During the dawn of chemistry
, when the temperature of the young Universe had fallen below some 4,000 kelvin, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse ...order of their ionization potential. With their higher ionization potentials, the helium ions He
and He
were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. In this metal-free and low-density environment, neutral helium atoms formed the Universe's first molecular bond in the helium hydride ion HeH
through radiative association with protons. As recombination progressed, the destruction of HeH
created a path to the formation of molecular hydrogen. Despite its unquestioned importance in the evolution of the early Universe, the HeH
ion has so far eluded unequivocal detection in interstellar space. In the laboratory the ion was discovered
as long ago as 1925, but only in the late 1970s was the possibility that HeH
might exist in local astrophysical plasmas discussed
. In particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of HeH
. Here we report observations, based on advances in terahertz spectroscopy
and a high-altitude observatory
, of the rotational ground-state transition of HeH
at a wavelength of 149.1 micrometres in the planetary nebula NGC 7027. This confirmation of the existence of HeH
in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination.
Abstract
M82 is an archetypal starburst galaxy in the local Universe. The central burst of star formation, thought to be triggered by M82's interaction with other members in the M81 group, is driving ...a multiphase galaxy-scale wind away from the plane of the disk that has been studied across the electromagnetic spectrum. Here, we present new velocity-resolved observations of the C
ii
158
μ
m line in the central disk and the southern outflow of M82 using the upGREAT instrument on board SOFIA. We also report the first detections of velocity-resolved (Δ
V
= 10 km s
−1
) C
ii
emission in the outflow of M82 at projected distances of ≈1–2 kpc south of the galaxy center. We compare the C
ii
line profiles to observations of CO and H
i
and find that likely the majority (>55%) of the C
ii
emission in the outflow is associated with the neutral atomic medium. We find that the fraction of C
ii
actually outflowing from M82 is small compared to the bulk gas outside the midplane (which may be in a halo or tidal streamers), which has important implications for observations of C
ii
outflows at higher redshift. Finally, by comparing the observed ratio of the C
ii
and CO intensities to models of photodissociation regions, we estimate that the far-ultraviolet (FUV) radiation field in the disk is ∼10
3.5
G
0
, in agreement with previous estimates. In the outflow, however, the FUV radiation field is 2–3 orders of magnitudes lower, which may explain the high fraction of C
ii
arising from the neutral medium in the wind.
Abstract
We present SOFIA-upGREAT observations of C ii emission of Infrared Dark Cloud (IRDC) G035.39-00.33, designed to trace its atomic gas envelope and thus test models of the origins of such ...clouds. Several velocity components of C ii emission are detected, tracing structures that are at a wide range of distances in the Galactic plane. We find a main component that is likely associated with the IRDC and its immediate surroundings. This strongest emission component has a velocity similar to that of the 13CO(2–1) emission of the IRDC, but offset by ∼3 km s−1 and with a larger velocity width of ∼9 km s−1. The spatial distribution of the C ii emission of this component is also offset predominantly to one side of the dense filamentary structure of the IRDC. The C ii column density is estimated to be of the order of ∼1017–1018 cm−2. We compare these results to the C ii emission from numerical simulations of magnetized, dense gas filaments formed from giant molecular cloud (GMC) collisions, finding similar spatial and kinematic offsets. These observations and modellingof C ii add further to the evidence that IRDC G035.39-00.33 has been formed by a process of GMC–GMC collision, which may thus be an important mechanism for initiating star cluster formation.
ABSTRACT We study the effects of an asymmetric radiation field on the properties of a molecular cloud envelope. We employ observations of carbon monoxide (12CO and 13CO), atomic carbon, ionized ...carbon, and atomic hydrogen to analyze the chemical and physical properties of the core and envelope of L1599B, a molecular cloud forming a portion of the ring at 27 pc from the star Λ Ori. The O8 star provides an asymmetric radiation field that produces a moderate enhancement of the external radiation field. Observations of the C ii fine structure line with the GREAT instrument on SOFIA indicate a significant enhanced emission on the side of the cloud facing the star, while the C i, 12CO and 13CO J = 1-0 and 2-1, and 12CO J = 3-2 data from the Purple Mountain Observatory and APEX telescopes suggest a relatively typical cloud interior. The atomic, ionic, and molecular line centroid velocities track each other very closely, and indicate that the cloud may be undergoing differential radial motion. The H i data from the Arecibo GALFA survey and the SOFIA/GREAT C ii data do not suggest any systematic motion of the halo gas, relative to the dense central portion of the cloud traced by 12CO and 13CO.
