Research ArticleASTROPHYSICS

The local spiral structure of the Milky Way

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Science Advances  28 Sep 2016:
Vol. 2, no. 9, e1600878
DOI: 10.1126/sciadv.1600878
  • Fig. 1 Spiral galaxies.

    (A) M 51. [Credit: Hubble Space Telescope WFPC2] (B) NGC 1232. [Credit: FORS, 8.2-meter Very Large Telescope Antu, European Southern Observatory]

  • Fig. 2 Location of HMSFRs determined by trigonometric parallax.

    Sources presented in this paper are indicated with the blue circles with white outlines, and those from Paper I with blue squares. The parallax data in the Perseus (black squares) and Sagittarius (magenta squares) arms are also presented. The blue solid and dot lines are log spiral fits to the sources in the Local Arm and in the spur, respectively. They have pitch angles of 11.6° ± 1.8° and 18.3° ± 5.9°. The Galactic center (red star) is at (0,0) and the Sun (red Sun symbol) is at (0,8.34). Distance error bars (1σ) are indicated, but many are smaller than the symbols. The background gray disks provide scale, with radii corresponding in round numbers to the Galactic bar region (≈4 kpc), the solar circle (≈8 kpc), and corotation of the spiral pattern and Galactic orbits (≈12 kpc). The short Cosmic Background Explorer “boxy-bar” and the “long” bar (1921) are indicated with shaded ellipses.

  • Fig. 3 Location of HMSFRs with parallaxes superposed on a CO l-V diagram from the CfA 1.2-m survey (22).

    Sources presented in this paper are indicated with white circles with black outlines, and others with black squares. Velocity error bars (1σ) are indicated. The solid line is a log spiral fit to the sources in the Local Arm (blue for l > 70°, black for an extrapolation at l < 70°), whereas the dotted line corresponds to the spur indicated in Fig. 2. LSR, Local Standard of Rest.

  • Table 1 Parallaxes and proper motions.

    Column 2 is the parallax in milli–arc seconds. Column 3 is the parallax converted to distance in kiloparsec (1 pc ≈ 3.26 ly). Columns 4 and 5 are proper motions on the sky, eastward (μx = μαcosδ) and northward (μy = μδ) in units of milli–arc second year−1, respectively.

    MaserΠDΠ
    (kpc)
    μxμy
    Name(milli–arc second)(milli–arc second year−1)(milli–arc second year−1)
    G054.10−00.080.231 ± 0.031Embedded Image−3.13 ± 0.48−5.57 ± 0.48
    G058.77+00.640.299 ± 0.040Embedded Image−2.70 ± 0.10−6.10 ± 0.21
    G059.47−00.180.535 ± 0.024Embedded Image−1.83 ± 1.12−6.60 ± 1.12
    G059.83+00.670.253 ± 0.024Embedded Image−2.92 ± 0.07−6.03 ± 0.05
    G071.52−00.380.277 ± 0.013Embedded Image−2.48 ± 0.04−4.97 ± 0.07
    G108.18+05.511.101 ± 0.033Embedded Image+0.16 ± 0.09−2.17 ± 0.35
    G109.87+02.111.208 ± 0.025Embedded Image−1.03 ± 0.10−2.62 ± 0.27
    G213.70−12.601.166 ± 0.021Embedded Image−1.25 ± 0.09+2.44 ± 0.28

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/9/e1600878/DC1

    Supplementary Text

    table S1. Details of the epochs observed.

    table S2. Positions and source properties of the reference maser spots and the background sources for the first epoch.

    table S3. Parallaxes and proper motions.

    table S4. Parallax and proper motion measurements.

    fig. S1. Parallax and proper motion data and fits for G054.10−00.08.

    fig. S2. Parallax and proper motion data and fits for G058.77+00.64.

    fig. S3. Parallax and proper motion data and fits for G059.47−00.18.

    fig. S4. Parallax and proper motion data and fits for G059.83+00.67.

    fig. S5. Parallax and proper motion data and fits for G071.52−00.38.

    fig. S6. Parallax and proper motion data and fits for G108.18+05.51.

    fig. S7. Parallax and proper motion data and fits for G109.87+02.11.

    fig. S8. Parallax and proper motion data and fits for G213.70−12.60.

    References (2339)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • table S1. Details of the epochs observed.
    • table S2. Positions and source properties of the reference maser spots and the background sources for the first epoch.
    • table S3. Parallaxes and proper motions.
    • table S4. Parallax and proper motion measurements.
    • fig. S1. Parallax and proper motion data and fits for G054.10−00.08.
    • fig. S2. Parallax and proper motion data and fits for G058.77+00.64.
    • fig. S3. Parallax and proper motion data and fits for G059.47−00.18.
    • fig. S4. Parallax and proper motion data and fits for G059.83+00.67.
    • fig. S5. Parallax and proper motion data and fits for G071.52−00.38.
    • fig. S6. Parallax and proper motion data and fits for G108.18+05.51.
    • fig. S7. Parallax and proper motion data and fits for G109.87+02.11.
    • fig. S8. Parallax and proper motion data and fits for G213.70−12.60.
    • References (2339)

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