The unidentified infrared (UIR) bands, whose carriers are thought to be organics, have been widely observed in various astrophysical environments. However, our knowledge of the detailed chemical composition and formation process of the carriers is still limited. We have synthesized laboratory organics named Quenched Nitrogen-included Carbonaceous Composite (QNCC) by quenching plasma produced from nitrogen gas and hydrocarbon solids. Infrared and X-ray analyses of QNCC showed that infrared properties of QNCC well reproduce the UIR bands observed in novae and amine structures contained in QNCC play an important role in the origin of the broad 8 m feature, which characterizes the UIR bands in novae. QNCC is at present the best laboratory analog of organic dust formed around dusty classical novae, which carries the UIR bands in novae via thermal emission process [Endo et al.(2021)].

In this paper, I review several dust evolution studies based on the DustPedia nearby galaxy sample. I first present the dust spectral energy distribution model, implementing a hierarchical Bayesian method, that we have developed. I then discuss the dust evolution trends we have derived among (integrated) and within (resolved) galaxies. In particular, we show that the trend of dust-to-gas ratio with metallicity is clearly non-linear, indicating the need for grain growth in the interstellar medium. Our trend is closer to the one derived with damped Lyα systems than what was suggested by previous studies. We finally demonstrate the universal processing of small amorphous carbon grains by stellar photons.

Dust absorbs stellar emission and reradiates this energy in the far-infrared (FIR). FIR observations hence give us a direct view of the dust, and allow us to study its properties. Unfortunately, FIR observations are only available for a small subset of galaxies. In this work, we estimate the global FIR emission from global UV-NIR observations. We show that a machine learning method clearly outperforms a SED modelling approach. For each galaxy, we not only predict the FIR flux across the 6 Herschel bands, but also estimate individual uncertainties. We inspect the worst predictions, and investigate how the machine learning predictor generalizes on new data. Our predictor can be used as a virtual observatory, which is especially useful now that there is still no confirmed next-generation FIR telescope.

The estimation of interstellar dust masses is an important pursuit in our understanding of both local and early Universe – see e.g. the “dust budget crisis”. One of the most used methods of estimating dust masses – dust emission fitting – requires an estimate of the dust opacity at far-infrared and submillimeter wavelengths, but in most models this quantity is based on extrapolation rather than on actual measurements. It is becoming more and more evident that the opacity in typical dust models differs from that of dust analogs measured in the lab, meaning that astronomical dust mass estimations may need to be revised. To estimate the systematic errors introduced by this mismatch, we calculated dust emission for a model where dust far-infrared opacity is the same as that measured in lab samples, then we fit the synthetic emission with a typical (modified blackbody) dust model. Our results show that, if interstellar dust is indeed similar to the lab dust analogs, most fits may overestimate dust masses by as much as an order of magnitude.

Interstellar dust is traced by not only thermal emission but also scattered light. The scattered light spectrum observed from ultraviolet (UV) to near-infrared (IR) is useful to constrain some dust properties, such as size distribution, albedo, and composition. Milky Way Galaxy is a unique environment to observe the diffuse scattered light because we can extract it by removing the contribution of starlight. We have observed the UV to near-IR scattered light with space instruments, including Diffuse Infrared Background Experiment (DIRBE), Hubble Space Telescope (HST), and Multi-purpose Infra-Red Imaging System (MIRIS). The scattered light spectrum is marginally consistent with prediction from a recent dust model including carbonaceous and silicate grains with polycyclic aromatic hydrocarbon (PAH). Based on the MIRIS observation of a diffuse cloud, we compare the scattered light color with the dust model with or without grains larger than 1 micrometer. The result shows that the color is consistent with the model without the large grains, which is consistent with recent simulations of dust growth in low-density regions. However, some observations have shown the spectral excess at ∼ 0.6 micrometer wavelength, suggesting the presence of extended red emission (ERE) which cannot be explained by the conventional dust model.

