[en] We analyze the intrinsic flux ratios of various visible–near-infrared filters with respect to 3.5 μm for simple and composite stellar populations (CSPs), and their dependence on age, metallicity, and star formation history (SFH). UV/optical light from stars is reddened and attenuated by dust, where different sightlines across a galaxy suffer varying amounts of extinction. Tamura et al. (2009) developed an approximate method to correct for dust extinction on a pixel-by-pixel basis, dubbed the “${\mathrm{\beta <!--\; ??\; -->}}_V$” method, by comparing the observed flux ratio to an empirical estimate of the intrinsic ratio of visible and ∼3.5 μm data. Through extensive modeling, we aim to validate the “${\mathrm{\beta <!--\; ??\; -->}}_V$” method for various filters spanning the visible through near-infrared wavelength range, for a wide variety of simple and CSPs. Combining Starburst99 and BC03 models, we built spectral energy distributions (SEDs) of simple (SSP) and composite (CSP) stellar populations for various realistic SFHs, while taking metallicity evolution into account. We convolve various 0.44–1.65 μm filter throughput curves with each model SED to obtain intrinsic flux ratios ${\mathrm{\beta <!--\; ??\; -->}}_{\mathrm{\lambda <!--\; ??\; -->},0}$. When unconstrained in redshift, the total allowed range of ${\mathrm{\beta <!--\; ??\; -->}}_{V,0}$ is 0.6–4.7, or almost a factor of eight. At known redshifts, and in particular at low redshifts (z ≲ 0.01), ${\mathrm{\beta <!--\; ??\; -->}}_{V,0}$ is predicted to span a narrow range of 0.6–1.9, especially for early-type galaxies (0.6–0.7), and is consistent with observed ${\mathrm{\beta <!--\; ??\; -->}}_V$ values. The ${\mathrm{\beta <!--\; ??\; -->}}_{\mathrm{\lambda <!--\; ??\; -->}}$ method can therefore serve as a first-order dust-correction method for large galaxy surveys that combine JWST (rest-frame 3.5 μm) and HST (rest-frame visible–near-IR) data.

[en] It has been suggested that merging plays an important role in the formation and the evolution of elliptical galaxies. While gas dissipation by star formation is believed to steepen metallicity and color gradients of the merger products, mixing of stars through dissipation-less merging (dry merging) is believed to flatten them. In order to understand the past merging history of elliptical galaxies, we studied the optical-near-infrared (NIR) color gradients of 204 elliptical galaxies. These galaxies are selected from the overlap region of the Sloan Digital Sky Survey (SDSS) Stripe 82 and the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). The use of optical and NIR data (g, r, and K) provides large wavelength baselines, and breaks the age-metallicity degeneracy, allowing us to derive age and metallicity gradients. The use of the deep SDSS Stripe 82 images makes it possible for us to examine how the color/age/metallicity gradients are related to merging features. We find that the optical-NIR color and the age/metallicity gradients of elliptical galaxies with tidal features are consistent with those of relaxed ellipticals, suggesting that the two populations underwent a similar merging history on average and that mixing of stars was more or less completed before the tidal features disappeared. Elliptical galaxies with dust features have steeper color gradients than the other two types, even after masking out dust features during the analysis, which can be due to a process involving wet merging. More importantly, we find that the scatter in the color/age/metallicity gradients of the relaxed and merging feature types decreases as their luminosities (or masses) increase at M > 10^11.4 M_☉ but stays large at lower luminosities. Mean metallicity gradients appear nearly constant over the explored mass range, but a possible flattening is observed at the massive end. According to our toy model that predicts how the distribution of metallicity gradients changes as a result of major dry merging, the mean metallicity gradient should flatten by 40% and its scatter becomes smaller by 80% per a mass-doubling scale if ellipticals evolve only through major dry merger. Our result, although limited by a number statistics at the massive end, is consistent with the picture that major dry merging is an important mechanism for the evolution for ellipticals at M > 10^11.4 M_☉, but is less important at the lower mass range.

