Galactic Quadrant Research Articles

Open superclusters

We define an open supercluster (OSC) as a cluster of at least six open clusters (OCs) born from the same giant molecular cloud (GMC). We surveyed the recent catalogs of OCs based on Gaia data and relevant literature to find 17 OSCs of the third Galactic quadrant, along with 190 likely members of them. OSCs are frequent enough to be considered an extra class of objects in the hierarchy of star formation. Some of these supersystems are new and most of them contain more members than previously thought. The detailed study of some OSCs lead to the discovery of four new young OCs that are members of them, named Casado-Hendy 2–5. In certain instances, subgroups with distinct proper motions (PMs) or 3D positions have been found within an OSC, suggesting the presence of multiple generations of stars formed from several bursts of star formation within the same GMC. OSCs are typically unbound and tend to disintegrate on timescales of ∼0.1 Gyr. The present results confirm that young OCs tend to form primordial groups and suggest that globular clusters (GCs) are not formed from the accretion of OSCs, that is, at least in the local Universe at late times.

On the Structure of the Sagittarius Spiral Arm in the Inner Milky Way

We report measurements of trigonometric parallax and proper motion for two 6.7 GHz methanol and two 22 GHz water masers located in the far portion of the Sagittarius spiral arm as part of the BeSSeL Survey. Distances for these sources are estimated from parallax measurements combined with three-dimensional kinematic distances. The distances of G033.64−00.22, G035.57−00.03, G041.15−00.20, and G043.89−00.78 are 9.9 ± 0.5, 10.2 ± 0.6, 7.6 ± 0.5, and 7.5 ± 0.3 kpc, respectively. Based on these measurements, we suggest that the Sagittarius arm segment beyond about 8 kpc from the Sun in the first Galactic quadrant should be adjusted radially outward relative to previous models. This supports the suggestion of Xu et al. that the Sagittarius and Perseus spiral arms might merge in the first quadrant before spiraling inward to the far end of the Galactic bar.

The Molecular Clouds in a Section of the Third Galactic Quadrant: Observational Properties and Chemical Abundance Ratio between CO and its Isotopologues

We compare the observational properties between 12CO, 13CO, and C18O and summarize the observational parameters based on a 7069-cloud sample from the Milky Way Imaging Scroll Painting CO survey in a section of the third Galactic quadrant. We find that the 13CO angular area () generally increases with that of 12CO (), and the ratio of to is 0.38 by linear fitting. We find that the 12CO and 13CO flux are tightly correlated as with both fluxes calculated within the 13CO-bright region. This indicates that the abundance is a constant as for all samples under the assumption of local thermodynamic equilibrium (LTE). Additionally, we observed that the X-factor is approximately constant in a large sample of molecular clouds. Similarly, we find with both fluxes calculated within the C18O-bright region, which indicates that the abundance ratio stays at the same value of across the molecular clouds under the LTE assumption. The linear relationships of versus and versus hold not only for the 13CO-bright region and C18O-bright region, but also for the entire molecular cloud scale with a lower flux ratio. The abundance ratio inside the clouds shows a strong correlation with the column density and temperature. This indicates that the ratio is dominated by a combination of chemical fractionation, selective dissociation, and the self-shielding effect inside the clouds.

Distributions and Physical Properties of Molecular Clouds in the Third Galactic Quadrant: l = [219.°75, 229.°75] and b = [−5.°25, 5.°25

We present the results of an unbiased 12CO/13CO/C18O (J = 1–0) survey in a portion of the third Galactic quadrant (TGQ): 219.°75 ≤ l ≤ 229.°75 and −5.°25 ≤ b ≤ 5.°25. The high-resolution and high-sensitivity data sets help to unravel the distributions and physical properties of the molecular clouds (MCs) in the mapped area. In the LSR velocity range from ∼−1 to ∼85 km s−1, the molecular material successfully traces the Local, Perseus, and Outer arms. In the TGQ, the Outer arm appears to be more prominent than that in the second Galactic quadrant (SGQ), but the Perseus arm is not as conspicuous as that in the SGQ. A total of 1,502 12CO, 570 13CO, and 53 C18O molecular structures are identified, spanning over ∼2 and ∼6 orders of magnitude in size and mass, respectively. Tight mass–radius correlations and virial parameter–mass anticorrelations are observable. Yet, it seems that no clear correlations between velocity dispersion and effective radius can be found over the full dynamic range. The vertical distribution of the MCs renders evident pictures of the Galactic warp and flare.

