The origin of dust in early-type galaxies (ETGs) remains a long-standing question, with proposed sources being mass loss from evolved stars, galaxy mergers, or grain growth in the interstellar medium. To investigate the dominant source of dust in ETGs, we analyzed near-infrared spectra of 30 ETGs obtained with AKARI, focusing on the SiO and CO absorption features tracing the photospheres of old stellar populations. We also derived the dust mass using near- to far-infrared photometric data obtained by 2MASS, WISE, and AKARI. We find that the dust mass correlates with the summed equivalent widths of the SiO and CO absorption features. This trend suggests that a significant fraction of dust in ETGs may originate from mass loss from evolved stars, consistent with an internal production scenario. The dust mass shows no anti-correlation with diffuse X-ray luminosities, suggesting that dust in ETGs is not strongly interacting with X-ray plasma. Moreover, polycyclic aromatic hydrocarbons (PAHs) are detected in the near-infrared spectra. We find that the PAH intensity shows no correlation with the equivalent widths of SiO and CO, but correlates with the luminosity of hot and warm dust components. This suggests that PAHs may be of external origin associated with galaxy merger remnants, heated by the activities of galactic nuclei.

Interstellar hydrocarbon dust containing aromatic and aliphatic hydrocarbons, like polycyclic aromatic hydrocarbons (PAHs), is believed to be processed by various factors including UV radiation fields and mechanical shocks in the galactic environments. We systematically investigate the processing of hydrocarbon dust, especially the likely causes for the variations of the luminosity ratio of aliphatic to aromatic hydrocarbon emission features, using the near-infrared (IR) spectral features at wavelengths 3.3 mu m and 3.4-3.6 mu m observed with AKARI/IRC. We analyzed 243 near-IR spectra of 240 star-forming (ultra-)luminous IR galaxies (total IR luminosity, L-IR > 10(11) L-circle dot), 119 spectra of 105 star-forming IR galaxies (1010 L < L-IR < 1011 L), and 94 spectra of 65 sub-IR galaxies (L-IR < 10(10) L-circle dot), in addition to 232 spectra of 36 Galactic H II regions as a reference sample. We performed near-IR spectral model fitting to estimate the luminosities of the aromatic and aliphatic hydrocarbon features and the H I recombination line Br alpha. The result indicates that the luminosity ratios of the aliphatic to the aromatic hydrocarbons (L-aliphatic/L-aromatic) in the sample galaxies show considerably large variations, compared to those in the Galactic H II regions, L-aliphatic/L(aromatic)systematically decreasing with L-IR and L-Br alpha. We find that (sub-)IR galaxies with continuum colors bluer at 4 mu m tend to have higher L-aliphatic/L-aromatic, which is likely to reflect the intrinsic nature of PAHs outside the H II region where the PAHs remain non-processed by strong UV radiation fields. We also find that some ultra-luminous IR galaxies with continuum colors redder at 4 mu m show extremely low L-aliphatic/L-aromatic, which is likely to be caused by blending aliphatic emission and absorption features due to the presence of an obscured galactic nucleus in merger systems.

Phosphorus (P) is one of the key ingredients for life, yet its origins in galaxies remain poorly understood. In order to investigate the production of P by supernovae, we performed near-infrared (IR) [P ii] and [Fe ii] line mapping of 26 Galactic supernova remnants (SNRs) with the Infrared Survey Facility and Kanata telescopes, using the narrow-band filters tuned to these lines. By combining our data with archival [Fe ii] maps from UKIRT, we detected both the [P ii] and [Fe ii] emissions in five SNRs, only the [Fe ii] emission in 15 SNRs, and no line emissions in the remaining six. Using the observed [P ii]$/$[Fe ii] ratios and upper limits for non-detections, we derived the ${\rm P}/{\rm Fe}$ abundance ratios, which vary by up to two orders of magnitude among our sample SNRs. This suggests that the production rate of P and/or the degree of dust destruction may differ from remnant to remnant, the latter being due to the fact that P is volatile while Fe is mostly locked in dust grains. We used the mid- and far-IR maps to examine the dust content for the five SNRs where both the line emissions are detected. As a result, we find that high ${\rm P}/{\rm Fe}$ abundance ratios in the northern and south-eastern regions of Cassiopeia A and the Crab Nebula, respectively, are not likely due to dust destruction but may reflect an asymmetric ejection of P during supernova explosions. In the Crab Nebula, it is also possible that near-IR [Ni ii] emission contaminates the observed flux in the south-eastern region, suggesting that the ${\rm Ni/Fe}$ abundance ratio, rather than the ${\rm P}/{\rm Fe}$ abundance ratio, is relatively high in this part of the remnant.

