Bringing high spatial resolution to the far-infrared

The far-infrared (FIR) regime is one of the wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist. None of the medium-term satellite projects like SPICA, Millimetron, or the Origins Space Telescope will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO), light hydrides, and especially from water lines would open the door for transformative science. A main theme will be to trace the role of water in proto-planetary discs, to observationally advance our understanding of the planet formation process and, intimately related to that, the pathways to habitable planets and the emergence of life. Furthermore, key observations will zoom into the physics and chemistry of the star-formation process in our own Galaxy, as well as in external galaxies. The FIR provides unique tools to investigate in particular the energetics of heating, cooling, and shocks. The velocity-resolved data in these tracers will reveal the detailed dynamics engrained in these processes in a spatially resolved fashion, and will deliver the perfect synergy with ground-based molecular line data for the colder dense gas.

The Herschel SPIRE Fourier Transform Spectrometer Spectral Feature Finder – IV. Neutral carbon detection in the SPIRE FTS spectra

ABSTRACT The SPIRE Fourier Transform Spectrometer (FTS) Spectral Feature Finder (FF), developed within the Herschel Spectral and Photometric Imaging Receiver (SPIRE) FTS instrument team, is an automated spectral feature fitting routine that attempts to find significant features in SPIRE FTS spectra. The 3P1–3P0 and 3P2–3P1 neutral carbon fine structure lines are common features in carbon-rich far-infrared astrophysical sources. These features can be difficult to detect using an automated feature detection routine due to their typically low amplitude and line blending. In this paper, we describe and validate the FF subroutine designed to detect the neutral carbon emission observed in SPIRE spectral data.

Integrated approach to the PDR/H ii complex by the application of carbon radio recombination lines in the millimetre range and fine-structure lines of C ii and O i

ABSTRACT We have performed self-consistent calculations to estimate the physical parameters of photodissociation regions (PDRs) associated with objects, namely, NGC 2024, Orion A and W3, using far-infrared continuum emission, fine-structure lines of C ii and O i, and radio recombination lines of carbon. Typically, PDRs separate H ii regions from the molecular cloud; therefore, necessary corrections for the contribution to C ii line emission due to the H ii region are made. For that purpose, using observational data, theoretical calculations are performed to obtain the best fit for the said observations. Three parameters, angular size, θ (in arcminutes), far-ultraviolet radiation field G0, and hydrogen density nH (which gives electron density and temperature), are varied, and the sets of parameters (G0 and nH) obtained for the NGC 2024, Orion A and W3 PDRs are (7.6 × 104 and 1.2 × 105 cm−3), (2.8 × 105 and 2.3 × 105 cm−3) and (3.7 × 105 and 1.9 × 105 cm−3), respectively. The relationship between line and continuum emissions from PDRs associated with H ii regions leads us to conclude that exciting stars for the NGC 2024, Orion A and W3 H ii regions are O8–O9V, O6–O7V and O5–O6V, respectively.

A dense, solar metallicity ISM in the z = 4.2 dusty star-forming galaxy SPT 0418−47

We present a study of six far-infrared fine structure lines in the z = 4.225 lensed dusty star-forming galaxy SPT 0418−47 to probe the physical conditions of its interstellar medium (ISM). In particular, we report Atacama Pathfinder EXperiment (APEX) detections of the [OI] 145 μm and [OIII] 88 μm lines and Atacama Compact Array (ACA) detections of the [NII] 122 and 205 μm lines. The [OI] 145 μm/[CII] 158 μm line ratio is ∼5× higher compared to the average of local galaxies. We interpret this as evidence that the ISM is dominated by photo-dissociation regions with high gas densities. The line ratios, and in particular those of [OIII] 88 μm and [NII] 122 μm imply that the ISM in SPT 0418−47 is already chemically enriched to nearly solar metallicity. While the strong gravitational amplification was required to detect these lines with APEX, larger samples can be observed with the Atacama Large Millimeter/submillimeter Array (ALMA), and should allow observers to determine if the dense, solar metallicity ISM is common among these highly star-forming galaxies.

Properties of galaxies at z ≈ 7 – 9 revealed by ALMA

Understanding properties of galaxies in the epoch of reionization (EoR) is a frontier in the modern astronomy. With the advent of ALMA, it has become possible to detect far-infrared fine structure lines (e.g. [CII] 158 μm and [OIII] 88 μm) and dust continuum emission in star-forming galaxies in the EoR. Among these lines, our team is focusing on [OIII] 88 μm observations in high-z galaxies. After the first detection of [OIII] in the epoch of reionization (EoR) in 2016 from our team at z = 7.21, there are now more than ten [OIII] detections at z > 6 up to z = 9.11. Interestingly, high-z galaxies typically have very high [OIII]-to-[CII] luminosity ratio ranging from 3 to 12 or higher, demonstrating [OIII] is a powerful tracer at high-z. The high luminosity ratios may imply that high-z galaxies have low gas-phase metallicity and/or high ionization states.

Особенности электронного парамагнитного резонанса примеси железа в кристаллах HgSe

The electron-spin-resonance spectra of transition metal ions Fe in the HgSe matrix are analyzed. The spectra have an appearance typical of the Fe^3+ ion, i.e., they consist of five fine-structure lines with a splitting that corresponds to a weak crystal field. The spectra are observed at temperatures of up to 50 K. The spectral lines are deformed and have a Dyson shape. An analysis of the temperature dependences of the line amplitudes shows that a transition from paramagnetic ordering to ferromagnetic ordering occurs with decreasing temperature, with the Curie temperature T ≈ 7 K.

The nature of molecular cloud boundary layers from SOFIA [O I] observations

Context. Dense highly ionized boundary layers (IBLs) outside of the neutral Photon Dominated Regions (PDRs) have recently been detected via the 122 and 205 μm transitions of ionized nitrogen. These layers have higher densities than in the Warm Ionized Medium (WIM) but less than typically found in H II regions. Observations of [C II] emission, which is produced in both the PDR and IBL, do not fully define the characteristics of these sources. Observations of additional probes which just trace the PDRs, such as the fine structure lines of atomic oxygen, are needed derive their properties and distinguish among different models for [C II] and [N II] emissison. Aims. We derive the properties of the PDRs adjacent to dense highly ionized boundary layers of molecular clouds. Methods. We combine high-spectral resolution observations of the 63 μm [O I] fine structure line taken with the upGREAT HFA-band instrument on SOFIA with [C II] observations to constrain the physical conditions in the PDRs. The observations consist of samples along four lines of sight (LOS) towards the inner Galaxy containing several dense molecular clouds. We interpret the conditions in the PDRs using radiative transfer models for [C II] and [O I]. Results. We have a 3.5-σ detection of [O I] toward one source but only upper limits towards the others. We use the [O I] to [C II] ratio, or their upper limits, and the column density of C+ to estimate the thermal pressure, Pth, in these PDRs. In two LOS the thermal pressure is likely in the range 2–5 × 105 in units of K cm−3, with kinetic temperatures of order 75–100 K and H2 densities, n(H2) ~ 2–4 × 103 cm−3. For the other two sources, where the upper limits on [O I] to [C II] are larger, Pth ≲105 (K cm−3). We have also used PDR models that predict the [O I] to [C II] ratio, along with our observations of this ratio, to limit the intensity of the Far UV radiation field. Conclusions. The [C II] and [N II] emission with either weak, or without any, evidence of [O I] indicates that the source of dense highly ionized gas traced by [N II] most likely arises from the ionized boundary layers of clouds rather than from H II regions.