Characterising primeval galaxies entails the challenging goal of observing galaxies with modest star formation rates (SFR < 100 Mȯyr−1) and approaching the beginning of the reionisation epoch (z > 6). To date a large number of primeval galaxies have been identified thanks to deep near-infrared surveys. However, to further our understanding on the formation and evolution of such primeval objects, we must investigate their nature and physical properties through multi-band spectroscopic observations. Information on dust content, metallicity, interactions with the surrounding environment, and outflows can be obtained with ALMA observations of far-infrared (FIR) lines such as the [Cii] at 158 μm and [Oiii] at 88 μm. Here, we, thus, discuss the recent results unveiled by ALMA observations and present new [Cii] observations of BDF-3299, a star-forming galaxy at z = 7.1 showing a spatial and spectral offset between the rest-frame UV and the FIR lines emission.

Syntheses of carbon dust analogues are key experiments in laboratory astrophysics, as an approach to study some chemical and topological features of interplanetary and interstellar carbon dust. We report a comparative experimental study for carbon dust analogues obtained in (1) an atmospheric pressure dielectric barrier discharge (DBD), fed with helium – saturated hydrocarbons gas mixtures, (2) a low pressure radio frequency (RF) discharge and (3) a pulsed laser deposition (PLD) experiment with a Nd:YAG laser and a graphite target. The aliphatic –C–H stretching band, known as the 3.4 micron feature, as well as the CH2/CH3 ratio, the H/C ratio value and the physical appearance at microscopic scale, show a variability that is influenced by the synthesis method and the experimental parameters of each specific technique.

Polycyclic aromatic hydrocarbons (PAH) and their derivatives, including protonated and cationic species, are suspected to be carriers of the unidentified infrared (UIR) emission bands observed from the galactic and extragalactic sources. We investigated the infrared (IR) spectra of protonated nonplanar PAHs: corannulene (C20H10) and sumanene (C21H12), that are regarded as a fragments of a fullerene,C60. The protonated corannulene H+ C20H10 and sumanene H+ C21H12 were produced in seperate experiments by bombarding a mixture of corannulene/sumanene and para-hydrogen (p-H2) with electrons during deposition at 3.2 K. During maintenance of the electron-bombarded matrix in darkness the intensities of IR lines of protonated corannulene decreased because of neutralization by electrons that were slowly released from the trapped sites whereas the hydrogenated species were produced. The observed lines were classified into several groups according to their responses to darkness and secondary irradiation at 365 nm/385 nm LEDs. Spectral assignments were derived based on a comparison of the observed spectra with those predicted with the B3PW91/6-311+ +G(2d,2p) method. The observed IR spectrum of hub-H+ C20H10, the most stable protonated isomer, resembles several bands of the Class-A UIR bands.

Observations of the mid-infrared (mid-IR, 3-15 μm) spectra of photo-dissociation regions reveal ubiquitous, broad and intense emission bands, the aromatic infrared bands (AIBs), attributed to polycyclic aromatic hydrocarbons (PAHs). Studies of the AIBs showed spectral variations (e.g. in the band positions) between different astrophysical objects, or even within single object, thanks to hyperspectral images. The James Webb Space Telescope (JWST) will allow to get further spectral and spatial details compared to former space observatories. This will come with large data sets, which will require specific tools in order to perform efficient scientific analysis.

We propose in this study a method based on blind signal separation to reduce the analysis of such large data set to that of a small number of elementary spectra, spectrally representative of the data set and physically interpretable as the spectra of populations of mid-IR emitters. The robustness and fastness of the method are improved compared to former algorithms. It is tested on a ISO-SWS data set, which approaches the best the characteristics of JWST data, from which four elementary spectra are extracted, attributed to cationic, neutral PAHs, evaporating very small grains and large and ionized PAHs.

