The First Mid-Infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment Towards the Orion Hot Core
Sarah Nickerson, Naseem Rangwala, Sean Colgan, Curtis DeWitt, Xinchuan Huang, Kinsuk Acharyya, Maria Drozdovskaya, Ryan C. Fortenberry, Eric Herbst, Timothy J. Lee
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20 pages, 6 figures, submitted to ApJ, comments welcome
We present the first mid-infrared (MIR) detections of HNC and H13CN in the interstellar medium, and numerous, resolved HCN rovibrational transitions. Our observations span 12.8 to 22.9 micron towards the hot core Orion IRc2, obtained with the Echelon-Cross-Echelle Spectrograph aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Exceptional, ~5 km/s, resolution distinguishes individual rovibrational transitions of the HNC and HCN P, Q, and R branches; and the H13CN R branch. This allows direct measurement of the species' excitation temperatures, column densities, and relative abundances. HNC and H13CN exhibit a local standard rest velocity of -7 km/s that may be associated with an outflow from nearby radio source I and an excitation temperature of about 100 K. We resolve two velocity components for HCN, the primary component also being at -7 km/s with temperature 165 K. The hottest component, which had never before been observed, is at 1 km/s with temperature 309 K. This is the closest component to the hot core's centre measured to date. The derived 12C/13C=13 is below expectation for Orion's Galactocentric distance, but the derived HCN/HNC=72 is expected for this extreme environment. Compared to previous sub-mm and mm observations, our SOFIA line survey of this region shows that the resolved MIR molecular transitions are probing a distinct physical component and isolating the chemistry closest to the hot core.
We report here the first detection in the interstellar medium of the cyanomidyl radical (HNCN). Using the Yebes 40m and the IRAM 30m telescopes, we have targeted the doublets of the $N$=2$-$1, 4$-$3, 5$-$4, 6$-$5, and 7$-$6 transitions of HNCN toward the molecular cloud G+0.693-0.027. We have detected three unblended lines of HNCN, these are the $N$=6$-$5 doublet and one line of the $N$=4$-$3 transition. Additionally we present one line of the $N$=5$-$4 transition partially blended with emission from other species. The Local Thermodynamic Equilibrium best fit to the data gives a molecular abun…
Unmasking the physical information inherent to interstellar spectral line profiles with Machine Learning. I. Application of LTE to HCN and HNC transitions
We analyze HCN and HNC emission in the nearby starburst galaxy NGC 253 to investigate its effectiveness in tracing heating processes associated with star formation. This study uses multiple HCN and HNC rotational transitions observed using ALMA via the ALCHEMI Large Program. To understand the conditions and associated heating mechanisms within NGC 253's dense gas, we employ Bayesian nested sampling techniques applied to chemical and radiative transfer models which are constrained using our HCN and HNC measurements. We find that the volume density $n_{\text{H}_{2}}$ and cosmic ray ionization ra…
We have studied optical properties of interstellar dust around the Orion A molecular cloud to investigate the size distribution and the composition of dust grains. Orion A is one of the most studied molecular clouds in the solar vicinity ($d \simeq 400\ \rm{pc}$). In this paper, we used optical and near-infrared photometric data. The optical data were obtained by $BVRI$ bands imaging observations. The near-infrared data consisting of $JHK_{S}$ bands were taken from 2MASS point source catalog. We produced some color excess maps around Orion A, and measured their ratios such as $E(R-I)/E(B-V)$. …
The [CII] $158\,μ\mathrm{m}$ fine-structure line is one of the dominant coolants of the neutral interstellar medium. It is hence one of the brightest far-infrared emission lines and can be observed not only in star-forming regions throughout the Galaxy, but also in the diffuse interstellar medium and in distant galaxies. [CII] line emission has been suggested to be a powerful tracer of star-formation. We aim to understand the origin of [CII] emission and its relation to other tracers of interstellar gas and dust. This includes a study of the heating efficiency of interstellar gas as traced by …
