Keywords

We address the physical and kinematical properties of Wolf–Rayet [WR] central stars (CSs) and their host planetary nebulae (PNe). The studied sample comprises all [WR] CSs that are currently known. The analysis is based on recent observations of the parallax, proper motion, and color index of [WR] CSs from the Gaia space mission's early third release (eDR3) catalog, as well as common nebular characteristics. The results revealed an evolutionary sequence, in terms of decreasing T_eff, from the early hot [WO 1] to the late cold [WC 12] stars. This evolutionary sequence extends beyond [WR] CS temperature and luminosity to additional CS and nebular characteristics. The statistical analysis shows that the mean final stellar mass and evolutionary age of the [WR] CS sample are 0.595 ± 0.13 M_⊙ and 9449 ± 2437 yr, respectively, with a mean nebular dynamical age of 7270 ± 1380 yr. In addition, we recognize that the color of the majority (∼85%) of [WR] CSs tends to be red rather than their genuine blue color. The analysis indicates that two-thirds of the apparent red color of most [WR]s is attributed to the interstellar extinction whereas the other one-third is due to the PN self-extinction effect.

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.

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.

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.

We have conducted ALMA CO isotopes and 1.3 mm continuum observations toward filamentary molecular clouds of the N159W-South region in the Large Magellanic Cloud with an angular resolution of ∼025 (∼0.07 pc). Although the previous lower-resolution (∼1'') ALMA observations revealed that there is a high-mass protostellar object at an intersection of two line-shaped filaments in ¹³CO with the length scale of ∼10 pc, the spatially resolved observations, in particular, toward the highest column density part traced by the 1.3 mm continuum emission, the N159W-South clump, show complicated hub-filamentary structures. We also discovered that there are multiple protostellar sources with bipolar outflows along the massive filament. The redshifted/blueshifted components of the ¹³CO emission around the massive filaments/protostars have complementary distributions, which is considered to be possible evidence for a cloud–cloud collision. We propose a new scenario in which the supersonically colliding gas flow triggers the formation of both the massive filament and protostars. This is a modification of the earlier scenario of cloud–cloud collision, by Fukui et al., that postulated the two filamentary clouds occur prior to the high-mass star formation. A recent theoretical study of the shock compression in colliding molecular flows by Inoue et al. demonstrates that the formation of filaments with hub structure is a usual outcome of the collision, lending support for the present scenario. The theory argues that the filaments are formed as dense parts in a shock compressed sheet-like layer, which resembles "an umbrella with pokes."

We present ALMA observations of CO isotopes and 1.3 mm continuum emission toward the N159E-Papillon Nebula in the Large Magellanic Cloud (LMC). The spatial resolution is 025–028 (0.06–0.07 pc), which is a factor of 3 higher than previous ALMA observations in this region. The high resolution allowed us to resolve highly filamentary CO distributions with typical widths of ∼0.1 pc (full width half maximum) and line masses of a few 100 M_⊙ pc⁻¹. The filaments (more than ten in number) show an outstanding hub-filament structure emanating from the nebular center toward the north. We identified for the first time two massive protostellar outflows of ∼10⁴ yr dynamical age along one of the most massive filaments. The observations also revealed several pillar-like CO features around the Nebula. The H ii region and the pillars have a complementary spatial distribution and the column density of the pillars is an order of magnitude higher than that of the pillars in the Eagle nebula (M16) in the Galaxy, suggesting an early stage of pillar formation with an age younger than ∼10⁵ yr. We suggest that a cloud–cloud collision triggered the formation of the filaments and protostar within the last ∼2 Myr. It is possible that the collision is more recent, as part of the kpc-scale H i flows come from the tidal interaction resulting from the close encounter between the LMC and SMC ∼200 Myr ago as suggested for R136 by Fukui et al.

