Keywords

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.

We carry out an optical morphological and infrared spectral study for two young planetary nebulae (PNs) Hen 2-158 and Pe 1-1 to understand their complex shapes and dust properties. Hubble Space Telescope optical images reveal that these nebulae have several bipolar-lobed structures and a faint arc with a clear boundary is located at the northwestern side of Pe 1-1. The presence of this arc-shaped structure suggests that the object interacts with its nearby interstellar medium. Spitzer IRS spectroscopic observations of these young nebulae clearly show prominent unidentified infrared emission features and a weak silicate band in Pe 1-1, indicating that Hen 2-158 is a carbon-rich nebula and Pe 1-1 has a mixed chemistry dust environment. Furthermore, we construct two three-dimensional models for these PNs to realize their intrinsic structures. The simulated models of the nebulae suggest that multipolar nebulae may be more numerous than we thought. Our analyses of spectral energy distributions for Hen 2-158 and Pe 1-1 show that they have low luminosities and low stellar effective temperatures, suggesting that these nebulae are young PNs. A possible correlation between typical multipolar young PNs and nested nebulae is also discussed.

We present large-scale (2° × 2°) observations toward the molecular cloud M120.1+3.0, using ¹²CO, ¹³CO and C¹⁸O (J = 1 − 0) data from the Purple Mountain Observatory 13.7 m millimeter telescope. The distance of the cloud is measured to be ∼1.1 kpc. Using the ¹³CO data, we identify a main filament F1 and two sub-filaments F2 and F3 in the cloud, which together show a "hub-filament" structure. Filaments F1 and F2 are thermally supercritical. Furthermore, F1 displays clear localized systematic motions in the ¹³CO position–velocity diagram, which could be explained by accretion along the filament. The mean estimated accretion rate is ∼132 M_⊙ Myr⁻¹. Approximately 150 ¹³CO clumps are identified in the cloud, of which 39 are gravitationally bound. Most of these virialized clumps are well distributed along the supercritical filaments F1 and F2. Based on the complementary infrared and optical data, we identify ∼186 young stellar objects in the observed area and extract five clusters within the dense ridge of F1. The calculated star formation rate (SFR) surface densities (Σ_SFR) in the clusters range from 1.4 to 2.5 M_⊙ Myr⁻¹ pc⁻², with a mean value of ∼2.0 M_⊙ Myr⁻¹ pc⁻². We therefore regard them as mini-starburst cluster candidates. The comparison between Σ_SFR and column density N_gas along the skeleton of F1 suggests that star formation is closely related to the dense gas in the cloud. Along the main filament F1, five bipolar outflows are also found. All these results indicate intense star-forming activities in the M120.1+3.0 molecular cloud.

Infrared bubbles provide a unique opportunity to study the interactions between massive stars and surrounding material. We conduct a multi-wavelength study on the environment and star formation around an infrared bubble N 13. Three dust clumps and two molecular clumps are identified around N 13, which are all distributed on the layer. Young stellar objects (YSOs) are carefully searched using infrared colors and YSO candidates of WISE and Gaia DR2, and three Class I/II YSOs are found in N 13. In addition, four O-type stars identified in N 13 are probably the exciting stars. The dynamical and fragmentation ages of N 13 are 0.32–0.35 and 1.37–2.80 Myr respectively, which suggest that the radiation-driven implosion model may be dominant in N 13. By comparing the small-size bubble N 13 (R ∼ 1.9 pc) and the larger-size bubble G15.684-0.29 (R ∼ 15.7 pc) we found that star formation activity is more active in the large-size bubble. Brief comparisons of ten bubbles show that small-size bubbles have a small ratio of kinetic age versus the fragmentation time. Triggering star formation may be more active in bubbles with larger ratio between kinetic and fragmentation ages. Furthermore, the collect and collapse mechanism may play the dominant role in the large-size ones.