The Molecular Clouds in a Section of the Third Galactic Quadrant: Cloud Catalog

We present results of cloud catalogs of 12CO, 13CO, and C18O (J = 1–0) in a section of the third Galactic quadrant over (195° < l < 220°, ∣b∣ < 5°) from the Milky Way Imaging Scroll Painting project. The data were acquired with the PMO 13.7 m millimeter telescope with ∼50″angular resolution. We construct three molecular cloud catalogs containing information of 12CO, 13CO, and C18O from the position–position–velocity (PPV) data cubes. The 12CO cloud catalog contains 7069 samples identified based on the DBSCAN algorithm. We develop a new algorithm, the stacking bump algorithm, for identifying 13CO and C18O emission by searching for weak signals in the original spectra of 13CO and C18O within the boundary in PPV space defined by the 12CO cloud. Above the 2σ threshold level, we identified 1197 clouds having 13CO emission and 32 clouds having C18O emission. We test the stacking bump algorithm in the noise-only datacube and find that the 2σ threshold can effectively avoid the possibility of false detection generated by noise. The results proved that the new algorithm has high accuracy and completeness. Statistics of peak intensity, projected angular area, line width, and flux of the clouds show that the power-law indices obtained from different isotopic lines are close to each other.

Modeling the Vertical Distribution of the Milky Way’s Flat Subsystem Objects

This paper is an initial stage of consideration of the general problem of joint modeling of the vertical structure of a Galactic flat subsystem and the average surface of the disk of the Galaxy, taking into account the natural and measurement dispersions. We approximate the average surface of the Galactic disk in the region covered by the data with a general (polynomial) model and determine its parameters by minimizing the squared deviations of objects along the normal to the model surface. The smoothness of the model, i.e., its order n, is optimized. An outlier elimination algorithm is applied. The developed method allows us to simultaneously identify significant details of the Galactic warping and estimate the offset z ☉ of the Sun relative to the average (in general, non-flat) surface of the Galactic disk and the vertical scale of the object system under consideration for an arbitrary area of the disk covered by data. The method is applied to data on classical Cepheids. Significant local extremes of the average disk surface model were found based on Cepheid data: the minimum in the first Galactic quadrant and the maximum in the second. A well-known warp (lowering of the disk surface) in the third quadrant has been confirmed. The optimal order of the model describing all these warping details was found to be n o = 4. The local (for a small neighborhood of the Sun, n o = 0) estimate of pc is close to the non-local (taking into account warping, n o = 4) pc (statistical and calibration uncertainties are indicated), which suggests that the proposed modeling method eliminates the influence of warping on the z ☉ estimate. However, the non-local estimate of the vertical standard deviation of Cepheids pc differs significantly from the local pc, which implies the need to introduce more complex models for the vertical distribution outside the Sun’s vicinity.

Unveiling Hidden Stellar Aggregates in the Milky Way: 1656 New Star Clusters Found in Gaia EDR3

We report 1656 new star clusters found in the Galactic disk (∣b∣ < 20°) beyond 1.2 kpc, using Gaia EDR3 data. Based on an unsupervised machine-learning algorithm, DBSCAN, and following our previous studies, we utilized a unique method to do the data preparation and obtain the clustering coefficients, which proved to be an effective way to search blindly for star clusters. We tabulate the physical parameters and member stars of the new clusters, and present some interesting examples, including a globular cluster candidate. The cluster parameters and member stars are available in machine-readable format in the online journal. We examine the new discoveries and discuss their statistical properties. The proper-motion dispersions and radii of the star clusters are the same as those previously reported. The new clusters beyond 1.2 kpc are older than those in the solar neighborhood, and the new objects found in the third Galactic quadrant present the lowest line-of-sight extinctions. Combined with our previous results, the total population of new clusters and candidates detected through our method is 2541, corresponding to 55% of all newly published clusters in the Gaia era. The number of cataloged Gaia star clusters was also increased to nearly 6000. In the near future, it will be necessary to make a unified confirmation and member star determination for all reported clusters.