We present the first high spectral resolution mid-infrared survey in the Orion BN/KL region, covering 7.2 to 28.3 micron. With SOFIA/EXES we target the enigmatic source Orion IRc2. While this is in the most prolifically studied massive star-forming region, longer wavelengths and molecular emission lines dominated previous spectral surveys. The mid-infrared observations in this work access different components and molecular species in unprecedented detail. We unambiguously identify two new kinematic components, both chemically rich with multiple molecular absorption lines. The "blue clump" has …
Examination of emission lines in high-velocity resolution optical spectra of the Orion Nebula confirms that the velocity component on the red wing of the main ionization front emission line is due to backscattering in the Photon Dominated Region. This scattered light component has a weak wavelength dependence that is consistent with either general interstellar medium particles or particles in the foreground of the Orion Nebula Cluster. An anomalous line-broadening component that has been known for 60+ years is characterized in unprecedented detail. Although this extra broadening may be due to …
Mapping Interstellar Ice Inventory toward Class 0 Protostars in Star-forming Region Orion A with JWST Data
Ural Federal University（乌拉尔联邦大学）；Institute of Astronomy of the Russian Academy of Sciences（俄罗斯科学院天文研究所）；Institute of Natural Sciences and Mathematics, Ural Federal University（乌拉尔联邦大学自然科学与数学研究所）；Xinjiang Astronomical Observatory, Chinese Academy of Sciences（中国科学院新疆天文台）
Little is known about the chemistry of isocyanates (compounds with the functional group R-N=C=O) in the interstellar medium, as only four of them have been detected so far: isocyanate radical (NCO), isocyanic acid (HNCO), N-protonated isocyanic acid (H$_2$NCO$^+$) and methyl isocyanate (CH$_3$NCO). The molecular cloud G+0.693-0.027, located in the Galactic Centre, represents an excellent candidate to search for new isocyanates since it exhibits high abundances of the simplest ones, HNCO and CH$_3$NCO. After CH$_3$NCO, the next complex isocyanates are ethyl isocyanate (C$_2$H$_5$NCO) and vinyl …
Quantum chemical cluster calculations show that reactions of C$^+$ with HCN or HNC embedded in the surface of an icy grain mantle can account for the formation of a recently detected molecule, glycolonitrile, which is considered to be an important precursor to ribonucleic compounds. Reactions of cations deposited on ice mantles with minimal kinetic energy have been found theoretically to result in previously unknown pathways to significant organic compounds in protostellar systems and the interstellar medium. In density functional theory cluster calculations involving up to 24H$_2$O, C$^+$ rea…
We report the first identification in space of H2NC, a high-energy isomer of H2CN that has been largely ignored in chemical and astrochemical studies. The observation of various unidentified lines around 72.2 GHz in the cold dark cloud L483 motivated the search for, and successful detection of, additional groups of lines in harmonic relation. After an exhaustive high-level ab initio screening of possible carriers, we confidently assign the unidentified lines to H2NC based on the good agreement between astronomical and theoretical spectroscopic parameters and sound spectroscopic and astrochemic…
Isomers in Interstellar Environments (I): The Case of Z- and E-Cyanomethanimine
在这项工作中，我们提出的Z-和E-氰基甲亚胺（HNCHCN），这两者都是可能的前体的核碱基腺嘌呤的化学研究的结果。对氢原子参与的反应进行了量子化学从头计算。我们发现，H + Z/E-HNCHCN导致H-加成以及H-$_2$ -提取的反应通过类似的短程势垒进行，双分子速率系数为$\sim10^{-17}$ cm $^{3}$ s $^{-1}$。这些结果随后被纳入天体化学模型，并用于模拟巨大的分子云G+0.693。从这些模型中获得的计算丰度与以前的观测数据进行了比较，发现是在良好的协议，与$\sim3$的预测[Z/E]比-略小于以前推导出的值$6.1\pm2.4$。我们发现，在我们的模拟中的[Z/E]比主要是由于离子分子的破坏率驱动的两个构象的不同的永久偶极子。基于这些结果，我们提出了一个通用的经验法则，估计在星际环境中的异构体的丰度。
Surveying the Whirlpool at Arcseconds with NOEMA (SWAN). IV. Extent of active galactic nucleus feedback on the interstellar medium
Universität Bonn（波恩大学）；Observatorio Astronómico Nacional (IGN)（国家天文台（西班牙地理与测绘研究所））；The Ohio State University（俄亥俄州立大学）；Center for Cosmology and Astro-Particle Physics, Ohio State University（俄亥俄州立大学宇宙学与天体粒子物理中心）；National Astronomical Observatory of Japan（日本国立天文台）；Max Planck Institute for Radio Astronomy（马克斯·普朗克射电天文研究所）；University of Arkansas（阿肯色大学）