Centaurus A (Cen A) is the nearest galaxy hosting an active galactic nucleus (AGN), which produces powerful radio and X-ray jets extending to hundreds of kiloparsecs from the center. At 15 kpc northeast (NE) and 12 kpc southwest (SW) in the halo along the jet from the nucleus of Cen A, dust clouds accompanying the H alpha emission are detected. For both NE and SW clouds, past studies suggested that star formation may have been induced through interactions between the AGN jet and the surrounding intergalactic media. For these clouds, we performed dust model fitting of infrared (IR) spectral energy distributions (SEDs) created from the archival data of WISE, Spitzer, and Herschel. Then we compare the IR emission properties of the dust clouds with the far-ultraviolet (UV) emission using the archival data of GALEX/FUV. As a result, we find that the interstellar radiation field intensity G(0) (and thus the dust temperature) in the NE cloud suggests star formation activity, while that in the SW cloud does not. The local far-UV intensity and G(0) in the NE region are significantly larger than those expected for the far-UV radiation originating from the central region of Cen A and its dust-scattered component, respectively. In contrast, the local far-UV intensity and G(0) in the SW region are compatible with them. The polycyclic aromatic hydrocarbon (PAH) emission is detected for both NE and SW clouds. The mass abundance ratios of PAH to dust are similar for both clouds and significantly lower than that in the central region of Cen A. We suggest that the dust clouds and the PAHs in the clouds are associated with the broken ring-like structure of H I gas which is thought to be a remnant of the past gas-rich merger and that shocks by the jet responsible for the middle lobe on the north side may have triggered the star formation in the NE cloud.

Recent near- and mid-infrared (IR) observations have revealed the existence of appreciable amounts of aromatic and aliphatic hydrocarbon dust in the harsh environments of active galactic nuclei (AGNs), the origins of which are still under discussion. In this paper, we analyze the near-IR spectra of AGNs obtained with AKARI in order to systematically study the properties of the aromatic and aliphatic hydrocarbon dust affected by AGN activity. We performed spectral fitting and spectral energy distribution fitting for our sample of 102 AGNs to obtain the fluxes of the aromatic and aliphatic spectral features, the total IR luminosity (LIR), and the fractional luminosity of AGN components (LAGN/LIR). As a result, we find that Laromatic/LIR is systematically lower for the AGN sample and especially lower for AGNs with the aliphatic feature seen in the absorption than for star-forming galaxies (SFGs), while Laliphatic/Laromatic is systematically higher for the AGN sample than for the SFG sample, increasing with AGN activity indicated by LAGN/LIR. In addition, the profiles of the aliphatic emission features of the AGN sample are significantly different from those of the SFG sample in that the AGNs have systematically stronger feature intensities at longer wavelengths. We conclude that both aromatic and aliphatic hydrocarbon dust are likely of circumnuclear origin, suggesting that a significant amount of the aliphatic hydrocarbon dust may come from a new population created through processes such as the shattering of large carbonaceous grains by AGN outflows.

