The Spiral Structure of the Outer Milky Way in Hydrogen

Levine, E. S.; Blitz, Leo; Heiles, Carl

doi:10.1126/science.1128455

Cited by 180 publications

(233 citation statements)

References 17 publications

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“…The subtraction of this smoothed image from the deprojected one leaves only the sharp features. An unsharp masking technique similar to this has recently been used to clarify the arm structure of our Galaxy ( Levine et al 2006). This unsharp masking also sharpens the subtraction residuals present in the images, and so identification of real features requires care.…”

Section: Structures In the Diskmentioning

confidence: 99%

Hubble Space TelescopeAdvanced Camera for Surveys Coronagraphic Observations of the Dust Surrounding HD 100546

Ardila¹,

Golimowski²,

Krist³

et al. 2007

ApJ

156

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We present HST ACS coronagraphic observations of HD 100546, a B9.5 star, 103 pc away from the Sun, taken in the F435W, F606W, and F814W bands. Scattered light is detected up to 14 00 from the star. The observations are consistent with the presence of an extended flattened nebula with the same inclination as the inner disk. The well-known ''spiral arms'' are clearly observed and trail the rotating disk material. Weaker arms never before reported are also seen. The interarm space becomes brighter, but the structures become more neutral in color at longer wavelengths, which is not consistent with models that assume that they are due to the effects of a warped disk. Along the major disk axis, the colors of the scattered light relative to the star are Á( F435W À F606W ) % 0:0Y0:2 mag and Á( F435W À F814W ) % 0:5Y1 mag. To explain these colors, we explore the role of asymmetric scattering, reddening, and large minimum sizes on ISM-like grains. We conclude that each of these hypotheses by itself cannot explain the colors. The disk colors are similar to those derived for Kuiper Belt objects, suggesting that the same processes responsible for their colors may be at work here. We argue that we are observing only the geometrically thick, optically thin envelope of the disk, while the optically thick disk responsible for the far-IR emission is undetected. The observed spiral arms are then structures on this envelope. The colors indicate that the extended nebulosity is not a remnant of the infalling envelope but reprocessed disk material.

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Section: Structures In the Diskmentioning

confidence: 99%

Hubble Space TelescopeAdvanced Camera for Surveys Coronagraphic Observations of the Dust Surrounding HD 100546

Ardila¹,

Golimowski²,

Krist³

et al. 2007

ApJ

156

View full text Add to dashboard Cite

show abstract

“…The physical properties of the simulated unique structures in the outer part ( kpc) of the Galactic gas disk R ∼ 30 can be tested against previous and ongoing observational studies of H i properties of the Galaxy (e.g., M04; Levine et al 2006;McClure-Griffiths et al 2006). Although detailed comparison of ongoing and future observations will be given in our future papers, here we briefly discuss the previous observations shown in Figures 1 and 2 of M04 compared to model B in a more quantitative manner.…”

Section: Discussionmentioning

confidence: 99%

The Magellanic impact: Collision between the Outer Galactic H i Disk and the Leading Arms of the Magellanic Stream

Bekki

McClure-Griffiths

2007

ApJ

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We show that collisions between the outer Galactic H i disk and the leading arms (LAs) of the Magellanic stream (MS) can create giant H i holes and chimney-like structures in the disk. Based on the results of our Nbody simulations of the last 2.5 Gyr of evolution of the interaction of the Large and Small Magellanic Clouds (LMC and SMC, respectively) with the Galaxy, we investigate when and where the LAs can pass through the Galactic plane after the MS formation. We then investigate hydrodynamical interaction between LAs and the Galactic H i disk ("the Magellanic impact") by using our new hydrodynamical simulations with somewhat idealized models of the LAs. We find that about 1%-3% of the initial gas mass of the SMC, which consists of the LAs, can pass through the outer part ( kpc) of the Galactic H i disk about 0.2 Gyr ago. We also find that R p 20-35 the Magellanic impact can push out some fraction (∼1%) of the outer Galactic H i disk to form 1-10 kpc-scale H i holes and chimney-like bridges between the LAs and the disk.

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“…13. It is no surprise that a 4-fold symmetric, constant pitch angle spiral cannot reproduce all the features simultaneously, as there are several examples in the literature of the Milky Way spiral arms deviating from such an idealised form (Taylor & Cordes 1993;Russeil 2003;Levine et al 2006). Given the small longitude range covered by the science demonstration field, the loci of such modified spiral arms are to be taken as illustrative only, showing the potential for the complete SEDIGISM survey at high-resolution to provide strong constraints of the positions of the Galactic arms towards the inner Galaxy.…”

Section: Galactic Distribution Of Molecular Cloudsmentioning

confidence: 99%

SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium

Schüller

Csengeri

Urquhart

et al. 2017

A&A

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Context. The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. Many large-scale surveys of the Galactic plane have been conducted recently, allowing for rapid progress in this field. Nevertheless, a sub-arcminute resolution global view of the large-scale distribution of molecular gas, from the diffuse medium to dense clouds and clumps, and of their relationship to the spiral structure, is still missing. Aims. We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. Methods. The SEDIGISM survey covers 78 deg 2 of the inner Galaxy (−60CO. This isotopologue of CO is less abundant than 12 CO by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the 13 CO(2 -1) and C 18 O(2 -1) lines, plus several transitions from other molecules. Results. The observations have been completed. Data reduction is in progress, and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. To illustrate the scientific potential of this survey, preliminary results based on a science demonstration field covering −20 • ≤ ≤ -18.5 • are presented. Analysis of the 13 CO(2 -1) data in this field reveals compact clumps, diffuse clouds, and filamentary structures at a range of heliocentric distances. By combining our data with data in the (1-0) transition of CO isotopologues from the ThrUMMS survey, we are able to compute a 3D realization of the excitation temperature and optical depth in the interstellar medium. Ultimately, this survey will provide a detailed, global view of the inner Galactic interstellar medium at an unprecedented angular resolution of ∼30 .

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The Spiral Structure of the Outer Milky Way in Hydrogen

Cited by 180 publications

References 17 publications

Hubble Space TelescopeAdvanced Camera for Surveys Coronagraphic Observations of the Dust Surrounding HD 100546

Hubble Space TelescopeAdvanced Camera for Surveys Coronagraphic Observations of the Dust Surrounding HD 100546

The Magellanic impact: Collision between the Outer Galactic H i Disk and the Leading Arms of the Magellanic Stream

SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium

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