arXiv subjects

Toyoaki Suzuki

Publications and source records attributed to Toyoaki Suzuki.

At least 19 recordsLinked to original sources

arXiv2025

A systematic study on the aromatic and aliphatic hydrocarbon emission features of nearby galaxies using AKARI near-IR spectra

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 um and 3.4-3.6 um observed with AKARI/IRC. We analyzed 243 near-IR spectra of 240 star-forming (U)LIRGs (the total IR luminosity, $L_\rm{IR}>10^{11}\ L_\odot$), 119 spectra of 105 star-forming IRGs ($10^{10}\ L_\odot<L_\rm{IR}<10^{11}\ L_\odot$), and 94 spectra of 65 sub-IRGs ($L_\rm{IR}<10^{10}\ L_\odot$), in addition to 232 spectra of 36 Galactic HII 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 HI recombination line Br$\rmα$. The result indicates that the luminosity ratios of the aliphatic to the aromatic hydrocarbons ($L_\rm{ali}/L_\rm{aro}$) in the sample galaxies show considerably large variations, compared to those in the Galactic HII regions, $L_\rm{ali}/L_\rm{aro}$ systematically decreasing with $L_\rm{IR}$ and $L_\rm{Brα}$. We find that (sub-)IRGs with continuum colors bluer at 4 um tend to have higher $L_\rm{ali}/L_\rm{aro}$, which is likely to reflect the intrinsic nature of PAHs outside the HII region where the PAHs remain non-processed by strong UV radiation fields. We also find that some ULIRGs with continuum colors redder at 4 um show extremely low $L_\rm{ali}/L_\rm{aro}$, 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.

astro-ph.GA↗

arXiv2025

A systematic study on the properties of aromatic and aliphatic hydrocarbon dust in active galactic nuclei with AKARI near-infrared spectroscopy

Recent near- and mid-infrared (IR) observations reveal 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 to systematically study the properties of the aromatic and aliphatic hydrocarbon dust a ected by the AGN activity. We perform the spectral fitting and the 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 (L_IR), and the fractional luminosity of AGN components (L_AGN/L_IR). As a result, we find that L_aromatic/L_IR is systematically lower for the AGN sample, especially much lower for AGNs with the aliphatic feature seen in the absorption, than for star-forming galaxies (SFGs), while L_aliphatic/L_aromatic is systematically higher for the AGN sample than for the SFG sample, increasing with the AGN activity indicated by L_AGN/L_IR. In addition, the profiles of the aliphatic emission features of the AGN sample are significantly di erent from those of the SFG sample in that the AGNs have the feature intensities systematically stronger at longer wavelengths. We conclude that both aromatic and aliphatic hydrocarbon dust are likely of circumnuclear origins, suggesting that a significant amount of the aliphatic hydrocarbon dust may come from a new population created through processes such as shattering of large carbonaceous grains by AGN outflows.

astro-ph.GA↗

arXiv2025

Magnetic fields in the massive star-forming region NGC 6334 and their relationship with the properties of dust filaments probed by [CII] and PAH emissions

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 [CII] line mapping observation with a Fabry-Pérot spectrometer on board a 100-cm TIFR balloon-borne far-infrared telescope toward NGC 6334, and revealed the relationship between the plane-of-sky (POS) magnetic fields and [CII] 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. On the other hand, the POS magnetic fields tend to be parallel or random for the other filaments in NGC 6334. The [CII] emission shows a distribution well aligned with the main filament. Strong [CII] emission is also seen in the hub-filament system. Since the main filament is sandwiched between two HII regions, it is most likely that gas is efficiently accreting from the shells of the HII regions along the magnetic field resulting in active star formation. This is consistent with the NGC 6334 being bright in [CII] emission.

astro-ph.GA↗

arXiv2024

Processing of hydrocarbon dust in star-forming galaxies revealed with AKARI

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 $(L_{\mathrm{IR}})$ for 138 star-forming galaxies at redshift $z\ <\ 0.3$. Using near-infrared 2.5-5 $\mathrm{μm}$ spectra obtained with AKARI, we derived the luminosities of the aromatic hydrocarbon feature at 3.3 $\mathrm{μm}$ ($L_\mathrm{aromatic}$) and the aliphatic hydrocarbon feature at 3.4-3.6 $\mathrm{μm}$ ($L_\mathrm{aliphatic}$). We also derived $L_\mathrm{IR}$ 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 $L_\mathrm{IR}$ tend to exhibit lower $L_\mathrm{aliphatic}/L_\mathrm{aromatic}$ ratios. Furthermore, we find that there is an anti-correlation between $L_\mathrm{aliphatic}/L_\mathrm{aromatic}$ ratios and the radiation field strength, and also that the galaxies with low $L_\mathrm{aliphatic}/L_\mathrm{aromatic}$ ratios are dominated by merger galaxies. These results support that hydrocarbon dust is processed through photodissociation in strong radiation fields and/or shocks during merging processes of galaxies; the $L_\mathrm{aliphatic}/L_\mathrm{aromatic}$ ratio is likely to decrease in such harsh interstellar conditions since the aliphatic bonds are known to be chemically weaker than the aromatic bonds.