Context. The C ii 158 μm fine structure line is one of the dominant cooling lines in star-forming active regions. Together with models of photon-dominated regions, the data is used to constrain the ...physical properties of the emitting regions, such as the density and the radiation field strength. According to the modeling, the C ii 158 μm line integrated intensity compared to the CO emission is expected to be stronger in lower metallicity environments owing to lower dust shielding of the UV radiation, a trend that is also shown by spectral-unresolved observations. In the commonly assumed clumpy UV-penetrated cloud scenario, the models predict a C ii line profile similar to that of CO. However, recent spectral-resolved observations by Herschel/HIFI and SOFIA/GREAT (as well as the observations presented here) show that the velocity resolved line profile of the C ii emission is often very different from that of CO lines, indicating a more complex origin of the line emission including the dynamics of the source region. Aims. The Large Magellanic Cloud (LMC) provides an excellent opportunity to study in great detail the physics of the interstellar medium (ISM) in a low-metallicity environment by spatially resolving individual star-forming regions. The aim of our study is to investigate the physical properties of the star-forming ISM in the LMC by separating the origin of the emission lines spatially and spectrally. In this paper, we focus on the spectral characteristics and the origin of the emission lines, and the phases of carbon-bearing species in the N159 star-forming region in the LMC. Methods. We mapped a 4′ × (3′–4′) region in N159 in C ii 158 μm and N ii 205 μm with the GREAT instrument on board SOFIA. We also observed CO(3–2), (4–3), (6–5), 13CO(3–2), and C i 3P1–3P0 and 3P2–3P1 with APEX. All spectra are velocity resolved. Results. The emission of all transitions observed shows a large variation in the line profiles across the map and in particular between the different species. At most positions the C ii emission line profile is substantially wider than that of CO and C i. We estimated the fraction of the C ii integrated line emission that cannot be fitted by the CO line profile to be 20% around the CO cores, and up to 50% at the area between the cores, indicating a gas component that has a much larger velocity dispersion than the ones probed by the CO and C i emission. We derived the relative contribution from C+, C, and CO to the column density in each velocity bin. The result clearly shows that the contribution from C+ dominates the velocity range far from the velocities traced by the dense molecular gas. Spatially, the region located between the CO cores of N159 W and E has a higher fraction of C+ over the whole velocity range. We estimate the contribution of the ionized gas to the C ii emission using the ratio to the N ii emission, and find that the ionized gas contributes ≤19% to the C ii emission at its peak position, and ≤15% over the whole observed region. Using the integrated line intensities, we present the spatial distribution of ICII/IFIR. Conclusions. This study demonstrates that the C ii emission in the LMC N159 region shows significantly different velocity profiles from that of CO and C i emissions, emphasizing the importance of velocity resolved observations in order to distinguish different cloud components.
One of the most versatile and attractive extensions to the successful yet incomplete Standard Model of particle physics is Supersymmetry – a theory the ATLAS experiment at the Large Hadron Collider ...is looking for in its recorded data. Due to the nature of proton-proton collisions, the recorded physics events are mainly produced via the strong force. This fact makes searches for the superpartners of the gluon and the quarks particularly promising. This document provides an overview of searches for squarks and gluinos using the ATLAS experiment and describes two of the major analyses in detail. The analysis strategies are outlined, the results discussed and interpreted. Finally, an outlook onto other searches for strongly produced Supersymmetry with ATLAS is given.
The cosmic deuterium fraction, set by primordial nucleosynthesis and diminished by subsequent astration, is a valuable diagnostic tool to link the protosolar nebula to the history of star formation. ...However, in the present-day Solar System, the deuterium fraction in various carriers varies by more than an order of magnitude and reflects environmental conditions rather than the protosolar value. The latter is believed to be preserved in the atmospheres of the gas giant planets, yet determinations inferred from the CH 3 D/CH 4 pair require a larger fractionation correction than those from HD/H 2 , which are close to unity. The question of whether a stratospheric emission feature contaminates the absorption profile forming in subjacent layers was never addressed, owing to the lack of spectral resolving power. Here we report on the determination of the Jovian deuterium fraction using the rotational ground-state line of HD ( J = 1–0) at λ 112 μm. Employing the GREAT heterodyne spectrometer on board SOFIA, we detected the HD absorption and, thanks to the high resolving power, a weak stratospheric emission feature underneath; the former is blue-shifted with respect to the latter. The displacement is attributed to a pressure-induced line shift and reproduced by dedicated radiative-transfer modeling based on recent line-profile parameters. Using atmospheric standard models, we obtained D/H = (1.9 ± 0.4) × 10 −5 , which agrees with a recent measurement in Saturn’s atmosphere and with the value inferred from solar-wind measurements and meteoritic data. The result suggests that all three measurements represent bona fide protosolar D/H fractions. As a supplement and test for the consistency of the layering assumed in our model, we provide an analysis of the purely rotational J = 6–5 line of CH 4 (in the vibrational ground state, at λ 159 μm).
Abstract
We present new observations of C
ii
2
P
3/2
→
2
P
1/2
fine structure line emission from an isolated molecular cloud using the upGREAT instrument on board SOFIA. These data are analyzed ...together with archival CO
J
=1–0 and H
i
21 cm emission spectra to investigate the role of converging atomic gas flows in the formation of molecular clouds. Bright C
ii
emission is detected throughout the mapped area that likely originates from photodissociation regions excited by UV radiation fields produced by newborn stars within the cloud. Upon spatial averaging of the C
ii
spectra, we identify weak C
ii
emission within velocity intervals where the H
i
21 cm line is brightest; these are blueshifted relative to velocities of the CO and bright C
ii
emission by 4 km s
−1
. The brightness temperatures, velocity dispersions, and alignment with H
i
21 cm velocities connect this C
ii
emission component to the cold, neutral atomic gas of the interstellar medium, known as the cold, neutral medium (CNM). We propose that this CNM feature is an accretion flow onto the farside of the existing molecular cloud. The mass infall rate is 3.2 × 10
−4
M
⊙
yr
−1
. There is no direct evidence of a comparable redshifted component in the C
ii
or H
i
21 cm spectral lines that would indicate the presence of a converging flow.
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![[C ii] Spectral Mapping of ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X_1538-4357/small "[C ii] Spectral Mapping of the Galactic Wind and Starbursting Disk of M82 with SOFIA")
![Velocity resolved [C ii], [...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361_1432-0746/small "Velocity resolved [C ii], [C i], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities")
