Quiescent Gas Research Articles

Transient behaviour of a rarefied gas around a sphere caused by impulsive rotation

Abstract

Влияние начальных условий на скорость фронта ламинарного пламени в газовых смесях

The scatter in laminar flame front speed caused by both an error in the composition of the combustible mixture and initial disturbances is reported. It's shown how the configuration of the initially planar front in laminar flame initial disturbances in a gas mixture of the same composition affects the scatter of speeds of expanding spherical flames. The experimental results previously obtained by the authors, demonstrating the scatter in the speed of the laminar flame front in an initially quiescent gas mixture of constant composition under the same conditions, are explained by integrating the Sivashinsky equation with various initial disturbances. The influence of combustible mixture composition errors on the parameters determining the speed of the flame front is analyzed. These parameters were recalculated for a possible scatter in the mixture composition, obtained based on data on the accuracy of the equipment used in previously published experiments.

Physical Conditions in Shocked Interstellar Gas Interacting with the Supernova Remnant IC 443*

Abstract We present the results of a detailed investigation into the physical conditions in interstellar material interacting with the supernova remnant (SNR) IC 443. Our analysis is based on a comprehensive examination of high-resolution far-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope of two stars behind IC 443. One of our targets (HD 43582) probes gas along the entire line of sight through the SNR, while the other (HD 254755) samples material located ahead of the primary supernova shock front. We identify low-velocity quiescent gas in both directions and find that the densities and temperatures in these components are typical of diffuse atomic and molecular clouds. Numerous high-velocity components are observed in the absorption profiles of neutral and singly ionized atomic species toward HD 43582. These components exhibit a combination of greatly enhanced thermal pressures and significantly reduced dust-grain depletions. We interpret this material as cooling gas in a recombination zone far downstream from shocks driven into neutral gas clumps. The pressures derived for a group of ionized gas components at high positive velocity toward HD 43582 are lower than those of the other shocked components, pointing to pressure inhomogeneities across the remnant. A strong, very high velocity component near −620 km s−1 is seen in the absorption profiles of highly ionized species toward HD 43582. The velocity of this material is consistent with the range of shock velocities implied by observations of soft thermal X-ray emission from IC 443. Moderately high velocity gas toward HD 254755 may represent shocked material from a separate foreground SNR.

High-velocity interstellar absorption associated with the supernova remnant W28

ABSTRACT We present an analysis of moderately high-resolution optical spectra obtained for the sightline to CD−23 13777, an O9 supergiant that probes high-velocity interstellar gas associated with the supernova remnant W28. Absorption components at both high positive and high negative velocity are seen in the interstellar Na i D and Ca ii H and K lines towards CD−23 13777. The high-velocity components exhibit low Na i/Ca ii ratios, suggesting efficient grain destruction by shock sputtering. High column densities of CH+, and high CH+/CH ratios, for the components seen at lower velocity may be indicative of enhanced turbulence in the clouds interacting with W28. The highest positive and negative velocities of the components seen in Na i and Ca ii absorption towards CD−23 13777 imply that the velocity of the blast wave associated with W28 is at least 150 km s−1, a value that is significantly higher than most previous estimates. The line of sight to CD−23 13777 passes very close to a well-known site of interaction between the supernova remnant and a molecular cloud to the north-east. The north-east molecular cloud exhibits broad molecular line emission, OH maser emission from numerous locations, and bright extended GeV and TeV γ-ray emission. The sightline to CD−23 13777 is thus a unique and valuable probe of the interaction between W28 and dense molecular gas in its environs. Future observations at ultraviolet and visible wavelengths will help to better constrain the abundances, kinematics, and physical conditions in the shocked and quiescent gas along this line of sight.

A limit on Planck-scale froth with ESPRESSO

ABSTRACT Some models of quantum gravity predict that the very structure of space–time is ‘frothy’ due to quantum fluctuations. Although the effect is expected to be tiny, if these space–time fluctuations grow over a large distance, the initial state of a photon, such as its energy, is gradually washed out as the photon propagates. Thus, in these models, even the most monochromatic light source would gradually disperse in energy due to space–time fluctuations over large distances. In this paper, we use science verification observations obtained with ESPRESSO at the Very Large Telescope to place a novel bound on the growth of space–time fluctuations. To achieve this, we directly measure the width of a narrow Fe ii absorption line produced by a quiescent gas cloud at redshift $z$ ≃ 2.34, corresponding to a comoving distance of ≃5.8 Gpc. Using a heuristic model where the energy fluctuations grow as σE/E = (E/EP)α, where EP ≃ 1.22 × 1028 eV is the Planck energy, we rule out models with α ≤ 0.634, including models where the quantum fluctuations grow as a random walk process (α = 0.5). Finally, we present a new formalism where the uncertainty accrued at discrete space–time steps is drawn from a continuous distribution. We conclude, if photons take discrete steps through space–time and accumulate Planck-scale uncertainties at each step, then our ESPRESSO observations require that the step size must be at least ≳ 1013.2lP, where lP is the Planck length.