astro-ph.GA↗

arXiv2021

Infrared Absorption and its Sources of CdZnTe at Cryogenic Temperature

To reveal the infrared absorption causes in the wavelength region between electronic and lattice absorptions, we measured the temperature dependence of the absorption coefficient of $p$-type low-resistivity ($\sim 10^2~{\rm Ωcm}$) CdZnTe crystals. We measured the absorption coefficients of CdZnTe crystals in four-wavelength bands ($λ=6.45$, 10.6, 11.6, 15.1$~μ$m) over the temperature range of $T=8.6-300$ K with an originally developed system. The CdZnTe absorption coefficient was measured to be $α=0.3-0.5$ ${\rm cm^{-1}}$ at $T=300$ K and $α=0.4-0.9$ ${\rm cm^{-1}}$ at $T=8.6$ K in the investigated wavelength range. With an absorption model based on transitions of free holes and holes trapped at an acceptor level, we conclude that the absorption due to free holes at $T=150-300$ K and that due to trapped-holes at $T<50$ K are dominant absorption causes in CdZnTe. We also discuss a method to predict the CdZnTe absorption coefficient at cryogenic temperature based on the room-temperature resistivity.

astro-ph.IM↗

arXiv2019

A systematic study of Galactic infrared bubbles along the Galactic plane with AKARI and Herschel. II. Spatial distributions of dust components around the bubbles

Galactic infrared (IR) bubbles, which can be seen as shell-like structures at mid-IR wavelengths, are known to possess massive stars within their shell boundaries. In our previous study, Hanaoka et al. (2019) expanded the research area to the whole Galactic plane ($0^{\circ} \leq l \leq 360^{\circ}$, $|b| \leq 5^{\circ}$) and studied systematic differences in the shell morphology and the IR luminosity of the IR bubbles between inner and outer Galactic regions. In this study, utilizing high spatial-resolution data of AKARI and WISE in the mid-IR and Herschel in the far-IR, we investigate the spatial distributions of dust components around each IR bubble to discuss the relation between the star-formation activity and the dust properties of the IR bubbles. For the 247 IR bubbles studied in Hanaoka et al. (2019), 165 IR bubbles are investigated in this study, which have the Herschel data ($|b| \leq 1^{\circ}$) and known distances. We created their spectral energy distributions on a pixel-by-pixel basis around each IR bubble, and decomposed them with a dust model consisting of polycyclic aromatic hydrocarbons (PAHs), hot dust, warm dust and cold dust. As a result, we find that the offsets of dust heating sources from the shell centers in inner Galactic regions are systematically larger than those in outer Galactic regions. Many of the broken bubbles in inner Galactic regions show large angles between the offset and the broken shell directions from the center. Moreover, the spatial variations of the PAH intensity and cold dust emissivity around the IR bubbles in inner Galactic regions are larger than those in outer Galactic regions. We discuss these results in light of the interstellar environments and the formation mechanism of the massive stars associated with the IR bubbles.

astro-ph.GA↗

arXiv2018

A systematic study of Galactic infrared bubbles along the Galactic plane with AKARI and Herschel

Galactic infrared (IR) bubbles, which have shell-like structures in the mid-IR wavelengths, are known to contain massive stars near their centers. IR bubbles in inner Galactic regions ($|$l$|\leq$ 65$^{\circ}$, $|$b$|\leq$ 1$^{\circ}$) have so far been studied well to understand the massive star formation mechanisms. In this study, we expand the research area to the whole Galactic plane (0$^{\circ}\leq$ l $<$360$^{\circ}$, $|$b$|\leq$ 5$^{\circ}$), using the AKARI all-sky survey data. We limit our study on large bubbles with angular radii of $>1'$ to reliably identify and characterize them. For the 247 IR bubbles in total, we derived the radii and the covering fractions of the shells, based on the method developed in \citet{Hattori2016}. We also created their spectral energy distributions, using the AKARI and Herschel photometric data, and decomposed them with a dust model, to obtain the total IR luminosity and the luminosity of each dust component, i.e., polycyclic aromatic hydrocarbons (PAHs), warm dust and cold dust. As a result, we find that there are systematic differences in the IR properties of the bubbles between inner and outer Galactic regions. The total IR luminosities are lower in outer Galactic regions, while there is no systematic difference in the range of the shell radii between inner and outer Galactic regions. More IR bubbles tend to be observed as broken bubbles rather than closed ones and the fractional luminosities of the PAH emission are significantly higher in outer Galactic regions. We discuss the implications of these results for the massive stars and the interstellar environments associated with the Galactic IR bubbles.

