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The Milky Way's molecular disk thickens and warps together, with a ~220 pc unwarped floor, implying warp and flare share one origin.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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A 24,724-cloud catalog from the MWISP CO survey reveals nearby sheet-like curtain clouds, interarm spurs, a ~220 pc inner molecular disk thickness, and a falling cloud velocity dispersion with galactocentric radius.

T0 review reviewed 2026-08-05 challenge →

load-bearing objection Strong catalog and new structures; the thickness–warp correlation is likely an artifact of distance priors and should not be taken at face value. the 3 major comments →

arxiv 2508.14547 v1 pith:P6JY3UKK submitted 2025-08-20 astro-ph.GA

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

Xin Zhou , Ji Yang , Yan Sun , Qing-Zeng Yan , Lixia Yuan , Yang Su , Xuepeng Chen , Shaobo Zhang This is my paper
classification astro-ph.GA
keywords molecular cloudsGalactic structureGalactic warpGalactic flareCO surveysMWISPkinematic distancesspiral arms
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper maps molecular gas in two longitude strips of the Milky Way with the MWISP CO survey and builds a catalog of 24,724 molecular clouds. From this census it tries to establish how the Galactic molecular disk is structured vertically: where it is thick, where it is warped, and whether the two are connected. Its central claim is that the disk's thickness and warp amplitude follow a straight-line relation, intercepting at about 220 pc when the warp height is zero — the disk's intrinsic unwarped thickness. The paper also reports clouds aggregating in an inter-arm region, a thinner disk between arms, and a cloud-to-cloud velocity dispersion that falls with galactocentric radius. A sympathetic reader would care because a single linear thickness–warp relation, if real, means the warp and flare of the Milky Way's gas disk are not independent phenomena but different expressions of one underlying tilt.

Core claim

The paper builds a 24,724-cloud catalog from MWISP CO data in two Galactic fields, assigns kinematic distances (with a full distance-probability density function for the ambiguous positive-velocity clouds in G50), and Gaussian-fits each spiral-arm segment's height distribution. The central result is a linear relation between segment FWHM thickness and segment height (warp amplitude), with a ~220 pc intercept at zero warp height. That intercept is read as the molecular disk's intrinsic unwarped thickness, matching the thick molecular disk and thin H I disk in the inner Galaxy. Because segments at similar galactocentric radius that differ in both thickness and warp still fall on the same line,

What carries the argument

The load-bearing object is the catalog of 24,724 molecular clouds extracted by connectivity in position–position–velocity space from the MWISP CO data cubes, combined with per-segment Gaussian fits to the cloud height distribution. Kinematic distances come from the Brand & Blitz rotation curve, with a full distance-probability density function (Reid et al. 2016, 2019) resolving near/far ambiguity for positive-velocity G50 clouds; each spiral-arm segment's zgal histogram is fit by a Gaussian, and the FWHM (thickness) is plotted against the Gaussian center (warp height). The linear fit to that plot carries the central claim.

Load-bearing premise

The inner-Galaxy thickness and warp measurements rest on kinematic distances assigned by a method whose priors assume clouds sit near spiral arms within a disk scale height; if those priors compress the derived heights, the ~220 pc intercept and the thickness–warp correlation could be partly manufactured by the distance assignment rather than measured from the Milky Way.

What would settle it

Measure parallax- or extinction-based distances for a few dozen molecular clouds in the Sagittarius-G50 and Perseus-G50 segments, recompute their zgal heights without the spiral-arm and disk-height priors, and check whether the Gaussian FWHM and the ~220 pc thickness–warp intercept survive; if independent heights give a thinner disk or no linear relation, the reported correlation is a distance-prior artifact.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