We develop a few science cases, using the PRIMA far-infrared (FIR) probe, aimed at achieving several breakthroughs in our understanding of the dust properties and their evolution. We argue that the specific observational capabilities of PRIMA, namely, its unprecedented sensitivity over the whole FIR range and the possibility to obtain continuous spectra between lambda=24 and 235 mu m, are essential to progress in our understanding of the physics of the interstellar medium (ISM) and galaxy evolution. Our science cases revolve around observations of nearby galaxies. We discuss the importance of detecting the IR emission of the diffuse ISM of these galaxies, including very low-metallicity systems. We also discuss the opportunity of detecting various solid-state features to understand the mineralogy of interstellar grains. Finally, we stress the unique opportunity brought by the possible simultaneous measures of both the dust continuum and the FIR fine-structure gas lines. These science cases could be distributed in a few large programs. (c) 2025 Society of Photo-Optical Instrumentation Engineers (SPIE)

We report findings from near-infrared imaging observations of 17 young and middle-aged supernova remnants (SNRs) in the Magellanic Clouds to examine the impact of SNR shocks on dust destruction and the possible detection of supernova ejecta. We have analyzed [P II ] (1.189 μ m) and [Fe II ] (1.257 and 1.644 μ m) narrowband images obtained with the InfraRed Survey Facility 1.4 m telescope at the South African Astronomical Observatory. We calculate the P/Fe abundance ratio, X (P/Fe), using the [P II ]/[Fe II ] line ratio, which provides valuable information on dust content and/or processing in the interstellar medium (ISM) because P is not depleted while Fe is a refractory species. Only 6 of 17 SNRs show emission features in both [P II ] and [Fe II ]. Among these, N49, N63A, and N206 exhibit X (P/Fe) ratios between 1.2 and 3.0 X _⊙ (P/Fe), which are many times smaller than the general ISM ratio (e.g., Orion Bar ∼15 X _⊙ (P/Fe)), suggesting significant destruction of dust grains by the shocks. In contrast, the remnants of SN 1987A, N157B, N158A, and the clump studied in N206 have P/Fe abundance ratios that are comparable to or higher than the general ISM. For SN 1987A, the high X (P/Fe) ratio may result from the lack of Fe in the gas phase, although the flux densities fluctuate constantly due to shocks. For N157B, N158A, and the clump in N206, many interpretations are being explored, including Fe atoms bound primarily to dust grains, material from supernova ejecta, and photoionization from nearby H II regions.

We carried out the near-infrared ($JHK_{\rm s}$) imaging polarimetric observation with the polarimeter SIRPOL on the Infrared Survey Facility (IRSF) 1.4 m telescope and [C ii] line mapping observation with a Fabry–Pérot spectrometer on board a 100 cm TIFR balloon-borne far-infrared telescope toward NGC 6334, We reveal the relationship between the plane-of-sky (POS) magnetic fields and [C ii] emission lines to investigate the star formation in the molecular cloud. The polarization vector map shows that the POS magnetic fields are approximately perpendicular to the main filament elongation of NGC 6334. However, the POS magnetic fields tend to be parallel or random for the other filaments in NGC 6334. The [C ii] emission shows a distribution well aligned with the main filament. Strong [C ii] emission is also seen in the hub–filament system. Because the main filament is sandwiched between two H ii regions, it is most likely that gas is efficiently accreting from the shells of the H ii regions along the magnetic field, resulting in active star formation. This is consistent with NGC 6334 being bright in [C ii] emission.

