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A schematic of the Galactic rotation curve to illustrate how the CO profiles are used to determine location of molecular clouds. The colour-scale displays the expected kinematic line-of-sight velocity (km s −1 ) from the reference point of the Sun for the entire coverage of the Mopra CO Survey. Four spiral arms, the Galactic Centre, and the location of the Sun are also overlaid. The spiral arms are modelled as having a pitch angle of 13.1 • , a central bar length of 2.2 kpc inclined at −30 • to our sightline, a Galactic Centre distance of 8.0 kpc and a flat rotation curve with velocity 220 km s −1 (Vallée 2016).
Source publication
We present observations of the Mopra carbon monoxide (CO) survey of the Southern Galactic Plane, covering Galactic longitudes spanning l = 250 ○ (–110 ○ ) to l = 355 ○ (–5 ○ ), with a latitudinal coverage of at least | b | < 1 ○ , totalling an area of >210 deg ² . These data have been taken at 0.6 arcminute spatial resolution and 0.1kms –1 spectral...
Contexts in source publication
Context 1
... average line profiles for both 12 CO and 13 CO cubes are presented in the Appendix (from Figs. 12 to 32). All cubes cover 1 × 2 degrees area (l × b, |b| < 1 • ), and the cubes are centred at each longitude degree. An illustrative example of this is the line profile of G300, Fig. 22a. This covers an area between ±1 • in latitude and from longitude 300 • to longitude 301 • , centred at 300.5 • ...
Context 2
... arms. The velocity of the peak positions change as we move through Galactic longitude. Thus the position and the velocity change of the spiral arms can be inspected using spectra of the cubes. The expected line of sight velocity for the emission from any position within the survey region under the assumption of Galactic rotation can be seen in Fig. 2, overlaid with the position of the spiral arms from the model of Vallée ...
Context 3
... is usually caused by multiple spiral arms along the line of sight. A notable example of this is G310's spectrum ( Figure Appendix 24a). One of the two prominent peaks is from the Sagittarius Arm (v = −40 km s −1 ) whereas the higher peak emission comes from the Scutum-Crux Arm (v = −53 km s −1 ). ...
Context 4
... of the two prominent peaks is from the Sagittarius Arm (v = −40 km s −1 ) whereas the higher peak emission comes from the Scutum-Crux Arm (v = −53 km s −1 ). G330 is another useful example as its spectrum shows three prominent peaks caused by the Sagittarius Arm, Scutum Arm, and Norma Arm with peak velocities at −45, −64, and −97 km s −1 respectively ( Figure Appendix 28a). ...
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Citations
... Our unbiased sample provides an ideal test bed to investigate whether mass flows are common in filaments, and further revealing their properties. Of the 42 filaments, we are able to retrieve molecular line cubes for 20 filaments from public surveys (Jackson et al. 2006;Barnes et al. 2015;Umemoto et al. 2017;Schuller et al. 2017Schuller et al. , 2021Cubuk et al. 2023). These provide 13 CO(1-0), 12 CO(1-0), or 13 CO(2-1) cubes that well resolve the filaments. ...
Filamentary structure is important for the ISM and star formation. Galactic distribution of filaments may regulate the star formation rate in the Milky Way. However, interstellar filaments are intrinsically complex, making it difficult to study quantitatively. Here, we focus on linear filaments, the simplest morphology that can be treated as building blocks of any filamentary structure. We present the first catalog of 42 ``straight-line'' filaments across the full Galactic plane, identified by clustering of far-IR Herschel HiGAL clumps in position-position-velocity space. We use molecular line cubes to investigate the dynamics along the filaments; compare the filaments with Galactic spiral arms; and compare ambient magnetic fields with the filaments' orientation. The selected filaments show extreme linearity ($>$10), aspect ratio (7-48), and velocity coherence over a length of 3-40 pc (mostly $>$10 pc). About 1/3 of them are associated with spiral arms, but only one is located in arm center, a.k.a. ``bones'' of the Milky Way. A few of them extend perpendicular to the Galactic plane, and none is located in the Central Molecular Zone (CMZ) near the Galactic center. Along the filaments, prevalent periodic oscillation (both in velocity and density) is consistent with gas flows channeled by the filaments and feeding the clumps which harbor diverse star formation activities. No correlation is found between the filament orientations with Planck measured global magnetic field lines. This work highlights some of the fundamental properties of molecular filaments and provides a golden sample for follow-up studies on star formation, ISM structure, and Milky Way structure.
Context. Filamentary structure is important for the ISM and star formation. Galactic distribution of filaments may regulate the star formation rate in the Milky Way. However, interstellar filaments are intrinsically complex, making them difficult to study quantitatively.
Aims. Here we focus on linear filaments, the simplest morphology that can be treated as building blocks of any filamentary structure.
Methods. We present the first catalog of 42 straight-line filaments across the full Galactic plane, identified by clustering of far-IR Herschel HiGAL clumps in position–position–velocity space. We investigated the dynamics along the filaments using molecular line cubes, compared the filaments with Galactic spiral arms, and compared ambient magnetic fields with the filaments’ orientation.
Results. The selected filaments show extreme linearity (> 10), aspect ratio (7–48), and velocity coherence over a length of 3–40 pc (mostly > 10 pc). About one-third of them are associated with spiral arms, but only one is located in the arm center (known as the “skeleton” of the Milky Way). A few of them extend perpendicular to the Galactic plane, and none is located in the Central Molecular Zone (CMZ) near the Galactic center. Along the filaments, prevalent periodic oscillation (both in velocity and density) is consistent with gas flows channeled by the filaments and feeding the clumps that harbor diverse star formation activity. No correlation is found between the filament orientations with Planck measured global magnetic field lines.
Conclusions. This work highlights some of the fundamental properties of molecular filaments and provides a golden sample for follow-up studies on star formation, ISM structure, and Milky Way structure.