Star formation is governed by the interplay between gravity and turbulence in most of molecular clouds. Recent theoretical works assume that dense gas, whose column density is above a critical value in the column density probability distribution function (N-PDF), where gravity starts to overcome turbulence, becomes star-forming gas and will collapse to form stars. However, these high-density gases will include some very turbulent areas in the clouds. Will these dense but turbulent gases also form stars? We test this scenario in Ophiuchus molecular cloud using N-PDF analysis and find that at least in some regions, the turbulent, dense gas is not forming stars. We identified two isolated high-density structures in Ophiuchus, which are gravitationally unbound and show no sign of star formation. Their high densities may come from turbulence.

We revisit the mass–size relation of molecular cloud structures based on the column density map of the Cygnus-X molecular cloud complex. We extract 135 column density peaks in Cygnus-X and analyze the column density distributions around these peaks. The averaged column density profiles, N(R), around all the peaks can be well fitted with broken power-laws, which are described by an inner power-law index n, outer power-law index m, and the radius R_TP and column density N_TP at the transition point. We then explore the M–R relation with different samples of cloud structures by varying the N(R) parameters and the column density threshold, N₀, which determines the boundary of a cloud structure. We find that only when N₀ has a wide range of values, the M–R relation may largely probe the density distribution, and the fitted power-law index of the M–R relation is related to the power-law index of N(R). On the contrary, with a constant N₀, the M–R relation has no direct connection with the density distribution; in this case, the fitted power-law index of the M–R relation is equal to 2 (when N₀ ≥ N_TP and n has a narrow range of values), larger than 2 (when N₀ ≥ N_TP and n has a wide range of values), or slightly less than 2 (when N₀ < N_TP).

We investigate the formation of multiple images as the radio signals from fast radio bursts (FRBs) pass through the plane of a plasma clump. The exponential model for the plasma clump is adopted to analyze the properties of the multiple images. By comparing with the classical dispersion relations, we find that one image has exhibited specific inverse properties to others, such as their delay times at high frequency is higher than that at low frequency, owing to the lensing effects of the plasma clump. We demonstrate that these inverse effects should be observable in some repeating FRBs. Our results predict deviation in the estimated dispersion measure (DM) across multiple images, consistent with the observations of FRB 121102 and FRB 180916.J0158+65. If other plasma lenses have effects similar to an exponential lens, we find that they should also give rise to a similar dispersion relation in the multiple images. For some repeating FRBs, analysis of the differences in time delay and in DM between multiple images at different frequencies can serve as a method to reveal the plasma distribution.

We present a large-scale simultaneous survey of the CO isotopologues (¹²CO, ¹³CO, and C¹⁸O) J = 1–0 line emission toward the Galactic plane region of l = 10665 to 10950 and b = −185 to 095 using the Purple Mountain Observatory 13.7 m millimeter-wavelength telescope. Except for the molecular gas in the solar neighborhood, the emission from the molecular gas in this region is concentrated in the velocity range of [−60, −35] km s⁻¹. The gas in the region can be divided into four clouds, with mass in the range of ∼10³–10⁴ M_☉. We have identified 25 filaments based on the ¹³CO data. The median excitation temperature, length, line mass, line width, and virial parameter of the filaments are 10.89 K, 8.49 pc, 146.11 M_⊙ pc⁻¹, 1.01 km s⁻¹, and 3.14, respectively. Among these filaments, eight have virial parameters of less than 2, suggesting that they are gravitationally bound and can lead to star formation. Nineteen H ii regions or candidates have previously been found in the region and we investigate the relationships between these H ii regions/candidates and surrounding molecular clouds in detail. Using morphology similarity and radial velocity consistency between H ii regions/candidates and molecular clouds as evidence for association, and raised temperature and velocity broadening as signatures of interaction, we propose that 12 H ii regions/candidates are associated with their surrounding molecular clouds. In the case of the H ii region of S142, the energy of the H ii region is sufficient to maintain the turbulence in the surrounding molecular gas.