We propose a mission concept, called the space interferometer laboratory voyaging towards innovative applications (SILVIA), designed to demonstrate ultra-precision formation flying between three spacecraft separated by 100 m. SILVIA aims to achieve submicrometer precision in relative distance control by integrating spacecraft sensors, laser interferometry, low-thrust, and low-noise micro-propulsion for real-time measurement and control of distances and relative orientations between spacecraft. A 100 m scale mission in a near-circular low Earth orbit has been identified as an ideal, cost-effective setting for demonstrating SILVIA, as this configuration maintains a good balance between small relative perturbations and low risk of collision. This mission will fill the current technology gap towards future missions, including gravitational wave observatories such as the decihertz interferometer gravitational wave observatory (DECIGO), designed to detect the primordial gravitational-wave background, and high-contrast nulling infrared interferometers such as the large interferometer for exoplanets (LIFE), designed for direct imaging of thermal emissions from nearby terrestrial planet candidates. The mission concept and its key technologies are outlined, paving the way for the next generation of high-precision space-based observatories.

Theoretical calculations predict that high-resolution spectroscopy of H2O gas lines in the mid-infrared region is the most promising method to observationally identify the snow-line, which has been proposed as the critical factor separating gas giants from solid planets in the planetary formation process. This requires the spectroscopic observations from space with R = lambda/Delta lambda >= 30, 000. For this purpose, we propose a mid-infrared (10-18 mu m) high-resolution spectrometer to be onboard the GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) mission. We are developing "immersion grating" spectroscopy technology for high-resolution spectroscopy in space. We have chosen CdZnTe as a candidate for the optical material. We report the current status of the development of the CdZnTe immersion grating, including evaluation of its optical properties (absorption coefficient and refractive index) at cryogenic temperatures, development of an anti-reflection coating with a moth-eye structure for wide-wavelength coverage, and verification of machinability for grating production. We plan to make a prototype spectrometer to demonstrate the capability of the immersion grating with ground-based observations in the N-band (lambda = 8-13 mu m) and beyond.

We present the current status of our development of a new near-infrared spectrometer for the InfraRed Survey Facility (IRSF) 1.4-m telescope, located in South Africa. The spectrometer is designed to cover the wavelength range of 1.0-1.6 mu m with the spectral resolution of 550 at 1.2 mu m and 730 at 1.6 mu m and have a small number of optical surfaces to achieve a high optical throughput of 55%. The spectrometer is also equipped with a near-infrared slit viewer with a 3' x4' field of view to perform precise spectral monitoring and mapping. We have tentatively completed the development of the instrument by using a commercial InGaAs detector and confirmed its expected sensitivity and spectral resolution by test observations with the Kagoshima University 1-m telescope. We now plan to replace the current detector with a new InGaAs detector developed for astronomical observations. The new detector covers the same wavelength range as the current one but has a significantly lower dark current and a larger array format, which enables us to upgrade the spectrometer to have higher sensitivity and spectral resolution. We plan to mount the spectrometer on the IRSF telescope by early 2025 after the detector is replaced and the second test observation with the Kagoshima University telescope is done.

GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is one of the three candidates of ISAS/JAXA's Strategic L-class mission for the 2030s. The 1.2 m aperture, 50 K cryogenic space telescope with the wide-field camera (WFC) will provide the 1,260 square arcmin field-of-view for five photometric bands between 2 and 8 mu m. The high resolution spectrometer (HRS) will observe the 10-18 mu m with a wavelength resolution of 30,000. The GREX-PLUS WFC field-of-view is 130 times larger than that of the James Webb Space Telescope and similar to those of Euclid and Roman Space Telescope. Since these two survey missions are limited to the wavelength less than around 2 mu m, GREX-PLUS will extend the wavelength coverage beyond 2 mu m, providing versatile legacy imaging survey significantly improved from previous Spitzer imaging survey in the same wavelength range. The spectral resolution of the GREX-PLUS HRS is 10 times higher than that of the James Webb Space Telescope, opening a new window of the mid-infrared high-resolution spectroscopy from space. The main scientific themes are the galaxy formation and evolution and the planetary system formation and evolution. The GREX-PLUS WFC aims to detect the first generation of "bright" galaxies at redshift z > 15. The GREX-PLUS HRS aims to resolve the Kepler motion of water vapor molecules and identify the location of the water "snowline" in similar to 100 proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of super massive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on. This paper presents the status of the concept design of GREX-PLUS, including telescope system, WFC, HRS, cooling system, and spacecraft bus system.