[en] A data-driven understanding of the reaction mechanism of the O3-type Na[Li${}_{1/3}$Mn${}_{2/3}$]O${}_2$-layered cathode model is systematically performed to decouple the complex correlations of covariate scale-dependent variables in diagnosing and solving structural problems for facilitating nonhysteretic and reversible (nHR) oxygen capacities using interpretable machine learning (ML) assisted by density functional theory. A large dataset of vacancy formation energies depending on the desodiation mode for the oxide is investigated in detail, and it provides two numerical principles: i) linearizing the energy landscape and ii) steepening its slope to reach the ideal reaction. The heatmaps comprising Pearson coefficient correlation values are broken down into two-scale components: i) macroscopic and ii) local structure features. Deriving the overall mitigation of scale-dependent covariate variables in negative correlation potentially leads to nHR anionic redox upon (dis)charging. Containing the scale-dependent features, the interpretable ML model based on a gradient-boosting machine predicts each formation energy well. With data-driven comprehension, honeycomb- and turtle-type superstructures (TS) have been suggested depending on the thermodynamic (un)favorable pathways during desodiation from a local structural perspective, and the dangling O${}^{2-<!--\; ???\; -->}$ in the TS is a critical origin leading to the formation of O${}_2$ molecules trapped in the bulk. (© 2024 Wiley‐VCH GmbH)

[en] An intriguing mechanical seed (MS) concept that modulates (in)homogeneous Li metal growth is proposed based on an in-depth understanding of its fundamental mechanism using unified atomistic computations. A large dataset of thermodynamic energies for Li disordered phase decouples the dual-body interactions into three components: i) crystal-like, ii) long, and iii) short bonds of Li-Li based on machine learning assisted by density function theory calculations. The contributions of these dual-body interactions offer a mechanical factor for controlling the disordered-ordered phase transition during electrochemical deposition. Macroscopic molecular dynamics simulations systematically construct the core-shell sphere and cross-sectional models to reinforce the MS premise. The former reveals that the lower energy level of disordered phase under the moderate compression causes a slow phase kinetics, whereas the strain-free mode exhibits a relatively fast transition. In addition, the cross-sectional model exhibits a smooth surface landscape for the strain-optimized case. These observations are attributed to the surface area evolutions depending on the MS conditions and elucidate the dynamic atomic displacements near the grain boundary from a local structural perspective. The proposed mechanical design concept facilitates uniform Li growth and is expected to be a global parameter in harnessing the full potential of Li metal batteries. (© 2023 Wiley‐VCH GmbH)

[en] Activity at the centers of galaxies, during which the central supermassive black hole is accreting material, is nowadays accepted to be rather ubiquitous and most probably a phase of every galaxy's evolution. It has been suggested that galactic mergers and interactions may be the culprits behind the triggering of nuclear activity. We use near-infrared data from the new Infrared Medium-Deep Survey and the Deep eXtragalactic Survey of the VIMOS-SA22 field and radio data at 1.4 GHz from the FIRST survey and a deep Very Large Array survey to study the environments of radio active galactic nuclei (AGNs) over an area of ∼25 deg² and down to a radio flux limit of 0.1 mJy and a J-band magnitude of 23 mag AB. Radio AGNs are predominantly found in environments similar to those of control galaxies at similar redshift, J-band magnitude, and (M_u – M_r ) rest-frame color. However, a subpopulation of radio AGNs is found in environments up to 100 times denser than their control sources. We thus preclude merging as the dominant triggering mechanism of radio AGNs. By fitting the broadband spectral energy distribution of radio AGNs in the least and most dense environments, we find that those in the least dense environments show higher radio-loudness, higher star formation efficiencies, and higher accretion rates, typical of the so-called high-excitation radio AGNs. These differences tend to disappear at z > 1. We interpret our results in terms of a different triggering mechanism for these sources that is driven by mass loss through winds of young stars created during the observed ongoing star formation.

