Evidence of a bisymmetric spiral in the Milky Way

Francis, Charles; Anderson, Erik

doi:10.1111/j.1365-2966.2012.20693.x

Cited by 31 publications

(37 citation statements)

References 35 publications

(46 reference statements)

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“…We adopt the parameters from Benjamin et al (2005) and Churchwell et al (2009) because of the overall consistency of the bar and spiral arm structures. We note that there are more recent studies of the MW's structures (e.g., Francis & Anderson 2012;Robin et al 2012;Wegg et al 2015). For example, in Figure 1, the inner part of the Perseus arm passes the far end of the bar and overlaps with the near 3 kpc arm (see Churchwell et al 2009).…”

Section: Structures Of the Mwmentioning

confidence: 77%

Evolution of Molecular and Atomic Gas Phases in the Milky Way

Koda

Scoville

Heyer

2016

ApJ

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We analyze radial and azimuthal variations of the phase balance between the molecular and atomic interstellar medium (ISM) in the Milky Way (MW) using archival CO( J=1-0) and HI 21 cm data. In particular, the azimuthal variations-between the spiral arm and interarm regions-are analyzed without any explicit definition of the spiral arm locations. We show that the molecular gas mass fraction, i.e.,, varies predominantly in the radial direction: starting from~100% at the center, remaining 50% toR 6 kpc and decreasing to ∼10%-20% at = R 8.5 kpc when averaged over the whole disk thickness (from ∼100% to ≳60%, then to ∼50% in the midplane). Azimuthal, arm-interarm variations are secondary: only~20% in the globally molecule-dominated inner MW, but becoming larger, ∼40%-50%, in the atom-dominated outskirts. This suggests that in the inner MW the gas remains highly molecular ( > f 50% mol ) as it moves from an interarm region into a spiral arm and back into the next interarm region. Stellar feedback does not dissociate molecules much, and the coagulation and fragmentation of molecular clouds dominate the evolution of the ISM at these radii. The trend differs in the outskirts where the gas phase is globally atomic ( < f 50% mol ). The HI and H 2 phases cycle through spiral arm passage there. These different regimes of ISM evolution are also seen in external galaxies (e.g., the LMC, M33, and M51). We explain the radial gradient of f mol using a simple flow continuity model. The effects of spiral arms on this analysis are illustrated in the Appendix.

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Section: Structures Of the Mwmentioning

confidence: 77%

Evolution of Molecular and Atomic Gas Phases in the Milky Way

Koda

Scoville

Heyer

2016

ApJ

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“…Kharchenko et al (2012) used a two-arm spiral model with a low pitch angle (from Piskunov et al 2006); this model has many turns around the Galactic center before reaching the Sun, and thus many unproven tangents to the arm segments. Francis & Anderson (2012) used light intensity from the 2 μm All Sky Survey catalog, and suggested a two-arm spiral model, with a low pitch angle, predicting 11 tangents to the arms toward the Galactic center, namely at longitudes 260…”

Section: Appendixmentioning

confidence: 99%

The Spiral Arms of the Milky Way: The Relative Location of Each Different Arm Tracer Within a Typical Spiral Arm Width

Vallée

2014

111

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From the Sun's location in the Galactic disk, different arm tracers (CO, H i, hot dust, etc.) have been employed to locate a tangent to each spiral arm. Using all various and different observed spiral arm tracers (as published elsewhere), we embark on a new goal, namely the statistical analysis of these published data (data mining) to statistically compute the mean location of each spiral arm tracer. We show for a typical arm cross-cut, a separation of 400 pc between the mid-arm and the dust lane (at the inner edge of the arm, toward the Galactic center). Are some arms major and others minor? Separating arms into two sets, as suggested by some, we find the same arm widths between the two sets. Our interpretation is that we live in a multiple (four-arm) spiral (logarithmic) pattern (around a pitch angle of 12• ) for the stars and gas in the Milky Way, with a sizable interarm separation (around 3 kpc) at the Sun's location and the same arm width for each arm (near 400 pc from mid-arm to dust lane).

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“…There is no consensus on the number, pitch angle, and shape of Galactic spiral arms (Vallée 2005;Hou et al 2009;Lépine et al 2011;Siebert et al 2012;Francis & Anderson 2012;Vallée 2014a,b;Griv et al 2014;Bobylev 2014;Pettitt et al 2014). The Sun's location within the dust obscured Galactic disc is a complicating factor to observe the Galactic structure.…”

Section: Introductionmentioning

confidence: 99%

Tracing the Galactic spiral structure with embedded clusters

Camargo

Bonatto

Bica

2015

Monthly Notices of the Royal Astronomical Society

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In the present work we investigate the properties of 18 embedded clusters (ECs). The sample includes 11 previously known clusters and we report the discovery of 7 ECs on WISE images, thus complementing our recent list of 437 new clusters. The main goal is to use such clusters to shed new light on the Galactic structure by tracing the spiral arms with cluster distances. Our results favour a four-armed spiral pattern tracing three arms, Sagitarius-Carina, Perseus, and the Outer arm. The SagitariusCarina spiral arm is probed in the borderline of the third and fourth quadrants at a distance from the Galactic centre of d 1 ∼ 6.4 kpc adopting R ⊙ = 7.2 kpc, or d 2 ∼ 7.2 kpc for R ⊙ = 8.0 kpc. Most ECs in our sample are located in the Perseus arm that is traced in the second and third quadrants and appear to be at Galactocentric distances in the range d 1 = 9 − 10.5 kpc or d 2 = 9.8 − 11.3 kpc. Dolidze 25, Bochum 2, and Camargo 445 are located in the Outer arm that extends along the second and third Galactic quadrants with a distance from the Galactic centre in the range of d 1 = 12.5 − 14.5 kpc or d 2 = 13.5 − 15.5 kpc. We find further evidence that in the Galaxy ECs are predominantly located within the thin disc and along spiral arms. They are excellent tools for tracing these Galactic features and therefore new searches for ECs can contribute to a better understanding of the Galactic structure. We also report an EC aggregate located in the Perseus arm.

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Evidence of a bisymmetric spiral in the Milky Way

Cited by 31 publications

References 35 publications

Evolution of Molecular and Atomic Gas Phases in the Milky Way

Evolution of Molecular and Atomic Gas Phases in the Milky Way

The Spiral Arms of the Milky Way: The Relative Location of Each Different Arm Tracer Within a Typical Spiral Arm Width

Tracing the Galactic spiral structure with embedded clusters

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