68 research outputs found
Large Population of ALMA Galaxies at z>6 with Very High [OIII]88um to [CII]158um Flux Ratios: Evidence of Extremely High Ionization Parameter or PDR Deficit?
We present our new ALMA observations targeting [OIII]88um, [CII]158um,
[NII]122um, and dust continuum emission for three Lyman break galaxies at
z=6.0293-6.2037 identified in the Subaru/Hyper Suprime-Cam survey. We clearly
detect [OIII] and [CII] lines from all of the galaxies at 4.3-11.8sigma levels,
and identify multi-band dust continuum emission in two of the three galaxies,
allowing us to estimate infrared luminosities and dust temperatures
simultaneously. In conjunction with previous ALMA observations for six galaxies
at z>6, we confirm that all the nine z=6-9 galaxies have high [OIII]/[CII]
ratios of L[OIII]/L[CII]~3-20, ~10 times higher than z~0 galaxies. We also find
a positive correlation between the [OIII]/[CII] ratio and the Lya equivalent
width (EW) at the ~90% confidence level. We carefully investigate physical
origins of the high [OIII]/[CII] ratios at z=6-9 using Cloudy, and find that
high density of the interstellar medium, low C/O abundance ratio, and the
cosmic microwave background attenuation are responsible to only a part of the
z=6-9 galaxies. Instead, the observed high [OIII]/[CII] ratios are explained by
10-100 times higher ionization parameters or low photodissociation region (PDR)
covering fractions of 0-10%, both of which are consistent with our [NII]
observations. The latter scenario can be reproduced with a density bounded
nebula with PDR deficit, which would enhance the Lya, Lyman continuum, and C+
ionizing photons escape from galaxies, consistent with the [OIII]/[CII]-Lya EW
correlation we find.Comment: 20 pages, 18 figures, Accepted for publication in Ap
Allelic Expression Changes in Medaka (Oryzias latipes) Hybrids between Inbred Strains Derived from Genetically Distant Populations
Variations in allele expressions between genetically distant populations are one of the most important factors which affects their morphological and physiological variations. These variations are caused by natural mutations accumulated in their habitats. It has been reported that allelic expression differences in the hybrids of genetically distant populations are different from parental strains. In that case, there is a possibility that allelic expression changes lead to novel phenotypes in hybrids. Based on genomic information of the genetically distant populations, quantification and comparison of allelic expression changes make importance of regulatory sequences (cis-acting factors) or upstream regulatory factors (trans-acting modulators) for these changes clearer. In this study, we focused on two Medaka inbred strains, Hd-rR and HNI, derived from genetically distant populations and their hybrids. They are highly polymorphic and we can utilize whole-genome information. To analyze allelic expression changes, we established a method to quantify and compare allele-specific expressions of 11 genes between the parental strains and their reciprocal hybrids. In intestines of reciprocal hybrids, allelic expression was either similar or different in comparison with the parental strains. Total expressions in Hd-rR and HNI were tissue-dependent in the case of HPRT1, with high up-regulation of Hd-rR allele expression in liver. The proportion of genes with differential allelic expression in Medaka hybrids seems to be the same as that in other animals, despite the high SNP rate in the genomes of the two inbred strains. It is suggested that each tissue of the strain difference in trans-acting modulators is more important than polymorphisms in cis-regulatory sequences in producing the allelic expression changes in reciprocal hybrids
The Hyper Suprime-Cam SSP survey: Overview and survey design
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2-m Subaru telescope on the summit of Mauna Kea in Hawaii. A team of scientists from Japan, Taiwan, and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey
Controlling Rashba spin-orbit interaction in quantum wells by adding symmetric potential
