43 research outputs found
Ferromagnetism in a Hubbard model for an atomic quantum wire: a realization of flat-band magnetism from even-membered rings
We have examined a Hubbard model on a chain of squares, which was proposed by
Yajima et al as a model of an atomic quantum wire As/Si(100), to show that the
flat-band ferromagnetism according to a kind of Mielke-Tasaki mechanism should
be realized for an appropriate band filling in such a non-frustrated lattice.
Reflecting the fact that the flat band is not a bottom one, the ferromagnetism
vanishes, rather than intensified, as the Hubbard U is increased. The exact
diagonalization method is used to show that the critical value of U is in a
realistic range. We also discussed the robustness of the magnetism against the
degradation of the flatness of the band.Comment: misleading terms and expressions are corrected, 4 pages, RevTex, 5
figures in Postscript, to be published in Phys. Rev. B (rapid communication
障害者就労支援事業所との協働活動の展開について
活動報告departmental bulletin pape
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
Lyman "bump" galaxies - I. Spectral energy distribution of galaxies with an escape of nebular Lyman continuum
It is essential to know galactic emissivity and spectrum of Lyman continuum
(LyC) in order to understand the cosmic reionization. Here we consider an
escape of nebular LyC from galaxies and examine the consequent spectral energy
distribution. It is usually assumed that hydrogen nebular LyC mostly produced
by bound-free transitions is consumed within photo-ionized nebulae (so-called
"on-the-spot" approximation). However, an escape of the continuum should be
taken into account if stellar LyC escapes from galaxies through
"matter-bounded" nebulae. We show that the escaping hydrogen bound-free LyC
makes a strong bump just below the Lyman limit. Such a galaxy would be observed
as a Lyman "bump" galaxy. This bump results from the radiation energy
re-distribution of stellar LyC by nebulae. The strength of the bump depends on
electron temperature in nebulae, escape fraction of stellar and nebular LyC,
hardness of stellar LyC (i.e. metallicity, initial mass function, age and star
formation history), and IGM attenuation. We can use the bump to find very young
( Myr), massive ( ), and extremely metal-poor (or
metal-free) stellar populations at . Because of the bump, 900 \AA-to-1500
\AA luminosity density ratio (per Hz) becomes maximum (2--3 times larger than
the stellar intrinsic ratio) when about 40% of the stellar LyC is absorbed by
nebulae. The total number of escaping LyC photons increases due to the escape
of nebular LyC but does not exceed the stellar intrinsic one. The radiation
energy re-distribution by nebulae reduces the mean energy of escaping LyC only
by % relative to that of stellar LyC. Therefore, the effect of the
escape of nebular LyC on the reionization process may be small.Comment: MNRAS in pres
SYNTHESIS OF SUBSTITUTED t-BUTYL 3-ALKYLOXINDOLE-3-CARBOXYLATES FROM DI-t-BUTYL (2-NITROPHENYL)MALONATES
Using a novel tandem reduction-cyclization, we synthesized t-butyl 3-alkyloxindole-3-carboxylates from the di-t-butyl 2-alkyl-2-(2-nitrophenyl)malonate. Introduction of an α-substituent to the di-t-butyl 2-(2-nitrophenyl)-malonates and addition of acid promoted reactivity. This methodology was successfully applied to gram-scale-synthesis of the t-butyl 3-methyloxindole-3-carboxylate 1 and 3-hydroxymethyl-3-methyloxindole 2 without silica gel column chromatography.Part of this work was supported by the Kansai University Subsidy for Supporting Young Scholars, 2015 “Development of macrocyclization reaction via a photoaffinity reaction”, JSPS KAKENHI Grant Number 15K18903, Grant-in-Aid for Young Scientists (B) – Japan and MEXT – Supported Program for the Strategic Research Foundation at Private Universities (2013–2017) – Japan.2015年度関西大学若手研究者育成経
EMPRESS. XII. Statistics on the Dynamics and Gas Mass Fraction of Extremely-Metal Poor Galaxies
We present demography of the dynamics and gas-mass fraction of 33 extremely
metal-poor galaxies (EMPGs) with metallicities of and low
stellar masses of in the local universe. We conduct deep
optical integral-field spectroscopy (IFS) for the low-mass EMPGs with the
medium high resolution () grism of the 8m-Subaru FOCAS IFU instrument
by the EMPRESS 3D survey, and investigate H emission of the EMPGs.
Exploiting the resolution high enough for the low-mass galaxies, we derive gas
dynamics with the H lines by the fitting of 3-dimensional disk models.
We obtain an average maximum rotation velocity () of
and an average intrinsic velocity dispersion
() of for 15 spatially resolved EMPGs
out of the 33 EMPGs, and find that all of the 15 EMPGs have
suggesting dispersion dominated systems. There is a
clear decreasing trend of with the decreasing stellar
mass and metallicity. We derive the gas mass fraction () for
all of the 33 EMPGs, and find no clear dependence on stellar mass and
metallicity. These and trends should
be compared with young high- galaxies observed by the forthcoming JWST IFS
programs to understand the physical origins of the EMPGs in the local universe.Comment: 18 pages, 9 figures, accepted for publication in Ap