astro-ph.GA↗

arXiv2018

Enhanced dust emissivity power-law index along the western H$α$ filament of NGC 1569

We used a data set from AKARI and Herschel images at wavelengths from 7 $μ$m to 500 $μ$m to catch the evidence of dust processing in galactic winds in NGC 1569. Images show a diffuse infrared (IR) emission extending from the galactic disk into the halo region. The most prominent filamentary structure seen in the diffuse IR emission is spatially in good agreement with the western H$α$ filament (western arm). The spatial distribution of the $F_\mathrm{350}/F_\mathrm{500}$ map shows high values in regions around the super-star clusters (SSCs) and towards the western arm, which are not found in the $F_\mathrm{250}/F_\mathrm{350}$ map. The color-color diagram of $F_\mathrm{250}/F_\mathrm{350}$-$F_\mathrm{350}/F_\mathrm{500}$ indicates high values of the emissivity power-law index ($β_\mathrm{c}$) of the cold dust component in those regions. From a spectral decomposition analysis on a pixel-by-pixel basis, a $β_\mathrm{c}$ map shows values ranging from $\sim1$ to $\sim2$ over the whole galaxy. In particular, high $β_\mathrm{c}$ values of $\sim2$ are only observed in the regions indicated by the color-color diagram. Since the average cold dust temperature in NGC 1569 is $\sim30$ K, $β_\mathrm{c}<2.0$ in the far-IR and sub-mm region theoretically suggests emission from amorphous grains, while $β_\mathrm{c}=2.0$ suggests that from crystal grains. Given that the enhanced $β_\mathrm{c}$ regions are spatially confined by the HI ridge that is considered to be a birthplace of the SSCs, the spatial coincidences may indicate that dust grains around the SSCs are grains of relatively high crystallinity injected by massive stars originating from starburst activities and that those grains are blown away along the HI ridge and thus the western arm.

astro-ph.GA↗

arXiv2017

A star formation study of the ATLAS3D early-type galaxies with the AKARI all-sky survey

The star formation properties of early-type galaxies (ETGs) are currently the subject of considerable interest, particularly whether they differ from those of gas-rich spirals. We perform a systematic study of star formation in a large sample of local ETGs using polycyclic aromatic hydrocarbon (PAH) and dust emission, focusing on the galaxies' star formation rates (SFRs) and star formation efficiencies (SFEs). Our sample is composed of the 260 ETGs from the ATLAS3D survey, from which we use the cold gas measurements (HI and CO). The SFRs are estimated from stellar, PAH and dust fits to spectral energy distributions created from new AKARI measurements and literature data from WISE and 2MASS. The mid-infrared luminosities of non-CO-detected galaxies are well correlated with their stellar luminosities, showing that they trace (circum)stellar dust emission. CO-detected galaxies show an excess above these correlations, uncorrelated with their stellar luminosities, indicating that they likely contain PAHs and dust of interstellar origin. PAH and dust luminosities of CO-detected galaxies show tight correlations with their molecular gas masses, and the derived current SFRs are typically 0.01-1 Msun/yr. These SFRs systematically decrease with stellar age at fixed stellar mass, while they correlate nearly linearly with stellar mass at fixed age. The majority of local ETGs follow the same star-formation law as local star-forming galaxies, and their current SFEs do not depend on either stellar mass or age. Our results clearly indicate that molecular gas is fueling current star formation in local ETGs, that appear to acquire this gas via mechanisms regulated primarily by stellar mass. The current SFEs of local ETGs are similar to those of local star-forming galaxies, indicating that their low SFRs are likely due to smaller cold gas fractions rather than a suppression of star formation.

astro-ph.GA↗

arXiv2016

Fabrication and Analysis of Three-Layer All-Silicon Interference Optical Filter with Sub-Wavelength Structure toward High Performance Terahertz Optics