Heart of darkness: the influence of galactic dynamics on quenching star formation in galaxy spheroids

ABSTRACT Quenched galaxies are often observed to contain a strong bulge component. The key question is whether this reflects a causal connection – can star formation be quenched dynamically by bulges or the spheroids of early-type galaxies? We systematically investigate the impact of these morphological components on star formation, by performing a suite of hydrodynamical simulations of isolated galaxies containing a spheroid. We vary the bulge mass and scale radius, while the total initial stellar, halo, and gas mass are kept constant, with a gas fraction of 5 per cent. In addition, we consider two different sub-grid star formation prescriptions. The first follows most simulations in the literature by assuming a constant star formation efficiency per free-fall time, whereas in the second model it depends on the gas virial parameter, following high-resolution simulations of turbulent fragmentation. Across all simulations, central spheroids increase the gas velocity dispersion towards the galactic centre. This increases the gravitational stability of the gas disc, suppresses fragmentation and star formation, and results in galaxies hosting extremely smooth and quiescent gas discs that fall below the galaxy main sequence. These effects amplify when using the more sophisticated, dynamics-dependent star formation model. Finally, we discover a pronounced relation between the central stellar surface density and star formation rate (SFR), such that the most bulge-dominated galaxies show the strongest deviation from the main sequence. We conclude that the SFR of galaxies is not only set by the balance between accretion and feedback, but carries a (sometimes dominant) dependence on the gravitational potential.

On the Effects of UV Photons/X-Rays on the Chemistry of the Sgr B2 Cloud

Abstract The lines of HOC+, HCO, and CO+ are considered good tracers of photon-dominated regions (PDRs) and X-ray-dominated regions. We study these tracers toward regions of the Sgr B2 cloud selected to be affected by different heating mechanisms. We find the lowest values of the column density ratios of HCO+ versus HOC+, HCO, and CO+ in dense H ii gas, where UV photons dominate the heating and chemistry of the gas. The HOC+, HCO, and CO+ abundances and the above ratios are compared with those of chemical modeling, finding that high-temperature chemistry, a cosmic-ray ionization rate of 10−16 s−1, and timescales >105.0 yr explain well the HOC+ abundances in quiescent Sgr B2 regions, while shocks are also needed to explain the highest HCO abundances derived for these regions. The CO+ is mainly formed in PDRs, since the highest CO+ abundances of ∼(6–10) × 10−10 are found in H ii regions with electron densities >540 cm−3 and CO+ emission is undetected in quiescent gas. Among the ratios, the HCO+/HCO ratio is sensitive to the electron density, as it shows different values in dense and diffuse H ii regions. We compare SiO J = 2–1 emission maps of Sgr B2 with X-ray maps from 2004 and 2012. One known spot shown on the 2012 X-ray map is likely associated with molecular gas at velocities of 15–25 km s−1. We also derive the X-ray ionization rate of ∼10−19 s−1 for Sgr B2 regions pervaded by X-rays in 2004, which is quite low to affect the chemistry of the molecular gas.

The Gas–Star Formation Cycle in Nearby Star-forming Galaxies. I. Assessment of Multi-scale Variations