The incorporation of a symmetric electrostatic potential into quantum wells (QWs) is proposed as a method for modifying the coefficient a of the Rashba spin-orbit interaction. In a symmetric QW for which a = a(so)E(z), where E-z is the perpendicular electric field, the constant a(so) can be controlled by the symmetric potential. The sign reversal of a(so) with the increasing strength of the symmetric potential is demonstrated in (001)-oriented GaAs/AlGaAs QWs via a tight-binding model. The present findings can be used to realize structures with vanishing a in nonzero E-z
Suppressing effective magnetic field and spin-relaxation rate by tuning barrier compositions in a (111) quantum well
Adjusting compositions of two barriers forming a (111)-oriented InGaAs/AlGaAsSb quantum well (QW) is proposed as a method to eliminate the effective magnetic field due to the Rashba and linear-in-momentum Dresselhaus spin-orbit interactions in the zeroth and first orders in the gate electric field. The resulting suppressed Dyakonov-Perel spin relaxation is used to achieve a high on/off ratio of the spin-relaxation rate at room temperature in a double-QW structure
Spin relaxation in a zinc-blende (110) symmetric quantum well with δ doping
The spin relaxation of a two-dimensional electron system (2DES) formed in a symmetric quantum well is studied theoretically when the quantum well is parallel to the (110) plane of the zinc-blende structure, the spin polarization is perpendicular to the well, and electrons occupy only the ground subband. The spin-relaxation rate is calculated as a function of the distribution of donor impurities which are placed in the well layer. Considered processes of the spin relaxation are (1) the intrasubband process by impurity-potential-induced spin-orbit interaction (SOI), which is the Elliott-Yafet mechanism in the 2DES, and (2) virtual intersubband processes consisting of a spin flip by (2a) well-potential-induced SOI or (2b) the Dresselhaus SOI, and a scattering from an impurity. It is shown that all of the above processes disappear when all impurities are located on the center plane of the well. Even if impurities are distributed over three (110) atomic layers, the spin-relaxation rate is two orders of magnitude lower than that for the uniform distribution over the well width of 7.5 nm. In GaAs/AlGaAs type-I quantum wells, the processes (1) and (2a) interfere constructively, being dominant over (2b) for the well width of similar to 10 nm, while in some type-II quantum wells, they can interfere destructively
Spin relaxation in a quantum well by phonon scatterings
The spin relaxation due to the spin-orbit interaction (SOI) is studied theoretically in a quantum well with electrons occupying only the ground subband. First, it is shown that the coefficient of the Rashba SOI is proportional to b(off) - 1, in which the parameter boff, determined by the band offsets and the band gaps, passes through unity, for example, by changing x in Ga0.47In0.53As(well)/AlxGa1-xAsySb1-y (barrier). Second, it is derived that the transition matrix element of each spin-flip phonon scattering has the same proportionality factor b(off) - 1, in addition to the impurity scattering previously studied by the same authors [Phys. Rev. B 89, 075314 (2014)]. These findings suggest the possibility of strongly suppressing the spin-relaxation rate by choosing appropriate materials
Gate-voltage-induced switching of the Rashba spin-orbit interaction in a composition-adjusted quantum well
The coefficient alpha of the Rashba spin-orbit interaction is calculated in an asymmetric quantum well consisting of Ga0.47In0.53As (well), Al0.48In0.52As (left barrier), and AlxGa1-xAsySb1-y (right barrier) as a function of the external electric field perpendicular to the well E-z(ex) which is controlled by the gate voltage. This coefficient alpha, which depends on the band offset, can be tuned to be zero by adjusting the Al fraction x in the right barrier layer to the optimum value x(0) in the case where the wave function vanishes at the left heterointerface. Such a composition-adjusted asymmetric quantum well is proposed as a structure in which the magnitude of a can be switched by changing the polarity of E-z(ex). The calculation shows that, when vertical bar x - x(0)vertical bar 40 for a large enough vertical bar E-z(ex)vertical bar (vertical bar E-z(ex)vertical bar > 10(7) V/m for a well width of 20 nm), which results in the on/off spin-relaxation-rate ratio exceeding 10(3) in the Dyakonov-Perel mechanism
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