We propose an all-silicon multi-layer interference filter composed solely of silicon with sub-wavelength structure (SWS) in order to realize high performance optical filters operating in the THz frequency region with robustness against cryogenic thermal cycling and mechanical damage. We demonstrate fabrication of a three-layer prototype using well-established common micro-electro-mechanical systems (MEMS) technologies as a first step toward developing practical filters. The measured transmittance of the three-layer filter agrees well with the theoretical transmittances calculated by a simple thin-film calculation with effective refractive indices as well as a rigorous coupled-wave analysis simulation. We experimentally show that SWS layers can work as homogeneous thin-film interference layers with effective refractive indices even if there are multiple SWS layers in a filter.

astro-ph.IM↗

arXiv2015

Multiplexed readout demonstration of a TES-based detector array in a resistance locked loop

TES-based bolometer and microcalorimeter arrays with thousands of pixels are under development for several space-based and ground-based applications. A linear detector response and low levels of cross talk facilitate the calibration of the instruments. In an effort to improve the properties of TES-based detectors, fixing the TES resistance in a resistance-locked loop (RLL) under optical loading has recently been proposed. Earlier theoretical work on this mode of operation has shown that the detector speed, linearity and dynamic range should improve with respect to voltage biased operation. This paper presents an experimental demonstration of multiplexed readout in this mode of operation in a TES-based detector array with noise equivalent power values (NEP) of $3.5\cdot 10^{-19} $W/$\sqrt{\mathrm{Hz}}$. The measured noise and dynamic properties of the detector in the RLL will be compared with the earlier modelling work. Furthermore, the practical implementation routes for future FDM systems for the readout of bolometer and microcalorimeter arrays will be discussed.

physics.ins-det↗

arXiv2013

Difference in the spatial distribution between H_2O and CO_2 ices in M82 found with AKARI

With AKARI, we obtain the spatially-resolved near-infrared (2.5 - 5.0 um) spectra for the nearby starburst galaxy M82. These spectra clearly show the absorption features due to interstellar ices. Based on the spectra, we created the column density maps of H_2O and CO_2 ices. As a result, we find that the spatial distribution of H_2O ice is significantly different from that of CO_2 ice; H_2O ice is widely distributed, while CO_2 ice is concentrated near the galactic center. Our result for the first time reveals variations in CO_2/H_2O ice abundance ratio on a galactic scale, suggesting that the ice-forming interstellar environment changes within a galaxy. We discuss the cause of the spatial variations in the ice abundance ratio, utilizing spectral information on the hydrogen recombination Brα and Brβ lines and the polycyclic aromatic hydrocarbon 3.3 um emission appearing in the AKARI near-infrared spectra.

astro-ph.GA↗

arXiv2012

Molecular-beam epitaxial growth of a far-infrared transparent electrode for extrinsic Germanium photoconductors

We have evaluated the optical and electrical properties of a far-infrared (IR) transparent electrode for extrinsic germanium (Ge) photoconductors at 4 K, which was fabricated by molecular beam epitaxy (MBE). As a far-IR transparent electrode, an aluminum (Al)-doped Ge layer is formed at well-optimized doping concentration and layer thickness in terms of the three requirements: high far-IR transmittance, low resistivity, and excellent ohmic contact. The Al-doped Ge layer has the far-IR transmittance of >95 % within the wavelength range of 40--200 microns, while low resistivity (~5 ohm-cm) and ohmic contact are ensured at 4 K. We demonstrate the applicability of the MBE technology in fabricating the far-IR transparent electrode satisfying the above requirements.

cond-mat.mtrl-sci↗

arXiv2012

The Central Region of the Barred Spiral Galaxy NGC1097 Probed by AKARI Near-Infrared Spectroscopy

With the Infrared Camera on board AKARI, we carried out near-infrared (2.5-5.0 micron) spectroscopy of the central kiloparsec region of the barred spiral galaxy, NGC1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the area of ~50"*10" with the resolution of ~5", covering about a half of the ring and the galactic center. As a result, we spatially resolve the starburst ring in the polycyclic aromatic hydrocarbon 3.3 micron, the aliphatic hydrocarbon 3.4-3.6 micron features, and the hydrogen Br alpha 4.05 micron emission. They exhibit spatial distributions significantly different from each other, indicating that the environments vary considerably around the ring. In particular, the aliphatic features are enhanced near the bar connecting the ring with the nucleus, where the structure of hydrocarbon grains seems to be relatively disordered. Near the center, the continuum emission and the CO/SiO absorption features are strong, which indicates that the environments inside the ring are dominated by old stellar populations. The near-infrared spectra do not show any evidence for the presence of nuclear activity.