Peering into the Milky Way by FAST: III. Magnetic fields in the Galactic halo and farther spiral arms revealed by the Faraday effect of faint pulsars

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive radio telescope for pulsar observations. We make polarimetric measurements of a large number of faint and distant pulsars using the FAST. We present the new measurements of Faraday rotation for 134 faint pulsars in the Galactic halo. Significant improvements are also made for some basic pulsar parameters for 15 of them. We analyse the newly determined rotation measures (RMs) for the Galactic magnetic fields by using these 134 halo pulsars, together with previously available RMs for pulsars and extragalactic radio sources and also the newly determined RMs for another 311 faint pulsars which are either newly discovered in the project of the Galactic Plane Pulsar Snapshot (GPPS) survey or previously known pulsars without RMs. The RM tomographic analysis in the first Galactic quadrant gives roughly the same field strength of around 2~$\mu$G for the large-scale toroidal halo magnetic fields. The scale height of the halo magnetic fields is found to be at least 2.7$\pm$0.3~kpc. The RM differentiation of a large number of pulsars in the Galactic disk in the Galactic longitude range of $26^{\circ}<l<90^{\circ}$ gives evidence for the clockwise magnetic fields (viewed from the north Galactic pole) in two interarm regions inside the Scutum arm and between the Scutum and Sagittarius arm, and the clockwise fields in the Local-Perseus interarm region and field reversals in the Perseus arm and beyond.

Jet from the enigmatic high-latitude star BP Psc and evolutionary status of its driving source

ABSTRACT BP Psc is an active late-type (sp:G9) star with unclear evolutionary status lying at high-galactic latitude b = −57°. It is also the source of the well collimated bipolar jet. We present results of the proper motion and radial velocity study of BP Psc outflow based on the archival Hα imaging with the GMOS camera at 8.1-m Gemini-North telescope as well as recent imaging and long-slit spectroscopy with the SCORPIO multimode focal reducer at 6-m BTA telescope of SAO RAS. The 3D kinematics of the jet revealed the full spatial velocity up to ∼140 km s−1 and allows us to estimate the distance to BP Psc system as D = 135 ± 40 pc. This distance leads to an estimation of the central source luminosity L* ≈ 1.2 L⊙, indicating that it is the ≈1.3M⊙ T Tauri star with an age t ≲ 7 Myrs. We measured the electron density of order Ne ∼ 102 cm−3 and mean ionization fraction f ≈ 0.04 within the jet knots and estimated upper limit of the mass-loss rate in NE lobe as $\dot{M}_{\rm out}\approx 1.2\cdot 10^{-8}{\rm M}_{\odot }\,{\rm yr}^{-1}$. The physical characteristics of the outflow are typical for the low-excitation YSO jets and consistent with the magnetocentrifugal mechanism of its launching and collimation. Prominent wiggling pattern revealed in Hα images allowed us to suppose the existence of a secondary substellar companion in a non-coplanar orbit and estimate its most plausible mass as Mp ≈ 30MJup. We conclude that BP Psc is one of the closest to the Sun young jet-driving systems and its origin is possibly related to the episode of star formation triggered by expanding supershells in second Galactic quadrant.

An Updated View of the Milky Way from Maser Astrometry

Astrometric observations of maser sources in the Milky Way, using the Very Long Baseline Interferometry (VLBI) technique, have been exploited to determine the spiral structure of our Galaxy. Several major spiral arms have now been pinpointed in the first and second Galactic quadrants. Fundamental Galactic parameters such as the distance to the Galactic Centre and the rotation curve and speed have been determined. In this review, we discuss the latest results from the Bar and Spiral Structure Legacy survey, the VLBI Exploration of Radio Astrometry survey and other VLBI arrays and compare them with astrometric measurements of stars from the Gaia mission. In particular, we present the peculiarities of the individual spiral arms and a thorough discussion of the methods to determine different Galactic parameters as well as the obtained values.

The observed age gradient in the Milky Way—as a test for theories of spiral arm structure

Some important predictions from 4 main models of spiral arm formation are tested here, using observational data acquired for the Milky Way galaxy. Many spiral arm models (density wave, tidal wave, nuclear Lyapunov tube, or dynamic transient wave) have some consistencies with some of the observations, and some inconsistencies.Our 4 tests consist of the relative locations and relative speeds of different arm tracers away from the dust lane, and the global arm pitch angle as obtained over two Galactic quadrants and several Galactic radii, as well as the arm’s continuity of shape from Galactic quadrant IV to Galactic quadrant I.In the Milky Way, an age gradient is observed from different arm tracers, amounting to 12.9 pm 1.1 Myrs/kpc, or a relative speed from the dust lane of 76 pm 10 km/s. The presence of an age gradient is predicted by the density waves, but is not consistent with the predictions of the tidal waves, of the nuclear Lyapunov tubes, nor of the dynamic transient recurrent waves.

Open clusters with proper motions fully separatedfrom the field stars using Gaia DR2

ABSTRACT The study of open star clusters makes us understand a lot about the composition and construction of the Milky Way Galaxy. Thanks to the Gaia DR2 database that helps us to get the genetic members of star clusters using their proper motions and parallaxes, and estimating their physical properties in a very accurate way. This study aims to detect the reasons that make clusters (within 2 kpc) have proper motions completely separated from the background field stars. We studied a large sample of open stellar clusters taken from Dias’s catalogue and drew the vector point diagrams using the astrometric data of Gaia DR2. By visual inspection, we specified 108 objects as separated clusters and 377 ones as melted clusters. We studied their mean parameters in the four galactic quadrants of the Milky Way Galaxy.

Distances of galactic radio pulsars; first quadrant: −2° &amp;lt; ℓ &amp;lt; 90° and −2° &amp;lt; b &amp;lt; 2°

ABSTRACT Distance versus dispersion measure relations are constructed for Galactic radio pulsars in small solid angle intervals. The calculations are based on some basic criteria, as well as using the independent distance measurements of well examined pulsars for the first Galactic quadrant, including Galactic central directions. Values of average free electron density for these regions are derived from the fits to distance versus dispersion measure relations and checked for consistency and smoothness. The effects of plasma in the Galactic arms and within the central parts of the Galactic bulge region are also compared and discussed. Our adopted distances for the radio pulsars are compared with the ones given in some other models. Some basic results on distributions of the radio pulsars and the plasma are presented.

Superposing the Magnetic Spiral Structure of the Milky Way, on the Stellar Spiral Arms—Matching the Unique Galactic Magnetic Field Reversal Zone with Two Galactic Spiral Arm Segments

To pinpoint the peak location of the synchrotron total intensity emission in a spiral arm, we use a map of the spiralarm locations (from the observed arm tangent). Thus In a typical spiral arm in Galactic Quadrant I, we find the peak of the synchrotron radiation to be located about 220 +/-40 pc away from the inner arm edge (hot dust lane) inside the spiral arm. While most of the galactic disk has a clockwise largescale magnetic field, we make a statistical analysis to delimitate more precisely the smaller reverse annulus wiith a counterclockwise galactic magnetic field. We find an annulus width of 2.1 +/-0.3 kpc (measured along the Galactic radius), located from 5.5 to 7.6 kpc from the Galactic Center). The annulus does not overlay with a single spiral arm -- it encompasses segments of two different spiral arms. Using a recent delineation of the position of spiral arms, the field-reversed annulus is seen to encompass the Crux-Centaurus arm (in Galactic Quadrant IV) and the Sagittarius arm (in Galactic Quadrant I).

Evidence of distant spiral arms in the Galactic disk quadrant IV from VVV red clump giants

AbstractThe discovery of new clear windows in the Galactic plane using the VVV near-IR extinction maps allows the study of the structure of the Milky Way (MW) disk. The ultimate goal of this work is to map the spiral arms in the far side of the MW, which is a relatively unexplored region of our Galaxy, using red clump (RC) giants as distance indicators. We search for near-IR clear windows located at low Galactic latitudes ($|b|&lt; 1$deg) in the MW disk using the VVV near-IR extinction maps. We have identified two new windows named VVV WIN 1607–5258 and VVV WIN 1475–5877, respectively, that complement the previously known window VVV WIN 1713–3939. We analyse the distribution of RC stars in these three clear near-IR windows and measure their number density along the line of sight. This allows us to find overdensities in the distribution and measure their distances along the line of sight. We then use the VVV proper motions in order to measure the kinematics of the RC stars at different distances. We find enhancements in the distance distribution of RC giants in all the studied windows, interpreting them as the presence of spiral arms in the MW disk. These structures are absent in the current models of synthetic population for the same MW lines of sight. We were able to trace the end of the Galactic bar, the Norma arm, as well as the Scutum–Centaurus arm in the far disk. Using the VVV proper motions, we measure the kinematics for these Galactic features, confirming that they share the bulk rotation of the Galactic disk.