Observations with the Wisconsin ${\rm{H}}\alpha$ Mapper reveal a large, diffuse ionized halo that surrounds the Small Magellanic Cloud (SMC). We present the first kinematic ${\rm{H}}\alpha$ survey of an extended region around the galaxy, from $({\ell },b)=(289\buildrel{\circ}\over{.} 5,-35\buildrel{\circ}\over{.} 0)$ to $(315\buildrel{\circ}\over{.} 1,-5\buildrel{\circ}\over{.} 3)$ and covering $+90\leqslant {v}_{\mathrm{LSR}}\leqslant +210\ \mathrm{km}\,{{\rm{s}}}^{-1}$. The ionized gas emission extends far beyond the central stellar component of the galaxy, reaching similar distances to that of the diffuse neutral halo traced by 21 cm observations. ${\rm{H}}\alpha$ emission extends several degrees beyond the sensitivity of current H i surveys toward smaller galactic longitudes and more negative galactic latitudes. The velocity field of the ionized gas near the SMC appears similar to the neutral halo of the galaxy. Using the observed emission measure as a guide, we estimate the mass of this newly revealed ionized component to be roughly $(0.8\mbox{--}1.0)\times {10}^{9}\,{M}_{\odot }$, which is comparable to the total neutral mass in the same region of $(0.9\mbox{--}1.1)\times {10}^{9}\,{M}_{\odot }$. We find ratios of the total ionized gas mass divided by the total neutral plus ionized gas mass in three distinct subregions to be: (1) 46%–54% throughout the SMC and its extended halo, (2) 12%–32% in the SMC Tail that extends toward the Magellanic Bridge, and (3) 65%–79% in a filament that extends away from the SMC toward the Magellanic Stream. This newly discovered, coherent ${\rm{H}}\alpha$ filament does not appear to have a well-structured neutral component and is also not coincident with two previously identified filaments traced by 21 cm emission within the Stream.

The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end, we present the first targeted ALMA Band 6 1.3 mm continuum and spectral line survey toward high-mass starless clump candidates, selecting a sample of 12 of the most massive candidates ($4\times {10}^{2}\,{M}_{\odot }\lesssim {M}_{\mathrm{cl}}\lesssim 4\times {10}^{3}\,{M}_{\odot }$) within ${d}_{\odot }\lt 5\,\mathrm{kpc}$. The joint $12+7\,{\rm{m}}$ array maps have a high spatial resolution of $\lesssim 3000\,\mathrm{au}$ ($0.015\,\mathrm{pc}$, θ_syn ≈ 08) and have high point-source mass-completeness down to $M\approx 0.3\,{M}_{\odot }$ at $6{\sigma }_{\mathrm{rms}}$ (or $1{\sigma }_{\mathrm{rms}}$ column density sensitivity of $N=1.1\times {10}^{22}\,{\mathrm{cm}}^{-2}$). We discover previously undetected signposts of low-luminosity star formation from $\mathrm{CO}$ $J=2\to 1$ and $\mathrm{SiO}$ $J=5\to 4$ bipolar outflows and other signatures toward 11 out of 12 clumps, showing that current MIR/FIR Galactic plane surveys are incomplete to low- and intermediate-mass protostars (${L}_{\mathrm{bol}}\lesssim 50\,{L}_{\odot }$), and emphasizing the necessity of high-resolution follow-up. We compare a subset of the observed cores with a suite of radiative transfer models of starless cores. We find a high-mass starless core candidate with a model-derived mass consistent with ${29}_{15}^{52}\,{M}_{\odot }$ when integrated over size scales of $R\lt 2\times {10}^{4}\,\mathrm{au}$. Unresolved cores are poorly fit by radiative transfer models of externally heated Plummer density profiles, supporting the interpretation that they are protostellar even without detection of outflows. A high degree of fragmentation with rich substructure is observed toward 10 out of 12 clumps. We extract sources from the maps using a dendrogram to study the characteristic fragmentation length scale. Nearest neighbor separations, when corrected for projection with Monte Carlo random sampling, are consistent with being equal to the clump average thermal Jeans length (${\lambda }_{{\rm{j}},\mathrm{th}}$; i.e., separations equal to $0.4\mbox{--}1.6\times {\lambda }_{{\rm{j}},\mathrm{th}}$). In the context of previous observations that, on larger scales, see separations consistent with the turbulent Jeans length or the cylindrical thermal Jeans scale ($\approx 3\mbox{--}4\times {\lambda }_{{\rm{j}},\mathrm{th}}$), our findings support a hierarchical fragmentation process, where the highest-density regions are not strongly supported against thermal gravitational fragmentation by turbulence or magnetic fields.