Hydrocarbon dust is one of the dominant components of interstellar dust, which mainly consists of polycyclic aromatic hydrocarbons and aliphatic hydrocarbons. While hydrocarbon dust is thought to be processed in interstellar radiation fields or shocks, detailed processing mechanisms are not completely understood yet. We investigate the processing of hydrocarbon dust by analyzing the relation between the luminosities emitted by hydrocarbon dust and the total infrared luminosities (L-IR) for 138 star-forming galaxies at redshift z<0.3. Using near-infrared 2.5-5 mu m spectra obtained with AKARI, we derived the luminosities of the aromatic hydrocarbon feature at 3.3 mu m (L-aromatic) and the aliphatic hydrocarbon feature at 3.4-3.6 mu m (L-aliphatic). We also derived L-IR and the radiation field strength by modeling the spectral energy distributions of the 138 galaxies with AKARI, WISE, and IRAS photometry data. We find that galaxies with higher L-IR tend to exhibit lower L-aliphatic/L-aromatic ratios. Furthermore, we find that there is an anti-correlation between L-aliphatic/L-aromatic ratios and the radiation field strength, and also that the galaxies with low L-aliphatic/L-aromatic ratios are dominated by merger galaxies. These results support the suggestion that hydrocarbon dust is processed through photodissociation in strong radiation fields and/or shocks during merging processes of galaxies; the L-aliphatic/L-aromatic ratio is likely to decrease in such harsh interstellar conditions since the aliphatic bonds are known to be chemically weaker than the aromatic bonds.

We examine spatial variations of the C^0/CO abundance ratio (X_C/CO) in the vicinity of the γ-ray supernova remnant W51C, based on [CI] (^3P_1-^3P_0), ^12CO(1-0), and ^13CO(1-0) observations with the ASTE and Nobeyama 45-m telescopes. We find that X_C/CO varies in a range of 0.02-0.16 (0.05 in median) inside the molecular clouds of A_V>100 mag, where photodissociation of CO by the interstellar UV is negligible. Furthermore, X_C/CO is locally enhanced up to by a factor of four near the W51C center, depending on the projected distance from the W51C center. In high-A_V molecular clouds, X_C/CO is determined by the ratio of the cosmic-ray (CR) ionization rate to the H_2 density, and we find no clear spatial variation of the H_2 density against the projected distance. Hence, the high CR ionization rate may locally enhance X_C/CO near the W51C center. We also find that the observed spatial extent of the enhanced X_C/CO (∼17 pc) is consistent with the diffusion distance of CRs with the energy of 100 MeV. The fact suggests that the low-energy CRs accelerated in W51C enhance X_C/CO. The CR ionization rate at the X_C/CO-enhanced cloud is estimated to be 3×10^-16 s^-1 on the basis of time-dependent PDR simulations of X_C/CO, the value of which is 30 times higher than that in the standard Galactic environment. These results demonstrate that [CI] is a powerful probe to investigate the interaction between CRs and the interstellar medium for a wide area in the vicinity of supernova remnants.

We perform a systematic study of evolutionary stages and stellar masses of young stellar objects (YSOs) in the Large Magellanic Cloud (LMC) to investigate properties of star formation of the galaxy. There are 4825 sources in our YSO sample, which are constructed by combining the previous studies identifying YSOs in the LMC. Spectral energy distributions of the YSOs from optical to infrared wavelengths were fitted with a model consisting of stellar, polycyclic aromatic hydrocarbon and dust emissions. We utilize the stellar-to-dust luminosity ratios thus derived to study the evolutionary stages of the sources; younger YSOs are expected to show lower stellar-to-dust luminosity ratios. We find that most of the YSOs are associated with the interstellar gas across the galaxy, which are younger with more gases, suggesting that more recent star formation is associated with larger amounts of the interstellar medium (ISM). N157 shows a hint of higher stellar-to-dust luminosity ratios between active star-forming regions in the LMC, suggesting that recent star formation in N157 is possibly in later evolutionary stages. We also find that the stellar mass function tends to be bottom-heavy in supergiant shells (SGSs), indicating that gas compression by SGSs may be ineffective in compressing the ISM enough to trigger massive star formation. There is no significant difference in the stellar mass function between YSOs likely associated with the interface between colliding SGSs and those with a single SGS, suggesting that gas compression by collisions between SGSs may also be ineffective for massive star formation.