If this is right

  • The molecular disk has an intrinsic FWHM thickness near 220 pc when unwarped, consistent with the thick molecular disk and thin H I disk in the inner Galaxy.
  • Warp and flare of the Galactic disk are homologous; models such as a tilted dark halo gain support.
  • Inter-arm molecular gas exists as spurs, and the inter-arm disk is thinner than adjacent spiral-arm regions, complicating simple spiral-pattern pictures.
  • Kinematic distance errors shrink with galactocentric radius because cloud-to-cloud velocity dispersion falls, improving outer-Galaxy mapping.
  • The Perseus-G120 segment's split velocity distribution and large dispersion indicate a spiral shock there, a kinematic signature to test elsewhere.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If confirmed with independent distances, the same ~220 pc intercept should appear at other longitudes where the molecular disk can be traced into the warp, making it a global disk property rather than a feature of these two fields.
  • The thickness–warp slope could be compared across tracers (H I, stars, molecular gas); a common slope would point to a gravitational, halo-driven origin rather than local gas physics.
  • The falling velocity dispersion with radius implies CO-based maps of the outer Galaxy become more distance-accurate farther out, which could sharpen spiral-arm models beyond the solar circle once shock regions like Perseus-G120 are masked.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

3 major / 5 minor

Summary. Using MWISP 12CO, 13CO, and C18O (J=1–0) data, the paper builds a catalog of 24,724 molecular clouds in two Galactic longitude fields, G50 (44.75°–60.25°) and G120 (119.75°–130.25°). It reports new nearby sheet-like 'curtain' clouds, a catalog-based view of spiral-arm aggregation, interarm substructures ('G50 Perseus-Outer interarm spurs'), a thinner molecular layer in the interarm region, a linear correlation between disk thickness and warp height with a ~220 pc unwarped inner-Galaxy thickness, and a decreasing cloud-to-cloud velocity dispersion with galactocentric radius. The catalog and the outer-Galaxy spatial distributions are the main observational deliverables; the thickness–warp correlation is the central physical claim.

Significance. If confirmed, the study provides a valuable public MC catalog (doi:10.57750/sciencedb.21145) from an unbiased survey, with explicit extraction criteria and useful comparisons against GRS, SEDIGISM, CHIMPS, and COHRS. The outer-Galaxy estimates are based on kinematic distances that are comparatively free of the inner-Galaxy near/far ambiguity, making the warp/flare trends in G120 and the outer G50 plausible. The curtain MCs and interarm spurs are observationally interesting, though their physical interpretation remains preliminary. The central claim of a universal thickness–warp relation with a 220 pc intercept is not yet established: it depends on inner-Galaxy distances assigned with a prior-based method that encodes the very disk properties being measured, and the linear fit includes several segments the authors themselves describe as poorly constrained. The potential reward is real, but the required robustness analysis is currently missing.

