Cold carbon chemistry in the interstellar medium is well-known for its efficient production of linear carbon chain molecules. Among the many variations on these species are the symmetric top methylpolyynes and methylcyanopolyynes (CH₃C_2nH and CH₃C_2n−1N, where n=1,2,3...). Despite their widespread presence in environments with rich carbon chemistry, the main formation mechanisms of these molecules are still not well understood. With the high sensitivity and broad frequency coverage obtained by the ongoing GOTHAM (Green Bank Telescope Observations of TMC-1: Hunting for Aromatic Molecules) survey of TMC-1, we have the opportunity to study the spectral signatures of these carbon chains in great detail. In this talk, we will present a rigorous study of the methyl carbon chains in TMC-1, in addition to the discovery of the largest interstellar symmetric top, methylcyanotriacetylene (CH₃C₇N). Making use of the second data release of GOTHAM in combination with Markov-Chain Monte Carlo simulation and spectral line stacking techniques, we detect statistically significant emission from the K=0 and K=1 components of this molecule, and derive its abundance and excitation conditions in TMC-1. Furthermore, by carrying out the same analysis for the many other methylpolyynes and methylcyanopolyynes that show emission lines in our data, and comparing our results with predictions of chemical models, we assess the chemistry governing the production of this class of molecules in this source and compare it with that of other carbon chain species.

Large difference of chemical compositions between molecular clouds and comets is a big question for astrochemistry. The case of a pre-biotic molecule CH₃NCO is one of them. The abundance ratio of [CH₃NCO]/[HNCO] is high in the comet 67P ( > 4, [1]), although it is low (0.02 − 0.3, e.g., [2]) in molecular clouds. An abundance of CH₃NCO is expected to be held and/or increased during evolutionary process of a cloud. A pair of an old core and a young core having the similar chemical compositions needs to be investigated for this evolutionary process. In this work, we aimed to detect CH₃NCO in the middle (M) core, which is relatively older than the north (N) core, in the Galactic Center star-forming region Sagittarius B2 with the 45 m telescope of Nobeyama Radio Observatory. The rotational transitions of J = 10 → 9 to 13 → 12 for CH₃NCO were detected in the 85 − 114 GHz region. The column density and the rotational temperature are derived to be N = (4.3 ± 2.1) × 10¹³ cm⁻² and T_rot = (32 ± 9) K, respectively, assuming local thermal equilibrium. Similarly, an abundance of HNCO is estimated to be N = (1.3 ± 0.5) × 10¹⁵ cm⁻² (T_rot = 21 ± 2 K), giving the ratio of [CH₃NCO]/[HNCO] = 0.032. Thus, as a simplest model, it is suggested that an abundance of CH₃NCO is held during evolutionary process of the Sagittarius B2 region.
[1] Goesmann et al., Science, 349, 689 (2015). [2] Halfen et al., ApJ, 812, L5 (2015).

The cyanide and isocyanide (-CN and -NC) pairs of isomers have been used regularly to probe the physical conditions and history of interstellar sources and to improve the accuracy and predictive power of astrochemical models. Two examples are the strong sensitivity of the HCN/HNC abundance ratio to the gas kinetic temperaturesA. Hacar, A. D. Bosman, and E. F. van Dishoeck, A&A 635, A4(2020)nd the dependence of the CH₃CN/CH₃NC abundance ratio to the cosmic-ray ionization ratesE. R. Willis, et al., A&A, 636, A29 (2020) Yet, despite the numerous detections of cyanides in astronomical environments, there have been very few confirmed detections of isocyanides. Alongside C_nH_2n+1CN, one of the most frequently observed families of cyanide species in cold sources are the cyanopolyynes (HC_2nCN). In contrast to their ubiquity, the only isocyanide version that had been successfully detected is HCCNC, the isomer of HC₃N. In this talk, we will present the first astronomical detection of the largest isocyanide molecule, isocyanodiacetylene (HC₄NC), using the data available from the GOTHAM (Green Bank Telescope Observations of TMC-1: Hunting for Aromatic Molecules) observational program of TMC-1B. A. McGuire, et al., ApjL, 900, L10 (2020) Assisted by a cutting-edge application of spectral line stacking and matched filtering techniques, we determined the NC/CN isomeric intensity ratios of the HC_2nNC/HC_2nCN family rigorously for n=1 and 2 toward TMC-1 and provided an upper limit of that for n=3. The abundance ratios derived from observations helped in constraining the interplay between -CN and -NC formation chemistry and their dependence on the physico-chemical history of the source. This work also demonstrated the need for a detailed investigation of the related formation pathways in the laboratory.

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Footnotes:

A. Hacar, A. D. Bosman, and E. F. van Dishoeck, A&A 635, A4(2020)a E. R. Willis, et al., A&A, 636, A29 (2020). B. A. McGuire, et al., ApjL, 900, L10 (2020).

Polycyclic Aromatic Hydrocarbons (PAHs) have long been invoked in the study of interstellar and protostellar sources, but the unambiguous identification of any single PAH has proven elusive until very recently. As a result, the formation mechanism for this important class of molecules remains poorly constrained. Here, we will discuss the dedicated and sustained effort to explore the aromatic content in the ISM at radio wavelengths with the GOTHAM (GBT Observations of TMC-1: Hunting for Aromatic Molecules) survey. We will focus on the first interstellar detection of a pure PAH, indene (C₉H₈), and how it fits within the context of the other recently detected cyclic molecules, including the cyanonaphthalenes (1- and 2-C₁₀H₇CN). Indene is found to be the most abundant organic ring detected in TMC-1 to date and is more abundant than predictions from astrochemical modeling with NAUTILUS by several orders of magnitude. This detection provides a new avenue of chemical inquiry where hydrocarbon abundances can now be directly compared to those of closely-related but CN-functionalized rings and creates a strong motivation to search for these species' cyano or pure ring counterparts.

We present a line survey of the cold dark core TMC-1 carried out with the YEBES 40m radio telescope in the Q-band. A new set of receivers have been installed in the telescope within the frame of the ERC synergy Nanocosmos project that allows to cover the whole 31-50 GHz band in dual polarization. The spectral resolution is 38.15 kHz. The sensitivity achieved so far varies between 0.3 and 1.5 mK, and allows to search for new molecules in a line by line (no stacking) detection procedure. These new data have permitted to detect the protonated species HC₅NH⁺Marcelino et al. 2020, A.&A., 643, L6 HC₃O⁺Cernicharo et al. 2020, A.&A., 642, L17 HC₃S⁺Cernicharo et al. 2021, A.&A., 643, L3 and CH₃CO⁺Cernicharo et al. 2021, A.&A., 646, L7 Each one of these species were detected first in TMC-1 by looking for unknown lines with harmonic frequency relations. All of them have been confirmed in the laboratory except HC₅NH⁺, for which our identification is based in high-level of theory ab initio calculations. Neutral molecules with low permanent dipole moment such as CH₂CHCCHCernicharo et al. 2021, A.&A., in press; 2021arXiv210210920C and CH₂CCHCCHCernicharo et al., 2021, A.&A., in pressave been also detected with a very large abundance. In addition, nitrile anions such as C₃N⁻ and C₅N⁻ have been also detected confirming the previous assigment of C₅N⁻ reported in the carbon-rich star IRC+10216 (Cernicharo et al. 2008, ApJ, 688, L83).

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Footnotes:

Marcelino et al. 2020, A.&A., 643, L6, Cernicharo et al. 2020, A.&A., 642, L17, Cernicharo et al. 2021, A.&A., 643, L3, Cernicharo et al. 2021, A.&A., 646, L7. Cernicharo et al. 2021, A.&A., in press; 2021arXiv210210920C, Cernicharo et al., 2021, A.&A., in pressh

The PO molecule has been identified towards the Orion-KL region based on a 3mm survey carried out with the ARO 12m. The J = 2.5-1.5 transition was observed, consisting of two lambda-doublets, both of which were detected. The PN (X¹Σ) J = 2-1 transition was also detected. Both PO and PN exhibited line profiles and LSR velocities characteristic of the Orion Plateau region, indicating that shocks are primarily responsible for their formation. A calculated PO/PN value of approximately 3 is similar to other molecular clouds where both species have been observed, suggesting that PO may be a relatively common molecule in star-forming regions.

