New Velocimetry and Revised Cartography of the Spiral Arms in the Milky Way—a Consistent Symbiosis

Vallée, J. P.

doi:10.1088/0004-6256/135/4/1301

Cited by 245 publications

(322 citation statements)

References 54 publications

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“…Figure 5c summarizes our determination of distance in a plot taken from Vallée (2008). The W43 complex (78-120 km s −1 , marker 1) lies between 5 and 7 kpc, where the distance increases with velocity, which we found to be located on the near branch.…”

Section: Determination Of the Distance Of W43mentioning

confidence: 87%

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Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

Carlhoff

Luong

Schilke

et al. 2013

A&A

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We aim to fully describe the distribution and location of dense molecular clouds in the giant molecular cloud complex W43. It was previously identified as one of the most massive star-forming regions in our Galaxy. To trace the moderately dense molecular clouds in the W43 region, we initiated W43-HERO, a large program using the IRAM 30 m telescope, which covers a wide dynamic range of scales from 0.3 to 140 pc. We obtained on-the-fly-maps in 13 CO (2-1) and C 18 O (2-1) with a high spectral resolution of 0.1 km s −1 and a spatial resolution of 12 . These maps cover an area of ∼1.5 square degrees and include the two main clouds of W43 and the lower density gas surrounding them. A comparison to Galactic models and previous distance calculations confirms the location of W43 near the tangential point of the Scutum arm at approximately 6 kpc from the Sun. The resulting intensity cubes of the observed region are separated into subcubes, which are centered on single clouds and then analyzed in detail. The optical depth, excitation temperature, and H 2 column density maps are derived out of the 13 CO and C 18 O data. These results are then compared to those derived from Herschel dust maps. The mass of a typical cloud is several 10 4 M while the total mass in the dense molecular gas (>10 2 cm −3 ) in W43 is found to be ∼1.9 × 10 6 M . Probability distribution functions obtained from column density maps derived from molecular line data and Herschel imaging show a log-normal distribution for low column densities and a power-law tail for high densities. A flatter slope for the molecular line data probability distribution function may imply that those selectively show the gravitationally collapsing gas.

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Section: Determination Of the Distance Of W43mentioning

confidence: 87%

“…This would then lead to an underestimated calculated excitation temperature. External heating, on the other hand, would result in an (c) Model of the spiral arm structure of the Milky Way from Vallée (2008). The position of the W43 complex is marked at (1), the fore-/background complexes at (2), (3), and (3 ).…”

Section: Excitation Temperaturementioning

confidence: 99%

Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

Carlhoff

Luong

Schilke

et al. 2013

A&A

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“…To define the spiral arms, we used the six observed longitudes in the 1st and 4th quadrants where the arms are seen tangentially, as derived by Vallée (2008b) rms deviations between the observed and predicted longitudes were used, together with the Carina-Perseus interarm distance (along the direction from the Galactic center to the Sun), and the accurate distance to the W3OH complex in the Perseus arm, to estimate the allowed range of pitch angles.…”

Section: The Geometry Of the Large-scale Magnetic Fieldmentioning

confidence: 99%

The large-scale magnetic field in the fourth Galactic quadrant

Nota¹,

Katgert²

2010

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Aims. We have re-examined the published rotation measures (RMs) of extragalactic point sources and pulsars with |b| < 3 • to study the magnetic field in the fourth Galactic quadrant. Methods. We reduced the influence of structure in electron density as much as possible by excluding objects for which Hα-data indicate large fluctuations in n e somewhere along the line of sight. We also excluded objects for which the RM may have been significantly "corrupted" by an intervening supernova remnant. We modeled RM(l), the longitude dependence of RM of the unaffected extragalactic sources and pulsars. We assumed several geometries for the large-scale field. All but one of those are based on logarithmic spiral arms (with various pitch angles and widths), while one has circular symmetry. We also made different assumptions about the large-scale n e -distribution. Results. The data suggest the following generic behaviour of the large-scale field in the 4th Galactic quadrant. The field is most likely organized along logarithmic spiral arms and shows two significant reversals: from the Norma arm (CCW field) to the Norma-Crux interarm region (CW field), and from the Norma-Crux interarm region to the Crux arm (CCW field). The present data do not constrain the field in and beyond the Crux-Carina interarm region. Although the models give a good description of the global character of RM(l), individual RM-estimates deviate by typically 15 times their measurement errors. We argue that these large deviations are most likely due to the "small-scale" field that dominates on scales of up to several hundred pc. Conclusions. The picture that emerges is thus of a field that has significant structure on smaller scales, but for which the average values in arms and interarm regions are nevertheless well-defined. In addition, this smaller-amplitude large-scale field appears to reverse at each arm-interarm boundary that we can study with the present data. We briefly discuss the link between these results and theoretical predictions.

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“…We considered models with analytical bars and N-body simulations (Mel'nik & Rautiainen 2009;Rautiainen & Mel'nik 2010). The classical model of Galactic spiral structure can explain the existence of so-called tangential directions related to the maxima in the thermal radio continuum as well as HI and CO emission, which are associated with the tangents to the spiral arms (Englmaier & Gerhard 1999;Vallée 2008). Models of a two-component outer ring can also explain the existence of some of the tangential directions which, in this case, can be associated with the tangents to the outer and inner rings.…”

Section: Introductionmentioning

confidence: 99%