The “Maggie” filament: Physical properties of a giant atomic cloud

Context. The atomic phase of the interstellar medium plays a key role in the formation process of molecular clouds. Due to the line-of-sight confusion in the Galactic plane that is associated with its ubiquity, atomic hydrogen emission has been challenging to study. Aims. We investigate the physical properties of the “Maggie” filament, a large-scale filament identified in H I emission at line-of-sight velocities, vLSR ~−54 km s−1. Methods. Employing the high-angular resolution data from The H I/OH Recombination line survey of the inner Milky Way (THOR), we have been able to study H I emission features at negative vLSR velocities without any line-of-sight confusion due to the kinematic distance ambiguity in the first Galactic quadrant. In order to investigate the kinematic structure, we decomposed the emission spectra using the automated Gaussian fitting algorithm GAUSSPY+. Results. We identify one of the largest, coherent, mostly atomic H I filaments in the Milky Way. The giant atomic filament Maggie, with a total length of 1.2 ± 0.1 kpc, is not detected in most other tracers, and it does not show signs of active star formation. At a kinematic distance of 17 kpc, Maggie is situated below (by ≈500 pc), but parallel to, the Galactic H I disk and is trailing the predicted location of the Outer Arm by 5−10 km s−1 in longitude-velocity space. The centroid velocity exhibits a smooth gradient of less than ±3 km s−1 (10 pc)−1 and a coherent structure to within ±6 km s−1. The line widths of ~10 km s−1 along the spine of the filament are dominated by nonthermal effects. After correcting for optical depth effects, the mass of Maggie’s dense spine is estimated to be 7.2−1.9+2.5 × 105 M⊙. The mean number density of the filament is ~4 cm−3, which is best explained by the filament being a mix of cold and warm neutral gas. In contrast to molecular filaments, the turbulent Mach number and velocity structure function suggest that Maggie is driven by transonic to moderately supersonic velocities that are likely associated with the Galactic potential rather than being subject to the effects of self-gravity or stellar feedback. The probability density function of the column density displays a log-normal shape around a mean of ⟨NH I⟩ = 4.8 × 1020 cm−2, thus reflecting the absence of dominating effects of gravitational contraction. Conclusions. While Maggie’s origin remains unclear, we hypothesize that Maggie could be the first in a class of atomic clouds that are the precursors of giant molecular filaments.

A Morphological Classification of 18,190 Molecular Clouds Identified in 12CO Data from the MWISP Survey

Abstract We attempt to visually classify the morphologies of 18,190 molecular clouds, which are identified in the 12CO(1–0) spectral line data over ∼450 deg2 of the second Galactic quadrant from the Milky Way Imaging Scroll Painting project. Using the velocity-integrated intensity maps of the 12CO(1–0) emission, molecular clouds are first divided into unresolved and resolved ones. The resolved clouds are further classified as nonfilaments or filaments. Among the 18,190 molecular clouds, ∼25% are unresolved, ∼64% are nonfilaments, and ∼11% are filaments. In the terms of the integrated flux of 12CO(1–0) spectra of all 18,190 molecular clouds, ∼90% are from filaments, ∼9% are from nonfilaments, and the remaining ∼1% are from unresolved sources. Although nonfilaments are dominant in the number of the discrete molecular clouds, filaments are the main contributor of 12CO emission flux. We also present the number distributions of the physical parameters of the molecular clouds in our catalog, including their angular sizes, velocity spans, peak intensities of 12CO(1–0) emission, and 12CO(1–0) total fluxes. We find that there is a systematic difference between the angular sizes of the nonfilaments and filaments, with the filaments tending to have larger angular scales. The H2 column densities of them are not significantly different. We also discuss the observational effects, such as those induced by the finite spatial resolution, beam dilution, and line-of-sight projection, on the morphological classification of molecular clouds in our sample.