Abstract The processes regulating star formation in galaxies are thought to act across a hierarchy of spatial scales. To connect extragalactic star formation relations from global and kiloparsec-scale measurements to recent cloud-scale resolution studies, we have developed a simple, robust method that quantifies the scale dependence of the relative spatial distributions of molecular gas and recent star formation. In this paper, we apply this method to eight galaxies with ∼1″ resolution molecular gas imaging from the Physics at High Angular resolution in Nearby GalaxieS–ALMA (PHANGS–ALMA) survey and PdBI Arcsecond Whirlpool Survey (PAWS) that have matched resolution, high-quality narrowband Hα imaging. At a common scale of 140 pc, our massive (log(M ⋆[M ⊙]) = 9.3–10.7), normally star-forming (SFR[M ⊙ yr−1] = 0.3–5.9) galaxies exhibit a significant reservoir of quiescent molecular gas not associated with star formation as traced by Hα emission. Galactic structures act as backbones for both molecular gas and H ii region distributions. As we degrade the spatial resolution, the quiescent molecular gas disappears, with the most rapid changes occurring for resolutions up to ∼0.5 kpc. As the resolution becomes poorer, the morphological features become indistinct for spatial scales larger than ∼1 kpc. The method is a promising tool to search for relationships between the quiescent or star-forming molecular reservoir and galaxy properties, but requires a larger sample size to identify robust correlations between the star-forming molecular gas fraction and global galaxy parameters.

Detonation initiation by compressible turbulence thermodynamic fluctuations

Theory and computations have established that thermodynamic gradients created by hot spots in reactive gas mixtures can lead to spontaneous detonation initiation. However, the current laminar theory of the temperature-gradient mechanism for detonation initiation is restricted to idealized physical configurations. Thus, it only predicts conditions for the onset of detonations in quiescent gases, where an isolated hot spot is formed on a timescale shorter than the chemical and acoustic timescales of the gas. In this work, we extend the laminar temperature-gradient mechanism into a statistical model for predicting the detonability of an autoignitive gas experiencing compressible isotropic turbulence fluctuations. Compressible turbulence forms non-monotonic temperature fields with tightly-spaced local minima and maxima that evolve over a range of timescales, including those much larger than chemical and acoustic timescales. We examine the utility of the adapted statistical model through direct numerical simulations of compressible isotropic turbulence in premixed hydrogen-air reactants for a range of conditions. We find strong, but not conclusive, evidence that the model can predict the degree of detonability in an autoignitive gas due to turbulence-induced thermodynamic gradients.

A multi-molecular line study of the star-forming globule CB88-230

Context. This paper relates to low-mass star formation in globules, and the interaction of newly-formed stars with their environment. We follow up on the results of our earlier observations of this globule. Aims. Our aim is to study the gas- and dust environment of the young stellar object (YSO) in globule CB88 230, the large-scale molecular outflow triggered by the jet driven by the YSO, and their interaction. Methods. We carried out submillimetre continuum and multi-line molecular observations with several single-dish facilities, mapping the core of the globule and the large-scale outflow associated with the YSO. Results. Dust continuum and molecular line maps (of 12CO, C18O, CS, CH3OH) show a flattened (axes ratio 1.5−1.7), asymmetric core with a full width at half maximum (FWHM)-diameter of 0.16−0.21 pc. Line profiles of 12CO, 13CO(2–1, 3–2), and CS(2–1) show self-absorption near the YSO; the absorption dip is at a slightly (~0.3 km s−1) redder velocity than that of the quiescent gas, possibly indicating infall of cooler envelope gas. The mass of the core, determined from C18O(1–0) observations, is about 8 M⊙, while the virial mass is in the range 5−8M⊙, depending on the assumed density distribution. We detect a slight velocity gradient (~0.98 km s−1 pc−1), though rotational energy is negligible with respect to gravitational and turbulent energy of the core. A fit to the spectral energy distribution of the core gives a dust temperature Td ≈ 18 K and a gas mass of ca. 2 M⊙ (assuming a gas-to-dust ratio of 100). More careful modelling of the sub-mm emission (not dominated by the relatively hot central regions) yields M ≈ 8M⊙. From the molecular line observations we derive gas temperatures of 10−20 K. A Bayesian analysis of the emission of selected molecules observed towards the YSO, yields Tkin ≈ 21.4 K (68% credibility interval 14.5−35.5 K) and volume density n(H2) ≈ 4.6 × 105 cm−3 (8.3 × 104−9.1 × 105 cm−3). We have mapped the well-collimated large-scale outflow in 12CO(3–2). The outflow has a dynamical age of a few 104 yr, and contains little mass (a few 10−2 M⊙). A misalignment between the axis of this large-scale outflow and that of the hot jet close to the YSO indicates that the outflow direction may be changing with time.