major comments (3)
  1. The inner-disk thickness and warp measurements are at risk of circularity. For positive-velocity G50 clouds, distances are assigned using the Reid et al. full distance-probability-density-function method, whose priors include spiral-arm positions and a disk scale height. The paper explicitly warns at the end of Section 3.3 that this sample is 'unsuitable for analysing inter-arm structures or structures distant from the Galactic plane.' Yet Section 3.4 uses exactly these distances for the Gaussian zgal fits of the Sagittarius-G50 and Perseus-G50 segments, which provide the low-warp/low-thickness anchor points of the Fig. 14 linear relation and hence the ~220 pc intercept. The additional 5σ-z cut (zgal ≳ 590 pc) also truncates the high-z tail. Please show quantitatively that the posterior z distribution is not prior-dominated, e.g., via injection-recovery tests, rerunning the analysis with
  2. The linear thickness–warp fit includes segments whose constraints are acknowledged to be weak: the paper states that the Outer-G120 and OSC-G120 segments are 'not well-constrained due to the limited number of MC samples,' and the Perseus-G120 segment has known distance systematics from the spiral shock. No error bars or covariance are shown for the Gaussian FWHM and mean-z values, and no sensitivity analysis is reported. A linear relation fit to roughly seven points, several of which are poorly constrained or systematically uncertain, is not robust. Please provide segment-by-segment fit parameters with uncertainties and recompute the fitted intercept and slope after removing each questionable segment (especially Perseus-G120 and Outer-G120), and after excluding all G50 positive-velocity/ambiguous-distance clouds.
  3. The claim that the G50 inter-arm molecular disk is thinner than the adjacent spiral-arm regions is supported only by a visual comparison and a statement that a 'statistical examination' shows significantly smaller variance. The test is not described: no statistic, null distribution, sample definition, or p-value is given. Since the inter-arm sample is selected partly from the distance-ambiguous positive-velocity G50 clouds (Section 3.3), it is important to show that the variance difference is not an artifact of the distance-PDF filtering. Please document the statistical test and provide the relevant numbers.
minor comments (5)
  1. [Throughout] Typos include 'repectively' (Section 3.1), 'Gravitional' (Introduction), and 'for for CCL4 and CCL5' (Figure 6 caption).
  2. [Fig. 14] The figure would benefit from visible error bars on both axes and labels identifying each segment, since the fitted relation is the paper's central claim.
  3. [Fig. 7 / Table 2] The radius definition differs between MWISP clouds (HWHM) and GRS clouds (equivalent radius); please state explicitly in the caption or text that this systematic difference affects the comparison and the fitted slope.
  4. [Section 3.4] The sentence 'The thickness of the Galactic molecular disk at a distance can be detected in its entirety' is difficult to parse; please rephrase.
  5. [Section 4] The summary lists 4753 MCs with unreliable distance measurements, but Section 3.3 does not explicitly define this total in one place; please reconcile the exclusion numbers for clarity.

Circularity Check

2 steps flagged

Inner-disk thickness–warp correlation is partially manufactured: the ambiguous-distance sample whose distances are assigned with a disk/arm-prior PDF is, by the paper's own admission, unsuitable for the thickness/warp analysis that anchors the 220 pc intercept; a self-cited 590 pc prior cut further truncates the sample.

specific steps
  1. self definitional [Section 3.3 and Section 3.4, Figure 14]
    "Since this method determines distance probabilities based on the measured deviation of clouds from both the spiral arms and the Galactic disk, the relevant sample is unsuitable for analysing inter-arm structures or structures distant from the Galactic plane."

    The full distance-PDF (Reid et al. 2016, 2019) assigns distances to positive-velocity G50 clouds using priors that include the spiral-arm loci and the Galactic disk. Section 3.4 then uses these same distance assignments to measure the vertical thickness (FWHM) and mean height (warp amplitude) of the Sagittarius-G50 and Perseus-G50 segments, which are included in Figure 14 and anchor the low-warp/low-thickness end of the fitted linear relation. The paper itself states this sample is unsuitable for analysing structures distant from the plane or inter-arm structures; using it for the disk-thickness and warp measurement means the output (FWHM ~ 220 pc intercept) is not independent of the assumed disk prior, so the derived thickness-warp correlation is partly self-defined.

  2. self citation load bearing [Section 3.3, distance exclusion; Section 3.4, Figures 12-14]
    "we additionally exclude those with mass exceeding the 1σ range of the Larson σv-M relation fitted here and those with heights exceeding the 5σ thickness of the Galactic thick molecular disk (i.e., zgal ≳ 590 pc; Su et al. 2021), to largely eliminate bias from samples affected by near- and far-distance ambiguities. According to this, 4106 MCs are eliminated from the analysis"

    The 590 pc height cut is taken from Su et al. (2021), a previous work by overlapping authors, and is used to truncate the ambiguous-distance sample before measuring the height distribution. Section 3.4 then fits Gaussian FWHMs and means to the surviving clouds of the same inner-Galaxy segments. The prior thickness value from the authors' own catalog therefore operates as an input cut on the very quantity later reported as the measured disk thickness; this makes the self-citation load-bearing for the 220 pc intercept and the warp-thickness correlation.