[en] It is proposed that the unified interplay between the chemical hardness of the Li-X (X = S, Se, and Te) bond and solid-state conversion kinetics enables intrinsic reshaping of materials for fabricating high-energy density lithium-sulfur batteries. This concept is evaluated using three cathode models: (i) Li${}_2$S, (ii) Se-doped Li${}_2$S (Se-Li${}_2$S), and (iii) Te-doped Li${}_2$S (Te-Li${}_2$S). Theoretical calculations reveal that the Li-X bond in the Se-Li${}_2$S cathode shows low chemical hardness, and the chemical hardness decreases at a higher rate for the Te-Li${}_2$S cathode. The local structural effect induces a decrease in the phase transition barrier during the solid-state conversion reaction in the Se- and Te-doped crystal phases, as revealed by electrochemical measurements and ex-situ X-ray photoelectron spectroscopy analysis. Investigation of the three sulfide-based cathodes sheds light on the mechanism behind the kinetics of phase transition in the solid-state conversion region, illuminating the intriguing concept of a local structure for harnessing the full potential of sulfur cathodes to achieve high-energy-density lithium-sulfur batteries. (© 2023 Wiley‐VCH GmbH)

[en] Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium-excessive layered-oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in $LiN{i}_{1/3}C{o}_{1/3}M{n}_{1/3}{O}_2$. The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries. (© 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

[en] The ΛCDM cosmological model successfully reproduces many aspects of the galaxy and structure formation of the universe. However, the growth of large-scale structures (LSSs) in the early universe is not well tested yet with observational data. Here, we have utilized wide and deep optical–near-infrared data in order to search for distant galaxy clusters and superclusters (0.8 < z < 1.2). From the spectroscopic observation with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope, three massive clusters at z ∼ 0.91 are confirmed in the SSA22 field. Interestingly, all of them have similar redshifts within Δ z ∼ 0.01 with velocity dispersions ranging from 470 to 1300 km s"−"1. Moreover, as the maximum separation is ∼15 Mpc, they compose a supercluster at z ∼ 0.91, meaning that this is one of the most massive superclusters at this redshift to date. The galaxy density map implies that the confirmed clusters are embedded in a larger structure stretching over ∼100 Mpc. ΛCDM models predict about one supercluster like this in our surveyed volume, consistent with our finding so far. However, there are more supercluster candidates in this field, suggesting that additional studies are required to determine if the ΛCDM cosmological model can successfully reproduce the LSSs at high redshift

[en] We present the first results of our survey for high-redshift quasars at $5\lesssim <!--\; ???\; -->z\lesssim <!--\; ???\; -->5.7$. The search for quasars in this redshift range has been known to be challenging due to the limitations of the filter sets used in previous studies. We conducted a quasar survey for two specific redshift ranges, 4.60 ≤ z ≤ 5.40 and 5.50 ≤ z ≤ 6.05, using multi-wavelength data that include observations made with custom-designed filters, is and iz. Using these filters and a new selection technique, we were able to reduce the fraction of interlopers. Through optical spectroscopy, we confirmed six quasars at 4.7 ≤ z ≤ 5.4 with $-<!--\; ???\; -->27.4<<!--\; <\; -->M_{1450}<<!--\; <\; -->-<!--\; ???\; -->26.4$ that recently were discovered independently by another group. We estimated black hole masses and Eddington ratios of four of these quasars from optical and near-infrared spectra, and found that these quasars are undergoing nearly Eddington-limited accretion that is consistent with the rapid growth of supermassive black holes in luminous quasars at z ∼ 5.

[en] Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars (M_1_4_5_0 > −24 mag) at z ≳ 6, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z ∼ 6 in a 12.5 deg"2 region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at ∼8443 Å, with emission lines redshifted to z = 5.944 ± 0.002 and rest-frame ultraviolet continuum magnitude M_1_4_5_0 = −23.59 ± 0.10 AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z ∼ 6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars. This suggests that the number of M_1_4_5_0 ∼ −23 mag quasars at z ∼ 6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS