Keywords

This paper presents an overview of the QUARKS survey, which stands for "Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures." The QUARKS survey is observing 139 massive clumps covered by 156 pointings at Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (λ ∼ 1.3 mm). In conjunction with data obtained from the ALMA-ATOMS survey at Band 3 (λ ∼ 3 mm), QUARKS aims to carry out an unbiased statistical investigation of massive star formation process within protoclusters down to a scale of 1000 au. This overview paper describes the observations and data reduction of the QUARKS survey, and gives a first look at an exemplar source, the mini-starburst Sgr B2(M). The wide-bandwidth (7.5 GHz) and high-angular-resolution (∼03) observations of the QUARKS survey allow for the resolution of much more compact cores than those could be done by the ATOMS survey, and to detect previously unrevealed fainter filamentary structures. The spectral windows cover transitions of species including CO, SO, N₂D⁺, SiO, H₃₀α, H₂CO, CH₃CN, and many other complex organic molecules, tracing gas components with different temperatures and spatial extents. QUARKS aims to deepen our understanding of several scientific topics of massive star formation, such as the mass transport within protoclusters by (hub-)filamentary structures, the existence of massive starless cores, the physical and chemical properties of dense cores within protoclusters, and the feedback from already formed high-mass young protostars.

Star-forming processes strongly influence the ISM chemistry. Nowadays, many high-quality databases are available at millimeter wavelengths. Using them, it is possible to carry out studies that review and deepen previous results. If these studies involve large samples of sources, it is preferred to use direct tools to study the molecular gas. With the aim of testing these tools such as the use of the HCN/HNC ratio as a thermometer, and the use of H¹³CO⁺, HC₃N, N₂H⁺ and C₂H as "chemical clocks," we present a molecular line study toward 55 sources representing massive young stellar objects at different evolutionary stages: infrared dark clouds (IRDCs), high-mass protostellar objects (HMPOs), hot molecular cores (HMCs) and ultracompact H ii regions. We found that the use of the HCN/HNC ratio as a universal thermometer in the ISM should be taken with care because the HCN optical depth is a big issue that can affect the method. Hence, this tool should be utilized only after a careful analysis of the HCN spectrum, checking that no line, neither the main nor the hyperfine ones, presents absorption features. We point out that the analysis of the emission of H¹³CO⁺, HC₃N, N₂H⁺ and C₂H could be useful to trace and distinguish regions among IRDCs, HMPOs and HMCs. The molecular line widths of these four species increase from the IRDC to the HMC stage, which can be a consequence of the gas dynamics related to the star-forming processes taking place in the molecular clumps. Our results not only contribute with more statistics, acting as a probe of such chemical tools, useful to obtain information in large samples of sources, but also complement previous works through the analysis of other types of sources.

Polycyclic aromatic hydrocarbons (PAHs), PANHs, and peptoids dust spectral calculations from the interstellar medium (ISM) are important for dust observations and theory. Our goal is to calculate the radiation spectrum of spherical PAHs dust clusters in a vacuum containing ionized and applied in the presence of an electric field. We propose a new simple computational model to calculate the size of three-dimensional spherical dust clusters formed by different initial dust structures. By the Vienna Ab-initio Simulation Package code, the density functional theory with the generalized approximation was used to calculate the electron density gradient and obtain the radiation spectrum of dust. When the radius of spherical dust clusters is ∼[0.009–0.042] μm, the dust radiation spectrum agrees well with the Z = 0.02 mMMP stellar spectra, and the PAHs radiation spectrum of NGC 4676 at wavelengths of (0–5] μm and (5–10] μm, respectively. In the ionized state, the N-PAH, C₁₀H₉N, 2(C₄H ₄)¹⁺, and peptoids 4(CHON), (C₈H₁₀N₂O₅)¹⁺ dust clusters at 3.3 μm, while the 2(C₂₂H₂₁N₃O ₂)¹⁺, 4(CHON) dust clusters at 5.2 μm have obvious peaks. There is a characteristic of part of PAHs and peptoids clusters radiation at the near-infrared wavelength of 2 μm. However, especially after applying an electric field to the dust, the emission spectrum of the dust increases significantly in the radiation wavelength range [3–10] μm. Consequently, the dust clusters of PAHs, PANHs, and peptoids of the radius size ∼[0.009–0.042] μm are likely to exist in the ISM.

The most extensive survey of carbon monoxide (CO) gas in the Taurus molecular cloud relied on ¹²CO and ¹³CO J = 1 → 0 emission only, distinguishing the region where ¹²CO is detected without ¹³CO (named mask 1 region) from the one where both are detected (mask 2 region) (Goldsmith et al. 2008; Pineda et al. 2010). We have taken advantage of recent ¹²CO J = 3 → 2 James Clerk Maxwell Telescope observations, where they include mask 1 regions to estimate density, temperature, and N(CO) with a large velocity gradient model. This represents 1395 pixels out of ∼1.2 million in the mark 1 region. Compared to Pineda et al. (2010) results and assuming a T_kin of 30 K, we find a higher volume density of molecular hydrogen of 3.3 × 10³ cm⁻³, compared to their 250–700 cm⁻³, and a CO column density of 5.7 × 10¹⁵ cm⁻², about a quarter of their value. The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium. Future observations to extend the ¹²CO J = 3 → 2 mapping further away from the ¹³CO-detected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.

H/D accretion, especially onto ionized fullerenes, is expected to be very efficient in space. In this work, we study hydrogenated and deuterated fullerene cations and their photodissociation behavior in the gas phase. The experimental results show that hydrogenated fullerene cations (i.e., [C₆₀H_n]⁺ and [C₇₀H_n]⁺, n up to 30) and deuterated fullerene cations (i.e., [C₆₀D_n]⁺ and [C₇₀D_n]⁺, n up to 21) are formed efficiently through the ion-atom collision reaction pathway. Upon irradiation, the hydrogenated and deuterated fullerene cations dissociate into fullerene cations and H/H₂ or D/D₂ species. The structures of the newly formed hydrogenated and deuterated fullerene cations (C₅₈ and C₆₀) and the bonding energies for these reaction pathways are investigated by means of quantum chemical calculations. The competition between hydrogenation and dehydrogenation is confirmed, and the hydrogenation-to-dehydrogenation ratio in the accretion processes in the gas phase is determined. We infer that the proportion of accreted hydrogen and deuterium atoms on the surface of fullerenes is similar to that of hydrogen and deuterium atoms in the interstellar environment where these fullerenes are located, especially when the interstellar environments are similar to our experimental conditions, i.e., the hot environment.

Using quantum chemical calculations, we model the pathways for synthesizing two purine nucleobases, adenine and guanine, in the gas-phase interstellar environment, surrounded by neutral atomic hydrogen (H i). H i is found active in facilitating a series of fundamental proton transfer processes of organic synthesis, including bond formation, cyclization, dehydrogenation, and H migration. The reactive potential barriers were significantly reduced in the alternative pathways created by H i, leading to a remarkable increase in the reaction rate. The presence of H i also lowered the reactive activation temperature from 757.8 K to 131.5–147.0 K, indicating the thermodynamic feasibility of these pathways in star-forming regions where some of the reactants have been astronomically detected. Our findings suggest that H i may serve as an effective catalyst for interstellar organic synthesis.

Molecules reside broadly in the interstellar space and can be detected via spectroscopic observations. To date, more than 271 molecular species have been identified in interstellar medium or circumstellar envelopes. Molecular spectroscopic parameters measured in laboratory make the identification of new species and derivation of physical parameters possible. These spectroscopic parameters are systematically collected into databases, two of the most commonly used being the CDMS and JPL databases. While new spectroscopic parameters are continuously measured/calculated and added to those databases, at any point in time it is the existing spectroscopic data that ultimately limits what molecules can possibly be identified in astronomical data. In this work, we conduct a meta-analysis of the CDMS and JPL databases. We show the statistics of transition frequencies and their uncertainties in these two databases, and discuss the line confusion problem under certain physical environments. We then assess the prospects of detecting molecules in common ISM environments using a few facilities that are expected to be conducting spectroscopic observations in the future. Results show that CSST/HSTDM and SKA1-mid have the potential to detect some complex organic molecules, or even amino acids, with reasonable assumptions about ISM environments.

The research of infall motion is a common means to study molecular cloud dynamics and the early process of star formation. Many works had been done in-depth research on infall. We searched the literature related to infall study of molecular cloud since 1994, summarized the infall sources identified by the authors. A total of 456 infall sources are cataloged. We classify them into high-mass and low-mass sources, in which the high-mass sources are divided into three evolutionary stages: prestellar, protostellar and H ii region. We divide the sources into clumps and cores according to their sizes. The H₂ column density values range from 1.21 × 10²¹ to 9.75 × 10²⁴ cm⁻², with a median value of 4.17 × 10²² cm⁻². The H₂ column densities of high-mass and low-mass sources are significantly separated. The median value of infall velocity for high-mass clumps is 1.12 km s⁻¹, and the infall velocities of low-mass cores are virtually all less than 0.5 km s⁻¹. There is no obvious difference between different stages of evolution. The mass infall rates of low-mass cores are between 10⁻⁷ and 10⁻⁴ M_⊙yr⁻¹, and those of high-mass clumps are between 10⁻⁴ and 10⁻¹ M_⊙yr⁻¹ with only one exception. We do not find that the mass infall rates vary with evolutionary stages.

Diffuse interstellar bands (DIBs) have always been a mysterious existence in astronomical research. In this work, we provide more DIB samples to slightly uncover this mystery. With the LAMOST medium-resolution survey (MRS) spectra, we detected three DIBs λ6379, λ6614, and λ6660, obviously superimposed on the spectra of 11,003 stars. These spectra cover spectral types from O to K, which can provide a large number of candidates for further research on DIBs. The sample shows a clear positive correlation between the strength of DIBs and extinction, which agrees with the result in the literature. In addition, there exist two peaks in each of the velocity distribution of these three DIBs, and the velocity differences between two peaks of each pair are consistent. The reason for the two velocity components is due to the Galactic rotation.

The spectral observations and analysis for the W80 region are presented by using the data of Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N) with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). A total of 2982 high-quality nebular spectra have been obtained in the 20 square degree field of view which covers the W80 complex, and the largest sample of spectral data has been established for the first time. The relative intensities, radial velocities (RVs), and full widths at half maximum (FWHMs) are measured with the high spectral resolution of LAMOST MRS-N, for Hα λ6563 Å, [N ii] λλ6548 Å, 6584 Å, and [S ii] λλ6716 Å, 6731 Å emission lines. In the field of view of the whole W80 region, the strongest line emissions are found to be consistent with the bright nebulae NGC 7000, IC 5070, and LBN 391, and weak line emissions also exist in the Middle Region, where no bright nebulae are detected by the wide-band optical observations. The large-scale spectral observations of the W80 region reveal the systematic spatial variations of RVs and FWHMs, and several unique structural features. A "curved feature" to the east of NGC 7000, and a "jet feature" to the west of LBN 391 are detected to be showing larger RVs. A "wider FWHM region" is identified in the eastern part of NGC 7000. The variations of [S ii]/Hα ratios display a gradient from southwest to northeast in the NGC 7000 region, and manifest a ring shape around the "W80 bubble" ionized by an O-type star in L935. Further spectral and multi-band observations are guaranteed to investigate in detail the structural features.