We examine spatial variations of the C-0/CO abundance ratio (X-C/CO) in the vicinity of the gamma-ray supernova remnant W 51 C, based on [C i] (P-3(1)-P-3(0)), (CO)-C-12(1-0), and (CO)-C-13(1-0) observations with the ASTE and Nobeyama 45 m telescopes. We find that X-C/CO varies in a range of 0.02-0.16 (0.05 in median) inside the molecular clouds of A(V) > 100 mag, where photodissociation of CO by the interstellar UV is negligible. Furthermore, X-C/CO is locally enhanced by a factor of up to four near the W 51 C center, depending on the projected distance from the W 51 C center. In high-A(V) molecular clouds, X-C/CO is determined by the ratio of the cosmic-ray (CR) ionization rate to the H-2 density, and we find no clear spatial variation of the H-2 density against the projected distance. Hence, the high CR ionization rate may locally enhance X-C/CO near the W 51 C center. We also find that the observed spatial extent of the enhanced X-C/CO (similar to 17 pc) is consistent with the diffusion distance of CRs with an energy of 100 MeV. This fact suggests that the low-energy CRs accelerated in W 51 C enhance X-C/CO. The CR ionization rate in the X-C/CO-enhanced cloud is estimated to be 3 x 10(-16) s(-1) on the basis of time-dependent photodissociation region simulations of X-C/CO, the value of which is 30 times higher than that in the standard Galactic environment. These results demonstrate that [C I] is a powerful probe to investigate the interaction between CRs and the interstellar medium for a wide area in the vicinity of supernova remnants.

Abstract. We performed wave-optics-based numerical simulations at mid-infrared wavelengths to investigate how the presence or absence of entrance slits and optical aberrations affect the spectral resolving power R of a compact, high-spectral-resolving-power spectrometer containing an immersion-echelle grating. We tested three cases of telescope aberration (aberration-free, astigmatism, and spherical aberration), assuming the aberration budget of the Space Infrared Telescope for Cosmology and Astrophysics, which has a 20     μm wavelength diffraction limit. In cases with a slit, we found that the value of R at around 10 to 20  μm is approximately independent of the assumed aberrations, which is significantly different from the prediction of geometrical optics. Our results also indicate that diffraction from the slit improves R by enlarging the effective illuminated area on the grating window and that this improvement decreases at short wavelengths. For the slit-less cases, we found that the impact of aberrations on R can be roughly estimated using the Strehl ratio.

The application of superelastic alloys to microvibration isolators for a spacecraft was studied. The superelastic alloy in this study is characterized by a wide hysteresis loop in the stress-strain curve, which dissipates a large amount of energy even with a slight change in stress. Prototype struts with damping mechanisms utilizing such characteristics were developed, and an isolation system consisting of the damping struts was investigated. The isolation system was designed to satisfy the requirements of the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), which has several mechanical cryocoolers to cool down the entire telescope to cryogenic temperature. Since the vibrations generated by the cryocoolers can be transmitted to the telescope and deteriorate the pointing stability, SPICA is designed to integrate all cryocoolers into cooler plates and isolate the plates from vibrations with the isolation system. The simulation method to design the isolation system was developed and validated by comparing the estimation with the test results of a bipod with a pair of the damping struts.