astro-ph.GA↗

arXiv2011

Properties of dust and PAHs in the hot plasma of the elliptical galaxy NGC4125 revealed with AKARI and Spitzer

We present the spatial distributions of dust and polycyclic aromatic hydrocarbons (PAHs) in the elliptical galaxy NGC4125, revealed by AKARI and Spitzer. NGC4125 is relatively bright in the dust and the PAH emision for elliptical galaxies, although it certainly possesses diffuse interstellar hot plasma indicated by the high spatial resolution X-ray data of Chandra. We investigate how the dust and PAHs interact with the X-ray plasma or avoid the interaction by comparing their spatial distributions. We find that the distributions of the PAHs and dust are different from each other, both showing a significant deviation from a smooth stellar distribution. The PAH emission predominantly comes from a dust lane, a compact dense molecular gas region in the galactic center, where the PAHs are likely to have been protected from the interaction with the X-ray plasma. The dust emission has more extended structures similar to the distribution of the X-ray plasma, suggesting their interaction to some extent. We also discuss a possible origin of the dust and PAHs in the galaxy.

astro-ph.CO↗

arXiv2011

Far-infrared emission from intergalactic medium in Stephan's Quintet revealed by AKARI

The Stephan's Quintet (SQ, HCG92) was observed with the Far-Infrared Surveyor (FIS) aboard AKARI in four far-infrared (IR) bands at 65, 90, 140, and 160 um. The AKARI four-band images of the SQ show far-IR emission in the intergalactic medium (IGM) of the SQ. In particular, the 160 um band image shows single peak emission in addition to the structure extending in the North-South direction along the shock ridge as seen in the 140 um band, H2 emission and X-ray emission. Whereas most of the far-IR emission in the shocked region comes from the cold dust component, shock-powered [CII]158um emission can significantly contribute to the emission in the 160 um band that shows a single peak at the shocked region. In the shocked region, the observed gas-to-dust mass ratio is in agreement with the Galactic one. The color temperature of the cold dust component (~20 K) is lower than that in surrounding galaxies (~30 K). We discuss a possible origin of the intergalactic dust emission.

astro-ph.CO↗

arXiv2011

AKARI Near-Infrared Spectroscopic Observations of Interstellar Ices in Edge-on Starburst Galaxy NGC253

We present the spatially-resolved near-infrared (2.5-5.0 um) spectra of the edge-on starburst galaxy NGC253 obtained with the Infrared Camera onboard AKARI. Near the center of the galaxy, we clearly detect the absorption features of interstellar ices (H_2O: 3.05 um, CO_2: 4.27 um, and XCN: 4.62 um) and the emission of polycyclic aromatic hydrocarbons (PAHs) at 3.29 um and hydrogen recombination line Br alpha at 4.05 um. We find that the distributions of the ices differ from those of the PAH and gas. We calculate the column densities of the ices and derive the abundance ratios of N(CO_2)/N(H_2O) = 0.17 +- 0.05. They are similar to those obtained around the massive young stellar objects in our Galaxy (0.17 +- 0.03), although much stronger interstellar radiation field and higher dust temperature are expected near the center of NGC253.

astro-ph.GA↗

arXiv2010

Origin of the dust emission from Tycho's SNR

Aims: We investigate the spatial distribution of dust emission around Tycho's SNR to understand its origin. We distinguish the dust associated with the SNR from that of the surrounding ISM. Methods: We performed mid- to far-infrared imaging observations of the remnant at wavelengths of 9, 15, 18, 24, 65, 90, 140, and 160um using the Infrared Camera and the Far-Infrared Surveyor onboard AKARI. We compared the AKARI images with the Suzaku X-ray image and the 12CO image of Tycho's SNR. Results: All the AKARI images except the 9, 140, and 160um band images show a shell-like emission structure with brightness peaks at the north east (NE) and north west (NW) boundaries, sharply outlining part of the X-ray shell. The 140 and 160um bands are dominated by cold dust emission from the surrounding ISM near the NE boundary. Conclusion: We conclude that the dust emission at the NE boundary comes from the ambient cloud interacting with the shock front, while the origin of the dust emission at the NW boundary is rather unclear because of the absence of prominent interstellar clouds near the corresponding region. We cannot rule out the possibility that the latter is mostly of an SN ejecta origin.

astro-ph.GA↗