A 3 mm Spectral Line Survey toward the Barred Spiral Galaxy NGC 3627

Abstract We conduct spectral line survey observations in the 3 mm band toward a spiral arm, a bar-end, and a nuclear region of the nearby barred spiral galaxy NGC 3627 with the IRAM 30 m telescope and the Nobeyama 45 m telescope. Additional observations are performed toward the spiral arm and the bar-end in the 2 mm band. We detect 8, 11, and 9 molecular species in the spiral arm, the bar-end, and the nuclear region, respectively. Star formation activities are different among the three regions, and in particular, the nucleus of NGC 3627 is known as a low-ionization nuclear emission region/Seyfert 2 type nucleus. In spite of these physical differences, the chemical composition shows impressive similarities among the three regions. This result means that the characteristic chemical composition associated with these regions is insensitive to the local physical conditions such as star formation rate, because such local effects are smeared out by extended quiescent molecular gas on scales of 1 kpc. Moreover, the observed chemical compositions are also found to be similar to those of molecular clouds in our Galaxy and the spiral arm of M51, whose elemental abundances are close to those in NGC 3627. Therefore, this study provides us with a standard template of the chemical composition of extended molecular clouds with the solar metallicity in nearby galaxies.

Femtosecond Laser Tagging in R134a with Small Quantities of Air

Femtosecond laser tagging is demonstrated for the first time in R134a (1,1,1,2-tetrafluoroethane) gas and in mixtures of R134a with small quantities of air. A systematic study of this tagging method is explored through the adjustment of gas pressure, mixture ratio, and laser properties. It is found that the signal strength and lifetime are greatest at low pressures for excitation at both the 400 and 800 nm laser wavelengths. The relative intensities of two spectral peaks in the near-UV emission change as a function of gas pressure and can potentially be used for local pressure measurements. Single-shot precision in pure R134a is demonstrated in quiescent gas. One standard deviation (68%) of the uncertainty lies within of the mean velocity in a 0.1 atm pressure quiescent flow using a delay time of and within using a delay of . The variable parameter space is chosen to mimic conditions used in NASA Langley Research Center’s Transonic Dynamics Tunnel. Good signal-to-noise ratio is achieved for low-pressure conditions, especially in a pure freon environment. The precision and signal lifetime demonstrate the feasibility of using this technique for measuring representative Transonic Dynamics Tunnel flowfields in a bench-top laboratory setting.

Chemical tracers in proto-brown dwarfs: CO, ortho-H2CO, para-H2CO, HCO+, CS observations

We present a study of the CO isotopologues and the high-density tracers H$_{2}$CO, HCO$^{+}$, and CS in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30m telescope to observe the $^{12}$CO (2-1), $^{13}$CO (2-1), C$^{18}$O (2-1), C$^{17}$O (2-1), H$_{2}$CO (3-2), HCO$^{+}$ (3-2), and CS (5-4) lines in 7 proto-BDs. The hydrogen column density for the proto-BDs derived from the CO gas emission is $\sim$2-15 times lower than that derived from the dust continuum emission, indicating CO depletion from the gas-phase. The mean H$_{2}$CO ortho-to-para ratio is $\sim$3 for the proto-BDs and indicates gas-phase formation for H$_{2}$CO. We have investigated the correlations in the molecular abundances between the proto-BDs and protostars. Proto-BDs on average show a factor of $\sim$2 higher ortho-to-para H$_{2}$CO ratio than the protostars. Possible explanations include a difference in the H$_{2}$CO formation mechanism, spin-selective photo-dissociation, self-shielding effects, or different emitting regions for the ortho and para species. There is a tentative trend of a decline in the HCO$^{+}$ and H$_{2}$CO abundances with decreasing bolometric luminosity, while the CS and CO abundances show no particular difference between the proto-BDs and protostars. These trends reflect the scaled-down physical structures for the proto-BDs compared to protostars and differences in the peak emitting regions for these species. The C$^{17}$O isotopologue is detected in all of the proto-BDs as well as the more evolved Class Flat/Class II BDs in our sample, and can probe the quiescent gas at both early and late evolutionary stages.