We have complemented existing observations of HI absorption with new observations of HCO$^+$, C$_2$H, HCN, and HNC absorption from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Northern Extended Millimeter Array (NOEMA) in the direction of 20 background radio continuum sources with $4^\circ \leq |b| \leq 81^\circ$ to constrain the atomic gas conditions that are suitable for the formation of diffuse molecular gas. We find that these molecular species form along sightlines where $A_V \gtrsim 0.25$, consistent with the threshold for the HI-to-H$_2$ transition at solar metallicit…
The formation of hydrides by gas-phase reactions between H2 and a heavy element atom is a very selective process. Reactions with ground-state neutral carbon, oxygen, nitrogen, and sulfur atoms are very endoergic and have high energy barriers because the H2 molecule has to be fragmented before a hydride bond is formed. In cold interstellar clouds, these barriers exclude the formation of CH, OH, NH, and SH radicals through hydrogen abstraction reactions. Here we study a very energetically unfavorable process, the reaction of N(4S) atoms with H2 molecules. We calculated the reaction rate coeffici…
Interstellar dust affects astronomical observations through absorption and reddening, yet this extinction is also a powerful tool for studying interstellar matter in galaxies. 3D reconstructions of dust extinction and density in the Milky Way have suffered from artefacts such as the fingers-of-god effect and negative densities, and have been limited by large computational costs. Here we aim to overcome these issues with a novel algorithm that derives the 3D extinction density of dust in the Milky Way using a latent variable Gaussian Process and variational inference. Our model maintains non-ne…
We report the detection of the ground state rotational emission of ammonia, ortho-NH$_3$ $(J_K=1_0\rightarrow0_0)$ in a gravitationally lensed, intrinsically hyperluminous, star-bursting galaxy at $z=2.6$. The integrated line profile is consistent with other molecular and atomic emission lines which have resolved kinematics well-modelled by a 5 kpc-diametre rotating disc. This implies that the gas responsible for NH$_3$ emission is broadly tracing the global molecular reservoir, but likely distributed in pockets of high density ($n\gtrsim5\times10^4$ cm$^{-3}$). With a luminosity of $2.8\times…
Centro de Astrobiología (CAB), CSIC-INTA（西班牙天体生物学中心（CAB），西班牙国家航空航天技术研究所与西班牙高等科学研究委员会联合）；Universidad Complutense de Madrid（马德里康普顿斯大学）；Astrophysik/I. Physikalisches Institut, Universität zu Köln（科隆大学第一物理研究所天体物理学部）；Institut de Ciències de l’Espai (ICE), CSIC（空间科学研究所，西班牙高等科学研究委员会）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚太空研究所）；Department of Astronomy, University of Florida（佛罗里达大学天文系）
In this study, 36 cores (30 starless and 6 protostellar) identified in Orion were surveyed to search for inward motions. We used the Nobeyama 45 m radio telescope, and mapped the cores in the $J = 1\rightarrow0$ transitions of HCO$^+$, H$^{13}$CO$^+$, N$_2$H$^+$, HNC, and HN$^{13}$C. The asymmetry parameter $δV$, which was the ratio of the difference between the HCO$^+$ and H$^{13}$CO$^+$ peak velocities to the H$^{13}$CO$^+$ line width, was biased toward negative values, suggesting that inward motions were more dominant than outward motions. Three starless cores (10% of all starless cores sur…
HCN emission from translucent gas and UV-illuminated cloud edges revealed by wide-field IRAM 30m maps of Orion B GMC: Revisiting its role as tracer of the dense gas reservoir for star formation
The detection of CF$^+$ in interstellar clouds potentially allows astronomers to infer the elemental fluorine abundance and the ionization fraction in ultraviolet-illuminated molecular gas. Because local thermodynamic equilibrium (LTE) conditions are hardly fulfilled in the interstellar medium (ISM), the accurate determination of the CF$^+$ abundance requires one to model its non-LTE excitation via both radiative and collisional processes. Here, we report quantum calculations of rate coefficients for the rotational excitation of CF$^+$ in collisions with para- and ortho-H2 (for temperatures up…