full rationale

The paper is largely a survey paper: the 24,724-cloud catalog, the cloud identification, the outer-Galaxy G120 distances (mostly beyond the tangent-point ambiguity), the inter-arm spur detection, the curtain MCs, and the velocity-dispersion gradient are all independent, externally checkable results and are not circular. The central new physical claim, however, is the linear thickness-warp relation with a ~220 pc unwarped thickness and the inference of homologous origins. That claim depends on the Sagittarius-G50 and Perseus-G50 disk segments (Figure 14). For positive-velocity G50 clouds, distances are assigned by a full distance-probability-density-function method whose priors include the Galactic disk and spiral arms, and the paper explicitly warns this sample is unsuitable for analyzing inter-arm or far-from-plane structures. Section 3.4 nevertheless uses these distances for exactly that purpose, and additionally applies a 5σ cut at 590 pc based on the same group's prior work. The low-warp/low-thickness anchor of the fit is therefore partly generated by the assumed disk prior and by the self-cited truncation, rather than measured independently. The outer-Galaxy segments and the inter-arm-vs-arm thin-disk comparison provide some independent support, so the circularity is partial rather than total; but the headline intercept and the 'homologous origins' conclusion are significantly weakened.

Axiom & Free-Parameter Ledger

5 free parameters · 6 axioms · 1 invented entities

The catalog is data-driven and mostly independent. The key non-data input is the rotation curve and the distance-PDF priors; the latter are load-bearing for the inner-disk thickness claim. The 220 pc intercept and the velocity gradient are fitted quantities, not derived from first principles. The curtain cloud class is observational and has independent precedent.

free parameters (5)
  • Intercept of thickness-warp linear relation = ~220 pc
    Fitted intercept of FWHM versus warp height in Figure 14; interpreted as the intrinsic unwarped molecular disk thickness. It is an extrapolation, not an independent measurement.
  • Slope of thickness-warp linear relation = not quoted in text (shown in Figure 14)
    Second parameter of the linear fit used to claim correlation between flare and warp.
  • Radial gradient of cloud-to-cloud velocity dispersion = -0.71 +/- 0.05 km/s/kpc
    Slope of the linear fit in Figure 16; the quoted error is the fit error and does not include distance-assignment systematics.
  • Tangent-point velocity offset = 15 km/s
    Hand-chosen offset added to rotation-curve tangent-point velocities so that they match the observed 12CO terminal velocity. It is then used to conclude that MC peculiar velocities are commonly up to ~15 km/s.
  • Larson sigma_v-M fit parameters = not stated
    A Larson relation is fitted to the MWISP sample and its 1-sigma range is used to exclude ambiguous-distance MCs from the analysis.
axioms (6)
  • domain assumption Galactic rotation curve of Brand & Blitz (1993) with R0=8.15 kpc and Theta0=236 km/s (Reid et al. 2019)
    All kinematic distances, Rgal and zgal values derive from this curve. A different rotation curve would shift the inferred structures.
  • domain assumption Full distance-probability density function method (Reid et al. 2016, 2019) with priors on spiral arm locations and disk scale height
    Used for positive-velocity G50 MCs; the priors encode the very structures the paper later analyzes, creating circularity.
  • domain assumption X_CO conversion factor N(H2)/W(12CO)=1.8e20 cm-2 (K km/s)-1 (Dame et al. 2001)
    Converts CO integrated intensity to H2 column density and cloud mass; affects all mass estimates.
  • domain assumption Sun's height above Galactic midplane = 15.7 pc (Zhou et al. 2023; Su et al. 2019)
    Fixes the zgal=0 reference plane for all disk thickness and warp measurements.
  • domain assumption Larson relations are valid for Milky Way MCs and can be used to reject near/far distance solutions
    Used to exclude 4106 MCs with ambiguous distances; if the relation is not universal, the exclusion biases the sample.
  • domain assumption Perseus arm spiral shock model (Roberts 1972; Schwarz et al. 1995)
    Used to mark MCs in the -55 to -30 km/s velocity range as shock-affected and to interpret the split velocity distribution in Perseus-G120.
invented entities (1)
  • Curtain molecular clouds independent evidence
    purpose: A class of nearby MCs with large angular extent, small velocity dispersion, and inferred thin line-of-sight dimension, proposed to explain six structures around the Sun.
    The SEDIGISM survey had already classified similar objects as wispy clouds, and CCL3/CCL5 were previously studied with extinction-parallax distances, so the class is not entirely unsupported; the name is new.

reviewed 2026-08-05 · how reviews work

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Cite this review

Pith. "Pith review of Molecular Gas Distribution toward the Inner and Outer Galaxy Revealed by MWISP -- the Galactic Longitude 45\deg--60\deg and 120\deg--130\deg." pith.science (2026). https://pith.science/paper/P6JY3UKK

@misc{pith2026250814547,
  author       = {Pith},
  title        = {Pith review of: Molecular Gas Distribution toward the Inner and Outer Galaxy Revealed by MWISP -- the Galactic Longitude 45\deg--60\deg and 120\deg--130\deg},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/P6JY3UKK}},
  note         = {Machine review of arXiv:2508.14547}
}
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abstract

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.

Figures

Figures reproduced from arXiv: 2508.14547 by Ji Yang, Lixia Yuan, Qing-Zeng Yan, Shaobo Zhang, Xin Zhou, Xuepeng Chen, Yang Su, Yan Sun.

Figure 1
Figure 1. Figure 1: RMS noise maps of 12CO (J=1–0), 13CO (J=1–0), and C18O (J=1–0) line emission. MWISP project1 (see Su et al. 2019; Sun et al. 2020, and references therein, for details). We mapped two regions toward the inner and outer Galaxy, namely the G50 (l = 44.75◦– 60.25◦ ) and G120 (l = 119.75◦–130.25◦ ) re￾gions, both with the Galactic latitude |b| ≤ 5.25◦ . The 12CO (J=1–0), 13CO (J=1–0), and 1 http://english.dlh.p… view at source ↗
Figure 2
Figure 2. Figure 2: Signal-to-noise ratio distribution of 12CO (J=1–0), 13CO (J=1–0), and C18O (J=1–0) line emission. There are approximately 5.17 × 109 voxels in total. Normalized numbers of all voxels are shown by black solid lines, and selected voxels with signal-to-noise ratios below 3 for 12CO, 3.5 for 13CO, and 4.2 for C18O are shown by red solid lines. The negative intensity voxels are symmetrically mirrored to positiv… view at source ↗
Figure 3
Figure 3. Figure 3: Pseudo-tricolor image of the integrated intensity of 12CO (J=1–0) (blue), 13CO (J=1–0) (green), and C18O (J=1–0) (red) line emission in the velocity range of −115 to 20 km s−1 (top), and Galactic longitude-velocity (l-v) map of the three lines for the same field (bottom), for the G120 region. The data were initially moment-masked (see Dame 2011, for reference) to suppress noise while integrating over the l… view at source ↗
Figure 4
Figure 4. Figure 4: Same as [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Galactic velocity-latitude (v-b) maps of 12CO (J=1–0) (blue), 13CO (J=1–0) (green), and C 18O (J=1–0) (red) line emission in the Galactic longitude ranges of 119.75◦ to 130.25◦ (left) and 44.75◦ to 60.25◦ (right). The data were initially moment-masked to suppress noise. The C18O data was also masked using the 13CO mask. Regions of the same MCs as indicated in the l-v maps in Figures 3 and 4 are shown. The … view at source ↗
Figure 6
Figure 6. Figure 6: Middle row: 12CO (J=1–0) integrated intensity maps of selected MCs. The MCs are the same as those indicated in the l-v and v-b maps (see Figures 3, 4, and [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Histogram of radius (left) and radius-mass relation (right) for the MWISP clouds, overplotted with those for clouds from other literature catalogues, i.e., GRS (13CO (J=1–0); Rathborne et al. 2009; Roman-Duval et al. 2009, 2010), COHRS (12CO (J=3–2); Colombo et al. 2019), CHIMPS (13CO and C18O (J=3–2); Rigby et al. 2019), and SEDIGISM (13CO (J=2–1); Duarte-Cabral et al. 2021). The radius of the clouds are … view at source ↗
Figure 8