Super star cluster feedback driving ionization, shocks and outflows in the halo of the nearby starburst ESO 338-IG04

Context. Stellar feedback strongly affects the interstellar medium (ISM) of galaxies. Stellar feedback in the first galaxies likely plays a major role in enabling the escape of LyC photons, which contribute to the re-ionization of the Universe. Nearby starburst galaxies serve as local analogues allowing for a spatially resolved assessment of the feedback processes in these galaxies. Aims.We aim to characterize the feedback effects from the star clusters in the local high-redshift analogue ESO 338-IG04 on the ISM and compare the results with the properties of the most massive clusters. Methods. We used high quality VLT/MUSE optical integral field data to derive the physical properties of the ISM such as ionization, density, shocks, and performed new fitting of the spectral energy distributions of the brightest clusters in ESO 338-IG04 from HST imaging. Results.We find that ESO 338-IG04 has a large ionized halo which we detect to a distance of 9 kpc. We identify four Wolf-Rayet (WR) clusters based on the blue and red WR bump. We follow previously identified ionization cones and find that the ionization of the halo increases with distance. Analysis of the galaxy kinematics shows two complex outflows driven by the numerous young clusters in the galaxy. We find a ring of shocked emission traced by an enhanced [O I]/Hα ratio surrounding the starburst and at the end of the outflow. Finally we detect nitrogen enriched gas associated with the outflow, likely caused by the WR stars in the massive star clusters. Conclusions. Photoionization dominates the central starburst and sets the ionization structure of the entire halo, resulting in a density bounded halo, facilitating the escape of LyC photons. Outside the central starburst, shocks triggered by an expanding super bubble become important. The shocks at the end of the outflow suggest interaction between the hot outflowing material and the more quiescent halo gas.

ALMA [C i]3P1–3P0 Observations of NGC 6240: A Puzzling Molecular Outflow, and the Role of Outflows in the Global αCO Factor of (U)LIRGs

Abstract We present Atacama large millimeter/submillimeter array (ALMA) and compact array (ACA) [C i] ([C i](1–0)) observations of NGC 6240, which we combine with ALMA CO(2–1) and IRAM Plateau de Bure Interferometer CO(1–0) data to study the physical properties of the massive molecular (H2) outflow. We discover that the receding and approaching sides of the H2 outflow, aligned east–west, exceed 10 kpc in their total extent. High resolution ( ) [C i](1–0) line images surprisingly reveal that the outflow emission peaks between the two active galactic nuclei (AGNs), rather than on either of the two, and that it dominates the velocity field in this nuclear region. We combine the [C i](1–0) and CO(1–0) data to constrain the CO-to-H2 conversion factor ( ) in the outflow, which is on average . We estimate that 60 ± 20% of the total H2 gas reservoir of NGC 6240 is entrained in the outflow, for a resulting mass-loss rate of SFR. These energetics rule out a solely star formation-driven wind, but the puzzling morphology challenges a classic radiative-mode AGN feedback scenario. For the quiescent gas, we compute , which is at least twice the value commonly employed for (ultra) luminous infrared galaxies ((U)LIRGs). We observe a tentative trend of increasing ratios with velocity dispersion and measure r 21 > 1 in the outflow, whereas r 21 ≃ 1 in the quiescent gas. We propose that molecular outflows are the location of the warmer, strongly unbound phase that partially reduces the opacity of the CO lines in (U)LIRGs, hence driving down their global and increasing their r 21 values.

On the origin of phosphorus nitride in star-forming regions

Abstract We present multitransition observations of phosphorus nitride (PN) towards a sample of nine massive dense cores in different evolutionary stages. Using transitions with different excitation conditions, we have found for the first time that the excitation temperatures of PN are in the range ∼5–30 K. To investigate the main chemical route for the PN formation (surface-chemistry versus gas-phase chemistry), and the dominant desorption mechanism (thermal versus shock), we have compared our results with those obtained from molecules tracing different chemical and physical conditions (SiO, SO, CH3OH, and N2H+). We have found that the PN line profiles are very well correlated with those of SiO and SO in six out of the nine targets, which indicate that PN may be released by sputtering of dust grains due to shocks. This finding is corroborated by a faint but statistically significant positive trend between the PN abundance and those of SiO and SO. However, in three objects the PN lines have no hints of high-velocity wings, which indicates an alternative origin of PN. Overall, our results indicate that the origin of PN is not unique, as it can be formed not only in protostellar shocks, but also in colder and more quiescent gas through alternative pathways.

Stability of transonic jets with strong rarefaction waves for two-dimensional steady compressible Euler system

We study supersonic flow past a convex corner which is surrounded by quiescent gas. When the pressure of the upstream supersonic flow is larger than that of the quiescent gas, there appears a strong rarefaction wave to rarefy the supersonic gas. Meanwhile, a transonic characteristic discontinuity appears to separate the supersonic flow behind the rarefaction wave from the static gas. In this paper, we employ a wave front tracking method to establish structural stability of such a flow pattern under non-smooth perturbations of the upcoming supersonic flow. It is an initial-value/free-boundary problem for the two-dimensional steady non-isentropic compressible Euler system. The main ingredients are careful analysis of wave interactions and construction of suitable Glimm functional, to overcome the difficulty that the strong rarefaction wave has a large total variation.