The structure and kinematics of gaseous, disk–halo interfaces are imprinted with the processes that transfer mass, metals, and energy between galactic disks and their environments. We study the extraplanar diffuse ionized gas (eDIG) layer in the interacting, star-forming galaxy NGC 5775 to better understand the consequences of star formation feedback on the dynamical state of the thick-disk interstellar medium. Combining emission-line spectroscopy from the Robert Stobie Spectrograph on the Southern African Large Telescope with radio continuum observations from Continuum Halos in Nearby Galaxies—an EVLA Survey, we ask whether thermal, turbulent, magnetic field, and cosmic-ray pressure gradients can stably support the eDIG layer in dynamical equilibrium. This model fails to reproduce the observed exponential electron scale heights of the eDIG thick disk and halo on the northeast (${h}_{z,e}=0.6,7.5$ kpc) and southwest (${h}_{z,e}=0.8,3.6$ kpc) sides of the galaxy at R < 11 kpc. We report the first definitive detection of an increasing eDIG velocity dispersion as a function of height above the disk. Blueshifted gas along the minor axis at large distances from the midplane hints at a disk–halo circulation and/or ram pressure effects caused by the ongoing interaction with NGC 5774. This work motivates further integral field unit and/or Fabry–Perot spectroscopy of galaxies with a range of star formation rates to develop a spatially resolved understanding of the role of star formation feedback in shaping the kinematics of the disk–halo interface.

Previous studies have analyzed the energy injection into the interstellar matter due to molecular bubbles. They found that the total kinetic energies of bubbles are comparable to, or even larger than, those of outflows but still less than the gravitational potential and turbulence energies of the hosting clouds. We examined the possibility that previous studies underestimated the energy injection due to being unable to detect dim or incomplete bubbles. We simulated typical molecular bubbles and inserted them into the ¹³CO Five College Radio Astronomical Observatory maps of the Taurus and Perseus Molecular Clouds. We determined bubble identification completeness by applying the same procedures to both simulated and real data sets. We proposed a detectability function for both the Taurus and Perseus molecular clouds based on a multivariate approach. In Taurus, bubbles with kinetic energy less than ∼1 × 10⁴⁴ erg are likely to be missed. We found that the total missing kinetic energy in Taurus is less than a couple of 10⁴⁴ erg, which only accounts for around 0.2% of the total kinetic energy of identified bubbles. In Perseus, bubbles with kinetic energy less than ∼2 × 10⁴⁴ erg are likely to be missed. We found that the total missing kinetic energy in Perseus is less than 10⁴⁵ erg, which only accounts for around 1% of the total kinetic energy of identified bubbles. We thus conclude that previous manual bubble identification routines used in Taurus and Perseus can be considered to be energetically complete. Therefore, we confirm that energy injection from dynamic structures, namely outflows and bubbles, produced by star formation feedback are sufficient to sustain turbulence at a spatial scale from ∼0.1 to ∼2.8 pc.

We investigate the influence of Wolf–Rayet (W-R) stars on their surrounding star-forming molecular clouds. We study five regions containing W-R stars in the inner Galactic plane (l ∼ [14°–52°]), using multiwavelength data from near-infrared to radio wavelengths. Analysis of ¹³CO line data reveals that these W-R stars have developed gas-deficient cavities in addition to molecular shells with expansion velocities of a few kilometers per second. The pressure owing to stellar winds primarily drives these expanding shells and sweeps up the surrounding matter to distances of a few parsecs. The column densities of shells are enhanced by a minimum of 14% for one region to a maximum of 88% for another region with respect to the column densities within their central cavities. No active star formation—including molecular condensations, protostars, or ionized gas—is found inside the cavities, whereas such features are observed around the molecular shells. Although the expansion of ionized gas is considered an effective mechanism to trigger star formation, the dynamical ages of the H ii regions in our sample are generally not sufficiently long to do so efficiently. Overall, our results hint at the possible importance of negative W-R wind-driven feedback on the gas-deficient cavities, where star formation is quenched as a consequence. In addition, the presence of active star formation around the molecular shells indicates that W-R stars may also assist in accumulating molecular gas, and that they could initiate star formation around those shells.