Search for and Identification of Young Compact Galactic Supernova Remnants Using THOR

Young Supernova remnants (SNRs) with smaller angular sizes are likely missing from existing radio SNR catalogues, caused by observational constraints and selection effects. In order to find new compact radio SNR candidates, we searched the high angular resolution (25″) THOR radio survey of the first quadrant of the galaxy. We selected sources with non-thermal radio spectra. HI absorption spectra and channel maps were used to identify which sources are galactic and to estimate their distances. Two new compact SNRs were found: G31.299-0.493 and G18.760-0.072, of which the latter was a previously suggested SNR candidate. The distances to these SNRs are 5.0±0.3 kpc and 4.7±0.2 kpc, respectively. Based on the SN rate in the galaxy or on the statistics of known SNRs, we estimate that there are 15–20 not-yet detected compact SNRs in the galaxy and that the THOR survey area should contain three or four. Our detection of two SNRs (half the expected number) is consistent with the THOR sensitivity limit compared with the distribution of integrated flux densities of SNRs.

Cyano radical emission at small spatial scales towards massive protostars

Context. The cyano radical (CN), one of the first detected interstellar molecular species, is a key molecule in many astrochemical chains. In particular, it is detected towards molecular cores, the birth places of stars, and it is involved in the rich chemistry that takes place at these sites. Aims. At present, there are not many studies on the emission of this molecular species at small spatial scales towards massive young stellar objects. We therefore present a high-angular resolution CN study towards a sample of massive protostars, with the aim of unveiling the spatial distribution at the small scale of the emission of this radical in relation to star-forming processes. Methods. The interstellar CN has a strong emission line at the rest frequency 226 874.764 MHz, thus we searched for observing projects in the Atacama Large Millimeter Array (ALMA) database regarding high-mass star-forming regions observed at Band 6. The used data set was observed in ALMA Cycle 3 with angular and spectral resolutions of 0.′′7 and 1.13 MHz, respectively. A sample of ten high-mass star-forming regions located in the first Galactic quadrant were selected on the basis that they present a clear emission of CN at the mentioned frequency. Results. We found that the CN traces both molecular condensations and the diffuse and extended gas surrounding them. In general, the molecular condensations traced by the maximums of the CN emission do not spatially coincide with the peaks of the continuum emission at 1.3 mm, which trace the molecular cores where massive stars are born. Based on the presence or lack of near-IR emission associated with such cores, we suggest that our sample is composed of sources at different stages of evolution. The CN is present in all sources, suggesting that this radical may be ubiquitous along the different star formation stages, and hence it may be involved in different chemical reactions occurring during the period of star formation. Additionally, other molecules such as CH3OCHO and CH2CHCN were detected towards the continuum peaks of some of the analysed cores. We found that the missing flux coming from extended spatial scales that are filtered out by the interferometer is an important issue to take into account in the analysis of some spectral features and the spatial distribution of the emission.

The Discovery of the Largest Gas Filament in Our Galaxy, or a New Spiral Arm?

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we detect a giant HI filamentary structure in the sky region of 307$.\!\!^{\circ}$7 $<$ $\alpha$ $<$ 311$.\!\!^{\circ}$0 and 40$.\!\!^{\circ}$9 $<$ $\delta$ $<$ 43$.\!\!^{\circ}$4. The structure has a velocity range of $-$170 km s$^{-1}$ to $-$130 km s$^{-1}$, and a mean velocity of $-$150 km s$^{-1}$, putting it to a Galactocentric distance of 22 kpc. The HI structure has a length of 1.1 kpc, which appears to be so far the furthest and largest giant filament in the Galaxy and we name it Cattail. Its mass is calculated to be 6.5 $\times$ 10$^4$ M$_{\odot}$ and the linear mass density is 60 M$_{\odot}$ pc$^{-1}$. Its width is 207 pc, corresponding to an aspect ratio of 5:1. Cattail possesses a small velocity gradient (0.02 km s$^{-1}$ pc$^{-1}$) along its major axis. Together with the HI4PI data, we find that Cattail could have an even larger length, up to 5 kpc. We also identify another new elongated structure to be the extension into the Galactic first quadrant of the Outer Scutum-Centaurus (OSC) arm, and Cattail appears to be located far behind the OSC. The question about how such a huge filament is produced at the extreme Galactic location remains open. Alternatively, Cattail might be part of a new arm beyond the OSC, though it is puzzling that the structure does not fully follow the warp of the Galactic disk.