The giant molecular cloud Sgr B2 in the  ∼ 150 pc radius Central Molecular Zone (CMZ) of the Galactic center has played a central role in molecular radio astronomical observations. In spite of its large distance, over 70 molecules have been first detected in Sgr B2 since the discoveries of NH₃ and H₂O. Nevertheless there seems to be no consensus on the depth within the CMZ of this well observed cloud. It has not even been known whether Sgr B2, which is 101 pc distant on the plane of the sky from the central black hole Sgr A*, is to the front or the rear of Sgr A*. A trigonometric parallax measurement by Reid et al. (2009)Reid, M. J., Menten, K. M., Zheng, X. W., Bunthaler, A. & Xu, Y. 2009, ApJ, 105, 7548laced Sgr B2 130 pc in front of Sgr A* which would put it outside of the CMZ. Both Kruijssen et al. (2015) and Ridley et al. (2017) also placed Sgr B2 in front of Sgr A*. On the other hand Molinari et al (2011)Molinari, S., Bally, J., Noriega-Crespo, A. et al. 2011, ApJ, 735, L33laced Sgr B2 about 70 pc behind Sgr A* based on their dust continuum measurements. Recent observations of infrared lines of H₃⁺ and CO Oka, T. & Geballe, T. R. 2020, ApJ, 902, 9nd the conclusion from the analysis of their velocity profiles that diffuse gas in the CMZ is expanding radially at a velocity of 150 km s⁻¹ with the front of the expansion 150 pc from Sgr A* provides a useful tool for determining the location of Sgr B2 within the CMZ. Although currently there is no known infrared star usable for observations of H₃⁺ toward Sgr B2, the star ι, 2M17470898-2829561, 16.6 pc to the west of the center of Sgr B2, is sufficiently close that it probes much of the same gas; the similarity of the velocity profile of the H₃⁺ spectrum toward ι observed at the Gemini South Observatory and of H₂O⁺ Schilke, P., Comito, C. Müller, H. S. P., et al. 2010, A&A, 521, L11y Herschel Observatory toward Sgr B2 attest to this. Using the velocity profiles of infrared absorption lines of H₃⁺ toward the star ι and far infrared absorption lines of H₂O⁺, both of which molecular ions reside in diffuse clouds, we conclude that Sgr B2 is behind Sgr A* by at least 70 pc. Reid, M. J., Menten, K. M., Zheng, X. W., Bunthaler, A. & Xu, Y. 2009, ApJ, 105, 7548p Molinari, S., Bally, J., Noriega-Crespo, A. et al. 2011, ApJ, 735, L33p Oka, T. & Geballe, T. R. 2020, ApJ, 902, 9a Schilke, P., Comito, C. Müller, H. S. P., et al. 2010, A&A, 521, L11b

Searches have been conducted for various J=2-1 transitions of methanol at 3 mm in a sample of molecular clouds located 13-23.5 kpc from the Galactic Center, using the 12m telescope of the Arizona Radio Observatory (ARO). The sources are in the Cygnus arms, and typically are cold with T_K approximately 20 K. Multiple transitions of this organic molecule were detected in 19 clouds, including ones at distances of approximately 23.5 kpc. Typical abundances found for methanol are 1x10⁹. The results suggest that the Galactic Habitable Zone (GHZ) may exist much further from the Galactic Center than previously thought.

Galactic Habitability is a concept of growing popularity. So far, research has been done in understanding the temporal and spatial evolution of a Galactic Habitable Zone (GHZ) based on parameters such as local SN rate, host star metallicity, and age of the system. However, the popular GHZ literature does not account for the potential influence of molecular complexity at different spatial locations in the Galaxy. With the high sensitivity of ALMA, we are interested in exploring molecular complexity of star-forming clumps in these different spatial locations of the Galaxy. In this work, we focus on one complex organic molecule - Formamide (NH₂CHO) - which recent literature has identified as a potential key precursor to prebiotic life. Using ALMA archival data, we examine the presence and abundance of formamide at various galactocentric distances in the Galaxy. Several archival surveys were utilized for the search. Most extensively, we used the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey, to search for 7(0,7) → 6(1,6) transition of Formamide.