Figure 8. Figure 8: Kinematic distance of each identified MC in the G120 (left) and G50 (right) regions as a function of systemic velocity. The kinematic distances of the MCs are derived from the Galactic rotation curve of Brand & Blitz (1993) with the Sun’s galactocentric distance of 8.15 kpc and the circular rotation speed of 236 km s−1 (Reid et al. 2019). For MCs with positive systemic velocities in the G50 region, based o… view at source ↗
Figure 9
Figure 9. Figure 9: Systemic velocity versus the Galactic longitude for identified MCs in the G120 (left) and G50 (right) regions. The sizes of the circles indicate the physical sizes of the MCs (see [PITH_FULL_IMAGE:figures/full_fig_p016_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Integrated intensity (l-b; top) and Galactic longitude-velocity (l-v; bottom) maps of MCs in the G50 Perseus-Outer interarm spurs, with the intensity of all identified MCs shown in greyscale. The l-b and l-v maps are of the same field. The selected inter-arm MCs are the same as those indicated by the red crosses in the right panel of [PITH_FULL_IMAGE:figures/full_fig_p017_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Plan view of MC locations in the G120 and G50 regions from the northern Galactic pole. MC distances are estimated using the Galactic rotation curve and the full distance-probability density function method only for MCs with positive systemic velocity in the G50 region. The red dots mark the same selected MCs as those indicated by the red crosses in [PITH_FULL_IMAGE:figures/full_fig_p018_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Histogram of height from the Galactic plane for identified MCs (top), plot of height versus the Galactic longitude (middle), and plot of height versus galactocentric distance (bottom) in different segments of the Galactic disk. The disk segments are divided at galactocentric distances where the number of MCs reaches a local minimum for the G120 and G50 regions, respectively. MCs in the segments are primar… view at source ↗
Figure 13
Figure 13. Figure 13: Same as [PITH_FULL_IMAGE:figures/full_fig_p020_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Thickness (FWHM) as a function of height from the Galactic plane for different segments of the Galactic disk in regions G50 (diamonds) and G120 (crosses). The FWHMs and heights of each Galactic disk segment are obtained by fitting the MC height distribution shown in Figures 12 and 13. The segments around the Local arm, (i.e. the Local-G120 and Local-G50 segments) are excluded because their thicknesses are… view at source ↗
Figure 15
Figure 15. Figure 15: Histogram of modified systemic velocities for MCs in different segments of the Galactic disk. The systemic velocity of the MCs is modified by subtracting the baseline of velocity changes with the Galactic longitude for each disk segment, to eliminate the trend of velocity variations along the Galactic longitude. The baseline is obtained from a linear fit of the velocity variation with the Galactic longitu… view at source ↗
Figure 16
Figure 16. Figure 16: Cloud-to-cloud velocity dispersion as a function of galactocentric distance. The velocity dis￾persion is estimated by subtracting the distance-dependent velocity variation induced by projection effects from the dispersion of the modified velocity. The dispersion of the modified velocities for each Galactic disk segment is estimated by Gaussian fitting to the distribution of the modified systemic velocitie… view at source ↗

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This paper was first reviewed by deepseek-v4-flash on August 5, 2026.