~0.8) in the inner ~1 kpc while its median in disks is nearly constant at 0.60
when all galaxies are compiled. In the case that the constant of 0.7
is adopted, we found that the total molecular gas mass derived from
CO(=2-1) is underestimated/overestimated by ~20%, and at most by 35%.
The scatter of a molecular gas surface density within each galaxy becomes
larger by ~30%, and at most by 120%. Indices of the spatially resolved
Kennicutt-Schmidt relation by CO(=2-1) are underestimated by 10-20%,
at most 39% in 17 out of 24 galaxies. has good positive correlations
with star-formation rate and infrared color, and a negative correlation with
molecular gas depletion time. There is a clear tendency of increasing
with increasing kinetic temperature (). Further, we found that not
only but also pressure of molecular gas is important to
understand variations of . Special considerations should be made when
discussing molecular gas mass and molecular gas properties inferred from
CO(=2-1) instead of CO(=1-0).Comment: 29 pages, 18 figures, 5 tables. Accepted for publication in PASJ. The
original resolution version is available here
(https://astro3.sci.hokudai.ac.jp/~radio/coming/publications/COMING_IX_org_res.pdf
EMPRESS. XI. SDSS and JWST Search for Local and z~4-5 Extremely Metal-Poor Galaxies (EMPGs): Clustering and Chemical Properties of Local EMPGs
We search for local extremely metal-poor galaxies (EMPGs), selecting
photometric candidates by broadband color excess and machine-learning
techniques with the SDSS photometric data. After removing stellar contaminants
by shallow spectroscopy with Seimei and Nayuta telescopes, we confirm that
three candidates are EMPGs with 0.05--0.1 by deep Magellan/MagE
spectroscopy for faint {\sc[Oiii]}4363 lines. Using a statistical
sample consisting of 105 spectroscopically-confirmed EMPGs taken from our study
and the literature, we calculate cross-correlation function (CCF) of the EMPGs
and all SDSS galaxies to quantify environments of EMPGs. Comparing another CCF
of all SDSS galaxies and comparison SDSS galaxies in the same stellar mass
range (), we find no significant ()
difference between these two CCFs. We also compare mass-metallicity relations
(MZRs) of the EMPGs and those of galaxies at 0--4 with a steady
chemical evolution model and find that the EMPG MZR is comparable with the
model prediction on average. These clustering and chemical properties of EMPGs
are explained by a scenario of stochastic metal-poor gas accretion on
metal-rich galaxies showing metal-poor star formation. Extending the broadband
color-excess technique to a high- EMPG search, we select 17 candidates of
4--5 EMPGs with the deep ( mag) near-infrared JWST/NIRCam
images obtained by ERO and ERS programs. We find galaxy candidates with
negligible {\sc[Oiii]}4959,5007 emission weaker than the local
EMPGs and known high- galaxies, suggesting that some of these candidates may
fall in 0--0.01 , which potentially break the lowest metallicity limit
known to date
Detections of [C II] 158 m and [O III] 88 m in a Local Lyman Continuum Emitter, Mrk 54, and its Implications to High-redshift ALMA Studies
We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local
Lyman Continuum Emitter (LCE), obtained with FIFI-LS on the Stratospheric
Observatory for Infrared Astronomy. This is only the second time, after Haro
11, that [C II] 158 m and [O III] 88 m spectroscopy of the known LCEs
have been obtained. We find that Mrk 54 has a strong [C II] emission that
accounts for % of the total FIR luminosity, whereas it has only moderate
[O III] emission, resulting in the low [O III]/[C II] luminosity ratio of
. In order to investigate whether [O III]/[C II] is a useful
tracer of (LyC escape fraction), we examine the correlations of
[O III]/[C II] and (i) the optical line ratio of [O III]
5007 \AA/[O II] 3727 \AA, (ii) specific star formation rate, (iii) [O III] 88
m/[O I] 63 m ratio, (iv) gas phase metallicity, and (v) dust
temperature based on a combined sample of Mrk 54 and the literature data from
the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that
galaxies with high [O III]/[C II] luminosity ratios could be the result of high
ionization (traced by ), bursty star formation, high
ionized-to-neutral gas volume filling factors (traced by [O III] 88 m/[O
I] 63 m), and low gas-phase metallicities, which is in agreement with
theoretical predictions. We present an empirical relation between the [O
III]/[C II] ratio and based on the combination of the [O III]/[C
II] and correlation, and the known relation between
and . The relation implies that high-redshift galaxies with high
[O III]/[C II] ratios revealed by ALMA may have ,
significantly contributing to the cosmic reionization.Comment: 14 pages, 5 figures, Accepted for publication in Ap
SYNERGISTIC EFFECT OF Ni EXTRACTION AND ITS APPLICATION FOR WASTE SOLUTION IN Ni NON-ELECTRIC PLATING
Waste solution from the Ni non-electric plating process contains 4.0kg/㎥ Ni (II), 0.1kg/㎥ Fe (III), 0.01kg/㎥ Zn (II), 48kg/㎥ SO₄²⁻, 98kg/㎥ HP0₃²⁻ and 31kg/㎥ lactic acid as a typical composition. Solvent extraction, cementation, ion exchange resin and precipitation methods may be used for the treatment of this kind of solution. In this study, solvent extraction of Ni (II) is investigated using two kinds of extractant in order to clarify the relation between extraction percent age and pH for various extractant mixtures. As Ni ions have an octahedral structure with ligands, the synergistic effect for Ni extraction may be effected by using two types of extractants
EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z Primordial Galaxies?
We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with
low metallicities () and low stellar masses
(). Taking deep medium-high resolution
() integral-field spectra with 8.2-m Subaru, we resolve the small
inner velocity gradients and dispersions of the EMPGs with H emission.
Carefully masking out sub-structures originated by inflow and/or outflow, we
fit 3-dimensional disk models to the observed H flux, velocity, and
velocity-dispersion maps. All the EMPGs show rotational velocities () of 5--23 km s smaller than the velocity dispersions
() of 17--31 km s, indicating dispersion-dominated () systems affected by inflow and/or outflow. Except
for two EMPGs with large uncertainties, we find that the EMPGs have very large
gas-mass fractions of . Comparing our results with
other H kinematics studies, we find that
decreases and increases with decreasing metallicity, decreasing
stellar mass, and increasing specific star-formation rate. We also find that
simulated high- () forming galaxies have gas fractions and dynamics
similar to the observed EMPGs. Our EMPG observations and the simulations
suggest that primordial galaxies are gas-rich dispersion-dominated systems,
which would be identified by the forthcoming James Webb Space Telescope (JWST)
observations at .Comment: Submitted to ApJ; After revisio
Different biomass-allocation patterns among four tree species in heavily disturbed sites on a volcanic mountain in Hokkaido, northern Japan
We have compared biomass-allocation patterns and frequency of sprouting among saplings of four tree species (Larix kaempferi, Betula platyphylla var. japonica, Populus maximowiczii, and Populus sieboldii) growing on a volcanic mountain in Hokkaido, northern Japan. Growing conditions were very harsh on the mountainside. Leaf mass and fine root mass relative to root mass were larger in L. kaempferi, and L. kaempferi root mass was less than for the other species. Sprouting ratios were high for the broadleaved species. Different allometries and sprouting ratios among species suggest that survival strategies for L. kaempferi were different from those for the broadleaved species. L. kaempferi has greater ability to increase leaf mass under harsh growing conditions; this probably results in large photosynthetic production by L. kaempferi on the volcano. In contrast, the two Populus species and Betula platyphylla seem to maintain populations through their ability to produce sprouts from large root systems
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