Oxygen-rich supergiant stars undergo intense, sporadic mass loss often causing them to have highly directed, non-isotropic outflows. These outflows have been previously identified in the envelope of the supergiant VY CMa, both in the infrared and in molecular lines. In VY CMa, these flows are best traced by sulfur-bearing molecules SO₂ and SO. To further investigate the unusual properties of supergiant stars, we have conducted a 1 mm survey of another such object, NML Cyg. This survey revealed the presence of unusual species such as PO, AlO, NS, and PN in NML Cyg, as well as HCN, HCO+, CN, NaCl, SO, SiS, and SO₂ - an almost identical set of molecules as observed towards VY CMa. Two major asymmetric outflows have also been identified in the envelope of NML Cyg from the spectra of SO and SO₂, one blue-shifted and the other red-shifted. Spectral line analysis with the radiative transfer code ESCAPADE suggests that these two outflows are in random directions and are not bipolar in nature.

Chemically-active protostellar outflows provide unique laboratories to study shock chemistry in relatively simple physical environments. However, only a small handful of these types of sources are currently known. Recently, Tafalla & Hacar (2013) discovered a chemically-active outflow HH114. Images obtained with the IRAM 30m Telescope revealed strong emission in SiO, HCO⁺, HCN, CH₃OH, and CS in the redshifted and blueshifted lobes. Here we present SMA observations resolving the blue-shifted outflow of HH114. Leveraging the new wideband capabilities of the SMA, these new high-resolution maps reveal the rich chemistry displays complex morphologies coming from the shocked bullets and processing jet. We discuss the implications these observations can have on our understanding of shocked molecular outflows.

Molecular outflows are crucial for us to understand not only the internal structure and conditions close to protostars, but also probe the morphology and the dynamics of the chemistry in the surrounding cloud. But, the relationship of the chemistry and physics within these outflows is complex and not well constrained. Isolated molecular outflows provide simplified environments to constrain the underlying processes. However, the majority of isolated outflows originate from low-mass protostars, which have distinct chemistry relative to high-mass. Here, we utilized archival SMA observations of the young and isolated high-mass protostar I20126+4104 in order to study the chemical diversity and differentiation of both the disc and the outflow. We found that there is complex chemistry by distinguishing molecules such as HCN, CH₃OH, SO₂. We also assessed the relative column densities for these molecules.

Magnetic fields are thought to play a crucial role in the formation and evolution of protoplanetary disks by providing a means of angular momentum transport. However, finding observational evidence for the presence of magnetic fields in disks has proven difficult. Zeeman splitting observations offer a way to directly measure or put upper limits on line-of-sight magnetic field strengths in astronomical sources, as the circularly polarized signal produced by Zeeman splitting depends directly on the magnetic field strength along the line of sight. We present upper limits on the toroidal and vertical magnetic field strengths in the Class II protoplanetary disk AS 209 from ALMA observations of the CN 2-1 line. If magnetic disk winds are a significant mechanism of angular momentum transport in the disk, magnetic fields of a strength close to our upper limits would be sufficient to drive accretion at the rate previously inferred for regions near the protostar.

Hydrides are important molecular constituents of the interstellar and circumstellar media, but there are still many questions regarding their variety and formation. In the envelopes of asymptotic giant branch and red supergiant stars, hydrides like silane SiH₄, phosphine PH₃, ammonia NH₃, and water H₂O are known to form, but have been observed in stark overabundance relative to predictions of chemical equilibrium modelsAgundez et al., A&A 637, A59 (2020) Diatomic hydrides (species with the form XH) are natural precursors to their more hydrogenated counterparts, and could therefore be crucial in constraining this puzzling chemistry. In this talk, I will present our search for the hydrides silicon monohydride (SiH), phosphinidene (PH), and iron hydride (FeH) using the Stratospheric Observatory for Infrared Astronomy (SOFIA). We used the German Receiver for Astronomy at Terahertz Frequencies (GREAT) instrument to search for rotational emission lines of these molecules along the line of sight toward the chemically rich circumstellar envelopes of the evolved stars IRC+10216 and VY Canis Majoris. In these spectra we detected high-energy ro-vibrational lines from over a dozen molecules, though no significant emission from our target molecules was found. We derive upper limits on their abundances in each source, discuss how these findings influence our understanding of hydride chemistry in circumstellar envelopes, and outline the observational steps needed to further constrain this chemistry.

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Footnotes:

Agundez et al., A&A 637, A59 (2020).