Suspended liquid particle disturbance on laser-induced blast wave and low density distribution

The impurity effect of suspended liquid particles on the laser-induced gas breakdown was experimentally investigated in quiescent gas. The focus of this study is the investigation of the influence of the impurities on the shock wave structure as well as the low density distribution. A 532 nm Nd:YAG laser beam with an 188 mJ/pulse was focused on the chamber filled with suspended liquid particles 0.9 ± 0.63 μm in diameter. Several shock waves are generated by multiple gas breakdowns along the beam path in the breakdown with particles. Four types of shock wave structures can be observed: (1) the dual blast waves with a similar shock radius, (2) the dual blast waves with a large shock radius at the lower breakdown, (3) the dual blast waves with a large shock radius at the upper breakdown, and (4) the triple blast waves. The independent blast waves interact with each other and enhance the shock strength behind the shock front in the lateral direction. The triple blast waves lead to the strongest shock wave in all cases. The shock wave front that propagates toward the opposite laser focal spot impinges on one another, and thereafter a transmitted shock wave (TSW) appears. The TSW interacts with the low density core called a kernel; the kernel then longitudinally expands quickly due to a Richtmyer-Meshkov-like instability. The laser-particle interaction causes an increase in the kernel volume which is approximately five times as large as that in the gas breakdown without particles. In addition, the laser-particle interaction can improve the laser energy efficiency.

Molecular-cloud-scale Chemical Composition. I. A Mapping Spectral Line Survey toward W51 in the 3 mm Band

Abstract We have conducted a mapping spectral line survey toward the Galactic giant molecular cloud W51 in the 3 mm band with the Mopra 22 m telescope in order to study an averaged chemical composition of the gas extended over a molecular-cloud scale in our Galaxy. We have observed the area of 25′ × 30′, which corresponds to 39 pc × 47 pc. The frequency ranges of the observation are 85.1–101.1 GHz and 107.0–114.9 GHz. In the spectrum spatially averaged over the observed area, spectral lines of 12 molecular species and 4 additional isotopologues are identified. An intensity pattern of the spatially averaged spectrum is found to be similar to that of the spiral arm in the external galaxy M51, indicating that these two sources have similar chemical compositions. The observed area has been classified into five subregions according to the integrated intensity of 13CO(J = 1 − 0) ( ), and contributions of the fluxes of 11 molecular lines from each subregion to the averaged spectrum have been evaluated. For most of the molecular species, 50% or more of the flux comes from the subregions with from 25 to 100 K km s−1, which does not involve active star-forming regions. Therefore, the molecular-cloud-scale spectrum observed in the 3 mm band hardly represents the chemical composition of star-forming cores, but mainly represents the chemical composition of an extended quiescent molecular gas. The present result constitutes a sound base for interpreting the spectra of external galaxies at a resolution of a molecular-cloud scale (∼10 pc) or larger.

Is HESS J1912+101 Associated with an Old Supernova Remnant?

Abstract HESS J1912+101 is a shell-like TeV source that has no clear counterpart in multiwavelength. Using CO and H i data, we reveal that V LSR ∼ +60 km s−1 molecular clouds (MCs), together with shocked molecular gas and high-velocity neutral atomic shells, are concentrated toward HESS J1912+101. The prominent wing profiles up to V LSR ∼ +80 km s−1 seen in 12CO (J = 1–0 and J = 3–2) data, as well as the high-velocity expanding H i shells up to V LSR ∼ +100 km s−1, exhibit striking redshifted-broadening relative to the quiescent gas. These features provide compelling evidences for large-scale perturbation in the region. We argue that the shocked MCs and the high-velocity H i shells may originate from an old supernova remnant (SNR). The distance to the SNR is estimated to be ∼4.1 kpc based on the H i self-absorption method, which leads to a physical radius of 29.0 pc for the ∼(0.7–2.0) × 105 years old remnant with an expansion velocity of ≳40 km s−1. The +60 km s−1 MCs and the disturbed gas are indeed found to coincide with the bright TeV emission, supporting the physical association between them. Naturally, the shell-like TeV emission comes from the decay of neutral pions produced by interactions between the accelerated hadrons from the SNR and the surrounding high-density molecular gas.