Tracking the Outer Spiral Arms of the Galaxy in H<scp>i</scp>Absorption

Strasser, S.; Dickey, John M.; Taylor, A. R.; Boothroyd, Arnold I.; Gaensler, B. M.; Green, Anne; Kavars, D. W.; Lockman, Felix J.; Martín, P. G.; McClure-Griffiths, N. M.; Rothwell, Timothy A.; Stil, J. M.

doi:10.1086/522794

Cited by 52 publications

(63 citation statements)

References 29 publications

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“…4). The general shape of the l − v diagram agrees with one obtained with the VGPS data (Strasser et al 2007), but the higher resolutions reveal much finer details, such as the vertical lanes at l ∼ 31 • , 43 • , and ∼ 49 • , which are caused by absorption against the background continuum emission from the star-forming regions W43, W49, and W51, respectively (see also Fig. 2).…”

Section: H I Emissionsupporting

confidence: 81%

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview

Wang

Beuther

Rugel

et al. 2020

A&A

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Context. The Galactic plane has been observed extensively by a large number of Galactic plane surveys from infrared to radio wavelengths at an angular resolution below 40 . However, a 21 cm line and continuum survey with comparable spatial resolution is lacking. Aims. The first half of THOR data (l = 14.0 • − 37.9 • , and l = 47.1 • − 51.2 • , |b| ≤ 1.25 • ) has been published in our data release 1 paper. With this data release 2 paper, we publish all the remaining spectral line data and Stokes I continuum data with high angular resolution (10 -40 ), including a new H i dataset for the whole THOR survey region (l = 14.0 − 67.4 • and |b| ≤ 1.25 • ). As we published the results of OH lines and continuum emission elsewhere, we concentrate on the H i analysis in this paper. Methods. With the Karl G. Jansky Very Large Array (VLA) in C-configuration, we observed a large portion of the first Galactic quadrant, achieving an angular resolution of ≤ 40 . At L Band, the WIDAR correlator at the VLA was set to cover the 21 cm H i line, four OH transitions, a series of Hnα radio recombination lines (RRLs; n = 151 to 186), and eight 128 MHz-wide continuum spectral windows (SPWs), simultaneously.Results. We publish all OH and RRL data from the C-configuration observations, and a new H i dataset combining VLA C+D+GBT (VLA D-configuration and GBT data are from the VLA Galactic Plane Survey) for the whole survey. The H i emission shows clear filamentary substructures at negative velocities with low velocity crowding. The emission at positive velocities is more smeared-out, likely due to higher spatial and velocity crowding of structures at the positive velocities. Compared to the spiral arm model of the Milky Way, the atomic gas follows the Sagittarius and Perseus Arm well, but with significant material in the inter-arm regions. With the C-configuration-only H i+continuum data, we produced a H i optical depth map of the THOR areal coverage from 228 absorption spectra with the nearest-neighbor method. With this τ map, we corrected the H i emission for optical depth, and the derived column density is 38% higher than the column density with optically thin assumption. The total H i mass with optical depth correction in the survey region is 4.7×10 8 M , 31% more than the mass derived assuming the emission is optically thin. If we applied this 31% correction to the whole Milky Way, the total atomic gas mass would be 9.4-10.5×10 9 M . Comparing the H i with existing CO data, we find a significant increase in the atomic-to-molecular gas ratio from the spiral arms to the inter-arm regions.Conclusions. The high-sensitivity and resolution THOR H i dataset provides an important new window on the physical and kinematic properties of gas in the inner Galaxy. Although the optical depth we derive is a lower limit, our study shows that the optical depth correction is significant for H i column density and mass estimation. Together with the OH, RRL and continuum emission from the THOR survey, these new H i data provide the basis for high-angular-res...

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Section: H I Emissionsupporting

confidence: 81%

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview

Wang

Beuther

Rugel

et al. 2020

A&A

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“…Also in quadrant I, our green (outer Sagittarius) arm can be seen in H i emission down to −130 km s −1 (top of Figure 3 in Strasser et al 2007).…”

Section: The Longitude-velocity Mapsmentioning

confidence: 88%

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

Vallée

2008

The Astronomical Journal

244

283

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Recent advances in the determinations of the positions (pitch angle, shape, numbers, interarm separation) and velocities (rotation curve) of the spiral arms are evaluated and compared to previous determinations. Based on these results, an average cartographic model is developed that fits the means of basic input data and provides predictions for the locations of the arms in the Milky Way, for each galactic quadrant. For each spiral arm segment in each galactic quadrant, the LSR radial velocities are calculated for the radial distance as well as for its galactic longitude. From our velocimetric model, arm intercepts (between line of sights and spiral arms) are indicated in velocity space and may be used to find the distance and velocity to any arm, in a given longitude range. Velocity comparisons between model predictions and published CO velocity distribution are done for each galactic quadrant, with good results. Our velocimetric model is not hydromagnetic in character, nor is it a particle-simulation scheme, yet it is simple to use for comparisons with the observations and it is in symbiosis and consistent with our cartographic model (itself simple to use for comparisons with observations). A blending in velocity of the Perseus and Cygnus arms is further demonstrated, as well as an apparent longitude-velocity blending of the starting points of the four spiral arms near 4 kpc (not a physical ring). An integrated (distance, velocity) model for the mass in the disk is employed, to yield the total mass of 3.0 × 10 11 M Sun within a galactic radius of 28 kpc.

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“…The absorption spectra allow us to identify and study the foreground layers of HI gas. From these kinds of spectra we can determine the HI column density (Strasser et al 2007):…”

Section: Thrumms and Hops Datamentioning

confidence: 99%

NGC 6334 and NGC 6357: Hαkinematics and the nature of the H II regions

Russeil

Tigé

Adami

et al. 2016

A&A

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Aims. NGC 6334 and NGC 6357 are amongst the most active, optically visible Galactic star-forming complexes. They are composed of several H ii regions that have a significant impact on their surrounding. The aim of this paper is to present a kinematic study of the optical H ii regions that belong to NGC 6334 and NGC 6357.Methods. We use Fabry-Perot interferometer observations of the Hα line, which cover NGC 6334 and NGC 6357. These observations allow us to analyse the Hα line profiles to probe the kinematics of the ionised gas of both regions. We complement the Hα observations with multi-wavelength data to specify the nature of the H ii regions. Results. We determine the dynamical nature of the optical H ii regions that belongs to NGC 6334 and NGC 6357. In NGC 6334, GUM 61 is an expanding wind shell-like H ii region, GUM 64b exhibits a champagne flow, GM1-24 is the Hα counterpart of two larger regions and H ii 351.2+0.5 is, in fact, composed of two H ii regions. In NGC 6357, H ii 353.08+0.28 and H ii 353.09+0.63 are probably stellar wind-shaped bubble H ii regions, while H ii 353.42+0.45 is a classical photo-ionised H ii region. We suggest that, at large scale, star-formation seems to be triggered where large/old H ii regions intersect. Inversely, stellar formation seems to have already started in the NGC 6334 north-east filament, irrespective of any evident external H ii region impact. While NGC 6357 shows more complicated kinematics, NGC 6334 is characterised by a more active stellar formation.

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Tracking the Outer Spiral Arms of the Galaxy in HiAbsorption

Cited by 52 publications

References 29 publications

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview

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

NGC 6334 and NGC 6357: Hαkinematics and the nature of the H II regions

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Tracking the Outer Spiral Arms of the Galaxy in HiAbsorption

Cited by 52 publications

References 29 publications

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview

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

NGC 6334 and NGC 6357: Hαkinematics and the nature of the H II regions

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The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and H I overview