We have succeeded in synthesizing organics, ‘Quenched Nitrogen-included Carbonaceous Composite (QNCC)’, via plasma chemical vapor deposition (CVD) method, whose infrared spectral properties reproduce the characteristics of the unidentified infrared (UIR) bands observed around classical novae. Past studies have shown that the UIR bands observed around novae appear somewhat differently from those observed in other astrophysical environment and are predominantly characterized by the presence of a broad 8μm feature. The remarkable similarity between the infrared properties of QNCC and the UIR bands in novae indicates that QNCC should be considered as a strong candidate of the carriers of the UIR bands in novae. Finally, we have started a space exposure experiment of QNCC aiming to explore the evolutional link between the QNCC and the insoluble organic molecule (IOM) in carbonaceous condrite and, thus, to infer the origins of organics in our solar system.

PAH clusters are one candidate species for the interstellar “very small grains” or “VSGs”, i.e., dust grains small enough to be stochastically heated and contribute to the aromatic infrared emission bands (AIBs). This possibility motivated laboratory experiments on the infrared spectroscopy of PAH clusters using matrix isolation spectroscopy. The spectral shifts due to PAH clustering in argon matrices provide clues for the AIB contribution from PAH clusters in the interstellar medium. Here we review results from a number of small PAH species, extrapolation to the much larger PAHs believed to be present in the interstellar medium, and the implications for a PAH cluster contribution to the VSG population.

The James Webb Space Telescope (JWST) is expected to be launched in 2021. The JWST’s science instruments will provide high quality spectra acquired in the line of sight to young stellar objects whose interpretation will require a robust database of laboratory data. With this in mind, an experimental work is in progress in the Laboratory for Experimental Astrophysics in Catania to study the profile (shape, width, and peak position) of the main infrared bands of molecular species expected to be present in icy grain mantles. Our study also takes into account the modifications induced on icy samples by low-energy cosmic ray bombardment and by thermal processing. Here we present some recent results on deuterium hydrogen monoxide (HDO), N-bearing species, and carbon dioxide (CO2).

The mid-IR spectrum of the interstellar medium contains both aromatic and aliphatic hydrocarbon features. These are generally attributed to carbonaceous dust. The aliphatic component is of particular interest because it produces a significant 3.4 μm absorption feature. The optical depth of this feature is related to the number and type of aliphatic carbon C–H bonds in the line of sight. It is possible to estimate the column density of aliphatic carbon from quantitative analysis of the 3.4 μm interstellar feature, providing that the absorption coefficient of interstellar aliphatic hydrocarbon is known. We produced interstellar dust analogues with spectra closely matching astronomical observations. Using a combination of FTIR and 13C NMR spectroscopy, we determined an integrated absorption coefficient of the aliphatic component. The results thus obtained permit direct calibration of astronomical observations, providing rigorous estimates of the amount of aliphatic carbon in the ISM.

Star formation started as a cosmic process soon after the big bang and still continues in the Milky Way, although at a decreasing rate. The formation of dense interstellar clouds, their fragmentation and eventual collapse lead to the birth of stars. The nearby clouds provide the highest resolution for the study of this process. The progress is closely following the improvement of the infrared and radio-wavelength facilities that enables us to follow even the earliest stages of the star-formation process inside molecular clouds. On the other hand, modern numerical simulations can take into account most of the relevant physics and often provide a more direct access into the general principles of star formation. The comparison of observations and simulations is therefore essential. In this paper, will discuss star formation in the solar neighbourhood, concentrating on the prestellar phases leading up to the formation of protostars.

The apparent lack of cold molecular gas in blue compact dwarf (BCD) galaxies is at variance with their intense star-formation episode. The CO molecule, often used a tracer of H2 through a conversion function, is selectively photodissociated in dust-poor environments and, as a result, a potentially large fraction of H2 is expected to reside in the so-called CO-dark gas, where it could be traced instead by infrared cooling lines [CI], [CII], and [OI]. Although the fraction of CO-dark gas to total molecular gas is in theory expected to be relatively large in metal-poor galaxies, many uncertainties remain due to the difficulty in identifying the main heating mechanism associated to the cooling lines observed in such galaxies.

