arXiv subjects

Ji Yang

Publications and source records attributed to Ji Yang.

At least 19 recordsLinked to original sources

arXiv2026

CO Structures with Narrow Lines in Nearby Quiescent Regions

Using CO data from Phase I of the Milky Way Imaging Scroll Painting (MWISP) survey, we present a systematic study of molecular structures with narrow lines. We identify 57 CO structures, most of which exhibit low densities and subsonic/transonic turbulence. Among them, structures with large projected areas and diffuse, sheet-like geometries are identified as veil clouds. The low LSR velocities and the concentration of these CO structures toward both the Galactic center (e.g., Ophiuchus, Aquila) and anticenter (e.g., Cepheus, Taurus) regions suggest a local origin for the sample, as supported by distance measurements of about 200--300pc for a subset with relatively large angular extents. These nearby structures likely arise from large-scale compression driven by past supernova activity within the Local Bubble. The observed low-velocity-dispersion emission may trace quiescent regions where turbulence has decayed due to a lack of sustained energy injection. For diffuse veil clouds with an assumed magnetic field of ~10uG, ion-neutral friction may provide an additional mechanism for turbulent dissipation on sub-parsec scales corresponding to their thickness of 0.1--0.3pc. Tracing the atomic-to-molecular transition, veil clouds provide a unique window into the diffuse, quiescent precursor state of dense gas. They likely represent a widespread but previously overlooked component of the Galactic molecular gas reservoir, with significant implications for cloud formation and evolution, the total mass budget and spatial distribution of molecular gas, and the initial conditions of star formation as a related consequence.

astro-ph.GA↗

arXiv2026

Investigations of MWISP Bubbles: Identification and Analysis of Enclosed Molecular Bubbles by Weight Fields

Molecular bubbles are widely used as tracers of stellar feedback; yet, their identification in spectral-line surveys remains challenging because both cavity morphology and kinematic structure must be assessed consistently in position--position--velocity (PPV) space. We present the Bubble-Weight Fields (BWFields) framework, a PPV-based method that for the first time enables the automated and objective identification and analysis of enclosed molecular bubbles directly from spectral-line data cubes. BWFields constructs a bubble-weight field, $W_{l,b,v}$, which encodes cumulative evidence for cavity interiors by aggregating topological signatures across multiple signal-to-noise tiers and velocity-integration scales. Contiguous cavity interiors are segmented as weight-clumps and associated with surrounding molecular gas, linking candidate bubbles to the structure of their host clouds. Shell morphology is characterized using radial intensity profiles and emission-defined intensity skeletons, which capture the shell geometry as traced by the observed emission. Bubble kinematics are quantified using azimuthally sampled position-velocity (PV) diagnostics, along with a turbulence-normalized expansion significance, which serves as a direct measure of the expansion-like velocity organisation. Applied to MWISP $^{13}$CO observations of the G17 region, BWFields identifies a population of bubble candidates with a broad range of morphologies and velocity structures in complex environments. BWFields establishes a scalable and physically interpretable framework for molecular-bubble studies in large surveys, enabling systematic investigations of stellar feedback in the Galactic interstellar medium.

astro-ph.GA↗

arXiv2026

Statistical Properties of Molecular Clouds in the Milky Way: Insights from Three-Isotopologue CO Observations of the MWISP Project

We present a comprehensive statistical analysis of molecular cloud (MC) properties using the MWISP survey's 12CO, 13CO, and C18O (J = 1--0) data toward the inner (l = 45$^\circ$--60$^\circ$) and outer (l = 120$^\circ$--130$^\circ$) Galaxy. From a strict selection of 24,724 identified MCs, a final sample of 3,161 well-resolved MCs is established. We investigate the distributions of observational, morphological, and derived physical parameters, as well as their environmental dependencies and intercorrelations. Our analysis reveals that MCs are typically oblate and tend to align with the Galactic disk. A critical evaluation using a nearby subsample confirms significant distance-dependent selection effects for some parameters, nevertheless, the direction of changes in these parameters can indicate distance influence. We also examine several specific subsamples, revealing the distinct characteristics of MCs in the G120 spiral shock region, MCs in the G50 interarm spurs, C18O-bright MCs, and MCs with supra-Larson velocity dispersion. For instance, MCs with supra-Larson velocity dispersion are predominantly small and likely young clouds inheriting turbulence from the diffuse ISM. Notably, a comparison across tracers reveals that typical MCs have a turbulent, diffuse, 12CO-bright gas structure in their outer layers that does not contribute directly to star formation. In contrast, 13CO-bright gas represents a turning point where gravity becomes significant; C18O-bright gas is about gravity-dominated. Comprehensive correlation analysis confirms a flatter $\sigma_v$-size relation than classic Larson's law and a strong mass-size relation. Incorporating dimensional analysis, we derive minimal sets of eigenparameters from which most other observational and physical parameters can be estimated. This highlights the underlying scaling relations that governing cloud properties.

astro-ph.GA↗

arXiv2026

A study of the Physical Properties and Star Formation Activity of a Large Sample of Molecular Clouds: I Distances

Accurate distances to molecular clouds are crucial for determining their physical properties, understanding star formation, and tracing Galactic spiral structure. A number of 103,517 molecular clouds has been identified by the DBSCAN algorithm in the MWISP Phase I CO survey (l = 9.75-229.75 deg, |b| <= 5.25 deg), most of which lack reliable distances. In this work, we propose three independent methods, all of which match the molecular cloud's velocity-integrated intensity maps of 12CO lines from the MWISP with the three-dimensional dust extinction maps derived from Gaia, Pan-STARRS 1, and 2MASS, to determine molecular cloud distances. We present a catalog of 1,573 molecular clouds with robust distances ranging from approximately 150 pc to 3000 pc, 90 percent of which are measured for the first time, with typical statistical and systematic uncertainties of approximately 20% and 10%, respectively. We also derive their physical properties, such as their mass and sizes. This publicly available catalog of molecular clouds with distances provides a foundation for testing molecular cloud scaling relations and probing how cloud conditions influence star formation across diverse Galactic environments.

astro-ph.GA↗

arXiv2026

Discovery of a Featureless Tidal Disruption Event at z~1 with the Wide Field Survey Telescope

We report the discovery of tidal disruption event (TDE) WFST250820mmsw/AT2025wet by the 2.5-meter Wide Field Survey Telescope (WFST). It exhibits a blue nuclear flare throughout the observed evolution with a g-band peak magnitude ~22, which is about 3 magnitudes brighter than its host galaxy. A Keck/LRIS spectrum taken near the optical peak reveals a featureless blue continuum, with no discernible emission lines. However, its redshift can be accurately determined to be 1.037 by its host galaxy absorption lines. Blackbody fits to the multiband spectral energy distribution (SED) of AT2025wet yield a constant temperature of ~19,000K and a peak luminosity of (8.27 +0.92 -0.71)*10^44 erg s^-1 while actually the SED likely peaks at a much shorter wavelength than a 19,000K blackbody. The SED modeling of the host galaxy implies a stellar mass of ~10^11.2 M_odot and an estimated central black hole mass of ~10^8 M_odot, with no evidence of significant active galactic nucleus activity prior to the flare. All of these observations are well consistent with a featureless TDE scenario, making it the highest-redshift non-jetted TDE known to date. TDEs at such high redshift provide us a unique opportunity to explore the intrinsic SEDs of TDEs, particularly to test whether they peak in the extreme-UV regime, thereby addressing the missing energy puzzle and the origin of optical emission in TDEs. Ongoing surveys represented by WFST and the Legacy Survey of Space and Time (LSST) are expected to discover an increasing number of TDEs at higher redshifts, which will extend our census of SMBHs across redshift space and help unravel the mysteries of optical TDEs through direct probes of their UV emission.

astro-ph.HE↗

arXiv2026

A Comparative Study of TeV Gamma-Ray Sources with Various Objects

We investigate the relationships between LHAASO TeV gamma-ray sources and various kinds of objects, including pulsar wind nebulae (PWNe), supernova remnants (SNRs), HII regions, microquasars, and OB associations. We propose a Randomization-Adjusted Overlap Correlation (RAOC) method to statistically assess association probabilities and evaluate association proportions across catalogs. The results reveal statistically significant overlaps between LHAASO sources and SNRs, PWNe, and microquasars, supporting their role as important contributors to TeV gamma-ray emission. The estimated association proportions of LHAASO sources are 0.19$\pm$0.08 with SNRs, 0.20$\pm$0.04 with PWNe, and 0.027$\pm$0.008 with microquasars. The proportion of the gamma-ray sources associated with the subsample of shell-type SNRs is ~0.1. While HII regions also show potential association, particularly with the KM2A component, their large self-overlap ratio complicates precise estimation. In contrast, OB associations exhibit a high probability of chance coincidence, suggesting their limited contribution to TeV gamma-ray emission. Our analysis of TeV gamma-ray emission capabilities shows that ~60% of PWNe are gamma-ray bright in both the WCDA and KM2A energy ranges. For SNRs and microquasars, the TeV gamma-ray bright fraction is ~10%. The subsample of PWNe associated with molecular clouds (MCs) shows enhanced gamma-ray emission. Furthermore, positional analysis reveals a systematic offset of the gamma-ray sources overlapping with PWNe toward the associated MCs. These findings imply a role for MCs in PWN gamma-ray production. Additionally, self-correlation analysis indicates that about 70% of the WCDA and KM2A gamma-ray components share a common origin. The study also identifies selection effects in existing SNR catalogs and notes clustering among approximately 30% of HII regions within larger star-forming regions.

astro-ph.HE↗

arXiv2026

The radial velocity stability for reference sources in the MWISP CO survey

To assess the velocity stability of CO spectral lines in the Milky Way Imaging Scroll Painting (MWISP) survey, we employ a cross-correlation method to measure velocity shifts across $\sim$ 10,000 CO spectra from six reference sources observed over the ten-year duration of the survey. The standard deviations ($\sigma$) of these measured velocity shifts range from 0.03 to 0.23 km s$^{-1}$ for their $^{12}$CO lines and 0.03 to 0.16 km s$^{-1}$ for $^{13}$CO lines. We find that larger shifts are associated with broader linewidths, more pronounced differences between monthly and long-term variations, and a stronger correlation between velocity shifts of $^{12}$CO and $^{13}$CO lines. By examining the relation of velocity shifts with the Azimuth-Elevation of the telescope, as well as the velocity fields of these extended sources, we find that the velocity shifts exhibit systematic changes across different Azimuth-Elevation ranges. The patterns and amplitudes of these changes vary among sources and are closely linked to the extended velocity fields of sources. This indicates that the increased velocity shifts are primarily caused by pointing errors, which are more sensitive to reference sources with higher velocity gradients. We also provide high signal-to-noise, velocity-aligned template spectra for reference sources.

astro-ph.GA↗

arXiv2026

Resolving Primitive-Sharing Ambiguity in Long-Tailed TLS-Based Industrial MEP Point Cloud Segmentation via Spatial Context Constraints

In terrestrial laser scanning (TLS)-based mechanical, electrical, and plumbing (MEP) point cloud segmentation, safety-critical components such as reducers and valves are persistently misclassifed, blocking reliable engineering knowledge extraction. This stems from a dual crisis--extreme class imbalance (215:1) compounded by geometric ambiguity, since most tail classes share cylindrical primitives with dominant head classes--that existing frequencybased re-weighting methods cannot resolve. We propose spatial context constraints that exploit neighborhood prediction consistency to disambiguate locally similar structures. Our approach extends Class-Balanced (CB) Loss with two architecture-agnostic mechanisms: Boundary-CB, an entropy-based constraint that emphasizes ambiguous boundaries and encodes an MEP assemblytopology prior, and Density-CB, a density-based constraint that compensates for scan-dependent variations and encodes TLS sensor-physics knowledge. Both operate at the loss level and integrate into existing pipelines without backbone modifcations. On the Industrial3D dataset (612.7M labelled points from water treatment facilities), our method achieves 55.74% mIoU, exceeding the strongest of three representative fully supervised backbone baselines (39.83-52.48% mIoU), with a 21.7% relative improvement on tail-class performance (29.59% vs. 24.32%) while preserving head-class accuracy (88.14%). Components with primitive-sharing ambiguity show strong gains: reducer improves from 0% to 21.12% IoU, and valve improves by 24.3% relative. These results show that spatial context constraints reduce primitive-sharing errors in the target industrial MEP setting and support more reliable identifcation of safety-critical components for Digital Twin and Scan-to-BIM applications. Code: https://github.com/PointCloudYC/LongTail3D.git.

cs.CV↗

arXiv2025

How is Cold Gas Loaded into Galactic Nuclear Outflows?

The origin of the multiphase gas within the Fermi/eROSITA bubbles is crucial for understanding Galactic Center (GC) feedback. We use HI4PI data to investigate the kinematics and physical properties of high-velocity clouds (HVCs) toward the GC. Our results reveal that the HVCs exhibit a distinct asymmetric distribution, closely associated with the bar-driven tilted dust lanes and the distorted overshooting streams. We propose that powerful nuclear outflows interact with these gas-rich, off-plane structures, striping and entraining cold gas from the outer Galactic regions (R_GC~0.5--1.7 kpc) rather than solely from the region of the central molecular zone (CMZ; R_GC<0.3 kpc). In this scenario, as the Galactic bar drives gas inflows along the dust lanes, nuclear outflows simultaneously break through the CMZ, sweeping up and ablating cold gas from the boundary layer of these pre-existing structures. This process naturally accounts for the observed high turbulence, complex spectral signatures, and anomalous spatial-kinematic gas patterns, as well as multiwavelength asymmetries of the bubbles. The HVCs are accelerated to about 230--340 km/s over a dynamical time of ~3--6 Myr. When the multiphase, inhomogeneous composition of the gas is included, the estimated gas outflow rate reaches ~1 Msun/yr. This value is comparable to the bar-driven inflow rate, indicating a tightly coupled gas cycle in the inner Galaxy. Our research highlights the critical role of bar-driven gas dynamics and nuclear feedback in the secular evolution of the Milky Way, offering a valuable paradigm for investigating gas cycles in external galaxies.

astro-ph.GA↗

arXiv2025

The Milky Way Imaging Scroll Painting Survey: Data Release 1

We present the first data release (DR1) of the Milky Way Imaging Scroll Painting (MWISP) survey, a mapping in the J=(1-0) transition lines of 12CO, 13CO, and C18O toward the northern Galactic plane during 2011-2022. The MWISP survey was conducted using the PMO 13.7 m telescope at a spatial resolution of approximately 50" and a velocity resolution of 0.16 km/s at 115 GHz. DR1 fully covered 2310 square degrees within the Galactic longitude (l) and latitude (b) range of 9.75 deg =< l =< 229.75 deg and |b| =< 5.25 deg. The surveyed area was divided into cell units of 30'x30' for practical purposes and On-The-Fly (OTF) mapping was performed toward each target cell unit. The data were regridded into a regular 3D datacube in l-b-V_LSR with a pixel size of 30" in l-b axes and 0.16 km/s in theV_LSR axis. The median rms noise is 0.47 K, 0.25 K, and 0.25 K for 12CO, 13CO, and C18O, respectively. The equivalent 3 sigma sensitivity in 12CO luminosity is approximately 0.23 K km/s, making MWISP the most sensitive survey of its kind. In this paper, we describe the survey data, including the calibration, data cleaning, data mosaic processes, and the data products. The final mosaicked data cubes contain about 3.33x10^7 spectra (pixels) for each CO isotopologue line. Color composite images, made from the intensities of the isotopologue lines, and some concise descriptions are provided. We constructed a molecular cloud catalog based on the mosaicked 12CO data cube using the clustering algorithm DBSCAN, detecting 103,517 molecular clouds, 10,790 of which exhibit 13CO emission and 304 of which show C18O emission. Based on the histogram of voxel brightness temperature, we estimated a total 12CO flux of 7.69+/-0.38x10^7 K km/s arcmin^2, 82% of which is captured by the DBSCAN algorithm. The data, together with the cloud sample, provide unique information on molecular gas in the northern Milky Way.

astro-ph.GA↗

arXiv2025

Investigations of MWISP Clumps: 13CO Clump Source Catalog and Physical Properties

We present the first comprehensive catalogs of $^{13}$CO clumps from the Milky Way Imaging Scroll Painting (MWISP) project. By developing an equivalent global detection scheme integrated with the FacetClumps algorithm, we successfully extract 71,661 molecular clumps across a high-resolution $^{13}$CO data cube spanning 2310 deg$^2$ from the MWISP Phase I survey. To determine accurate distances, we design an automatic hierarchical distance decision method using signal regions as fundamental objects, effectively resolving the kinematic distance ambiguity problem and obtaining reliable measurements for 97.94% of the sample. Statistical analysis reveals that 65.3% of clumps are gravitationally bound, accounting for approximately 96.3% of the statistical total mass. Scaling relation analysis across multiple surveys reveals universal power-law behaviors in clump populations. Maser-associated clumps exhibit modified parameter distributions and scaling relations, revealing how active star formation alters clump dynamics and structure. These extensive catalogs establish a foundation for investigating molecular clump properties, star formation processes, and Galactic evolution.

astro-ph.GA↗

arXiv2025

Molecular Gas Distribution toward the Inner and Outer Galaxy Revealed by MWISP -- the Galactic Longitude 45\deg--60\deg and 120\deg--130\deg

Molecular clouds (MCs) are cradles of star and planet formation, thereby playing an important role in the evolution of galaxies. Based on the unbiased Milky Way Imaging Scroll Painting (MWISP) survey data of $^{12}$CO, $^{13}$CO, and C$^{18}$O (J=1--0) line emission in two regions toward the inner and outer Galaxy, i.e. the G50 ($44.75\deg \le l \le 60.25\deg$) and G120 ($119.75\deg \le l \le 130.25\deg$) regions, the distribution of molecular gas is studied. Both regions have Galactic latitudes of $|b| \le 5.25\deg$. A catalog containing 24724 MCs is constructed from the data. In our proximity, several molecular structures with large angular scales and small velocity dispersions are discovered, resembling curtains of mist. Beyond the nearby molecular gas, a clear aggregation of MCs along coherent structures in the Galactic plane is visible, sketching spiral arm structures. Nevertheless, the aggregation of MCs is also detected in the inter-arm region between the Perseus and Outer arms in the G50 region. The Galactic molecular disk in this inter-arm region is found to be thinner than that in the adjacent spiral arm region. In addition, the thickness of the Galactic molecular disk examined here is found to be correlated with the warp of it, indicating their homologous origins. The molecular disk has a typical thickness of ~220 pc in the inner Galaxy. Moreover, the dispersion of the MC systemic velocity decreases with increasing galactocentric radius, resulting in lower kinematic distance uncertainties at larger radii. However, the Perseus arm segment in the G120 region exhibits a relatively large cloud-to-cloud velocity dispersion and split components in its MC velocity distribution.

astro-ph.GA↗

arXiv2025

CU-JADE: A Method for Traversing Extinction Jumps along the Line of Sight

Although interstellar dust extinction serves as a powerful distance estimator, the solar system's location within the Galactic plane complicates distance determinations, especially for molecular clouds (MCs) at varying distances along the line of sight (LoS). The presence of complex extinction patterns along the LoS introduces degeneracies, resulting in less accurate distance measurements to overlapping MCs in crowded regions of the Galactic plane. In this study, we develop the CUSUM-based Jump-point Analysis for Distance Estimation (CU-JADE), a novel method designed to help mitigate these observational challenges. The key strengths of CU-JADE include: (1) sensitivity to detect abrupt jumps in Distance-$A_{\lambda}$ ($D$-$A$) datasets, (2) minimal systematic errors as demonstrated on both mock and observed data, and (3) the ability to combine CUSUM analysis with multiwavelength data to improve the completeness of distance measurements for nearby gas structures, even for extinction values as low as $\Delta A_{V} \gtrsim 0.15$ mag. By combining CO survey data with a large sample of stars characterized by high-precision parallaxes and extinctions, we uncovered the multilayered molecular gas distribution in the high-latitude Cepheus region. We also determined accurate distances to MCs beyond the Cygnus Rift by analyzing the intricate structure of gas and extinction within the Galactic plane. Additionally, we constructed a full-sky 3D extinction map extending to 4 kpc, which provides critical insights into dense interstellar medium components dominated by molecular hydrogen. These results advance our understanding of the spatial distribution and physical properties of MCs across the Milky Way.

astro-ph.GA↗

arXiv2025

A Glimpse of Satellite Galaxies in the Milky Way with the 2.5-meter Wide Field Survey Telescope (WFST): Bootes III and Draco

We carry out deep imaging of the Milky Way satellite galaxies, Bootes III and Draco, with WFST as one pilot observing program to demonstrate the capability of WFST. Combining catalogs with PS1 DR2 and Gaia DR3, we derive proper motions for candidate member stars in these two satellite galaxies over a 12-year time baseline, yielding uncertainties of ~1.8 mas/yr at 21 mag and ~3.0 mas/yr at 22 mag in the r band. The proper motions derived from bright and faint stars are consistent, indicating no significant variation in proper motion across stellar luminosity as these galaxies undergo tidal interactions with the MW. Meanwhile, we suggest that Bootes III represents the bound remnant of the progenitor galaxy that gave rise to the Styx stream, as evidenced by its elongated density profile and overdensity in both spatial and kinematic space. This is the first paper to use WFST to measure the proper motions of faint stars in Milky Way satellite galaxies. More detailed analyses will be presented in forthcoming papers from the wide field survey (WFS) program.

astro-ph.GA↗

arXiv2025

Cloud-to-cloud velocity dispersions across a Local arm segment

Using a large sample of 9617 molecular clouds (MCs) from the Milky Way Imaging Scroll Painting survey, we mainly measure one-dimensional cloud-to-cloud velocity dispersions across a 450 deg$^{2}$ segment of the Local arm in the Galactic second quadrant. We define the cloud-to-cloud velocity dispersion using two metrics: the standard deviation ($\sigma_{\rm bin}$) and flux-weighted root-mean-squared value ($\sigma_{\rm bin, w}$) of the centroid velocities of $^{12}$CO-detected MCs within spatial bins. The typical values of $\sigma_{\rm bin}$ and $\sigma_{\rm bin, w}$ are 7.5$\pm$0.5 km s$^{-1}$ and 6.2$\pm$0.5 km s$^{-1}$, respectively. After categorizing clouds by sizes into three types: Type $S$ (0.15 $-$ 1.2 pc), Type $M$ (1.2 $-$ 4.8 pc), and Type L ($\gtrsim$ 4.8 pc), we find that the spatial distribution of Type $S$ and $M$ MCs projected onto the Galactic longitude-latitude (l-b) plane is generally uniform. Additionally, the cloud-to-cloud velocity dispersion among Type $S$ clouds ($\sim$ 7.6 and 7.4 km s$^{-1}$ for $\sigma_{\rm bin}$ and $\sigma_{\rm bin, w}$, respectively) is systematically greater than that among Type $M$ clouds ($\sim$ 6.7 and 6.0 km s$^{-1}$ for $\sigma_{\rm bin}$ and $\sigma_{\rm bin, w}$, respectively), with differences of 0.9 $-$ 1.4 km s$^{-1}$. From these measurements, we estimate merger timescales between MCs to be approximately 0.3 to 0.9 Myr, which is shorter than their internal crossing timescales ($\sim$ 1 Myr for Type $S$, $\sim$ 2 Myr for Type $M$, and $\gtrsim$ 5 Myr for Type $L$). This disparity, particularly pronounced for larger Type $L$ clouds, suggests that MCs are dynamically transient structures, with their gas content changing due to frequent interactions with neighboring clouds.

astro-ph.GA↗

arXiv2025

Gas Transfer Between the Inner 3-kpc Disk and the Galactic Central Molecular Zone

We uncovered a more tilted molecular gas structure with highly negative velocities located near the dust lane. Our observations also show that the approaching gas flows from the overshoot process are captured by the bar gravitational and then flows towards the Galactic central molecular zone (CMZ) through the bar channel. The recycling gas from the overshoot effect, in conjunction with freshly accreted gas from the inner 3-kpc disk, accumulates significantly near R_GC~1/2R_bar and R_GC~2/3R_bar regions by adopting a bar length of ~3.2--3.4kpc. Importantly, within these regions, there are frequent collisions and substantial angular momentum exchanges between gas flows with different trajectories. In this scenario, the DISSIPATION processes arising from interactions between colliding flows, together with the varying torques induced by the nonaxisymmetric bar, effectively transfer the angular momentum of viscous gas outward, thereby driving the molecular gas to settle into the CMZ within ~3 orbital periods. A long-term gas inflow with an average rate of >1.1Msun/yr, coupled with intense transient accretion events that exceed the average rate by several times due to the overshoot effect, significantly regulates the gas distribution, physical properties, and dynamical evolution of the CMZ. These findings provide robust observational evidence for elucidating the intricate dynamics of molecular gas flows towards the CMZ. Our results show that gas dynamics has a significant impact on the secular evolution of both the Milky Way and the extragalactic gas-rich galaxies.

astro-ph.GA↗

arXiv2025

Examining Turbulence in Galactic Molecular Clouds -- I: A Statistical Analysis of Velocity Structures

We present a systematic analysis of the velocity structure functions (VSFs) of 167 molecular clouds with angular sizes greater than $\sim$176 arcmin$^2$ in three sectors of the Galactic mid-plane. We calculated the 1st- to 3rd-order VSFs and found that 60\% of the VSFs exhibit power-law distributions. The relative power-law exponents are consistent with predictions from intermittent turbulence models. Column density weighting reduces the proportion of power-law VSFs and steepens the VSF slopes, implying a reduction of turbulent energy in high-density regions. All clouds show small-scale intermittency, with slightly stronger intermittency in those molecular clouds showing none power-law VSFs. Negative VSF exponents that may indicate gravitational collapse are not observed in our sample. The scaling exponents of the observed VSFs do not correlate with the virial parameters of the molecular clouds. These two observations suggest that gravity-dominated scales in molecular clouds still need further investigation. Consistent VSF scaling exponents for the molecular clouds with significant power-law VSFs suggest large-scale external driving of turbulence in these molecular clouds. However, the driving mechanisms are likely not universal, as the power-law scaling coefficients in our results show relatively large scatter. The fact that nearly 40\% of the VSFs deviate to some extent from power-law distributions suggests that the influence of local environments on the internal turbulence of molecular clouds may not be negligible.

astro-ph.GA↗

arXiv2024

A new view of the Spiral Structure of the Northern Outer Milky Way in Carbon Monoxide

Based on 32162 molecular clouds from the Milky Way Imaging Scroll Painting project, we obtain new face-on molecular gas maps of the northern outer Galaxy. The total molecular gas surface density map reveals three segments of spirals, extending 16-43 kiloparsecs in length. The Perseus and Outer arms stand out prominently, appearing as quasi-continuous structures along most of their length. At the Galactic outskirts, about 1306 clouds connect the two segments of the new spiral arm discovered by Dame & Thaddeus (2011) in the first quadrant and Sun et al. (2015) in the second quadrant, possibly extending the arm into the outer third quadrant. Logarithmic spirals can be fitted to the CO arm segments with pitch angles ranging from 4 to 12 degree. These CO arms extend beyond previous CO studies and the optical radius, reaching a galactic radius of about 22 kiloparsecs, comparable to the HI radial range.

astro-ph.GA↗