Investigations of the Herschel Dwarf Galaxy Survey (DGS; Madden et al.2013) show that the heating mechanism in the neutral gas of BCDs cannot be dominated by the photoelectric effect on dust grains below some threshold metallicity due to the low abundance of dust and polycyclic aromatic hydrocarbons, implying that other heating mechanisms need to be invoked, along with a new interpretation of the corresponding infrared line diagnostics. In the study presented here and in Lebouteiller et al. (2017), we use optical and infrared lines to constrain the physical conditions in the HII region + HI region of the BCD I Zw 18 (18 Mpc; ≍2% solar metallicity) within a consistent photoionization and photodissociation model. We show that the HI region is entirely heated by a single ultraluminous X-ray source with important consequences on the applicability of [CII] to trace the star-formation rate and to trace the CO-dark gas. We derive stringent upper limits on the size of H2 clumps that may be detected in the future with JWST and IRAM/NOEMA. We also show that the nature of the X-ray source can be inferred from the corresponding signatures in the ISM. Finally we speculate that star formation may be quenched in extremely metal-poor dwarf galaxies due to X-ray photoionization.

This review examines observations of magnetic fields in molecular clouds, that is, at spatial scales ranging from tens to tenths of parsecs and densities up to hundreds of particles per cubic centimetre. I will briefly summarize the techniques for observing and mapping magnetic fields in molecular clouds. I will review important examples of observational results obtained using each technique and their implications for our understanding of the role of the magnetic field in molecular cloud formation and evolution. Finally, I will briefly discuss the prospects for advances in our observational capabilities with telescopes and instruments now beginning operation or under construction.

We investigate dynamics of slender magnetic flux tubes (MFT) in the accretion disks of young stars. Simulations show that MFT rise from the disk and can accelerate to 20-30 km/s causing periodic outflows. Magnetic field of the disk counteracts the buoyancy, and the MFT oscillate near the disk’s surface with periods of 10-100 days. We demonstrate that rising and oscillating MFT can cause the IR-variability of the accretion disks of young stars.

The unidentified infrared (UIR) bands have been ubiquitously observed in various astrophysical environments and consist of a series of emission features arising from aromatic and/or aliphatic C-C and C-H bonds [1]. Therefore, their carriers are thought to be related to interstellar organics. However, our knowledge on the true carriers of the UIR bands is still limited. Recently [4] has proposed Mixed Aromatic Aliphatic Organic Nanoparticles, which contains hetero atoms in addition to conventional hydrocarbon models, as a more realistic interpretation of the band carriers. The challenges toward identifying the carriers of the UIR bands are still ongoing. Past studies have shown that the UIR bands observed around classical novae, which characterized by the presence of broad feature around 8μm[2], are somewhat different from those observed in other astrophysical environment. Here we report the success of experimentally synthesizing the organics called Nitrogen-included Carbonaceous Compounds (NCC; [7]) whose infrared properties can reproduce the UIR bands observed in classical novae.

Investigating the distant extragalactic Universe requires a subtraction of the Galactic foreground. One of the major difficulties deriving the fine structure of the galactic foreground is the embedded foreground and background point sources appearing in the given fields. It is especially so in the infrared. We report our study subtracting point sources from Herschel images with Kriging, an interpolation method where the interpolated values are modelled by a Gaussian process governed by prior covariances. Using the Kriging method on Herschel multi-wavelength observations the structure of the Galactic foreground can be studied with much higher resolution than previously, leading to a better foreground subtraction at the end.

We estimate the column density of the Galactic foreground interstellar medium (GFISM) in the direction of extragalactic sources. All-sky AKARI FIS infrared sky survey data might be used to trace the GFISM with a resolution of 2 arcminutes. The AKARI based GFISM hydrogen column density estimates are compared with similar quantities based on HI 21cm measurements of various resolution and of Planck results. High spatial resolution observations of the GFISM may be important recalculating the physical parameters of gamma-ray burst (GRB) host galaxies using the updated foreground parameters.